SULTAN USAMA KHAN REPEATERS FOR TOPOLOGY PLANNING IN WCDMA MACRO CELLULAR NETWORKS Master of Science Thesis

Examiners: Prof. Jukka Lempiäinen

M.Sc. Panu Lähdekorpi

Examiners and topic approved in the

Faculty of Computing and Electrical

Engineering Council meeting on 3rd

of March 2010

ABSTRACT

TAMPERE UNIVERSITY OF TECHNOLOGY

Master’s Degree Program in RF Electronics

Sultan Usama Khan: Repeaters for Topology Planning in WCDMA Macro Cellular Networks

Master of Science Thesis, 77 pages and 10 Appendix pages

November 2010

Major: RF Electronics

Examiners: Professor Jukka Lempiäinen, M.Sc. Panu Lähdekorpi

Keywords: Radio network planning, Repeaters, Cellular Topologies, EDT, SINR

The task of radio network operators is getting tougher and tougher, in order to meet the constantly increasing demand for higher throughput mobile data services. The limited technical capabilities of network equipment and properties of the radio propagation environment is being the main hurdle. So far, the radio network planners have been successful in choosing proper tools (or equipment), techniques and doing vigilant planning, to create a cellular communication network providing high performance at minimum implementation cost. However, few of the techniques used are; competent selection of base station site locations or appropriate base station antenna configurations or using repeaters to name the few.

In this thesis, the performance of air-to-air analog repeaters for nominal clover leaf topology and triangular topology in a WCDMA based macro cellular network is investigated. The two topologies differs each other on site location and antenna configuration selection. Moreover, the effect of down tilting at the base station antenna on the network performance is also analyzed. However, the main target of the study was to determine optimum NodeB antenna tilt separating NodeB and repeater serving areas. At first, through simulations some system level key performance indicators (such as service probability, average DL cell throughput, NodeB transmit powers) are studied for both topologies, with and without repeaters. Secondly, numerical calculations are done using a model for shared data channel of high speed downlink packet access technique to determine and study signal-to-noise-interference ratio. The results show that the repeaters provide improvement in coverage and capacity of the network at high EDT angles, providing high throughput values. The results also show that the nominal topology performance is better than in triangular topology.

TIIVISTELMÄ

TAMPEREEN TEKNILLINEN YLIOPISTO

Master’s Degree Program in RF Electronics

Sultan Usama Khan: Toistimet WCDMA-makrosolukkoverkon topologiasuunnittelussa

Diplomityö, 77 sivua ja 10 liitesivua

Marraskuu 2010

Pääaine: RF Electronics

Tarkastajat: Professori Jukka Lempiäinen, DI Panu Lähdekorpi

Avainsanat: Radio network planning, Repeaters, Cellular Topologies, EDT, SINR

Jatkuvasti kasvava tarve korkean bittinopeuden mobiilidatapalveluille aiheuttaa yhä enemmän ja enemmän päänvaivaa radioverkkosuunnittelijoille laitteistojen teknisistä rajoitteista ja radiotien etenemisympäristön ominaisuuksista johtuen. Toistaiseksi, radioverkkosuunnittelijat ovat onnistuneet oikeita laitteistoja ja menetelmiä valitsemalla luomaan tietoliikenneverkon, joka tarjoaa korkean suorituskyvyn minimitoteutuskustannuksilla. Menetelmät viittaavat mm. tukiasemapaikan tehokkaaseen valintaan, tukiasema-antennien asetuksien menestyksekkääseen valintaan ja toistimien käyttöön.

Tässä diplomityössä tarkastellaan radiotiellä toimivien analogisten toistimien vaikutusta WCDMA-makrosolukkoverkon suorituskykyyn perinteisen apilanlehtitopologian sekä kolmiotopologian tapauksessa. Myös tukiasema-antennin pystykallistuksen vaikutusta verkon suorituskykyyn analysoidaan. Työn varsinainen tarkoitus oli suorittaa tukiasema-antennin pystykallistuskulman optimointia tukiaseman ja toistimen palvelualueiden erottamiseksi toisistaan. Simulaatioiden avulla selvitetään järjestelmätason suorituskykyindikaattorien (palvelun onnistumistodennäköisyys, alalinkin solun keskimääräinen läpäisybittinopeus, tukiaseman lähetysteho) käyttäytymistä kahden verkkotopologian tapauksessa toistimien kanssa ja ilman. Työssä selvitetään myös numeerisesti laskemalla keskimääräinen HSDPA-tekniikan jaetun datakanavan signaalihäiriökohinasuhde (SINR). Tuloksista nähdään, että toistimet tuovat parannusta verkon peittoon ja kapasiteettiin korkeilla tukiasema-antennin pystykallistuskulmilla tuoden myös parannusta bittinopeuksiin. Tulokset osoittavat lisäksi, että nominaalitopologia suoriutuu paremmin kuin kolmiotopologia.

PREFACE

The research work reported in this Master of Science Thesis has been done in the Radio Network Group at the Department of Communications Engineering, Tampere University of Technology, Finland. This research work was done without funding and completed in years 2009-2010.

Firstly, I would like to thank my supervisors Prof. Jukka Lempiäinen and M.Sc. Panu Lähdekorpi for their encouragement, valuable guidance, helpful support and patience during the whole working period. I would also like to thank my colleagues Ashok Kumar, Jaakko Penttinen and Janne Palttala for their fruitful technical discussions and useful technical hints for the work.

Secondly, I would like to thank my friends in Tampere, especially Mubashir Ali, Faizan ul Haq, Farhan Hameed, Muhammad Salman, Irfan Ullah and Jaakko Pitkänen for their support and providing a plenty of good unforgettable moments.

Finally, I would like to express my deepest gratitude and warmest thanks to my parents Prof. Sultan Nusrat Khan and Shahida Nusrat, and my brothers Sultan Waqas Khan, Sultan Shaheer Khan, Sultan Waleed Khan and Sultan Hasan Khan for their unconditional support, encouraging attitude and endless love. Without their contribution this would not have been possible.

Tampere, November 2010

Sultan Usama Khan

V

Table of Contents

1. Introduction ............................................................................................................ 1

2. Fundamentals of Cellular Systems .......................................................................... 3

2.1. The Cellular Network Concept ....................................................................... 3

2.1.1. Cell types ................................................................................................ 4

2.1.2. Sectorization ............................................................................................ 5

2.2. Cellular Radio Resources ............................................................................... 6

2.2.1. Cellular reuse concept.............................................................................. 6

2.2.2. Co-channel interference ........................................................................... 7

2.3. Propagation Environment ............................................................................... 8

2.3.1. Propagation models ................................................................................. 9

2.3.2. Okumura-Hata propagation model ......................................................... 10

3. Wideband CDMA principles and systems ............................................................. 12

3.1. Multiple Access Techniques ......................................................................... 12

3.1.1. Spread spectrum technology .................................................................. 13

3.1.2. Spread spectrum systems and interference ............................................. 13

3.2. CDMA in Cellular Networks ........................................................................ 14

3.2.1. Universal frequency reuse...................................................................... 14

3.2.2. Soft handover ........................................................................................ 15

3.2.3. Power control ........................................................................................ 15

3.3. Multipath Propagation and RAKE Reception ............................................... 15

3.3.1. Signal fading ......................................................................................... 16

3.3.2. RAKE receiver ...................................................................................... 17

3.4. Wideband CDMA Systems........................................................................... 18

3.4.1. Basic UMTS terminologies .................................................................... 18

3.4.2. UMTS Radio frame structure ................................................................. 19

3.5. WCDMA Communication Channels ............................................................ 20

3.5.1. Logical channels .................................................................................... 20

3.5.2. Transport channels................................................................................. 20

VI

3.5.3. Physical channels .................................................................................. 20

3.6. Radio Resource Management in WCDMA Systems ..................................... 21

3.6.1. Power control in UMTS ......................................................................... 21

3.6.2. Handover control ................................................................................... 22

3.6.3. Congestion control................................................................................. 23

3.7. High Speed Packet Access (HSPA) .............................................................. 23

3.7.1. High speed downlink packet access (HSDPA) ....................................... 24

3.7.2. High speed uplink packet access (HSUPA) ............................................ 25

4. UMTS radio network planning and network topologies ......................................... 27

4.1. Radio Network Planning Environment ......................................................... 27

4.2. Radio Network Planning Process .................................................................. 28

4.2.1. Dimensioning ........................................................................................ 29

4.2.2. Detailed planning .................................................................................. 29

4.2.3. Optimization .......................................................................................... 29

4.3. Radio Network Planning Process for UMTS................................................. 30

4.3.1. Configuration planning .......................................................................... 30

4.3.2. Topology planning................................................................................. 31

4.3.3. Code and parameter planning................................................................. 32

4.3.4. Operation optimization .......................................................................... 33

4.4. Radio Network Performance Indicators ........................................................ 33

4.4.1. Service probability................................................................................. 34

4.4.2. Other-to-own cell interference ............................................................... 34

4.4.3. Signal to interference and noise ratio (SINR) ......................................... 35

4.5. Radio Network Topologies ........................................................................... 35

4.5.1. Hexagonal network topology ................................................................. 35

4.5.2. Triangular network topology ................................................................. 36

4.5.3. Square network topology ....................................................................... 37

4.6. Antenna Down Tilting .................................................................................. 37

5. WCDMA repeaters ............................................................................................... 39

5.1. Introduction to Repeaters.............................................................................. 39

5.2. Repeater Equipment ..................................................................................... 39

VII

5.3. Repeater Configuration Parameters .............................................................. 41

5.3.1. Repeater gain ......................................................................................... 41

5.3.2. Repeater distance ................................................................................... 41

5.3.3. Repeater antenna height ......................................................................... 42

5.3.4. Hosting NodeB antenna ......................................................................... 42

5.4. Repeater Noise ............................................................................................. 42

5.5. Repeaters in UMTS ...................................................................................... 44

6. Simulations ........................................................................................................... 46

6.1. Simulations for Radio Network Planning ...................................................... 46

6.2. Static Simulations......................................................................................... 47

6.3. Static Simulator Framework ......................................................................... 47

6.4. Repeater Model in Simulator Framework ..................................................... 48

6.4.1. Repeater unit ......................................................................................... 49

6.4.2. Link loss and interference ...................................................................... 49

6.5. Simulation Scenarios .................................................................................... 50

6.5.1. Network topology configurations ........................................................... 50

6.5.2. Antenna configurations .......................................................................... 54

6.5.3. Radio network parameters ..................................................................... 54

6.6. Simulation and Numerical Analysis Models ................................................. 56

6.6.1. Repeater link loss model with antenna EDT implementation.................. 56

6.6.2. Orthogonality model .............................................................................. 58

6.6.3. Numerical calculation model for HSDPA SINR..................................... 59

7. Results .................................................................................................................. 61

7.1. Analysis of Simulated Results ...................................................................... 61

7.1.1. NodeB transmit power ........................................................................... 61

7.1.2. Average downlink cell throughput ......................................................... 63

7.1.3. Service probability................................................................................. 65

7.1.4. SINR ..................................................................................................... 66

7.1.5. Analysis of HS-DSCH SINR using different SINR thresholds ............... 69

7.1.6. Statistical analysis of HS-DSCH SINR in different scenarios ................. 72

7.2. Error Analysis .............................................................................................. 75

VIII

8. Conclusion and Discussions .................................................................................. 76

BIBILIOGRAPHY ................................................................................................... 78

APPENDIX A ........................................................................................................... 81

IX

List of Acronyms

1G First Generation

2G Second Generation

3G Third Generation

3GPP Third Generation Partnership Project

4G Fourth Generation

AC Admission Control

ACK Acknowledgment

BLER Block Error Rate

BS Base Station

CDMA Code Division Multiple Access

CQI Channel Quality Indicator

DS-CDMA Direct Sequence – CDMA

EDCH Enhanced Dedicated Channel

EDT Electrical Down Tilt

E-AGCH EDCH- Absolute Grant Channel

E-DPDCH Enhanced Dedicated Physical Data Channel

E-HICH EDCH-HARQ Indicator Channel

E-RGCH EDCH- Relative Grant Channel

FDD Frequency Division Duplex

FDMA Frequency Division Multiple Access

GSM Global System for Mobile communications

HARQ Hybrid Automatic Repeat Request

HC Handover Control

HHO Hard Handover

HSDPA High Speed Downlink Packet Access

HS-DPCCH High Speed-Dedicated Physical Control Channel

HS-DSCH High Speed-Downlink Shared Channel

HSPA High Speed Packet Access

X

HS-SCCH High Speed-Shared Control Channel

HSUPA High Speed Uplink Packet Access

ITU International Telecommunication Union

KPIs Key Performance Indicators

LC Load Control

LOS Line Of Sight

LTE Long Term Evolution

MDT Mechanical Down Tilt

MRC Maximal Ratio Combining

MS Mobile Station

NACK Negative Acknowledgment

NLOS Non Line Of Sight

NPSW Network Planning Strategies for Wideband CDMA

OFDMA Orthogonal FDMA

PC Power Control

QoS Quality of Service

RNC Radio Network Controller

RRM Radio Resource Management

SfHO Softer Handover

SHO Soft Handover

SIR Signal to Interference Ratio

SINR Signal to Interference and Noise Ratio

TDD Time Division Duplex

TDMA Time Division Multiple Access

TPC Transmit Power Control

TTI Transmission Time Interval

UE User Equipment

UMTS Universal Mobile Telecommunications System

UTRA Universal Terrestrial Radio Access

WCDMA Wideband CDMA

XI

List of Symbols

Wavelength

Orthogonality factor

a(hm) Mobile station antenna correction factor

cm Area correction factor

FB NodeB noise figure

fc Center frequency

FR Repeater noise figure

GB NodeB antenna gain

GD Repeater donor antenna gain

GR Repeater gain

Grx Receiver antenna gain

GS Repeater serving antenna gain

GT Combination of all gains and losses between UE and NodeB

Gtx Transmitter antenna gain

hbs Height of base station

hm Height of mobile station

i Other to own cell interference

Iother Other cell interference

Iown Own cell interference

k Boltzmann constant

LFS Free space path loss

LFRD Repeater donor feeder losses

LFRS Repeater serving feeder losses

Lp Path loss

LP Repeater path loss

LS Repeater service path loss

No Noise power at the output of NodeB

NTH Thermal noise density

XII

Ptx Transmitted signal power

Prx Received signal power

T Noise equivalent temperature

TB Noise equivalent temperature for NodeB

TR Noise equivalent temperature of repeater circuitry

SF Spreading factor

1

1. Introduction

In the last three decades the history of telecommunications has changed significantly. The advancements in the technology have made the mobile communication now possible and are ever improving. The current mobile communication system family can be categorized into different generations; analog based first generation (1G), circuit switched second generation (2G), packet switched third generation (3G) and lately IP based fourth generation (4G). However, with the technology developments, each proceeding generation provides better quality, capacity and bandwidth thus allowing wide range of services to be offered.

The major breakthrough in mobile communications was achieved at the advent of new millennium, when third generation partnership project (3GPP) provided the standards for new 3G mobile communication system; universal mobile telecommunication systems (UMTS). The radio access scheme used for this system was code division multiple access (CDMA), which allows greater capacity and higher data rates than the preceding systems. However, CDMA radio access technique generated some new difficulties for the radio network planners because it allowed the use of common frequency band in all cells of the network. Therefore, the capacity and coverage planning for UMTS network is done together because of the dominant other-to-own cell interference phenomenon.

The radio network planning is an ever continuous process. Even after the successful launch of the UMTS network, there is always further room for optimization. However, there are many different ways to optimize the successfully implemented UMTS network: adjusting the network parameters, down tilting of antennas or the use of wideband CDMA (WCDMA) repeaters, just to name a few.

There were two main purpose of this thesis. First to investigate the selected configurations for the WCDMA repeaters deployed in successfully operational UMTS network, for two different network topologies. The other main target of the study was attained by re-optimizing NodeB antenna tilt to separate NodeB and repeater serving areas. The re-optimization of NodeB antenna tilt was performed to determine the improvement in SINR levels in the network. The studies for this thesis are carried out by performing static simulations and numerical calculations for two different scenarios i.e. with and without repeaters, and constantly varied electrical down tilt (EDT) angle at

2

NodeB. The same set of simulation scenarios are used to investigate the behavior of UMTS network in case of two different network topologies. Thus, the target of research task is to determine the optimum EDT angle at NodeB and the better performing network topology, with or without repeaters.

The thesis is organized such that the brief overview of the fundamentals of cellular system and radio propagation model is presented in Chapter 2. Chapter 3 discusses about the basic WCDMA principles and systems (i.e. UMTS). The discussion is continued about the communication channels and radio resource management in WCDMA systems. At the end an overview about HSUPA (high speed uplink packet access) and HSDPA (high speed downlink packet access) is given. Chapter 4 describes the radio network planning process in general and for UMTS. A brief overview about the existing different network topologies is also presented. Chapter 5 explains about the WCDMA repeaters and their configuration parameters. Chapter 6 goes through the simulations and describes the different simulation scenarios related to studies of this thesis. Chapter 7 presents the simulation results, their analysis and the analysis of errors. Finally in the last chapter, the results are concluded and recommendations are made for future studies possible within the topic.

3

2. Fundamentals of Cellular Systems

This chapter provides the discussion on the basics of a cellular system. Firstly, the idea of cells and their types is discussed. Furthermore, brief overview of the efficient use of cellular resources is presented. Finally the propagation environment and its characteristics are briefly discussed.

2.1. The Cellular Network Concept

Mobile communication radio networks are also known as cellular networks. These networks provide a wireless connection for communication, for the users within the radio range of the network. These regions of radio coverage are termed as “cells”. The length and dimensions of each cell are dependent upon the system configuration and the transmission power levels of its serving BS (Base Station). A cellular network is constituted by multiple of these cells grouped together in a specific manner to form different tessellations.

The need of having a cellular network is to be able to get good coverage with mobility and at the same time to achieve enough user capacity for the whole system, without compromising the quality of the services provided by the system [1]. These targets are met by distributing the large geographical area of our interest into multiple smaller regions (or cells) each with its own set of allocated resources. However in actual practice a cell is overlapped by its adjacent cells at the edges. Still the regular shape of the cell must be known; “for systematic system design and adaptation for the future growth” [2]. Hence, some of the possible geometrical structures for a cell can be; a quadrilateral (preferably a square or a rectangle), an equilateral triangle and a hexagon as shown in Figure 2.1.

Figure 2.1: Different cellular structures (square, equilateral triangle, hexagon).

4

The cell structure is usually chosen from either of the geometrical structures shown in Figure 2.1. However, the chosen cellular structure should be able to serve even the weakest mobile link within the footprint of its serving BS. The footprint is defined as the service region of the BS transceiver.

2.1.1. Cell types

In a cellular network mostly the cells are categorized according to the region of their coverage i.e. the area covered by a single cell (or the horizontal radius of its coverage). These types of the cells are independent of the cellular geometrical structure used by the system. The types of the cells under discussion are presented in Figure 2.2. [1]

Figure 2.2: Combination of macro, micro and pico cells.

Macro cells have the largest horizontal radius ranging from 2 km up to several 20 km’s. These types of cells provide the largest coverage region. The BS antenna associated with these cells is placed well above the rooftop level or at the height which provides clear view of the surrounding or the terrain.

Micro cells have the coverage area less than the macro cells. They have the horizontal radius ranging from several hundred meters to few kilometers (i.e. 2 or 3 km). The height of the BS antenna associated with these cells is below the average rooftop level.

5

Pico cells have very limited area to serve within their coverage zone. The pico cells are typically used for indoor applications. The behavior of pico cells could be analogous to WiFi or hotspots.

The horizontal radius of these cells; macro, micro, pico varies depending upon the BS antenna height, antenna gain and radio propagation conditions considering the interference level within the tolerable limits. Mostly, different types of cells are used in combination with each other in order to enhance or improve the coverage or capacity of the system.

This combination of different cell types or in other words the splitting of macro cells into micro and/or pico cells is used to improve the capacity of the system. The macro cells have the largest coverage region but are deployed in the regions of low traffic density, such as highways, remote towns or villages. The micro cells are small in aspects of coverage but are used in locations with high user traffic density such as streets, town centers. The pico cells are most suitable for regions of very high traffic density and are usually deployed for indoor coverage. [2]

2.1.2. Sectorization

The cells are sectored or split up into much smaller cells or sectors to enhance the capacity of the system by limiting the co-channel and adjacent channel interference. When the number of users in a large cell increases more than the threshold of the cell, the large cell is split or sectored into few smaller cells (or sectors). Hence, this limits the interference levels within the tolerable limits and provides better manageability of the system. The cells are sectored, based on their serving antenna design i.e. the beam width of their BS antenna, as shown in Figure 2.3. The cells can be center excited as in case of omni-directional BS antenna, but in common practice the cells are corner or edge excited, as it provides better immunity to co-channel interference. [2]

Figure 2.3: Cell sectoring via BS antenna beam width.

6

2.2. Cellular Radio Resources

In wireless communication systems, especially considering the cellular networks, the radio resources are scarce and expensive. The need is to use the available radio resources sensibly and repeatedly without compromising the overall service performance of the system. The implementation of different radio access techniques, or the reuse of all set of radio resources (frequencies) after certain distance, can provide solutions to this problem.

2.2.1. Cellular reuse concept

In a cellular network, the combination of two or more cells results in the formation of the clusters. In each cluster, generally each cell is operating in a different group of radio frequency channels, and it is necessary that all the available groups of radio frequency channels are repeated in a single cluster. The clusters can be repeated as many times as necessary to provide coverage over the entire area but they should not overlap each other as shown in Figure 2.4 to avoid the interference.

Figure 2.4: Six clusters of cells with cluster size of 3.

The idea of repeating clusters leads to the need for better management of frequency channels in the network. The frequency reuse or planning is the design process of selecting and allocating the available frequency channel groups (or frequencies) to all the BSs in a cellular network in a sensible manner. The margin of frequency reuse in cellular networks is defined by the frequency reuse factor, which defines how often the group of frequencies can be repeatedly utilized. It also provides the information about the repetition of the clusters. The frequency reuse factor depends upon the morphology

7

and topology of the radio propagation environment and the implementation of radio network configuration. [2]

A properly chosen frequency reuse factor assists in improving the overall spectral efficiency of the system. In FDMA-TDMA (frequency division multiple access-time division multiple access) based networks such as GSM (global system for mobile communication), the performance is entirely dependent on the frequency reuse efficiency. In GSM networks, the allocated frequency band is grouped into smaller frequency sub-groups and reused over the whole coverage area. The frequency reuse factor in this case provides the appropriate distance, after which the same frequency sub-group (that has been used earlier) can be reused in the nearby cell present in the different cluster. Thus, the frequency reuse distance in fact provides the cluster size i.e. after how long distance the same cluster of frequencies can be repeated. Typically, the cluster size or the frequency reuse distance is in the range of 10 to 20 and it behaves as a function of radio propagation environment. [3]

In CDMA (code division multiple access) or WCDMA (wideband CDMA) based networks such as UMTS (universal mobile telecommunication systems) the same frequency band is used in all cells. The cells and users all are separated from each other by unique pseudo random codes. The frequency reuse factor in these networks is always one. Therefore the capacity in these systems also depends on the available number of pseudo random codes. However, the capacity in WCDMA systems is interference limited, because all the users interfere with each other in both uplink and downlink resulting in co-channel interference (both in uplink and downlink).

2.2.2. Co-channel interference

In WCDMA networks, both the users and neighbor BSs are distinguished of each other by unique pseudo random codes. However, these unique pseudo random codes lose their orthogonality (either partially or completely) due to the effects of multipath propagation and some other BSs transmit power related issues. Hence, the adverse effects of multipath propagation contribute to co-channel interference in both uplink and downlink directions as shown in Figure 2.5. The both uplink and downlink co-channel interference as shown in Figure 2.5 can be categorized as inter-cell interference (or other cell interference) and intra-cell interference (or own cell interference) [3].

8

Figure 2.5: Uplink and downlink co-channel interference in WCDMA network [3].

The other cell interference in uplink direction exists in the system because all the active UEs (user equipments) in the system are transmitting power in all directions. Although, the transmit power levels of the UEs are controlled by the power control commands from their serving BSs, (to tackle near far problem in WCDMA systems). But still transmit power of UEs from different (nearby) cells leaks in to other cells and contribute in other cell interference in uplink. In downlink, the other cell interference is due to the leakage of transmit power from BS’s in other cells. The own cell interference in the system is due to the rise in noise floor in uplink because of the different transmit power levels by different users in the network. Moreover, the co-channel interferences (i.e. own cell interference and other cell interference) are also at times bolstered by the characteristics of the radio propagation environment. [3]

2.3. Propagation Environment

In cellular communication systems, the radio propagation environment is defined as the surroundings of the path chosen by the radio signal to travel between the transmitter and the targeted receiver. There are different types of the propagation environments based on the terrain types i.e. if there is LOS (line of sight) path or the radio path is severely

9

obstructed by buildings or other obstacles [2]. The general categorization of the propagation environment is shown in Figure 2.6

Figure 2.6: Different propagation environments [2].

The outdoor propagation environment is further divided into two; macro cellular and micro cellular. This division is based on the placement height of BS antenna. The outdoor macro cellular environment is further break down into urban, sub-urban and rural areas based on the morphology of the terrain and the density of the obstacles in the radio path. In macro cellular environment the height of the BS antenna is above the average roof top level. However, the height of BS antenna for micro cellular environment is below the roof top level. The micro cellular networks are usually deployed in the region with the large number of buildings and high user density. The pico cellular deployment is used to provide cellular communication in indoor environment such as closed alleys, hallways, within buildings or malls. The BS antenna’s in indoor environment are deployed in such configuration, that they minimize the strong attenuation faced by the signal from the walls, floors, ceilings and other obstacles in the coverage area and improve the capacity of the system.

2.3.1. Propagation models

One of the most important parameters to evaluate the performance of any wireless communication system is the behavior of radio signal path between the transmitter and the receiver. It is because the strength of the radio signal is significantly altered by the morphology of the radio path. The radio path can be LOS and/or non-line of sight (NLOS) with some density of the obstacles in it. Thus, the propagation models are used to predict the average received signal strength at some distance from the transmitter. The simplest and fundamental propagation model is the free space propagation model, which explains the behavior of signal attenuation for the LOS radio path with no obstacles in between. The free space propagation loss depends on the distance from the transmitter and the frequency in use [2]. The model is given by equation 2.1.

10

= , (2.1)

where Ptx is the transmitted signal power, Prx is the received signal power, Gtx is the transmitter antenna gain, Grx is the receiver antenna gain, is wavelength of the signal and d is the distance between transmitter and the receiver [1]. However with the advancements in wireless communication systems and the use of modern technologies there is need for much more sophisticated propagation models which could predict the true nature of the received signal strength considering all the important and complicated details of the radio propagation environment.

2.3.2. Okumura-Hata propagation model

The Okumura-Hata propagation model is one of the most commonly used empirical propagation models for the macro cellular networks. The empirical propagation models consider the detailed information about the propagation environment, frequency and antenna heights, to predict the results as close to the measurements taken in real environment. The Okumura-Hata model is based on the field measurements carried out by Mr. Y. Okumura in and around the city of Tokyo, Japan in 1968 [5], which were later formulated by Mr. M. Hata in a mathematical form in 1980 [6]. Since the empirical models can easily be tuned according to any propagation environment, the Okumura-Hata model (originally based on the field measurements in Japan) can also be tuned according to any particular propagation environment of interest. Originally, the Okumura-Hata model was valid for carrier frequencies ranging from 150 MHz to 1500 MHz [1]. Later in 1999, a study program COST-231 was launched by European Union to extend the frequency range of Okumura-Hata model up to 2000 MHz, in order to use it for 3G (third generation) systems (such as UMTS) [7]. The mathematical form of the Okumura-Hata propagation model is given by equation 2.2.

= 69.55 + 26.16 ( ) 13.82 ( )

( ) + ([44.9 6.55 ) )), (2.2)

where a(hm) is mobile station antenna correction factor and its value is based on the further division of the macro-cellular environments as shown in Figure 2.6 [6].

The suggestions made by the COST-231 program were to make the original model compatible for 3G systems. Thus it changed the equation 2.2 proposed by Hata to the following form;

11

( ) 13.82 ( ) ( )

+([44.9 6.55 ) )) + , (2.3)

where the definitions of the parameters used in the above equations 2.2. and 2.3 are explained in the Tables 2.1 and 2.2 [4].

Table 2.1: Description of parameters in COST-231 propagation model

Parameter Description

fc Carrier frequency of the cellular system

hbs Height of the base station antenna

hm Height of the mobile station antenna

dkm Distance in km

Cm Area Correction factor, Cm<0 for rural and Cm>0 for urban.

Table 2.2: Frequency dependent constants define in COST-231 propagation model [7]

where A and B are the constants. The value of these constants is function of operating frequency band [7].

Parameter 150-1000 MHz 1500-2000 MHz

A 69,55 46,3

B 26,16 33,9

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3. Wideband CDMA principles and systems

This chapter introduces the basic characteristics and phenomenon’s associated with different WCDMA systems. The different WCDMA systems discussed here are UMTS and different variants of HSPA (high speed packet access). Moreover, the concept of RAKE reception is also discussed in accordance with multipath radio signal propagation. Finally, some radio resource management functions of a WCDMA system are discussed. In the end a brief overview of different variants of HSPA i.e. HSDPA and HSUPA are presented.

3.1. Multiple Access Techniques

The main aim in designing any cellular communication radio network is always to provide uninterrupted QoS (quality of service) to all the active users in the cell, using all the available radio resources as efficiently as possible. Since the radio spectrum is scarce and expensive, the available radio resources are to be shared between all users in the system. To overcome this problem different access techniques are deployed as shown in Figure 3.1.

Figure 3.1: Different access techniques; FDMA, TDMA, CDMA.

In these different multiple access techniques the radio resources are split in different domains such as frequency, time, and code; to be shared among all the users in the system. In FDMA, the allotted radio spectrum is divided into different frequency slots, where each slot is reserved for single user. To avoid interference between adjacent frequency slots, (large) guard bands are introduced between each slot. In TDMA, the whole radio spectrum in use is divided into small bursts called timeslots. Each user can

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use the entire timeslot for certain periods of time before it could be used by some other user in the system. In CDMA, the complete radio spectrum is used by all users at all times. Hence, each user is distinguished from each other by different pseudo-random code. [2], [3]

3.1.1. Spread spectrum technology

In CDMA systems there is no division of radio resources based on frequency or time. All the user and system level transmissions are spread over the entire common communication channel each distinguished from other by unique pseudo-random code. Therefore, CDMA systems can be categorized as the systems using spread spectrum technology. The principle of operation of any system using spread spectrum technique is presented in Figure 3.2.

Figure 3.2: The principle of spread spectrum system.

In spread spectrum system, at the transmission side the narrowband signal is modulated on to a certain frequency band. Then this modulated narrowband signal is spread using the unique pseudo-random code into a wideband signal. Later, this wideband signal is transmitted over the channel at specified carrier frequency. At the receiver side the process is reversed i.e. the received wideband signal from the channel is de-spread using the same pseudo-random code (which was used earlier for spreading). The de-spread narrowband signal is then demodulated to provide the original narrowband signal. The received wideband signal from the channel has the effects of both noise and interference from the environment. The receiver also considers these effects while de-spreading and demodulating. [8]

3.1.2. Spread spectrum systems and interference The spread spectrum technique is primarily used to implement CDMA method but it has also some other interesting properties. The spreading of narrowband modulated

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signal into the wideband signal makes it immune to the narrowband interference as shown in Figure 3.3. In Figure 3.3, the narrowband interference is added to the transmitted wideband signal from the channel. At the receiver side after de-spreading the received signal, the interference signal spreads and the transmitted user signal de-spreads. Thus, the targeted information signal is easily detected whereas the wide spread interference signal is neglected because of very low amplitude. [8]

Figure 3.3: The procedure of de-spreading in presence of interference.

3.2. CDMA in Cellular Networks

In cellular networks, different multiple access techniques are implemented to share the common resources allotted among all the users in the system. However, some multiple access schemes exhibits better performance over others. The CDMA scheme provides new horizons for the cellular communication because the scarce and expensive radio resources are not to be divided, but all the users in the system can use them simultaneously. Moreover, CDMA scheme enables some new features. [9]

3.2.1. Universal frequency reuse

The radio interface of the cellular networks implementing the CDMA scheme is shared by all the users simultaneously. The entire allotted spectrum is used for user and control transmissions. Each of these transmissions differ each other by unique pseudo-random codes. Since CDMA is a spread spectrum technique, the transmission codes spread the signal over the communication channel. The auto correlation and cross correlation properties of the transmission signals allow the entire spectrum to be reused in every cell in the network [2].

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3.2.2. Soft handover

One of the most important features of wireless cellular communication is to provide mobility for the users. Therefore, each mobile user can change its cell or network and still the user should have a continuous connection with the system. This user mobility related issue is controlled by network based events called handovers. In CDMA based systems due to universal frequency reuse concept, if a user is in the overlapping region between the cells it establishes the radio connection with both the cells at the same time. This special feature is known as soft handover (SHO). In the overlapping region also known as SHO region; the user establishes connections with all nearby BS. Hence, the UE uses the resources of all the cells involved in SHO region. In some situations, the SHO provides some gain (known as macro diversity gain) because the same signal is sent and received through different radio connections. The SHO gain minimizes the transmission power required in uplink and downlink [12]. [3]

3.2.3. Power control

In CDMA systems, all the users are using the same spectrum at the same time. Hence the users will interfere with each other and could degrade the performance of the system. Therefore, it is important to keep the transmit power levels checked. The power control feature ensures that both the user and control transmissions power levels are such that they cause minimum interference to the other users in the system [3]. The power control algorithm tunes the transmit power levels based on radio channel characteristics, fading conditions and offered services [12].

3.3. Multipath Propagation and RAKE Reception

The radio wave propagation is based on the propagation environment, such as outdoor and indoor. But the radio channel is characterized by multiple wave propagation phenomena. However, the wave propagation phenomena are reflections, diffractions and attenuation of the signal energy in the signal path. Hence, the received radio signal consists of the multiple reflected, diffracted and attenuated components of the original transmitted signal. The received radio signal has experienced multipath propagation and the environment is known as multipath environment, as shown in Figure 3.4. Hence the multipath propagation environment changes the characteristics of the transmitted radio signal. To understand the properties of the propagation environment different parameters such as angular spread, delay spread are used.

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The angular spread explains the deviation of incident angle of the received signal. It can be used to determine the effect of this incident angle deviation on the performance of diversity reception. However, the angular spread has much greater value in indoor and micro cellular environments compared with the macro cellular. The received radio signal is always the sum of its several replicas with different amplitudes and phases. Thus, the delay spread is used to explain the amount of variation of the multipath components (i.e. different replicas of the originally transmitted radio signal) as a function of delay. The delay spread is longer in macro cellular environments. [2], [3]

Figure 3.4: Multipath propagation environment.

3.3.1. Signal fading

The multipath environment causes rapid fluctuations in the amplitude of radio signal over a short interval of time or travel distance. These brisk fluctuations in the signal strength are influenced by the relative motion between the transmitter and receiver. This phenomenon is known as fast fading. On averaging the fast fading response of the signal, the slow fading (or log normal fading or long term fading) response of the radio signal is obtained. The slow fading is caused by the obstacles, such as buildings in the signal path. The slow fading averages the fast fluctuations in signal strength while the propagation slope is used to average the slow fading response of the signal. The propagation slope explains the attenuation experienced by the radio signal between the transmitter and the receiver over the distance. Figure 3.5 differentiates between the slow and fast fading. [1], [2]

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Figure 3.5: Fading effects of multipath signal.

3.3.2. RAKE receiver

In multipath environment, the replicas of the original transmitted signal with different amplitudes and phase delays arrive at the receiver. Therefore, to reconstruct the original signal, all the received replicas need to be summed up. In CDMA based systems such as UMTS, new receiver architecture is used known as RAKE receiver [10]. The task of RAKE receiver is to gather and combine the information from the multipath signal components arriving at least one-chip duration apart at the receiver [4]. The block diagram of the RAKE receiver is shown in Figure 3.6.

Figure 3.6: Block diagram of RAKE receiver.

The RAKE receiver consists of the fixed number of fingers; each finger is equipped with a correlator, channel estimator and phase rotator. The channel estimator tunes the amplitude according to certain attenuation factor and phase rotator equalizes the phases of fingers, before signal from each finger is combined using certain algorithm such as MRC (maximal ratio combining) [10].

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3.4. Wideband CDMA Systems

To enhance the capacity and achieve higher data rates in 2G cellular systems the international organizations, such as ITU (International Telecommunication Union) decided to develop new telecommunication standards. As a result, the 3G mobile communication systems such as UMTS and CDMA2000 evolved. Recently, ITU in association with 3GPP, which is the joint standardization project of the standardization bodies from Europe, Japan, Korea, the USA and China; are working on defining the technical specifications for 4G LTE (Long Term Evolution) systems [11]. The WCDMA UMTS standard includes two different radio interface duplex schemes; UTRA-FDD (Universal Terrestrial Radio Access-Frequency Division Duplex) and UTRA-TDD (UTRA-Time Division Duplex). The spectrum allocation in Europe, Japan, Korea and USA for WCDMA systems is shown in Table 3.1 [12].

Table 3.1: Spectrum allocation for WCDMA systems [12]

WCDMA Systems Uplink (MHz) Downlink (MHz) Total (MHz)

UMTS-FDD 1920-1980 2110-2170 2*60

UMTS-TDD 1900-1920 2010-2025 20+15

CDMA2000 (USA) 1850-1910 1930-1990 2*60

The UMTS cellular networks deployed so far use UTRA-FDD technique for their radio interface. In this technique, both the uplink and downlink channels are separated in different frequency paired channels. In UMTS, a 5 MHz band is used both in uplink and downlink. The UMTS uses DS-CDMA (Direct Sequence- CDMA) technique. Thus all the salient features of CDMA based systems are exploited to enhance the capacity and improve the overall performance of the system. The UMTS is WCDMA based system hence it uses spread spectrum technology. [12]

3.4.1. Basic UMTS terminologies

In UMTS, both the user and control data are spread before transmission and necessarily de-spread at the receiver. In spreading process, each data symbol (either user or control) is transformed in to number of chips thus increasing the bandwidth of the signal. The number of chips per data symbol is defined as spreading factor. The de-spread process is the exact opposite of the spreading; the received wideband signal is de-spread to provide the desired signal. In UMTS, both the user and control data transmissions are

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differentiated from each other by unique pseudo-random codes. There are two different codes implemented in any WCDMA based system; scrambling codes and channelization codes. The two different types of spreading codes are multiplied with the user and control data symbols to result in a wideband signal ready for transmission. The task of each of these codes varies in uplink and downlink, as illustrated in Table 3.2. [3]

Table 3.2: WCDMA system codes and their uses

Code Types Uplink Downlink

Scrambling Codes User separation Cell separation

Channelization Codes Data & Control Channels

from the same UE

Users within one cell

3.4.2. UMTS Radio frame structure

UTRA-FDD scheme is the most commonly deployed technique in UMTS cellular networks for the radio interface. In UTRA-FDD, two separate 5 MHz radio spectrums are used, one for uplink and one for downlink. Each of these 5 MHz bands consists of radio channels used for communication between UE and the network. These radio frequency channels carry all the data to be transmitted, which is fitted in the radio frame to be later mapped on to the physical channels for transmission over the air interface. A radio frame consists of 38,400 chips and 15 slots, where each slot carries a group of common channels and dedicated channels. The duration of a single radio frame is 10 ms hence resulting in a chip rate of 3.84 Mcps. A single slot in a radio frame consists of 2,560 chips with total slot duration of 666.7 µs. [3]

Figure 3.7: UMTS Radio frame structure [3].

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3.5. WCDMA Communication Channels

To establish any form of communication link between a MS (mobile station) and cellular network, a lot of information between the two entities is need to be exchanged. To carry the flow of data (i.e. the exchange of information), the communication channels are required. The communication channels provide both the logical and physical path for the data flow before, during and after the establishment of the communication link. There are three different types of communication channels in WCDMA system: logical channels, transport channels and physical channels. These channels exist in both uplink and downlink directions.

3.5.1. Logical channels In UMTS, the logical channels provide a logical path for data transfer services. The logical channels describe what type of data is to be transferred. Therefore, based on the type of the data flow the logical channels are further categorized to; control channels and traffic channels. The control channels are used to carry the control plane information within the system. However, the traffic channels are used to carry the user plane information. [3]

3.5.2. Transport channels

According to 3GPP specifications, the user plane and control plane information from logical channels is mapped on to the transport channels so it can be transferred over the air interface [13]. Hence, the transport channels carry the logical data from the application layer on to the transport layer. The transport channels are also further categorized to; common and dedicated transport channels. The common transport channels act as a resource i.e. shared among all or a group of users in a cell. However, the dedicated transport channel carries user and control information intended for single user only. [3], [12]

3.5.3. Physical channels

The user plane and control plane data carried by logical channels is carried over the air interface using transport channels mapped onto different physical channels. The physical channels are further categorized in to common and dedicated physical channels. The physical channels are available in both uplink and downlink directions. In

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uplink direction the control and data parts are code multiplexed. However, in downlink direction the control plane and user plane data are time multiplexed. Therefore, the user plane and control plane data is sent through the logical channels mapped on to different transport channels. The transport channel is also mapped through different physical channels to transfer data via air interface. The selection of different transport and physical channels depend upon the nature of data (either user or control), radio resource management and its related parameters [3]. [14]

3.6. Radio Resource Management in WCDMA Systems

The RRM (radio resource management) in any cellular system is responsible for the efficient utilization of all the resources related with its air interface. In WCDMA systems, the RRM includes PC (power control), HC (handover control) and the Congestion Control. The congestion control is further sub-divided into AC (admission control) and LC (load control). The combined functionality of these must provide optimum coverage, maximum planned capacity, guaranteed QoS and efficient utilization of radio resources keeping the overall interference within the tolerable limits. [12]

3.6.1. Power control in UMTS

In UMTS, the transmission power from BS and every UE constitutes to rise in overall interference of the interference limited system. To avoid exceeding the interference limit the transmission power levels needs to be kept in check. The power control algorithm is implemented to tune the transmit power levels based on radio channel characteristics, fading conditions and offered services [3]. The functionality of the power control algorithm is further divided into open loop and closed loop power control.

The open loop power control function is implemented in both directions (uplink and downlink). In uplink direction, the open loop power control function sets the initial transmit power levels for the UE and in downlink direction it determines the transmit power levels for the downlink channels. The open loop power control uses the measurement reports of the UE about the received power from the BS, and it then decides how to set the transmit downlink power levels. [3]

The closed loop power control function depends upon the feedback information from the other end of the communication link. This power control procedure is further

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divided into two different processes, both operating in parallel to each other; inner loop and outer loop power control. The inner loop power control is also known as the fast-closed loop power control. The fast closed loop controls the transmission power levels for UE and BS based on the received signal-to-interference ratio (SIR) level at BS and UE, to combat fading characteristics of the radio channel [15]. The TPC (transmit power control) commands are sent by UE and BS providing the information either to increase or decrease the transmission power levels. In UMTS both in uplink and downlink directions, the UE and BS measures the received SIR to compare it with the target SIR levels, set earlier by outer loop power control. If the measured uplink SIR is greater than the target SIR, the BS requests the UE to lower its transmission power. Similarly, if the measured uplink SIR is lower, then the UE increase its transmission power to attain the target SIR. In downlink the BS changes the transmission power levels in response to the TPC commands from the UE. [3], [12]

The outer loop power control provides the target SIR level for the inner loop power control. The outer loop power control adjusts the target SIR to achieve the desirable BLER (block error rate) for the particular service (voice or data) carried out by the UE. The change in the mobile speed or the multipath propagation environment also results in the adjustment of the target SIR. [16]

3.6.2. Handover control

The cellular concept presents the idea of mobility for users within different cells or network in a cellular system. In UMTS or in any network, the user based mobility issues are controlled by network based events called handovers [4]. In UMTS, the handover control supports different types of handover procedures such as HHO (hard handovers) only possible in HSPA, SHO (soft handovers) and SfHO (softer handovers).

In SHO, a mobile user is simultaneously connected to two or more different cells under the influence of same or different RNC (radio network controller). The SHO region is defined as the overlapping region between different cells. The users in SHO region utilize the resources of all the cells participating in SHO process. The readily participating cells are placed in an active set. However, the neighbor set or monitor set consists of the continuously monitored cells. The cells in neighbor or monitor sets replaces the bad performing cells in the active set. In certain situations, the SHO provides gain, known as macro diversity gain as discussed in 3.2.2. [15]

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In SfHO, a mobile user is simultaneously connected to two or more different cells controlled by the same BS (NodeB). SfHO is similar to the SHO procedure. However, in both SHO and SfHO, the mobile user is sharing resources from more than one cell thus reducing the overall radio capacity of the cell (and network also).

3.6.3. Congestion control

The capacity in UMTS is interference limited. Therefore, a large number of users can overload the system resulting in the performance degradation. Congestion control mechanisms are used to keep air interface load below pre-defined thresholds. The admission and load control are the congestion control techniques applied in parallel to optimize the quality and capacity of the UMTS network [3]. The admission control decides on the establishment of the new connections to the network. It estimates the rise in interference level and the effect on the overall system performance. The task of load control is to avoid the overload condition by maintaining all the existing connections at defined level of quality. But in case of overload condition, the load control algorithm follows a well-defined set of rules to re-achieve the targeted load in order to avoid the deterioration in the performance of the system. [12], [15]

3.7. High Speed Packet Access (HSPA)

In recent mobile communication systems there is a significant shift from the traditional circuit switched services towards packet switched services. The ITU in association with the 3GPP define and improve the standards for the efficient support of the packet based services. After the publication of WCDMA specifications in Release 99 the UMTS evolved. Furthermore, on exploring the room for some more improvements in packet access technology in WCDMA, 3GPP published Release 5 with HSDPA and later Release 6 with HSUPA. This HSPA technology provides significant enhancements in end to end service provision of packet switched services. Figure 3.8 shows the different specifications published by the 3GPP. [17]

Figure 3.8: 3GPP release schedule [11].

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The main aim of the HSPA technology is to provide seamless mobility for high speed data i.e. packet switched services. The HSPA systems can be implemented in 5 MHz carrier of the UMTS and can co-exist with existing 3GPP Release 99 system. But in HSPA technology the radio resources are shared among all the HSPA users in the system, hence requiring major changes in the architecture of the existing UMTS. Most of these changes are related to the RRM architecture of the system as shown in the Figure 3.9. [18]

Figure 3.9: HSDPA and HSUPA RRM architecture in Release 6 [18].

The basic aim of these changes is to provide higher throughput for high data rate applications with minimum latency in transmission. In HSPA technology the scheduling earlier performed by the RNC is now handled by NodeB, along with the QoS provision and dynamic resource allocation based on radio channel characteristics and interference variations. In addition, TTI (transmission time interval) is reduced to minimize the latency, support fast scheduler decisions and quick HARQ (hybrid automatic repeat request) retransmissions. [17]

3.7.1. High speed downlink packet access (HSDPA)

The HSDPA as defined in Release 5 specifications, can be deployed on the existing WCDMA based UMTS network architecture and it can enhance the WCDMA downlink packet data performance providing higher peak data rate, reduced latency and increased capacity. In HSDPA, the fixed radio resources such as codes and transmission power are shared among all the users in the network. Hence a new transport channel is

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developed for shared-channel transmission, known as HS-DSCH (high speed downlink shared channel). This channel also supports adaptive coding and modulation techniques, channel dependent scheduling (i.e. based on the CQI reports) and HARQ with soft combining [19]. And to support the signaling of HS-DSCH, two different channels are used; HS-SCCH (high speed shared control channel) in downlink and HS-DPCCH (high speed dedicated physical control channel) in uplink [18]. Figure 3.10 exhibits the flow of packet based user data and associated control signaling involved in HSDPA transmission. In HSDPA operation, the MS provides its channel quality reports i.e. CQI (channel quality indicator) on HS-DPCCH to NodeB. The scheduler at NodeB responds by sending the data for intended user on HS-DSCH and waits for its response. The MS replies with HARQ ACK or NACK message based on the outcome of the decoding process and could request for retransmissions in case of erroneous situation. [18]

Figure 3.10: HSDPA transmission scheme.

3.7.2. High speed uplink packet access (HSUPA)

The HSUPA specifications are defined by 3GPP in Release 6 to target the enhancement in uplink capabilities of the existing WCDMA based systems. Hence a new uplink transport channel is developed and it is known as E-DCH (enhanced dedicated channel). The E-DCH transport channel supports fast NodeB based scheduling, fast physical layer HARQ retransmissions with incremental redundancy and much shorter TTI [18]. Hence for scheduling control, E-AGCH (E-DCH absolute grant channel) and E-RGCH (E-DCH relative grant channel) are used. And for retransmission support E-HICH (E-DCH HARQ indicator channel) is developed. Finally, the user data is carried on E-DPDCH (enhanced dedicated physical data channel). Figure 3.11 depicts the flow of the user data and control signal in HSUPA transmission. In HSUPA operation, the MS informs NodeB of its sufficient resources (i.e. size of buffered data) for transmission and the

26

NodeB may respond with a resource allocation via E-AGCH or E-RGCH. The user responds to the grant and transmits data on E-DPDCH which is acknowledged by NodeB on E-HICH. [18]

Figure 3.11: HSUPA transmission scheme.

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4. UMTS radio network planning and network topologies

This chapter explains the procedural steps involved in radio network planning process in general. The explanation is continued for UMTS. Then some key performance indicators related to network planning are discussed. Finally, a brief overview of different radio network topologies is presented and in the end the idea of antenna down tilting is explored.

4.1. Radio Network Planning Environment

Radio network planning is a continuous process. In the process at first, the radio network plan is made. Then the plan is tested and finally implemented in the real environment. However, the planning process continues after the implementation, to further optimize the network. The further optimization is done by the continuous monitoring of the network. A functional radio network is planned by the radio network planner through the aid of different sophisticated and supportive radio planning tools. The radio planning tools are both software and hardware entities used at different planning phases. [3]

A radio network environment is modeled using simulation software. The simulations are carried out on modeled environment, to determine the maximum capacity and to predict (better) coverage regions. The network specific parameters, user traffic distributions, topographic and morphographic information of the environment are provided as an input to the simulator. After the simulation, the information about several parameters, such as SINR (signal to interference and noise ratio), transmit powers in uplink and downlink, Ec/N0 and other statistical data is obtained. These simulation results are further analyzed and used in planning of the actual radio network. The simulations are also performed after the implementation of the network, to further improve (or optimize) the performance of the network. [3]

After successful implementation of the planned radio network, field measurements are performed to explore the effects of the real life non-idealities such as network interference, fading and propagation channel characteristics. The data from the field measurements is used for optimization of the network. However, for the monitoring of

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the network, a network management system is deployed. It is external software which gathers statistical data of the KPIs (key performance indicators) of the network. The information gathered from both, the field measurements and network management system is fed to the planning tool, to assist the radio network planner in optimizing and designing the radio network. Figure 4.1 exhibits a radio network planning environment.

GGSN

Statistical data of KPIs

Planning Tool + Simulator

Field Measurements

RNC PSTNMSC/VLR

SGSN

GMSC

Internet

NodeB

NodeB

Figure 4.1: Radio network planning environment.

4.2. Radio Network Planning Process

A successful implementation of functional radio network involves very attentive planning process. The planning process for 2G networks is divided into three sections; network dimensioning, detailed planning and optimization of the network [3]. 3G networks follow the same planning procedure but with some changes [4]. Figure 4.2 depicts the planning procedure of a WCDMA based system.

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DimensioningNetwork LayoutNetwork elementsAntenna heights

Detailed PlanningConfiguration TopologyCode & parameter

OptimizationStatistical quality assessmentMonitoring & troubleshootingConfiguration adjustment

Figure 4.2: WCDMA planning process [3].

4.2.1. Dimensioning

The dimensioning is termed as pre-planning phase, because the network planner performs the rough estimations of the required coverage and capacity. Based on the raw information about the traffic density in the particular geographic region, the planner estimates the network layout and the required amount of BSs. The average antenna height must be defined in this phase in order to explain the radio propagation channel characteristics in next stage. [3]

4.2.2. Detailed planning

The detailed planning phase is pretty much similar to the dimensioning phase except for the fact that the hypothetical data used in earlier estimations is replaced by actual data. The detailed planning phase consists of configuration planning, topology planning and parameter planning as shown in Figure 4.2. The topology planning considers both coverage and capacity planning. A planning tool and/or simulator are required for the detailed planning phase. After this phase the network is ready to be launched. [3], [15]

4.2.3. Optimization

The optimization is known as post-planning phase because it continues even after the implementation of network. The statistical data of the KPIs gathered from the network management system is used to further improve the performance of the network. Also the information from the field measurements helps in tuning the network parameters. The optimization phase provides solution to the problems occurred after implementation or during monitoring of the network. [3]

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4.3. Radio Network Planning Process for UMTS

The radio network planning process for 3G systems is very similar to 2G systems with some exceptions discussed later in the chapter. Figure 4.2 exhibits the radio network planning process for UMTS. In UMTS, the dimensioning phase is similar compared to the detailed network planning. But in 3G systems (such as UMTS) the dimensioning is quite different from 2G systems, because the coverage and capacity planning cannot be done separately. In UMTS due to cell breathing phenomenon both coverage and capacity planning are combined together and is termed as topology planning [3]. [12]

4.3.1. Configuration planning

The configuration planning includes designing of hardware configurations of the required network elements for designed network plan. The designed network plan is based on the planning environment. It considers the physical limitations, such as the cost constraints and vendor specific system parameters. Moreover, the power budget is calculated in both uplink and downlink directions for different services (voice and data). The power budget considers different power gains and losses present in the communication path of the radio link. The results from the power budget calculations help in determining the cell ranges using the propagation models discussed in Section 2.3 [3]. Table 4.1 shows an example of UMTS power budget. [3]

Table 4.1: Example unbalanced UMTS power budget [3]

Parameter Speech Data Units

DL UL DL UL

Bit rate 12.2 12.2 384 64 kbps

Load 50 50 75 30 %

Thermal noise density -173.93 -173.93 -173.93 -173.93 dBm

Receiver noise figure 8 4 8 4 dB

Noise power at receiver -100.13 -104.13 -100.13 -104.13 dBm

Interference margin 3.01 3.01 6.02 1.55 dB

Total noise power at receiver

-97.12 -101.12 -94.11 -102.58 dBm

Processing gain 24.98 24.98 10 17.78 dB

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Required Eb/No 7 5 1.5 2.5 dB

Receiver sensitivity -115.10 -121.10 -102.61 -117.86 dBm

RX antenna gain 0 18 0 18 dBi

Cable loss / body loss 2 5 2 5 dB

Soft handover diversity gain

3 2 3 2 dB

Power Control headroom 0 3 0 3 dB

Required signal level -116.10 -133.10 -103.61 -129.86 dBm

TX power per connection 33 21 37 21 dBm

Cable loss / body loss 5 2 5 2 dB

TX antenna gain 18 0 18 0 dBi

Peak EIRP 46 19 50 19 dBm

Maximum allowed path loss

162.10 152.10 153.61 148.86 dBm

The power budget in Table 4.1 is unbalanced, as there is a clear difference in path loss in both uplink and downlink directions. However, the unbalanced power budget can be balanced using different techniques, such as reception diversity technique in uplink or deploying LNAs. Anyhow, it is observed that the results for the power budget calculations changes for different service profiles and loading conditions. To summarize, the results from configuration planning provide details about the link losses in uplink and downlink for coverage predictions, detailed NodeB configuration and configuration of its antenna line elements. [3], [15]

4.3.2. Topology planning

UMTS is an interference limited system. Therefore, interference from users within the cell (intra-cell) and other cells (inter-cell) has a significant impact on coverage and capacity planning of the system. Hence, each user contributes to the rise in overall noise of the system. The increase in the traffic density (i.e. network loading) varies the cell ranges, this phenomenon is known as cell breathing. In UMTS due to cell breathing, the coverage and capacity planning phases are combined as topology planning. Figure 4.3 depicts the WCDMA topology planning phases.

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Figure 4.3: WCDMA topology planning.

The coverage predictions in topology planning are performed to determine the cell ranges. The coverage predictions are based on the user defined coverage thresholds, used to estimate the coverage regions with cell overlapping and original dominance areas. Next, the system level simulations are performed such as Monte Carlo. In the simulation rounds, the estimations are made for different network loadings and service profiles for different (i.e. homogenous or heterogeneous) traffic distributions for certain clusters of cells, in order to have interference from both uplink and downlink included. Based on the results from the simulations the performance of the network is analyzed. The results of interest include the statistical data of the KPIs such as throughput, SINR, soft handovers etc. These results provide an idea whether the topology planning is done properly or needs to be improved. [3], [15]

4.3.3. Code and parameter planning

In CDMA based systems such as UMTS, before the network can be launched the radio resource planning needs to be performed. It involves code and parameter planning phases. In code planning, unique orthogonal codes are allocated to different cells to differentiate among users and physical channels. The code planning provides the management of radio resources in the network. In parameter planning the radio interface functionality is optimized. The parameters related to signaling, handover measurements and power control groups are defined for different connection modes. After the launch of the network, the parameters involved in the radio interface functionality can be optimized based on the requirements of radio propagation environment [3]. Figure 4.4 depicts the code and parameter planning phase. In Figure 4.4, the two BS’s B and C are separated from each other by unique orthogonal scrambling codes. Moreover, the MS is believed to be in SHO region. Thus, BSs A and C are part of the active set. [15]

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Figure 4.4: Code and parameter planning [3].

4.3.4. Operation optimization

In an operational network the performance evaluation is done by performing network inspections, field measurements and by monitoring the customer complaints. The results from the performance evaluations are analyzed to rectify network deficiencies and to identify future bottlenecks or drawbacks. Hence, this optimizes the network but optimization is an ever going process as it involves continuous verification and monitoring of the network. However, it is possible that at a certain point the network might not be further optimized. Hence, then the existing network requires an extension. The extension could be hardware or software or expansion of service area or by introduction of a new technology. [3], [12], [15]

4.4. Radio Network Performance Indicators

The performance of UMTS network is evaluated based on the analysis of the statistical data about the KPIs. The information about most of these indicators is gathered while carrying out the field measurements while some are obtained from network simulations before the network can be launched. However, in real life networks the information about KPIs is gathered from the network management system. However, all these

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indicators explain the operational behavior of the planned network. Some of the indicators of the interest are discussed below.

4.4.1. Service probability

The service probability provides the relationship between the successfully served users and un-served users in the system. In UMTS system, the users can be declined of service because of the following reasons; MS has attained its maximum transmit power limit, the uplink load limit of the network is reached, the NodeB total power limit is achieved or P-CPICH EC/Io limit is met. The service probability can be formulated as,

= , (4.1)

where Served users provide the information about the total number of users successfully served by the system and All users gives the total number of users available in the system. Typically, the target value for the Serv prob is near 100%. The information gathered from Serv prob helps in determining the efficiency of the network, i.e. how much users are served within a specific area in the network. [4], [12]

4.4.2. Other-to-own cell interference

In UMTS the same frequency band is repeated in neighboring cells thus causing cell coupling in terms of interference. This interference is termed as the other-to-own cell interference. It is a prominent performance indicator as it affects the noise rise in the network which ultimately affects the load handling capability of the network. The little i defines the relationship between other cell interference and own cell interference in one cell for uplink.

= , (4.2)

where Iown is described as the interference originating from own cell users and Iother is the corresponding total interference from other cells. In uplink ‘i’ is a NodeB specific parameter and is calculated for each cell. In downlink ‘i’ is MS specific parameter and calculated separately at each MS [20]. Typically in uplink ‘i’ ranges from 0.15 (for well isolated cells) to 1.2 (for poorly planned radio network) [15].

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4.4.3. Signal to interference and noise ratio (SINR) A UMTS network with HSDPA enabled features provides higher bit rates in downlink as compared to simple UMTS network. The performance of the HSDPA enabled UMTS network is estimated through the SINR of the HS-DSCH. The SINR for the link between the serving cell and a user is defined as [18];

( )

, (4.3)

where SF is the spreading factor used, is the distance dependent orthogonality factor according to a model in [21], Iown is the received interference originated from own cell users, Iother is the total received interference received from other cells, N is the received noise power and S is the power received on HS-DSCH. The SINR values are critical for the HSDPA link budget calculations as they predict the downlink received power at the MS.

4.5. Radio Network Topologies

The recent mobile communication systems are based on CDMA (i.e. UMTS) and OFDMA (i.e. LTE) radio access techniques. This is because CDMA or OFDMA access schemes are considered to be better performing than the traditional TDMA or FDMA. However, the performance of CDMA or OFDMA access scheme is strongly linked with network topologies or layouts deployed. Hence, the network topology in which the interference is smoothly distributed along the borders of the cell performs better as compared to the topology where the interference is directed to the center of cell. The network topologies (or layouts) are developed based on different tessellations such as; hexagon, triangle or square [22]. Moreover, each of these tessellations can have an omni-directional site or a group of sectors [23]. However, the main parameters in defining a network topology are cell size, site location, antenna sectorization and azimuth directions.

4.5.1. Hexagonal network topology

Hexagonal network topology is the most commonly used network topology because the hexagon tessellation provides coverage for larger areas with using the smaller number of cells. There are two different variants of layouts possible using hexagonal tessellation based on different site locations and different antenna directions [22]. In the first layout

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as depicted in Figure 4.5(a) the sites are located at the center of the polygon and the antennas are pointed towards the corners of the polygon. This first layout is also commonly known as hexagonal network layout and is mostly deployed in the USA. Figure 4.5(b) shows that in the second layout the sites are still located at the center of polygon. However, the antennas are pointed towards the vertices of the polygon instead of corners. The second layout is termed as nominal hexagonal layout or clover- leaf layout. The nominal hexagonal layout is commonly deployed in Europe [3].

Figure 4.5: (a) Hexagonal layout, (b) Nominal or Clover-leaf layout [3].

4.5.2. Triangular network topology

In triangular network topology, the polygon defining the cell is developed using the triangular tessellation. The triangular network topology is a novel network topology based on the modified hexagonal grid. The layout is planned such that the BS sites are located at the corners of the polygon with their antennas pointing towards the center of the polygon. The sites in novel triangular network topology are three sectored. Figure 4.6 depicts the novel triangular topology. [24]

Figure 4.6: Triangular network topology [24].

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In novel triangular topology, the sites have two different antenna beam width (or azimuth directions) combinations (30/150/270 degrees and 90/120/330 degrees) possible. The cell ranges in triangular network topology are long. Moreover, the problematic area (or the region with inadequate signal levels) is usually at the center of the polygon. However, with changes in BS site’s location or the antenna parameters the problematic area can be altered. [24]

4.5.3. Square network topology

In square network topology, the square tessellation is used to form a polygon that provides continuous network coverage. The polygons constructed with square tessellation have BS sites at their center with the antennas of sites pointing towards the corners of the polygon as depicted in Figure 4.7. However, the sites are four sectored with antenna beam widths of 45/135/225/315 degrees. Moreover, the cell ranges in the square network topology are small. [22]

Figure 4.7: Square network topology [22].

The shaded region in Figures 4.5(a), 4.5(b), 4.6 and 4.7 exhibits the dominance area of the sites. The dominance areas are entirely dependent upon the site and antenna configurations. One of the most common practices in changing the default configurations to improve the dominance areas is the down tilting of the antenna.

4.6. Antenna Down Tilting

The antenna down tilting has a significant impact on the system capacity and network coverage. Hence, the tilting is considered as an important parameter in radio network planning. The down tilting of the antenna restricts the antenna radiation pattern to

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certain area thus improving the signal level within that region and minimizing the interference radiation towards the other cells. However, excessive down tilting shrinks the service area of the antenna which might result in coverage problems at the cell borders. Therefore, an optimum tilt angle must be used based on different network topology, site or antenna configuration. [3], [25]

Figure 4.8: Antenna down tilting implementations.

There are two different implementations of antenna down tilting; mechanical down tilt (MDT) and electrical down tilt (EDT) as depicted in Figure 4.8. In MDT, the antenna element is physically down tilted i.e. the main lobe of the antenna radiation pattern is precisely directed towards the ground. The radiation pattern in the back lobe and side lobes directions are not tilted. Nevertheless, the impact of MDT in the network is that the interference to other cells in main lobe direction is reduced and the users near the antenna experience better signal levels. [3]

In EDT, the vertical radiation pattern of the antenna is uniformly down tilted in all horizontal directions, by directing the main lobe towards the ground and at the same time suppressing the back and side lobes of the radiation pattern. The EDT is carried out by adjusting the relative phases of antenna elements. The implementation of EDT in network reduces the interference radiation into other cells. Thus, EDT turns out to be a good choice for interference limited systems such as UMTS; because it reduces the other cell interference and allows the system to accommodate more users. [3]

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5. WCDMA repeaters

The repeater is the most important unit behind the studies presented in this document. Therefore, the discussion about repeaters and some of their key configuration parameters is done in the chapter. Moreover, a brief discussion on repeater noise is shown and finally the use of repeaters in UMTS is discussed.

5.1. Introduction to Repeaters

The main task of the repeater is to amplify the received signal and transmit it further forward. The repeater is a unit consisting of different antennas and cables. Repeaters can be added to the radio network to improve the overall coverage and capacity of the system. The repeaters can be deployed in indoor and outdoor radio environments. However, in this thesis the impact of repeaters on outdoor macro cellular WCDMA networks is studied. However in radio networks, the repeaters are implemented as a cost effective solution to fill in the coverage gaps or serve areas with increased traffic (as hotspots).

Typically for 2G systems, the repeaters are deployed to extend the coverage area or provide coverage to shadowed places where the overall network coverage is insufficient. However in interference limited 3G systems (such as UMTS) they can also be used to increase network capacity. [4]

5.2. Repeater Equipment

Functional repeater equipment consists of two antennas, an amplifier unit and cables required for connecting these parts. Figure 5.1 illustrates a typical outdoor repeater system with all the required equipment. The basic terminologies and parts of the equipment related to the repeaters are discussed below.

In the repeater system, the antenna which is coupled with the BS is called donor antenna and it establishes the connection with its serving BS. While, the other antenna is called serving antenna as it forwards the amplified signal earlier received by the donor antenna. The coverage area of the serving antenna is known as repeater service area. Typically, the antennas with higher directivity are used for donor antenna to minimize

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inter-cell interference and adverse effects of multipath channel. However, the repeater antennas can be either directional or isotropic. Moreover, it is preferred to use directive antennas rather than isotropic. It is because for isotropic antennas the isolation between donor and serving antennas is very poor. To make the repeater system operational in the network, power must be supplied to the repeater unit. [26]

Figure 5.1: An illustration of repeater system.

A repeater does not regenerate data it only amplifies the received data. Hence, the noise and interference within the received signal is also amplified. The repeater equipment may also experience self oscillation due to the poor isolation between the donor and serving antennas. In self oscillation phenomenon, the repeater will receive and amplify its own signal as illustrated in Figure 5.2. Hence to prevent self oscillation, the antennas with high front-to-back ratio are used which guarantees maximum antenna gain in the main antenna direction and maximum isolation in the reverse direction. [4], [26]

Figure 5.2: Repeater self-oscillation phenomenon [4].

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5.3. Repeater Configuration Parameters

The performance of the repeater system has a significant impact on the coverage and capacity of the network. In the next section, the parameters related to the repeater configuration are discussed.

5.3.1. Repeater gain

The repeater gain defines the amplification ratio of the received signal. It is independently adjustable in both uplink and downlink directions, typically up to 90 dB. Higher antenna gains are also possible by using antennas with narrow horizontal beam width. However, higher gains might initiate self oscillation phenomenon. Therefore, repeaters are equipped with AGC (automatic gain control) to keep the gain low enough to provide better isolation between donor and serving antennas [27].

5.3.2. Repeater distance

The positioning of repeater from the serving NodeB is critical. A repeater system can be placed at the border of the cell in order to extend the coverage and it is a common practice by the operators to provide coverage in rural areas. Moreover, if the repeater is placed within the cell or near the cell edge it improves the coverage and in some cases there might be improvement in capacity if repeater is used at hotspots. However, repeater location has less flexibility due to infrastructural, environmental, and governmental issues and rules. Figure 5.3 depicts the effects of repeater distance from the serving NodeB;

Figure 5.3: Effect of repeater distance.

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5.3.3. Repeater antenna height

The changes in repeater antenna height alter the link loss conditions, which ultimately varies the performance of the network. The change in height of the serving antenna affects the repeater cell propagation characteristics. While, varying the height of donor antenna there is significant change in donor link interference and performance. However, by changing the height of either of two antennas i.e. donor or serving, it is believed that the isolation between the two antennas increases [3], [4].

5.3.4. Hosting NodeB antenna

The repeater is transparent to its surrounding network thus NodeB does not know whether a repeater is installed in its coverage area or not. Hence, repeater is connected to its serving NodeB via directional radio link. However, repeater donor antenna could experience severe interference on donor link from other NodeBs in the nearby cells. Therefore, to tackle the received interference at repeater donor antenna, the hosting NodeB antenna should have LOS connection with the repeater donor antenna. Moreover, the serving NodeB could direct narrow horizontal beam width towards the repeater donor antenna by tilting the antenna.

5.4. Repeater Noise

Normally, repeaters have low noise generating properties but they still act as an additional noise source in the transmission path between UE and NodeB. The noise added by the repeater circuitry is thermal noise of the repeater equipment. Noise density of a component is expressed as,

= kT, (5.1)

where k is Boltzmann’s constant and T is the noise equivalent temperature of the component. Hence, the total thermal noise distribution at the NodeB receiver will be; [4], [32]

= k(T )G + k(T ), (5.2)

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where TR is the noise equivalent temperature of repeater circuitry, TB is the noise equivalent temperature for NodeB and GT is the combination of all gains and losses between the UE and NodeB.

G = G G L G , (5.3)

However, repeater antenna cable losses and other repeater implementation losses are also considered in the total path loss i.e. transmission path of the propagated radio signal between UE and NodeB via repeater. Thus, the transmission path between UE and NodeB via repeater can be divided in to two parts, donor link and serving link. The donor link (between the NodeB and repeater) is assumed to be in LOS thus can be modeled using Frii’s free space path loss. However, the serving link (between repeater and UE) usually experiences greater attenuation due to obstacles in path and is thus modeled using some empirical propagation model. Hence, the total link loss experienced by the radio signal will be the combination of direct link loss and repeater link loss. Figure 5.4 depicts the complete transmission path for the repeater installation and the parameter definitions for Figure 5.4 are presented in Table 5.1 [3], [4].

Table 5.1: Parameter definitions for transmission path of repeater

Symbol Description

FB NodeB noise figure

FR Repeater noise figure

LFB NodeB feeder losses

LFRD Repeater donor feeder losses

LFRS Repeater serving feeder losses

GB NodeB antenna gain

GD Repeater donor antenna gain

GS Repeater serving antenna gain

GR Repeater gain

LP Link loss between repeater and NodeB

LS Link loss between UE and repeater

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Figure 5.4: Transmission path for repeater installation.

5.5. Repeaters in UMTS

In UMTS, the repeaters can be deployed by the operators to enlarge coverage or improve the link quality within the areas with no coverage or low signal strength. UMTS is an interference limited system thus its coverage and capacity is affected by the addition of repeaters because the repeaters itself act as a source of interference to the system. However, there are both positive and negative effects of using repeaters in UMTS.

In UMTS, the repeaters do not provide any new (additional) radio resources to the system. The repeater shares the radio resources from its donor NodeB. Hence, sharing of radio resources might degrade the performance or lessen the capacity of the system. Thus, if installation, location (or position), antenna type and antenna gain for repeaters is selected wisely the adverse effects of repeaters on the network can be mitigated. For example if the repeater is placed near to its donor NodeB then there is increase in received noise level at NodeB in uplink which might changes the receiver sensitivity level [4]. However, when repeaters are planned to be added to the network, the power budget calculations are revised by considering the parameters related to repeater circuitry. Thus improper or any changes in repeater installation could have severe effects on the network which is designed considering earlier power budget calculations.

The main target of the repeater deployment in UMTS is to increase the cell coverage area. Usually, the repeaters steal users from the cell edge of the neighboring cells, as shown in Figure 5.5, which result in increase in loading at the donor cell. According, to cell breathing phenomenon, high load conditions increase the relative interference power in uplink which could degrade the performance of the network. To achieve maximum advantage by using repeaters and still keep the load conditions below the

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threshold level. The user density must be kept high in repeater coverage area because the repeaters lowers the transmit powers at NodeB allowing more power resources to accommodate more users in the network.

NodeB 1Repeater

NodeB 2 coverage area

NodeB 1 coverage area

RepeaterCoverage Area

NodeB 2

Figure 5.5: Repeaters impact on coverage.

The repeaters are transparent to its surrounding network. There are no soft handovers between repeaters and donor NodeB, because the users in repeater and its donor NodeB are considered in the same logical cell. In addition repeaters are suitable to extend coverage and improve signal quality. In UMTS, the pilot pollution is severe usually at cell edges i.e. there are many pilot signals from nearby NodeBs but without any one dominating. The repeater reduces the pilot pollution (at UE). The repeater brings the pilot signal of its host NodeB better than other NodeBs nearby. Hence, in doing so the repeater increases the cell dominance area of its donor NodeB. [28]

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6. Simulations

This chapter provides the information related to system level simulations performed for analyzing the behavior of repeaters in 3G systems for different radio network topologies. First, an overview of Matlab based simulator used during the study is shown, and then the support for repeater unit in the simulator is discussed. Finally, the simulation scenarios and the parameters and models used in the simulations are defined.

6.1. Simulations for Radio Network Planning

During radio network planning process different types of simulations are carried out to verify the capacity and the coverage of the earlier dimensioned radio network. Moreover, these simulations at times provide new horizons to the study in order to improve the performance of the existing radio networks. However, to perform the simulations for the radio network requires a simulator or a software tool. In case of radio network planning, the simulator is to be modeled in accordance with the real radio network environment. It is done so to plan a radio network with as realistic approach as possible.

From radio network planner perspective, the radio network simulator must be able to support both system level simulations and link level simulations. Usually, both system level and link level simulations are done in separate tools by separate people. In system level simulations, the simulation scenario is modeled according to the information provided about the overall system, such as information about radio resource management (RRM) functions. Where the information related to physical features of the radio link is considered for link level simulations.

The effect of repeaters and the EDT at the BS antenna for two different network topologies are investigated by performing simulations and carrying out numerical calculations analysis of some KPIs. However, before the simulation process is carried out, the simulator software is provided with some basic system level information, parameters for network configuration and some more scenario specific data to make the simulation scenario as close as possible to the real environment. After the simulations are completed, the simulator provides the results in forms of figures and statistical data, which are further analyzed to evaluate the performance of the simulated radio network.

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6.2. Static Simulations

The radio network simulations can be categorized into link level and system level. Moreover, the simulations can be further split up into static simulations and dynamic simulations. In this thesis, the simulations carried out were static in nature. In static simulations, various static time instances called ‘snapshots’ are used in analyzing the performance of the simulated scenario. However, to make the simulation results as close as possible to the real scenario (environment) different analysis methods and models are defined. Usually, in static simulations multiple simulation rounds (or snapshots) are carried out. The simulations performed for this thesis are static in nature. Several randomized snapshots are taken to analyze the performance of the simulated scenario. The concept of taking multiple snapshots is called Monte Carlo simulations. In Monte Carlo process, the results from different snapshots are combined to provide the average network performance estimation. Since, the number of users in network for each snapshot is Poisson distributed and their positions are also randomized. Hence, the planned network is eligible to work for wide variety of scenarios. In static simulations, the network operation cannot be analyzed as a function of time because the information gathered from the simulated network is from static time moments. [4], [29], [30]

6.3. Static Simulator Framework

The simulator software NPSW (network planning strategies for wideband CDMA) was used as a framework in the thesis. However, the original version 5.0.0 of this simulation software was modified extensively, to carry out simulations for different network scenarios, according to the target of this thesis [4]. However, NPSW simulation software consists of three main phases; general initialization phase, combined uplink and downlink iteration phase and post processing phase, as depicted in Figure 6.1 [29].

The initialization phase is the first step in simulation process; it reads all the user related, system related and control related parameters. After initialization phase the mandatory (pre-requisite) calculations are performed in order to present basis for further simulations and numerical calculations. Then next link losses are calculated from all NodeBs to all map pixels to simulate the propagation environment. However, the total number of map pixels (i.e. map resolution) defines the intensity and profoundness of the results. Thus, higher the map resolution larger the number of map pixels, which provides more accurate analysis of the simulated environment. The map resolution is user defined entity and can be changed before simulations. [29], [30]

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The next phase is iteration, combined uplink and downlink iterations for certain performance parameters are performed. The transmit powers in both uplink and downlink, along with soft handovers and NodeB loads are measured and adjusted as long as they are below defined thresholds [29].

Figure 6.1: NPSW simulator phases [29].

Finally, in post processing phase; the simulation ends and the earlier iteratively calculated information is processed. The post processed results are shown as different kinds of graphs and figures. However, before presenting the processed and iteratively calculated data, the simulation results are saved to text and data files for further post processing and analysis.

6.4. Repeater Model in Simulator Framework

Originally, the simulator software used in this thesis did not have any support for repeaters. Hence, an extension was made to the simulation software to support repeater implementation. The new extended simulation software with repeater support was used to carry out simulations in this thesis. However, the repeater implementation includes several issues which are discussed below. [4]

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6.4.1. Repeater unit

The repeater implementation was made possible by addition of some programs (programming code) to the simulation software. However, the parameters (e.g. repeater locations, repeater height, parent NodeB identification, gains, antenna types, tilting angles and antenna line losses etc) related to repeaters were provided (in a text file) as an input to the simulator. Figure 6.2, exhibits the screenshot from simulation software with repeater implementation in several UMTS cells. [4], [29]

Figure 6.2: Graphic representation for repeater implementation in simulation software framework.

6.4.2. Link loss and interference

Originally, in the simulation software framework the link loss calculations are done from every NodeB to all the map pixels (based on map resolution). The link loss calculations performed by the simulation software takes into account the selected propagation model (mostly COST 231-Hata), NodeB antenna patterns and gains.

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However, with the addition of repeaters there are additional link loss calculations to be performed for the users communicating with NodeB via repeaters. Therefore, all gains and losses from repeater installation are also considered for the additional link loss calculations.

In UMTS, the network interference is combination of both own cell interference and other cell interference. Hence, with the addition of repeaters to the network the repeater’s amplified interference also contributes to overall network interference. In the simulation software, an interference model is developed for calculation of the interference. The interference model considers the interference from all NodeBs in downlink and from all active users in uplink. Moreover, the additional interference due to repeaters is also calculated by using same interference model. The interference model, for the repeaters, considers the repeater link loss data and allocated transmit powers. However, due to repeater properties the total received power spectrum at repeater antennas is amplified. [29]

The interference model implemented in the simulation software calculates the own cell interference and other cell interference in both the directions i.e. uplink and downlink. In downlink the own cell interference is received from serving NodeB directly and also through own cell repeater which has a LOS connection to the serving NodeB. The other cell interference in downlink is from surrounding NodeBs. However, in uplink the own cell interference is from users within the footprint of the serving NodeB and service area of the repeater. The uplink other cell interference is from users in the nearby NodeBs. Therefore, it could be concluded that the interference in uplink is user specific and in downlink it is NodeB specific [29].

6.5. Simulation Scenarios

In this thesis, different system level simulations were carried out with and without repeaters. In the next subchapters the different simulation scenarios are discussed.

6.5.1. Network topology configurations

The simulations were done using two different network topologies. The network topologies under consideration were hexagonal (nominal clover leaf layout) and novel triangular as depicted in Figure 6.3(a) and Figure 6.3(b) respectively. The nominal clover leaf layout was constructed by nineteen 3 sectored NodeB sites forming a hexagonal grid with a site spacing of 1200 m. However, the triangular layout consisted

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of twenty-four 3 sectored NodeB sites with a site spacing of 1000 m. Moreover, both of the topologies i.e. nominal clover leaf and triangular were considered for simulations with and without repeaters. Hence, when adding the repeaters to the network, a repeater was placed for each of the nineteen 3 sectored NodeB sites in nominal layout. However, in case of triangular layout two different repeater scenarios were considered; first with a repeater for every six 3 sectored NodeB sites and second with three repeaters for every six 3 sectored NodeB sites. Figure 6.3 depicts all the layout scenarios with repeaters. [4], [24], [29]

(a)

(b) (c)

Figure 6.3: Different network layouts with repeaters; (a) nominal topology with repeaters, (b) triangular topology with 1 repeater and (c) triangular topology with 3 repeaters.

In all the three scenarios the repeaters were placed at certain distance from their serving NodeB. In nominal clover leaf topology the repeater were at 500 m and for triangular

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BS19 BS20

BS21

BS22

BS23

BS24

BS25 BS26

BS27 BS28

BS29

BS30

BS31 BS32

BS33 BS34

BS35

BS36

BS37 BS38

BS39 BS40

BS41

BS42

BS43 BS44

BS45

BS46

BS47

BS48

BS49 BS50

BS51

BS52

BS53

BS54 BS55 BS56

BS57

BS58

BS59

BS60 BS61 BS62

BS63

BS64

BS65

BS66 BS67 BS68

BS69

BS70

BS71

BS72

-3000 -2000 -1000 0 1000 2000 3000-3000

-2000

-1000

0

1000

2000

3000

BS1

BS2

BS3

BS4 BS5

BS6 BS7

BS8

BS9

BS10 BS11

BS12

BS13

BS14

BS15 BS16 BS17

BS18

BS19 BS20

BS21

BS22

BS23

BS24

BS25 BS26

BS27 BS28

BS29

BS30

BS31 BS32

BS33 BS34

BS35

BS36

BS37 BS38

BS39 BS40

BS41

BS42

BS43 BS44

BS45

BS46

BS47

BS48

BS49 BS50

BS51

BS52

BS53

BS54 BS55 BS56

BS57

BS58

BS59

BS60 BS61 BS62

BS63

BS64

BS65

BS66 BS67 BS68

BS69

BS70

BS71

BS72

REP1

REP2

REP3

REP4

REP5

REP6

REP7

REP8

REP9

REP10

REP11

REP12

REP13

REP14

REP15

REP16

REP17

REP18

REP19 REP

20 REP21

BS1

BS2

BS3

BS4 BS5

BS6 BS7

BS8

BS9

BS10 BS11

BS12

BS13

BS14

BS15 BS16 BS17

BS18

BS19 BS20

BS21

BS22

BS23

BS24

BS25 BS26

BS27 BS28

BS29

BS30

BS31 BS32

BS33 BS34

BS35

BS36

BS37 BS38

BS39 BS40

BS41

BS42

BS43 BS44

BS45

BS46

BS47

BS48

BS49 BS50

BS51

BS52

BS53

BS54 BS55 BS56

BS57

BS58

BS59

BS60 BS61 BS62

BS63

BS64

BS65

BS66 BS67 BS68

BS69

BS70

BS71

BS72

-3000 -2000 -1000 0 1000 2000 3000-3000

-2000

-1000

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topology the repeater is positioned at 750 m (approximately). Moreover, the repeaters in triangular topology were deployed such that their serving antennas were pointed towards the center of the layout. Thus, the problematic area, as identified in the triangular topology, was at the center of the layout. In this thesis, the repeater configuration was kept fixed for all the scenarios. However, the repeater gain was varied in accordance with the varying down tilt angle at the serving NodeB.

The propagation model considered was COST 231-Hata, with the area correction factor of -3dB and the building penetration loss of -15dB [3], [4]. However, to add more accurate OF (orthogonality factor) modeling the distance dependent orthogonality model of Molisch-Mehta was implemented [21]. To make the study homogenous, the user traffic distribution was kept within the studied region defined by a polygon as shown in Figure 6.4.

Figure 6.4: User distribution within the user defined polygon for nominal topology.

Figure 6.4 shows the user distribution for nominal topology with repeaters. The co-ordinates of the polygon formed by the user distribution are defined as an input to the simulator for all the topologies. The need to define the user distribution polygon is to keep all the users within the coverage zone of NodeB. Thus, the users will not wander at

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the edges of the map. Since, the simulation and numerical calculation provide averaged results. Thus, the obtained results will be properly representing the network. Moreover, a special studied region was also defined as depicted in Figure 6.5. Since, the network layout (either for nominal clover leaf or triangular) used has two tiers. Therefore, the first (or middle) tiers is chosen as studied region since it takes into account the NodeBs with identical coverage areas (i.e. the NodeBs at the border of the network are excluded from the analysis). Hence, the analysis of KPIs within the studied region makes the study more realistic. The region within the dark shaded boundary in the Figure 6.5 is the studied region.

Figure 6.5: Studied region in nominal topology without repeaters.

In each of the network layout scenario, the EDT angle at NodeB was varied from 0 to 10 degrees while the repeater configuration was fixed. However, the repeater gain was also varied to accommodate antenna pattern loss and noise due to repeater circuitry. The simulations were performed for macro cellular WCDMA UMTS network for voice users, using static simulation framework (software). The simulations were done for both cases i.e. with and without repeaters, for each of the network layout scenarios. Since the simulations done were Monte Carlo based, therefore the results from multiple snapshots were averaged and represented as figures. Apart from the static Monte Carlo based simulations, the numerical calculations for certain KPIs (i.e. HSDPA SINR) were also done and analyzed.

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6.5.2. Antenna configurations

In this thesis, the original antenna configuration files from KATHREIN-Werke KG were used for all NodeB and repeater antennas. According to these antenna configuration files, the antennas have 65o horizontal beam width [31]. Moreover as part of the study the EDT angle was varied at NodeB antenna from 0 to 10 degrees and the effects, of variation in EDT angle, on the repeater performance were analyzed. However, no mechanical down tilt was applied at both; NodeB and repeater antennas. Figure 6.6 exhibits the antenna radiation patterns of 65o horizontal beam width KATHREIN-Werke KG antennas used, with certain EDT angles.

Colors indicate EDT angles for 65 deg horizontal beamwidth antenna

Figure 6.6: Antenna radiation pattern of 65o horizontal beam width KATHREIN-Werke KG antennas at certain EDT angles [31].

The isolation between repeater antennas (i.e. donor and serving antennas) was assumed to be infinite for the simulations to avoid self oscillation phenomenon. However, this assumption is termed as valid because for networks with repeaters and no isolation, the resulting interference will completely block the cell. In real life the isolation between repeater antennas is at some adequate level which does not affect the network operation.

6.5.3. Radio network parameters

In this thesis for all the different simulation scenarios, a large number of parameters were used to define the radio access network elements. The parameter values for these radio network parameters are given in Tables 6.1, 6.2 and 6.3.

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Table 6.1: System level parameters

Parameter Value

Frequency UMTS 2100 MHz

CDMA bandwidth 3.84 MHz

Path loss model Hata- COST231

Building penetration loss 15 dB

Area correction factor -3 dB

Map dimensions [-3000,3000,-3000,3000]

Map resolutions 20 m

Transmission power per link 16 Watt

Total transmission power of own cell BS 20 Watt

Total transmission power of neighbor cell BS

12 Watt

Orthogonality model Mehta & Molisch

Traffic distribution Randomly distributed users within the user defined polygons

Std. deviation for log normal shadowing off

Table 6.2: Fixed parameter values for NodeB and UEs

Parameter Value

Mobile station antenna gain 0 dBi

Mobile station antenna height 1.5 m

Mobile station body loss 3 dB

Mobile station noise figure 8 dB

NodeB antenna down tilt (EDT) Varied from 0 to 10 degrees

NodeB antenna gain 17 dBi

NodeB antenna height 32 m

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NodeB cable losses 1.22 dB

NodeB noise figure 5 dB

NodeB TX power limit 41.5 dBm

Pilot TX power 33 dBm

Table 6.3: Fixed parameter values for repeaters

6.6. Simulation and Numerical Analysis Models

In this thesis, some special simulation models were designed according to the need of the work. Hence, few of the important models are discussed below.

6.6.1. Repeater link loss model with antenna EDT implementation

The repeater link loss model implemented in the simulator considers all the gains and losses related to the repeater configuration used. Since the main part of the study revolves around network topologies, the repeaters and antenna down tilting. Hence, antenna EDT implementation was also added to the repeater link loss model. Figure 6.7 exhibits the repeater link loss model with antenna EDT implementation. In Figure 6.7, the transmission path of the radio signals propagated between MS and (its serving) BS via repeater is illustrated. The transmission path is further categorized in to donor link and serving link. The donor link (between BS and repeater) is assumed to be in LOS. Thus, it is modeled using Frii’s free space path loss. However, the serving link (between repeater and MS) usually experiences greater attenuation due to obstacles in path. Hence, it is modeled using COST-231 Hata propagation model.

Parameter Value

Repeater antenna height 32 m

Repeater noise figure 3 dB

Repeater antenna down tilt (EDT) 5o

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Figure 6.7: Repeater system with antenna EDT implementation.

Therefore, the total link loss (LTotal) experienced by the radio signal is the combination of direct path loss (LD) and repeater path loss (LR), is given as (in dB scale) in equation 6.1.

= L + L , (6.1)

The variation in antenna EDT angle from 0 to 10 degrees changes the footprint of the BS as could be visualized from Figure 6.6. Simultaneously, due to variation in antenna EDT angle the signal strength at the repeater from its serving BS also changes. To maintain the repeater serving area coverage, the repeater gain is increased accordingly. Figure 6.8, shows the repeater gain as the function of EDT angle at BS antenna. In Figure 6.8, the changes in repeater gain for both the topologies (i.e. nominal clover leaf and triangular) involved in study is also shown.

In Figure 6.8, for both the topologies the curves for repeater gain follow the same trajectory. The same trajectory in repeater gain is because the same antenna configuration is used for repeaters in both the topologies. Typically, the repeaters could provide gain up to 90 dB to amplify the received weak radio signal [3]. However, in practice to achieve 90 dB of repeater gain is difficult, due to isolation problems between donor and serving antennas of repeater [33]. Hence, it would not be suitable to increase the EDT angle above 11 or 12 degrees or else the repeater gain saturates.

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Figure 6.8: Repeater Gain for different network topologies.

However, from Figure 6.8 the EDT angle at BS antenna for nominal clover leaf topology can be further increased as compared to the triangular topology. It is because the repeater gain is lower for the same EDT angle in nominal clover leaf topology than in triangular topology. The difference in repeater gains for both the topologies is due to the repeater placement (i.e. different repeater distances) in their respective topologies. Because larger the repeater distance lower will be the strength of received signal, thus higher the repeater gain. In nominal clover leaf topology, each repeater is associated with its parent BS and has a definite area to serve. While in triangular topology, the repeater density is low as (discussed in 6.5.1) illustrated in Figure 6.3(b) & 6.3(c) and the problematic area (region with inadequate signal levels) is large. The repeater gain tends to increase with increase in EDT angle. At high EDT angle the footprint of the BS shrinks allowing low strength signal to be received at repeater. Thus, repeater has to increase its gain in order to serve the users within its coverage region.

6.6.2. Orthogonality model

In WCDMA networks the main task is to maintain the orthogonality of the spreading codes to avoid intra cell interference. However, due to multipath effects in the propagation environment the orthogonality among the codes may destroy, thus increasing the interference levels. The OF quantifies the loss of orthogonality between the codes due to multipath propagation. Hence, to add more accurate OF modeling the

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distance dependent orthogonality model by Mehta and Molisch is implemented. Thus the mean value of the distance dependent OF ( ) is calculated from [21] as,

( ) = 1 exp , (6.2)

where r is the distance between MS and BS, a1, a2 and are the propagation environment dependent parameters.

6.6.3. Numerical calculation model for HSDPA SINR

The SINR in a WCDMA network considers three different types of interference sources. The three different interference sources under consideration are; own cell interference, other cell interference and thermal noise as earlier discussed in 4.4.3. HSDPA system implements CDMA as its access scheme, thus SINR for HSDPA system can also be determined by defining a model. However, the HSDPA SINR is numerically calculated by a model specifically designed for this simulation environment. In this SINR model, few of the system level parameters tabulated in Table 6.1 are taken in to account. The parameters taken in to account are transmission power per link, total transmission power of own cell BS, total transmission power of neighbor cell BS to name the few. The link loss calculations and the interference calculations are performed both in uplink and downlink directions by the model. Thus, the SINR level at each pixel is calculated. However, in this static simulator framework the serving cell (or NodeB) for HSDPA SINR is considered to be the one, that provides the strongest signal strength at the given pixel. Hence, the best SINR level calculated at each pixel is only considered. However, since repeaters are also part of the system, some modifications are made to the equation for SINR described in 4.4.3. The SINR for the link between the serving cell i and MS in location m using repeaters can be defined as; [34]

, (6.3)

where S, Iown , Ioth and N are the received powers defined as

= (1 + ),

= + ,

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= (1 + ),

where k is the Boltzmann’s constant, T is the noise temperature, B is the system bandwidth and FMS is the noise figure of the MS. Moreover, the parameters used in equation 6.3 are described in Table 6.4.

Table 6.4: Parameters involved in calculating SINR

Parameters Description

SF Spreading factor (SF=16 for HS-DSCH)

S Received power on HS-DSCH

Iown Received interference from serving cell

Ioth Received interference from other cells

pi Transmission power per link (or of HS-DSCH)

Pi Total transmission power of serving cell

Pn Total transmission power of neighbor cells

S,i Distance dependent OF for direct link

r,i Distance dependent OF for repeater link

WR Repeater weight factor

where WR is the ratio between link losses of the direct link and repeater link.

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7. Results

The simulation results for the different simulation scenarios described earlier in Chapter 6 are presented here. All of the results are based on the output data obtained from the static simulator framework used. However, most of the results are the averages from the user defined studied area (region of interest as shown in Figure 6.5) within the complete network area. Moreover, two different types of methods are used to estimate the performance of the simulated network. Firstly, Monte Carlo based simulations, which averages the results from different snapshots. Secondly, the numerical calculations are done by the simulator to determine the HS-DSCH SINR for the network.

The simulation results are obtained for two different network topologies with and without repeater implementation. Mainly, the study revolves around the network topologies, implementation of repeaters and EDT angle at the BS antenna. Therefore, the results presented are plotted as the function of EDT angle at the BS antenna. Moreover, the study involves the distance dependent orthogonality model (discussed in 6.6.2.) for more accurate OF modeling in the network.

7.1. Analysis of Simulated Results

This subchapter consists of the results, obtained both from Monte Carlo simulations and numerical calculations, as statistical data and figures for the different simulation scenarios defined in Chapter 6. The results presented for the analysis to estimate the performance of the network includes; NodeB transmit power, average downlink cell throughput, service probability, HS-DSCH SINR and its statistical analysis.

7.1.1. NodeB transmit power

In interference limited systems such as UMTS, the NodeB transmit power is an essential parameter in defining the capacity of the network. The average NodeB transmit powers for all the NodeB in the network is presented in a graphical manner in Figure 7.1. The result is for two different network topologies with and without repeaters as a function of EDT angle at the serving NodeB antenna. However, the graph in Figure 7.1 is constructed from the statistical numerical data gathered from simulations

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considering distance dependent orthogonality model but without any shadowing effects [21].

From Figure 7.1, the averaged NodeB transmit power tends to decrease together with increase in EDT angle. At high EDT angle the footprint or the coverage area of NodeB shrinks. Although not visible in Figure 7.1, the users which are closer to NodeB (i.e. within its footprint) are served while lots of (distant) users are declined of service due to coverage related issues. Hence, NodeB transmit at low power levels as it has to serve only nearby users (or within its coverage zone) in order to maintain the interference levels within tolerable limits in the network. However, at low EDT angles the coverage zone of NodeB is relatively larger as compared to the region for high EDT angle. Hence, the NodeB has to serve larger area and thus it requires high transmit power levels.

Figure 7.1: NodeB transmit power for different network topologies with & without repeaters.

Figure 7.1 exhibits that the NodeB transmit power levels are slightly higher when the repeaters are turned off as compared to the repeater on case. Since, in the simulator framework, the users are always served by NodeB providing best possible signal strength. Therefore, the distant users (or at cell edge) are served better by repeaters (when turned on) than NodeB. Therefore, NodeB does not have to transmit at high

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powers to serve the distant users (or at cell edge). Moreover, when repeaters are turned off the distant users (or at cell edge) have to be served by the NodeB or faces connection drop. In order to accommodate (provide service) to the distant users (or at cell edge) the NodeB transmit power levels become high.

It is evident from Figure 7.1, that for triangular topology, NodeB transmit power levels are slightly higher as compared to nominal clover leaf topology with repeaters. It is due to the placement of repeater and NodeB in the network, and also due to azimuth of their antennas. The nominal clover leaf topology is designed such to provide evenly distributed coverage while for triangular topology there always remains problematic area within the center of the hexagon [22]. However, when repeaters are turned off, the NodeB transmit power levels rises for nominal clover leaf topology as compared to triangular topology. The nominal clover leaf topology is designed such to provide smooth coverage in the network. Thus, in absence of repeaters the NodeBs increase their transmit power levels to maintain the smooth coverage in the network. Moreover, triangular topology is designed such to provide coverage in certain areas in the network allowing few coverage gaps (preferably at high EDT angles as depicted in figure A.19). Therefore, in absence of repeaters the NodeB endeavors to provide maximum coverage but fails to do so due to topology limitations. Thus, has slightly lower NodeB transmit power levels.

7.1.2. Average downlink cell throughput

The average downlink cell throughput for two different network topologies with and without repeaters as a function of EDT angle at the serving NodeB antenna is presented in a graphical manner in Figure 7.2. The resultant graphs are constructed from the data obtained by Monte Carlo based simulations for the user defined region discussed in Figure 6.4. Moreover, distance dependent orthogonality model but without any shadowing effects was taken in account during Monte Carlo simulations [21].

Figure 7.2 shows that the nominal clover leaf topology performs better than the triangular topology. Moreover, with addition or absence of repeaters in the network the nominal clover leaf topology still holds the edge. Since, in nominal clover leaf topology the interference is smoothly distributed [22], thus the overall interference level is within the tolerable limits allowing more users to be accommodated. Therefore, with large number of users the average DL cell throughput is high for nominal clover leaf topology as compared to triangular topology. Moreover, with addition of repeaters to nominal clover leaf topology the average DL cell throughput becomes insensitive to EDT variation at NodeB. Since, for nominal topology there is smooth coverage distribution

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[22] (as illustrated in Figures A.7 and A.8), thus repeaters acts as secondary NodeB’s and provide smooth coverage even at high EDT angles when footprint of NodeB has shrunk considerably small. Therefore, not visible in Figure 7.2, distant users from NodeB are served well by repeaters which contributes to stable average DL cell throughput. Moreover, in triangular topology even with addition of repeaters the average DL cell throughput does not have a significant improvement as compared to no repeater scenario particularly at high EDT angles. Since, for triangular topology the placement and azimuth of repeater is such that repeater strength is focused only to the center of the network (as illustrated in Figures 6.3(b), 6.3(c) and A.9 to A.16). At high EDT angles the coverage gaps remain unattended by repeaters. Hence, users in regions with bad signal strength (or coverage gaps) are deprived of service that lowers the average DL cell throughput. However, for triangular topology with three repeaters the average DL cell throughput is slightly better than (triangular) topology with single repeater because signal strength is much better with three repeaters in the center of the network. Therefore, with better signal strength more users could be accommodated that contributes to improvement in average DL cell throughput.

Figure 7.2: Avg. DL cell throughput for different network topologies with & without repeaters.

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7.1.3. Service probability

The service probability for two different network topologies with and without repeaters as a function of EDT angle at the serving NodeB antenna is presented in a graphical manner in Figure 7.3. However, the resultant graphs are generated by the statistical numerical data (i.e. service probabilities) extracted only for the NodeBs involved in study area polygon as shown in Figure 6.5. The distance dependent orthogonality model discussed in 6.6.2 was taken in account during the simulations.

Figure 7.3: Service probability for different network topologies with & without repeaters.

The addition of repeaters is very effective in increasing the overall performance of UMTS cellular communication network, if repeater configurations are made correctly and attentively [4]. Figure 7.3 exhibits same that with addition of repeaters the service probability levels in the system are improved. Since, repeaters increase and improve the coverage area (as illustrated in Figure 5.3) hence with large and improved service area more number of users are served easily, increasing the service probability levels in the network. However, larger the service probability higher will be the average DL cell throughputs therefore the graphs in 7.2 and 7.3 have pretty much identical pattern. Hence, nominal cover leaf topology with repeaters has smooth service probability and remains insensitive to EDT. Since, in nominal topology (as illustrated in Figures A.7

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and A.8) the repeaters themselves acts as secondary NodeB’s to provide smooth coverage even at high EDT angles when NodeB footprint does not cover the network completely. Therefore, not visible in Figure 7.3, distant users from NodeB are served well by repeaters which contributes to stable service probability level. Moreover, triangular topology with three repeaters has slightly higher service probability levels as compared to triangular topology with single repeater. Since, with three repeaters the signal strength is more improved within the network (especially in problematic zone) as compared for single repeater (as illustrated in Figures A.9 to A.16) thus allowing more users to be served. However, in absence of repeaters for both topologies, the service probability drops down considerably because of coverage gaps (at high EDT angles as illustrated in Figures A.1 to A.4 and A. 17 to A.19) or due to interference levels and antenna pattern loss (not visible in Figure 7.3).

Figure 7.3 shows that both the topologies either with or without repeaters respond differently to EDT. Moreover, with no EDT angle and at very high EDT angle (i.e. 10 degree) the difference in service probability levels is significant due to placement and antenna azimuth of repeater and NodeB in the layout. At 0 degree EDT angle, due to interference levels or antenna pattern losses or poor isolation between antennas, not visible in Figure 7.3 the service probability levels are significantly low. While at 10 degree of EDT the service probability is low because of coverage related problems i.e. large coverage gaps, bad signal strength. Moreover, with addition of repeaters the service probability levels are improved for both topologies at 0 and 10 degrees of EDT.

7.1.4. SINR

The average HS-DSCH SINR is obtained by the numerical calculations performed for the SINR model, earlier described in 6.6.3. The numerical calculations done for the SINR model considers the user defined polygon i.e. the studied area as shown in Figure 6.5. The obtained average HS-DSCH SINR is presented in graphical manner in Figure 7.4. However, the SINR presented in Figure 7.4 is for two different network topologies with and without repeaters as a function of EDT angle at the serving NodeB antenna. The distance dependent orthogonality model discussed in 6.6.2 was considered during numerical calculations.

Figure 7.4 exhibits that the average HS-DSCH SINR levels are slightly higher for the nominal clover leaf topology as compared to the triangular topology. In nominal clover leaf topology the interference is smoothly distributed along the borders of the hexagonal shaped cells. In WCDMA network, the interference is a sum of three different interference sources; own site signals, other site signals and thermal noise. Hence, SINR

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as discussed in 4.4.3 considers all three interference sources. Therefore, in nominal clover leaf topology the placement and azimuth of the NodeB antenna is planned such that the interference levels are low thus providing high SINR levels. However, in triangular topology the placement of NodeB controls the position of interference within the hexagonal shaped cells. Moreover, in triangular topology the interference is targeted at the center of the cell [22], [24]. Therefore, the serving area of the NodeB is hampered by the interference thus lowering the average SINR.

Figure 7.4: Avg. SINR for different network topologies with & without repeaters.

It is evident from Figure 7.4 that for both the topologies the SINR is higher with repeaters. Hence, the regions those are not properly served by NodeB due to high interference (not visible in Figure 7.4) or due to lower coverage (if noise is limiting the SINR) are served well by the repeaters. However, with addition of repeaters to the network the coverage region of NodeB is extended and divided into two different regions, NodeB serving region and repeater serving region (as shown in Figure 5.1). The users in repeater serving region (before the introduction of repeaters) experience inadequate signal levels and have low SINR. However, with repeaters implemented in the network the users in repeater serving region are served well and experience good SINR levels. Therefore, in absence of repeaters from the network (mostly with EDT angle above 6 degree) there are coverage gaps in the network and regions with high interference levels. Hence, the SINR is degraded in those regions that lower the overall average SINR in the network.

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From Figure 7.4 the SINR changes with the variations in the EDT angle at the NodeB antenna. The SINR tends to increase with increase in the EDT angle up to 9 degrees with repeaters for triangular topology. The improvement in SINR levels due to increase in tilting is because of decrease of interference in the network. The interference from other (nearby) cells is highest at 0 degree EDT angle. Thus, the users typically at the cell edge or at larger distance from NodeB experiences high levels of other cell interference due to no or less isolation between different cells. The SINR is dependent on the interference in the network (as discussed in 6.6.3.). Therefore, due to high other cell interference the SINR for the network is low. However, with addition of repeaters and gradual increase in EDT angle i.e. up to 9 degree the footprint of the NodeB starts to shrink. Thus, with lessen footprint of the NodeB the isolation between the nearby cells increases lowering the other cell interference and allowing high SINR. However, with very high EDT angles the footprint of NodeB has shrunk significantly creating regions with no or bad coverage (as depicted in Figures A.4, A.12, A.16 & A.20). Thus, the regions with bad or no coverage are served well by repeaters that allows high level of SINR overall in the network. Moreover, with further increase in EDT angle i.e. over 9 degrees the SINR starts to drop because the width of coverage gaps is even wide enough to be served by repeaters (at least for triangular topology). However, without repeaters the SINR levels increase only up to 6 degrees. Moreover, with further increase in EDT angle i.e. over 6 degree the SINR level starts to decline. The other cell interference is getting low at high EDT angles (i.e. over 6 degrees) due to higher isolation between the cells allowing the SINR level to improve. But at the same time the footprint of the NodeB also shrinks i.e. increasing the regions without or bad NodeB coverage (broadening the coverage gaps) that lowers the SINR levels considerably. Hence, lowering the overall average SINR levels in the network.

From Figure 7.4 it is also evident for nominal clover leaf topology with repeaters the SINR level never drop but steadily improve with increase in EDT angle. However, with no dip in the SINR level it is difficult to predict any optimum EDT angle for nominal clover leaf topology with repeaters. Hence, it might be interesting to determine how much more EDT could be applied in order to get some optimum EDT angle. The SINR (as discussed in 4.4.3.) also depends upon three different interference sources, other site signals, same site signals and thermal noise. However, to keep the noise floor constant the repeater gain is varied. Therefore, from Figure 6.8 the EDT angle could not be further increased since repeater gain is little above 75 dB. Hence, in practice repeater gain above 80 dB are not suitable. Thus, the SINR for further EDT angles could not be determined and neither do the EDT angle at which the SINR starts to dip.

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7.1.5. Analysis of HS-DSCH SINR using different SINR thresholds

In this subchapter the average HS-DSCH SINR from the subsection 7.1.4 is used. Based on the numerically calculated SINR data, the percentile of the regions with certain average HS-DSCH SINR range is determined within the studied area (as illustrated in Figure 6.5) for different topologies either with or without repeaters. However, during the calculations to determine the average HS-DSCH throughput; link adaptation and HARQ effects along with 15 HS-PDSCH codes was used [18]. The SINR is not only dependent on other cell and own cell interferences but also on orthogonality (as discussed in 4.4.3. and 6.6.3.) and UE receiver capabilities. Therefore, the average HS-DSCH SINR can be mapped for HS-DSCH throughputs (i.e. data rates) values as it remains almost the same for different propagation environments or multipath profiles [18]. Based on the results obtained from the numerical calculations of the SINR model described in 6.6.3; the single user performance in the network for both the topologies either with or without repeaters is analyzed by observing the SINR level. The SINR values are mapped to the HS-DSCH single user throughput. Table 7.1 specifies the mapping of HS-DSCH single user throughput for the different SINR levels in the network [18].

Table 7.1: HS-DSCH throughput mapping with SÌNR levels [18]

SINR levels (dB) HS-DSCH Throughput (Mbps)

7 0.7

10 1.3

14 2.6

17 4.1

19 5.2

21 5.6

Moreover, the percentile of regions for SINR levels less than 7 dB, 10 dB, 14 dB and greater than 17 dB are presented and explained in detail. The SINR threshold for 7 dB, 10 dB, 14 dB and 17 dB are selected because their percentage in the network is significant enough to be discussed. The percentile of regions for SINR greater than 19 dB and 21 dB are not exhibited, because the regions with SINR levels greater than 19 dB and 21 dB are very small.

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Figure 7.5: Percentile of regions with different average SINR thresholds in the network (a) 7 dB, (b) 10dB, (c) 14dB and (d) 17dB.

Figure 7.5 exhibits the plots for the percentiles of regions for different SINR thresholds. Moreover, the average SINR within the studied region for both topologies with and without repeaters is considered. However, at low EDT angles (i.e. ranging from 0 to 4 degrees) and at high EDT angles (i.e. ranging from 8 degree onwards) the changes in regions for different SINR thresholds are significant enough to be discussed.

The plots in Figure 7.5a, 7.5b and7.5c are almost identical as they all provide the more or less the same information. Similarly, the nominal clover leaf topology with repeaters in all the figures performs better i.e. has lowest percentile of regions with SINR levels below 7 dB, 10 dB and 14 dB respectively. Hence, it can be concluded that in nominal topology with repeaters there more regions with SINR levels above 14 dB. The high SINR levels in nominal clover leaf topology with repeaters as compared to triangular topology with repeaters are mainly due to two reasons. First, in nominal topology with repeater the placement and antenna azimuth of repeater is such that they provide (better) services in regions where NodeB fails to serve properly. Thus, the coverage distribution is smooth in the network. While in triangular topology with repeater, there are still regions with no coverage (as illustrated in figures A.11 to A.16). Because repeater

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density is low and repeaters are focused in only serving a single region (with coverage problems) at the center of the network. Moreover, in nominal topology with repeater the placement of repeater and NodeB is such that the interference is smoothly distributed along the borders of cell allowing high SINR levels to be achieved. However, for both the topologies without repeaters the percentile of regions with SINR levels less than 7 dB, 10 dB and 14 dB is more as compared to topologies with repeaters. Hence, it explains that repeaters do improve the performance of network. In absence of repeaters there are coverage gaps that remain unattended increasing the interference levels in the network. Thus, lowering the regions with good SINR (i.e. above 14 dB or more) in the network. Moreover, nominal topology without repeaters has slightly more regions with SINR levels less than 7 dB, 10 dB and 14 dB as compared to triangular topology respectively. Moreover, it appears as if triangular topology without repeaters performs better than nominal topology without repeaters. However, as shown in Figure 7.3, Figures A.1 to A.4 and Figures A.17 to A.20, triangular topology without repeaters have more regions without coverage as compared to nominal topology (without repeaters) and also have low service probability. In nominal topology without repeaters there are more served users as compared to triangular topology without repeaters because of network layout (or topology) configurations.

Figure 7.5a, 7.5b and 7.5c exhibits that at low EDT angles i.e. from 0 to 4 degrees, the percentile for regions with SINR levels less than 7 dB, 10 dB and 14 dB respectively is much higher as compared to SINR levels for EDT angles from 5 to 8 degrees. At low EDT angles from 0 to 4 degrees the isolation between sites is poor, interference levels and antenna pattern losses (not visible in Figure 7.5) are high thus contributing to increase in regions with low SINR levels. While at EDT angles from 5 to 8 degrees, the isolation between sites is little improved, the signal strength of NodeB and repeaters are focused within their respective coverage zones. Hence, this improves the service probability and SINR levels in network as shown in Figure 7.3 and 7.4. At high EDT angles i.e. from 8 degree onwards the percentile for regions with SINR levels below 7 dB and 10 dB increases because of coverage related problems. While for SINR levels less than 14 dB the percentile of regions does not increase. However, for nominal topology with repeaters there is no increase in regions with bad SINR levels but there is decrease in regions with SINR less than 14 dB (as shown in Figure 7.5c). Hence, due to smooth coverage distribution in nominal topology the SINR levels are slightly higher than 14 dB.

A figure 7.5d exhibit, the percentage of regions with SINR levels above 17 dB is higher for triangular topology than in nominal clover leaf topology. Moreover, addition or removal of repeaters from the topology does not have a significant effect on the percentage of regions with SINR above 17 dB. Since, the regions with SINR levels above 17 dB are near to the NodeB and/or repeaters. However, in both the topologies

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with repeaters the regions with SINR levels above 17 dB are slightly higher. The repeaters serve those areas well (such as cell edges and beyond) that are left unattended or experience poor signal strength from NodeB. The percentile of the region with SINR levels above 17 dB gets high with increase in EDT angle. Hence, at high EDT angles the signal strength from NodeB and repeaters (if present) is focused more to the users very near within its coverage zones. Thus, improving the isolation between sites, that lowers the interference levels and improves the SINR levels within the network.

7.1.6. Statistical analysis of HS-DSCH SINR in different scenarios

From 7.1.5 the percentile of the regions with certain average HS-DSCH SINR levels, within the studied area was known. However, it is still to determine how much is the improvement in the SINR levels when EDT is applied, comparing it with the reference case of nominal topology without repeaters and having 6 degree EDT angle (as shown in Figure 7.6. Figure 7.6 exhibits, the breakup of the entire map into regions of certain SINR levels; for nominal topology with no repeaters and 6 degrees of EDT angle at the NodeB serving antenna. Appendix A shows the figures with different SINR levels, for both the topologies with and without repeaters at 0, 3, 6 and 9 degrees of EDT angle.

Figure 7.6: SINR categorization for Nominal No Repeater with 6deg EDT.

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There were two main purpose of this thesis. First to investigate the selected configurations for the WCDMA repeaters deployed in successfully operational UMTS network, for two different network topologies. The other main target of the study was to determine the improvement in the average HS-DSCH SINR levels for two different topologies both with and without repeaters by re-optimizing the EDT angle at the NodeB serving antenna. Thus, the key results related to average HS-DSCH SINR levels are presented in Tables 7.2, 7.3 and 7.4. In the tables below the maximum, minimum and average SINR levels are presented for both the topologies with and without repeaters.

Table 7.2: Maximum SINR for both the topologies with varied EDT angle

Topology / EDT angles 0 3 6 9

Nominal without Repeaters 22,44 dB 22,48 dB 22,49 dB 22,52 dB

Nominal with Repeaters 22,41 dB 22,47 dB 22,48 dB 22,51 dB

Triangular with 1 Repeater 21,71 dB 21,71 dB 21,73 dB 21,75 dB

Triangular with 3 Repeaters 21,71 dB 21,71 dB 21,73 dB 21,74 dB

Triangular without Repeaters 20,95 dB 21,23 dB 21,32 dB 21,33 dB

From the data presented in Table 7.2, it could easily be narrated that the maximum value for HS-DSCH SINR levels remains almost the same. The maximum SINR level for both the topologies with and without repeaters is same. Since, mostly the maximum value for SINR is attained in regions with very low interference and good signal strength. Thus, the regions either near NodeB or repeaters could provide such high SINR levels.

Table 7.3: Minimum SINR for both the topologies with varied EDT angle

Topology / EDT angles 0 3 6 9

Nominal without Repeaters 5,71 dB 6,72 dB 7,89 dB 3,02 dB

Nominal with Repeaters 6,74 dB 6,17 dB 7,63 dB 9,02 dB

Triangular with 1 Repeater 1,84 dB 3,63 dB 6,67 dB 2,45 dB

Triangular with 3 Repeaters 1,59 dB 3,36 dB 7,22 dB 5,36 dB

Triangular without Repeaters 1,96 dB 3,71 dB 4,64 dB -5,39 dB

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The minimum SINR levels for both topologies with and without repeaters are presented in Table 7.3. From the statistical data tabulated above, nominal clover leaf topology does not seem to have much effect on SINR. The minimum SINR level for nominal clover leaf topology with and without repeaters is fairly same. However, at 9 degree of EDT angle for without repeater case, the SINR level is much worse compared to nominal topology with repeaters. The degradation in SINR level is due to fact at high EDT angles (such as 9 degree) the regions with no or bad coverage is more (as also depicted in figure A.4). Moreover, the minimum SINR values in triangular topology changes more with variations in EDT angle. However, the SINR levels are slightly better when repeaters are part of the network. The variation in minimum SINR levels for triangular topology is mainly due to placement and azimuth of NodeB (and repeaters if added), as they controls the interference distribution within the topology.

Table 7.4: Mean SINR for both the topologies with varied EDT angle

Topology / EDT angles 0 3 6 9

Nominal without Repeaters 10,52 dB 12,11 dB 12,84 dB 11,91 dB

Nominal with Repeaters 12,49 dB 12,86 dB 13,71 dB 14,22 dB

Triangular with 1 Repeater 10,66 dB 12,44 dB 13,47 dB 13,29 dB

Triangular with 3 Repeaters 10,54 dB 12,35 dB 13,41 dB 13,29 dB

Triangular without Repeaters 10,37 dB 12,18 dB 13,12 dB 12,14 dB

The mean SINR levels for both topologies are tabulated in Table 7.4. It can easily be deduced from the statistical data presented in table 7.4, that the mean SINR levels for nominal topology with and without repeaters remains pretty much the same apart for 9 degree of EDT angle. Moreover, in triangular topology both with and without repeaters the mean SINR is at same levels apart for 0 degree of EDT angle. Hence, it can be concluded that for both topologies with and without repeaters the SINR levels in most parts of the network will be good enough.

Hence, now from the above discussion few important queries related to research work can be answered. Therefore, from results and observations nominal topology performs better even at high EDT angles. The repeaters provide better improvement in nominal topology as compared to triangular topology. The repeaters also allow having high SINR levels near the NodeB (as discussed in section 7.1.1).

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7.2. Error Analysis

The two main error sources for this thesis work were the inaccuracies and short comings of the static simulator framework used and the ideal approximations for certain simulated parameters and components. Firstly, the issue related to the simulation tool was the used map resolution. The complete map obtained as a result of simulations consisted of almost 90,000 pixels of which the area of interest or studied area consisted of 9300 pixels. However, by increasing the map resolution the amount of pixels would have increased and the statistical data gathered from the simulation results and numerical calculations would have been more accurate and reliable. In practice it was not possible as on increasing the map resolution the memory usage of the system is fully utilized (i.e. falls short). Secondly, the simulation tool have certain inaccuracies as the propagation model (i.e. Okumura COST 231) used by it does not model well the scattering environment details. Moreover, the SINR level is calculated at each pixel by the specifically defined SINR model. But in the static simulator framework used, the serving cell (or NodeB) for SINR is considered to be the one that provides the strongest signal strength at the given pixel. Hence, the best SINR level calculated at each pixel is only considered. Therefore, the SINR calculations made by the simulation consider only the best server link. Hence, calculated SINR may not be true if the repeater serving area is overlapping with its parent NodeB.

The ideal approximations for certain parameters and components also add some error to the simulated results. For example, the repeaters considered in this thesis are analog and assumed to operate perfectly with ideal band pass filtering. Moreover, the antenna pattern isolation between the donor and serving antennas of the repeater unit is also assumed perfect. Finally, the main question (or the point of discussion) which remains is due to lack of accurate propagation modeling and exact values of other parameters. Whether, the simulated scenarios are realistic enough to provide sufficient data for repeater performance evaluation in both the topologies with varied EDT angle. However, it is still possible to observe the relative impact of repeaters, antenna tilt and topologies i.e. make an overall comparison.

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8. Conclusion and Discussions

In this thesis, the deployment of repeaters for two different topologies i.e. nominal clover leaf topology and triangular topology was studied. However, the study was further narrowed to explain the behavior of some KPIs in the network, when EDT angle is varied at the serving antenna of the NodeB. The numerically calculated HS-DSCH SINR was chosen as the key studied performance metric for HSDPA. Moreover, through Monte Carlo simulations service probability, average DL cell throughput and NodeB transmit powers were also investigated to analyze the performance of the network both with and without repeaters.

The results exhibit that for both nominal clover leaf topology and triangular topology the introduction of repeaters improves the overall performance of network. In absence of repeaters, there are coverage gaps in the network and the interference levels are high. Moreover, the variations in EDT angle at NodeB antenna also have their say on the performance of repeaters and overall performance of the network. At low EDT angles, the performance of the studied KPIs is below par. At low EDT angles, the isolation between cells is poor, interference levels are high within the network, antenna pattern losses also contribute to cause and signal strength is not much focused to the coverage zone. On increasing the EDT angle up to the optimum 9 degree, the performance of KPI improves resulting in overall improvement in network performance. The improvement in performance is due to proper isolation between cells and adequate signal levels within the coverage zone.

In this study the re-optimization of NodeB antenna tilt was performed to determine the improvement in HS-DSCH SINR levels within the network. The performance of HS-DSCH SINR was analyzed to determine achievable single user throughput for HSDPA network. The variations in NodeB antenna tilt had a significant effect on HS-DSCH SINR. At low EDT angles, the SINR levels are low due to poor cell isolation and high interference levels in the network. However, at high EDT angles the interference levels are low, cell isolation is good and signal strength within the coverage zone is improved. Moreover, as part of study, the performance of all the KPIs was also analyzed with respect to topology or layout changes. Hence, it was seen that all the KPIs performed better in nominal clover leaf topology as compared to triangular topology. The performance improvement in nominal topology was due to its layout configuration i.e. placement and azimuth of NodeB and repeaters in the network. In nominal clover leaf

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topology due to smooth coverage distribution the interference levels within the network were low. Thus, allowing the network to perform better.

Hence it can be concluded that the nominal clover leaf topology is much better than the triangular topology. Moreover, the introduction of repeaters to the network do improves the overall performance of the network. It was also found that variations in EDT angle do contribute to significant changes in the behavior of KPIs of the network. And the nominal clover leaf topology was less sensitive to variations in EDT angles as compared to novel triangular topology. An optimum EDT angle was determined based on the results, i.e. 6 degree for the both topologies without repeaters. However, with addition of repeaters to the topologies certain KPIs do perform better at much high EDT angles such as 9 degree.

Since the results were extracted from the data gathered from the simulations and numerical calculations, thus most of the results analyzed were averaged. Moreover, special care was taken to make the simulation scenarios as real as possible but still the inaccuracies and short comings of the static simulation framework cannot be avoided and are already discussed in error analysis.

Lastly, this work provided some idea about repeater performance in two different topologies (nominal clover leaf and triangular) but still there is plenty of room for further research related to repeaters possible. An interesting continuation would be to define a general formula in order to determine what might be an optimum position for repeater or use of repeater as relays within the network or use of repeater to improve outdoor-to-indoor coverage. Since, the simulations were done for HSDPA enabled UMTS network, therefore repeater can be an interesting tool to improve the coverage and capacity of HSDPA in UMTS networks.

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APPENDIX A

Figure A1: SINR categorization for Nominal No Repeater with 0deg EDT.

Figure A2: SINR categorization for Nominal No Repeater with 3deg EDT.

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Figure A3: SINR categorization for Nominal No Repeater with 6deg EDT.

Figure A4: SINR categorization for Nominal No Repeater with 9deg EDT.

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Figure A5: SINR categorization for Nominal with Repeater with 0deg EDT.

Figure A6: SINR categorization for Nominal with Repeater with 3deg EDT.

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Figure A7: SINR categorization for Nominal with Repeater with 6deg EDT.

Figure A8: SINR categorization for Nominal with Repeater with 9deg EDT.

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Figure A9: SINR categorization for Triangular with 1Repeater with 0deg EDT.

Figure A10: SINR categorization for Triangular with 1Repeater with 3deg EDT.

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Figure A11: SINR categorization for Triangular with 1Repeater with 6deg EDT.

Figure A12: SINR categorization for Triangular with 1Repeater with 9deg EDT.

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Figure A13: SINR categorization for Triangular with 3Repeaters with 0deg EDT.

Figure A14: SINR categorization for Triangular with 3Repeaters with 3deg EDT.

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Figure A15: SINR categorization for Triangular with 3Repeaters with 6deg EDT.

Figure A16: SINR categorization for Triangular with 3Repeaters with 9deg EDT.

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Figure A17: SINR categorization for Triangular without Repeaters with 0deg EDT.

Figure A18: SINR categorization for Triangular without Repeaters with 3deg EDT.

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Figure A19: SINR categorization for Triangular without Repeaters with 6deg EDT.

Figure A20: SINR categorization for Triangular without Repeaters with 9deg EDT.