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Transcript of How to Do Rf Planning
Chapter 1 Introduction
CHAPTER 1
INTRODUCTION
1.1 Introduction
The world has seen phenomenal changes in the telecommunication industry during the last
decades. Communication that was wired formerly is now performed wirelessly or in other
words by radio means. Thus, the wireless communication, which uncouples the telephone
from its wires, has exploded.
In 1985 the governing body of the European Postal Telephone and telegraph (PTT) and
CEPT set up a committee known as Group Special Mobile, later changed to Global System
for Mobile Communications (GSM). The advantages of GSM over the previous technologies
were, improved spectrum efficiency, international roaming, low cost mobile sets and base
stations (BSS), support for new services, high quality speech, compatibility with Integrated
Services Digital Network (ISDN) and other telephone companies [1].
The early years of the GSM were devoted mainly to the selection of the radio interface and
techniques for network access. Thus, since the very beginning radio access network is of
prime importance. The radio access network is the part that includes the base station
(BTS), the mobile station (MS) and the interface between them. The combination of
Frequency Division Multiple Access (FDMA) and Time Division Multiple access (TDMA)
technique is used in GSM networks and it can operate in frequency bands of 400MHz,
900MHz, 1800MHz and 2100MHz. The allocated operating band is divided into 200 KHz
channels called ARFCNs (Absolute Radio Frequency Channel Numbers) which are also
referred as physical channels. There are also logical channels in the GSM network that
carry user data (Traffic channels) and control information (Control channels). As the
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Chapter 1 Introduction
frequency is considered as limited resource, so for spectrum efficient utilization the concept
of frequency reuse is used. The basic construction block of the network is a “cell”. In a
cellular system like GSM, the coverage area is divided into hexagonal cells also called as
sector.
The designing of Radio Access Network (RAN) is a multidiscipline task that needs
balancing of competing requirements. Several objectives need to be achieved while
designing a RAN which are mainly classified as optimum radio coverage, sufficient network
capacity and quality of service.
In this project, the radio access network is to be designed for the given area or terrain
taking under consideration the specifications, allocated resources and requirements given
by Huawei, one of the world’s leading telecommunication vendor. The total cost for the
radio access network cost is given as: 2 Million $, one Base Transmission Station (BTS)
cost is 0.2 Million $, operating frequency bands are 900MHz and 1800MHz with 27
ARFCNs allocated, the number of users that are to be provided with services are 140,000
with GoS or blocking probability of 2%.
For sake of estimation and prediction, post processing RF tools are used. Here, such a tool
namely TEMS, Mapinfo and our own developed software Quick online Budget is used.
TEMS and Mapinfo are comprehensive planning tool to assist in fulfilling the requirements
of network designing and optimization. These tools were provided by Huawei and are
relatively new to us, so its exploration is the foremost task.
The process of RAN designing consists of two phases that are, pre-planning and system
growth phase. The phase one of preplanning can be accomplished in four discrete steps.
First step is of Coverage and traffic analysis, the objective is to provide optimum coverage
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Chapter 1 Introduction
and enable the network to have a capacity of at least 7,000 users. The aspect of network’s
coverage includes defining the clutter profile of the given terrain and the related signal
strength. The clutters are made for the sake of resource dimensioning. Dimensioning of the
resource means finding answers to two fundamental questions: How many traffic channels
(TCH) does a sector can handle and how many TCH are actually required in the area it is
covering? The result of the first step is the number of BTS per clutter needed to provide
required capacity and best possible coverage.
The second step is the nominal cell planning, which leads to a layout of cell pattern on the
given map. The propagation, frequency reuse and interferences are catered in second step.
A prediction model namely “Okumura-Hata” is used to estimate the propagation losses,
gains and received signal power. The frequency reuse pattern is chosen and two types of
interferences that are Co-channel (C/I) and adjacent channel (C/A) are decreased to
minimum possible level.
The step three consists of two major tasks that are, “Surveys of proposed Sites” and
“Tuning of prediction model”. The aspects like exact location, space for the equipment and
antenna types etc are checked in site survey which leads to the approval for physical
installment of BTS. The model tuning is done to enhance the accuracy of predictions model
applied in post processing tool. A transmitter is mounted on the proposed Site location and
the changes of one variable (losses) at different time interval are taken. Then each change
is analyzed to determine the modification factor for the model.
The final step for RAN designing is dimensioning of Base Control Stations (BSC) .So, at the
end of this fourth step the final design of radio access network is ready to be deployed.
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Chapter 2 Radio Access Network
CHAPTER 2
RADIO ACCESS NETWORK OVERVIEW
2.1 Introduction
The radio access network is between the mobile stations and the fixed infrastructure. It is
the most important part of the GSM system, being the key element to enable mobility and
wireless access. One of the main objectives of GSM is roaming. Therefore, in order to
obtain a complete compatibility between mobile stations and networks of different
operators, the radio interface must be completely defined.
In this chapter the Base Station Subsystem (BSS) is illustrated, giving the clear picture of
equipment used; its integration and respective working. The second part consisting of the
Radio interface gives a comprehensible idea of “which access technology is used and how
the mobile station gets connected to the GSM network.”
2.1.1 Base Station Subsystem
The Base Station subsystem (BSS) provides connection between MS and Network
Switching Subsystem (NSS) though Air interface. The BSS provides radio coverage on
prescribed geographical areas, known as the cells. The BSS consists of following parts:
1. Base Station Controller (BSC)
2. Base Transceiver station (BTS)
3. Transcoding Rate and Adaptation Unit (TRAU)
2.1.1.1 Base Station Controller (BSC)
The Base Station Controller (BSC) provides the connectivity of BTS to Mobile Switching
Center through E1 or microwave links. A group of BTSs are connected to a particular BSC
which manages the radio resources for them. Today's intelligent BTSs have taken over
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Chapter 2 Radio Access Network
many tasks that were previously handled by the BSCs. The primary function of the BSC is
call maintenance. The mobile stations normally send a report of their received signal
strength to the BSC every 480ms. With this information the BSC decides to initiate
handovers to other cells, control the BTS transmitter power, etc.
2.1.1.2 Base Transceiver station (BTS)
The BTS is the radio transmission equipment and covers each cell. BTS is also referred as
SITE. BTS can be divided into three parts,
i.) Radio Base Station (RBS)
a. Combiner Distribution Unit (CDU) - Multiplexing and de-multiplexing of signal.
b. Transceiver unit (TRX) - Used to provide communication path between mobile
station and Mobile Station Center when dedicated channel is assigned .Each TRX
has eight time slots.
c. Power Supply Unit (PSU) - Converts AC power to DC power (220 AC to 48 dc).
d. Control Module (CM) - Controls the micro wave link of the site that provides the
connectivity between BTS and BSC.
ii.) Transmission Module (TRM)
iii.) Power unit
Figure 2.1 shows the block diagram of RBS-900 illustrating the different elements of RBS.
Empty slots are left for future expansion.
Figure 2.1: Block diagram of RBS 900
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Chapter 2 Radio Access Network
2.1.1.3 Transcoding Rate and Adaptation Unit (TRAU)
The transcoder multiplexes four 16 Kbps speech or data (at 300, 600, and 1,200 bps)
channels. The 13 Kbps voice is brought up to a 16 Kbps level by inserting additional
synchronizing data. Then, four 16 Kbps channels are multiplexed onto a DS0 (64 Kbps)
channel.
There are two spots in GSM network where TRAU is placed,
1. At BTS in order to connect with BSC.
2. At BSC in order to connect with Mobile Switching Center (MSC).
2.1.2 GSM Radio Interface
The spectrum efficiency depends on the radio interface and the transmission of signals,
particularly in aspects such as the capacity of the system, techniques used in order to
decrease the interference and to improve the frequency reuse scheme. The specification of
the radio interface has an important influence on the spectrum efficiency.
2.1.2.1 Operating frequency bands
The operating frequency band is divided into uplink and downlink channels with a guard
band in between them. The uplink channel or reverse channel is from MS to BTS. The
downlink channel or forward channel is from BTS to MS. This table lists the specification of
the GSM–900, GSM–1800 and GSM–1900 system. For this project GSM-900 band is used.
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Chapter 2 Radio Access Network
Table 2.1: Specifications of GSM System
2.1.2.2 Multiple Access
A combination of Frequency Division Multiple Access (FDMA) and Time Division Multiple
Access (TDMA), combined with frequency hopping, has been adopted as the multiple
access schemes for GSM.
The 200 KHz carrier spacing is required to provide the necessary bit rate per carrier
frequency. The 200 kHz carrier spacing yields 125 carriers from the 25MHz spectrum
allocation. Because some of the energy in a GMSK modulated signal lies outside the
nominal 200KHz band, GSM recommends that carriers 1 and 124 will be used (guard band
of 200 KHz) in order to protect services using adjacent spectrum bands as shown in figure
2.2. These 124 possible carriers are defined for the uplink (Fu) and downlink (Fd) as
follows:
Fu (n) = 890.2 MHz + 0.2(n-1) MHz (0<n <125)
Fd (n)
= 925.2 MHz + 0.2(n-1) MHz (0<n <125)
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Chapter 2 Radio Access Network
Figure 2.2: FDMA/TDMA based radio channel concept
2.1.2.3 Channel types
There are two types of channels in GSM networks, the physical and the logical channels.
Physical channel: It is defined by specifying both, a carrier frequency
and a TDMA timeslot number. It is important to note that the frame
structure used on each physical channel is independent of those on the
other channels, most notably those with the same carrier frequency
assignment but different timeslot designations.
Logical channel: They are multiplexed into the physical channels.
Logical channels are, so to speak, laid over the grid of physical channels.
Each logic channel performs a specific task. Consequently the data of a
logical channel is transmitted in the corresponding timeslots of the
physical channel. During this process, logical channels can occupy a part
of the physical channel or even the entire channel.
There are two different types of logical channel within the GSM system:
i. Traffic channels (TCHs).
ii. Control channels (CCHs).
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Chapter 2 Radio Access Network
i. Traffic channels
Traffic channels carry user information such as encoded speech or user data. Traffic
channels are defined by using a 26-frame multi-frame structure. Two general forms are
defined:
a. Full rate traffic channels (TCH/F), at a gross bit rate of 22.8 kbps.
b. Half rate traffic channels (TCH/H), at a gross bit rate of 11.4 kbps.
ii. Control channels
Control channels carry system signalling and synchronisation data for control procedures
such as location registration, mobile station synchronisation, paging, random access etc.
between base station and mobile station. Three categories of control channel are defined:
a. Broadcast
b. Common
c. Dedicated
Table 2.2: Types and Functions of Control Channels
Channel Abbreviation Function/ ApplicationAccess Grant Channel - (DL) AGCH Resource allocation to MSBroadcast Common Control Channel – (DL)
BCCH Dissemination of general information
Cell Broadcast channel – (DL) CBCH Transmit cell broadcast messages
Fast Associated Control Channel – ( UL / DL)
FACCH For user network signalling
Paging Channel – ( DL ) PCH Paging for a mobile terminalRandom Access Channel – (UL) RACH Resource request made by
mobile terminalSlow Associated Control Channel (UL/DL) SACCH Used for transport of radio
layer parametersStand alone dedicated control (UL/DL) SDCCH For user network signallingSynchronization Channel (DL) SCH Synchronization of mobile
terminal
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Chapter 2 Radio Access Network
2.1.2.4 Interfaces
The following are the interfaces between different network entities of GSM. Figure 2.3
shows the placement of each interface.
Um or Air interface- it is between MS and BTS. It has gross data rate of
22.8kps (voice + data) and net data rate of 13kbps (voice).
Abis interface- it is between BTS and BSC. The interface comprises of
traffic and control channels. It has data rate of 16kbps.
A interface- it is between BSC and MCS. It has data rate of 64kps.
B interface- it is between MSC and VLR
C interface- it is between MSC and HLR
D interface- it is between HLR and VLR
E interface- it is between MSC and MSC
F interface- it is between MSC and EIR
G interface-it is between VLR and other MSC VLR
Figure 2.3: Interfaces of GSM network
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Chapter 2 Radio Access Network
2.1.2.5 Control Signalling on the GSM Radio Interface
Any flow of data in a network requires some additional information that helps the data to
reach the destination in the desired fashion. This additional information is known as
signalling. Signalling in GSM is required at all the interfaces, but radio network planners
deal mostly with the signalling between the mobile station and base station [2].
Signalling on all the interfaces except for the air-interface is done at 64 kbps. On the air-
interface the signalling can be done either by using the slow associated control channels
(SAACH), or by using the main channel itself wherein the signalling channel is sent instead
of sending the data – this is known as fast associated control channel (FAACH) signalling.
Fig 2.4 illustrate physical layer signalling protocol between entire network entities.
Figure 2.4: Physical layer Signalling protocol between network entities
The processing of protocols happen at different network entities, for example the
processing of Communication management (CM) is at MSC not on the BSC or BTS. The
functions of some important protocols are as follow [3].
Communication Management (CM) - Controls User Information
Mobility Management (MM) - Manages DB for Mobile location
Radio Resource (RR) - Provide communication link (MS to MSC)
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Chapter 2 Radio Access Network
Figure 2.5: 3 layer Signalling protocols between network entities
Figure 2.5 elaborates GSM specific signalling protocols of OSI layers on the radio interface.
Layer 2 signalling employs a modified version of the ISDN layer 2 signalling protocol, LAPD,
that is called LAPDm (m for modified). Layer 3 signalling on the GSM radio interface
contains control message exchanges between a numbers of protocol control processes.
These processes are Call Control (CC), Mobility Management (MM), Radio Resource
management (RR) [4].
2.2 Fundamentals of system design
The system design fundamentals include cellular concept and concept of frequency reuse.
GSM architecture is a cellular architecture. The region is divided into cells of hexagon
geometry. Hexagon are chosen because it covers largest area as compared to other
shapes of geometry like square or circle and it covers the region without leaving gap
between them.
2.2.1 Cell
A cell is defined as the area covered by one sector, i.e. one antenna system. The
hexagonal nature of the cell is an artificial shape (Figure 2.6). This shape is being closest to
circular, which represents the ideal coverage of the power transmitted by the base station
antenna. The circular shapes are themselves inconvenient as they have overlapping areas
of coverage; but, in reality, their shapes look like the one shown in the ‘practical’ view in
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Chapter 2 Radio Access Network
Figure 2.6. A practical network will have cells of non geometric shapes, with some areas not
having the required signal strength for various reasons.
Figure 2.6: Hexagonal Shape of Cell.
There are two main types of cell:
Omni directional cell - An omni-directional cell is defined as a BTS with an antenna
which transmits power equally in all directions (360 degrees) as shown in fig 2.7
Sector cell - A sector cell is the area of coverage from an antenna, which transmits
in a given direction only. The coverage area may be equal to 120˚ or 180˚.
Commonly BTS uses 3 sector cell with each antenna covering an area of 120˚ as
shown in fig 2.7 [5].
Figure 2.7: Omni Directional and Sector Cells
2.2.2 Site
A site is the position where the tower and antennas are located. Normally, a site has TRXs,
power supplies, radio base station units (RBS) etc. A site may serve an omni-cell or two or
more sector cells. In the first case the site is called an omni site, in the latter case a sector
site.
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Chapter 2 Radio Access Network
2.2.3 Cell Splitting
Cell splitting is a process of subdividing a congested cell into smaller cells each with its own
base station and a corresponding reduction in antenna height and transmitted power as
shown in fig 2.8. Cell splitting increase the capacity of cellular system since it increase the
number of times the channels are used.
Figure 2.8: Cell Splitting2.2.4 Cell Sectoring
It is the process of dividing a cell into three cells .Cell Sectoring keeps the cell radius
unchanged and seek methods to increase coverage and capacity. Sectoring increases
signal to noise ratio so that the cluster size may be reduced. Signal to noise ratio is
improved using directional antennas then capacity improvement is achieved by reducing the
number of cells in a cluster, thus increasing the frequency reuse [3]. The interference in
cellular system may be decreased by replacing a single omni directional antenna at the
base station by several directional antennas each radiating within specified sector as shown
in figure 2.9.
Figure 2.9: Cell Sectoring
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Chapter 2 Radio Access Network
2.2.5 Frequency Re–use
Frequency re-use means that two radio channels within the same network can use exactly
the same pair of frequencies, provided that there is a sufficient geographical distance (the
frequency re-use distance) between them so they will not interfere with each other. The
tighter frequency re-use plan, the greater the capacity potential of the network. Based on
the traffic calculations, the cell pattern and frequency re-use plan are worked out not only
for the initial network, but also for the future demands.
In [6], Groups of frequencies can be placed together into patterns of cells called clusters. A
cluster is a group of cells in which all available frequencies have been used once and only
once. Since the same frequencies can be used in neighboring clusters, interference may
become a problem. Therefore, the frequency reuse distance must be kept as large as
possible. However, to maximize capacity the frequency re-use distance should be kept as
low as possible.
The re-use patterns recommended for GSM are the 4/12 and the 3/9 pattern. 4/12 means
that there are four three-sector sites supporting twelve cells using twelve frequency groups.
The 3/9 cell pattern is use in the project as shown in figure 2.10.
.Figure 2.10: Frequency Reuse
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Chapter 2 Radio Access Network
2.2.6 Resource Dimensioning
In Radio Access Network, resource dimensioning is an important step of architecture
design. The architects study the system performance requirements and come up with an
architecture that meet or exceed the requirements in a cost effective fashion. Resources
mean any hardware or software entity needed to perform transactions initiated by users.
Resources are outgoing digital trunks, timeslots etc.
2.2.6.1 Busy Hour
The load handled by a system varies based on the time of day and day of the week. Most
systems are heavily loaded for a few hours in a day. The main objective of resource
dimensioning is to make sure that the system performs well during these busy hours. This
will make sure that the system has adequate resources to handle peak as well as off-peak
traffic.
2.2.6.2 Erlang
Erlang, a dimensionless unit is used in telephony as a statistical measure of the volume of
telecommunications traffic. It is named after the Danish telephone engineer A. K. Erlang,
the originator of traffic engineering and queuing theory. Traffic of one Erlang refers to a
single resource being in continuous use, or two channels being at fifty percent use. Erlang
can be calculated as:
A = λh 2.1
Where A = Traffic in Erlangs
λ = Arrival of new call per unit time.
h = Call holding time.
Alternatively it can be calculated as:
Erlang = (Average time for all resources / Total Time ) 2.2
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Chapter 2 Radio Access Network
Erlang calculation is used to determine whether the system is over provisioned or under
provisioned (too many or too few resource allocated). The traffic calculation is also used to
calculate E1 to determine how many voice lines are likely to be used during the busiest
hours.There are a range of different Erlang formulae to calculate these, including Erlang B
and Erlang C.
2.2.6.3 Blocking Probability
The blocking probability defines the chance that a user will be denied service due to lack of
resources. For example, a blocking probability of 0.01 means that 1% of the users will be
denied service. Blocking probability calculations refer to the busy hour only. Blocking
probability during the busy hour can be decreased by:
i. Increasing the resources in the system
ii. Offering incentives and discounts to encourage usage during off-peak
hours
2.2.6.4 Grade of Service
Grade of service is directly related to the blocking probability. A higher grade of service
guarantee to the user means ensuring a low blocking probability during the busy hours.
Providing a higher grade of service requires increasing the number of resources in the
system. Conversely, reducing number of resources; lower the system cost, but at the
expense of grade of service [6].
2.2.6.5 Erlang Calculations
There is a tradeoff between resource dimensioning and grade of service. The choice of
using the Erlang-B and Erlang-C formulas is dependent upon the handling of users when all
resources are busy.
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Chapter 2 Radio Access Network
Erlang-B is used when failure to get a free resource results in the user being denied
service. The users request is rejected as no free resources are available.
Erlang-C is used when failure to get a free resource results in the user being added into a
queue. The users stay in the queue until a free resource can be found.
The formulas of Erlang B and Erlang C works under the following conditions:
The number of customers is much larger than the number of resources available. In
general, the formula gives acceptable results if the number of customers is at least
10 times the total number of resources.
Requests from customers are independent of each other.
Customer requests are blocked/ queued only when no resources are available to
service them.
The resource is allocated exclusively to one customer for the specified period.
2.2.7 Clutter
Clutter is defined as the man-made and natural features that may impair radio frequency
propagation by reflection, diffraction, absorption, or scattering of the transmission waves.
There are various sources of clutter (morphological) data. The more current the clutter data,
the more accurate the propagation predictions will be. The benefits of updated clutter data
are:
Enhance coverage and reduce dropped calls
Predict the performance of wireless services
Optimize transmission site locations and reduce infrastructure costs
Some Clutter and Terrain Descriptions are:
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Chapter 2 Radio Access Network
2.2.7.1 Dense Urban:
Consist of densely built areas with mainly high buildings. Typically there is small number of
trees and vegetation within this area due to the density of buildings.
2.2.7.2 Urban:
Consist of metropolitan regions, industrial areas and closely spaced residential homes and
multi-storied apartments. Building density is high but may be interspersed with trees and
other vegetation.
2.2.7.3 Suburban:
Consist mainly of single family homes, shopping malls and office parks. Significant
vegetation, trees and parking lots are intermixed with buildings. Most buildings are 1 to 3
stories but significant exceptions do occur. Significant areas within small and medium cities
along with suburban communities surrounding major cities are examples of this
environment.
2.2.7.4 Rural/Quasi-Open:
Consist of open space with few buildings or residences. Major interconnecting highways,
farms, and barren land are found within rural areas. The largest variations in cell coverage
area are found in rural areas due to differences in vegetation and terrain.
2.2.7.5 Terrain:
Terrain descriptions focus on the land mass. Examples of terrain description are:
mountainous, desert, water (ocean, lake, and stream), etc. Types of terrains are
i. Forest: Foliage descriptions focus on the tree density and tree height.
ii. Roads: Roads are normally described in terms of their capacity to carry traffic. For
example, highways are described as being primary if they are heavily traveled multi-
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Chapter 2 Radio Access Network
lane roads (such as toll roads and inter-state highways). Smaller roads in and
around the city or town would be described as secondary roads.
2.2.8 Propagation Models:
The design of a new radio communication system starts with determination of a proper
location of the base station and determination of the frequency plan, both of which depend
highly on the propagation loss. By determining a model for the transmission of the
information through the channel, these two characteristics can be accurately determined.
In general the propagation model can be made in three steps. In the first step information
for the environment has to be considered. The second step includes the definition of
mathematical approximations of the physical propagation mechanisms, and the third step is
the formalization of the results of the previous two steps. These steps are described in
details in the following sections [7].
2.2.8.1 Influence of the Environment
The environments, where mobile radio systems are intended to be installed, are ranging
from in-door up to large rural areas. Wave propagation prediction methods are required
covering the whole range of macro-, micro, and pico –cells. In order to be described
accurately, different data is considered for the different types of environment. While for the
prediction of macro-cells terrain height information and land usage data is taken into
account for urban environment. Table 2.3 illustrate cell type definition
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Chapter 2 Radio Access Network
Table 2.3 Definition of types of cell
Cell type Cell radius Typical position of Base Station Antenna
Macro cell (large cell, terrain)
1km to 30 km Outdoor, mounted above rooftop level, heights of all surrounding buildings are below base station antenna height
Mini cell (small cell, suburban)
0.5 km to 3 km Outdoor, mounted above medium rooftop level, heights of some surrounding buildings are below base station antenna height
Micro cell (small cell, urban)
Up to 1 km Outdoor, mounted below medium rooftop-level, heights of all surrounding buildings are above base station antenna height
Pico Cell (indoor) Up to 500 m Indoor or outdoor mounted below roof top level.
2.2.8.2 Propagation phenomena and propagation loss
Calculation of the path loss is called prediction. Exact prediction is possible only for simpler
cases, such as the free space propagation or the flat-earth model. For practical cases the
path loss is calculated using a variety of approximations.
The propagation in free space can be characterized with the following formula:
L = 32.44 + 20log (f) + 20log (d) 2.3
Where f (MHz) is the operating frequency and d (km) is the distance between the
transmitter and the receiver.
The receiving power in free space is decreasing proportionally with the square root of the
distance, and additionally it is influenced by the following propagation mechanisms in the
mobile radio channel (fig. 2.11): shadowing, reflection, refraction, scattering, and diffraction.
Figure 2.11: Shadowing, Reflection, Refraction, Scattering, and Diffraction.
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Chapter 2 Radio Access Network
2.2.8.3 Modeling approaches
Three types of approaches have been used in order to find solutions for the problem of
channel planning.
Statistical methods (also called stochastic or empirical) are based on measured
and averaged losses along typical classes of radio channels.
Deterministic methods are based on the physical laws of wave propagation.
These methods produce more accurate and reliable predictions of the path loss
than the empirical methods; however, they are significantly more expensive in
computational effort and depend on the detailed and accurate description of all
objects in the propagation space, such as buildings, roofs, windows, doors, and
walls. The value of losses was provided for simulation purposes.
Semi-deterministic - combines the two methods described above.
2.2.8.4 Types of Propagation Model
The aim of propagation model is “to predict signal strength at a particular receiving point or
in a in a specific location area”. The propagation models are usually divided into:
i. Large-scale propagation models
ii. Small-scale propagation models
i. Large-scale propagation models
The large scale models normally are used to predict the mean signal strength for
transmitter-receiver separation distances (d) of several hundred meters apart. In general
when d > (5 * wavelength) the large scale model is applied.
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Chapter 2 Radio Access Network
ii. Small scale propagation models
Small scale model or fading models, describe rapid fluctuations of the received signal
strength over very short T-R separation distances (d) or short time durations. In general
small scale model is applied when d < (5 * wavelength).
2.2.9 Outdoor Propagation Model
Some of the outdoor propagation models are:
1. Longley-Rice Model
2. Durkin’s Model
3. Okumura Model
4. Hata Model
A proper system design requires accurate and reliable radio channel models, among which
the selection of prediction models are most important. Investigation of different existing
models and extensive measurements of mathematical equations; Okumura-Hata model is
selected. Okumura-Hata model is suitable in GSM 900 MHz network for macro - micro cells
and has better accuracy in dense urban areas especially for pico cells.
2.2.9.1 Okumura-Hata model
The Okumura-Hata model is a simple empirical approach for prediction. This model is
based on Japanese measurements done by Okumura, while the mathematical formulation
of the model is done by Hata.
The equations derived from the measurement data require only the four parameters;
therefore this model features very short computation time.
1. f is the frequency in MHz,
2. hbs is the base station antenna height above ground in m,
3. hms is the mobile station antenna height above ground in m,
4. d is the distance between BS and MS in km,
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Chapter 2 Radio Access Network
Figure 2.12: BTS and MS height for Okumura and Hata Model
Because of the calibration with measurement data the model is restricted to the following
ranges for the different parameters:
The operating frequency is between 150 MHz and 1500 MHz.
Height of the transmitter – 30 to 200m.
Height of the receiver – 1 to 10m.
Distance between transmitter and receiver – 1 to 10 km.
The basic transmission loss in dense urban areas is computed according to the formula:
2.4
Where hms is a correction factor with following values:
For Open Area, Suburbs, Medium city
) 2.5
For Large cities
2.6
2.7
In addition to the main formula for the dense urban case, there are some modifications for
rural (village, sub urban) and open areas.
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Chapter 2 Radio Access Network
2.8
2.9
These formulas describe the model in flat way, because they describe the wave
propagation without taking into account the local effects around the receiver, like reflection
or shadowing.
2.2.10 Problems and Solutions of Air Interface
Radio interface is the most vulnerable part of GSM connection. The air interface has to
cope with problems, such as variable signal strength due to presence of obstacles along the
way, radio frequencies reflecting from buildings, interference from other radio sources etc.
This section briefly discuss some of the problems occur during transmission of radio signals
and some solutions. Some of the most common problems are described below.
2.2.10.1 Problems
i. Shadowing
Shadowing occurs when there are physical obstacles including buildings between the BTS
and the MS (fig 2.13). Instead of reflecting the signal, these obstacles attenuate signal
strength. When the MS moves, the signal strength fluctuates depending on the obstacles
between the MS and BTS. Drop in strength are called fading dips.
Figure 2.13: Shadowing
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Chapter 2 Radio Access Network
Shadowing is generally a problem in the uplink direction; because BTS transmits
information at a much higher power compared that from MS. The solution to over come this
problem is known as Adaptive Power Control. Based on quality and strength of the received
signal, BTS informs MS to increase or decrease power as required.
ii. Multi-path Propagation
Multi path fading occurs when there is more than one transmission path to the MS or BTS,
and therefore more than one signal is arriving at the receiver. This may be due to buildings
either close to or far from the receiving device. Rayleigh fading and time dispersion are
forms of multi path fading.
Figure 2.14: Multi-path Propagation
In figure 2.14, the received signal is the sum of identical signals that differ only in phase
(and to some extent amplitude). A reflected signal that has traveled some distance causes
“Inter Symbol Interference” where as near reflection causes “Frequency Dips”.
iii. Time Alignment
Each MS on a call is allocated a time slot on a TDMA frame. This is an amount of time
during which the MS transmits information to the BTS. The information must also arrive at
the BTS within that time slot. The time alignment problem occurs when part of the
information transmitted by an MS does not arrive within the allocated time slot. Instead, that
part may arrive during the next time slot, and may interfere with information from another
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Chapter 2 Radio Access Network
MS using that other time slot. A large distance between the MS and the BTS causes time
alignment. Effectively, the signal cannot travel over the large distance within the given time.
Figure 2.15: Time alignment problem
In figure 2.15, an MS is assigned time slot 1 initially. During the call MS moves from position
A to position B. As distance increases, answer from MS arrives late at the BTS. The delay
becomes so long that the transmission from the MS in time slot 1 overlaps with the
information which the BTS receives in time slot 2 [3].
2.2.10.2 Solution to Problems
There are number of solutions to overcome these problems.
Channel Coding
Interleaving
Frequency hopping
Antenna Diversity
Time Advance
i. Channel Coding
Channel coding is normally used for overcome the problems caused by fading dips. In
channel coding, user data is coded using standard algorithms. This coding is not for
encryption, but for error detection and correction purposes
ii. Inter-leaving
Inter-leaving is the spreading of the coded speech into many bursts. By spreading the
information into many bursts, it is easy to recover the data even if one burst is lost.
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Chapter 2 Radio Access Network
Figure 2.16: Inter-Leaving of data
As shown in Figure 2.16, the bits of each block are sent in a non-consecutive manner. If
one block is lost in transmission, it is still manageable to recover the data [2].
iii. Frequency Hopping
In frequency hopping, the frequency on which the information is transmitted is changed for
every burst. In GSM there are 64 patterns of frequency hopping; one of them is a simple
cyclic or sequential pattern. The remaining 63 are known as pseudo-random patterns,
which an operator can choose from. Generally it does not significantly improve the
performance if there are less than four frequencies in the cell. The reasons of using
Frequency Hopping are:
Decreasing the probability of interference
Suppressing the effect of Rayleigh fading
iv. Antenna Diversity
Antenna diversity increases the received signal strength by taking advantage of the natural
properties of radio waves. Increased received signal strength at the BTS is achieved by
mounting two receiver antennae instead of one. Two Rx antennas are physically separated;
the probability that both of them are affected by a deep fading dip at the same time is low as
shown in figure 2.17. There are two primary diversity methods: space diversity and
polarization diversity.
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Chapter 2 Radio Access Network
Figure 2.17: Antenna Diversity
v. Timing advance
Solution to counteract the problem of time alignment. It works by instructing the misaligned
MS to transmit its burst earlier or later than it normally would. In GSM, the timing advance
information relates to bit-times. An MS is instructed to do its transmission by a certain
number of bit-times earlier or later related to previous position, to reach its timeslot at the
BTS in right time. Maximum 63 bit-times can be used in GSM systems. This limits GSM
normal cell size to 35km radius.
Figure 2.18: Timing Advance
As shown in figure 2.18 , BTS instruct MS to start sending information at TS-4 so that it
reaches at BTS on its allocated TS i.e. at TS-5.
2.2.11 Interference
The signal at the receiving antenna can be weak by virtue of interference from other
signals. These signals may be from the same network or may be due to man-made objects.
Interference is the major limiting factor in the performance of cellular radio systems.
Sources of interference include mobile in the same cell, a call in progress in a neighboring
cell, another base station operating in the same frequency band. Interference is a major
bottleneck in increasing capacity.
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Chapter 2 Radio Access Network
2.2.11.1 Co-channel Interference (C/I)
Co-channel interference is caused by the use of a same frequency close to another cell.
The former will interfere with the latter, leading to the terms interfering frequency (I) and
carrier frequency (C).The GSM specification recommends that the carrier-to-interference
(C/I) ratio is greater than 9 decibels (dB). However, its recommended that 12 dB be used as
planning criterion. This C/I ratio is influenced by the following factors:
i. The location of the MS
ii. Local geography and type of local scatters
iii. BTS antenna type, site elevation and position
Figure 2.19: Co-channel interference
2.2.11.2 Adjacent channel interference (C/A)
Adjacent frequencies (A), that is frequencies shifted 200 kHz from the carrier frequency (C),
must be avoided in the same cell and preferably in neighboring cells also. Although
adjacent frequencies are at different frequencies to the carrier frequency they can still
cause interference and quality problems. The GSM specification states that the carrier-to-
adjacent ratio (C/A) must be larger than -9dB. It is recommended that higher than 3 dB be
used as planning criterion.
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Chapter 2 Radio Access Network
Figure 2.20: Adjacent channel interference
By planning frequency re-use in accordance with well established cell patterns, neither co-
channel interference nor adjacent channel interference will cause problems. In reality cells
vary in size depending on the amount of traffic they are expected to carry. Therefore, real
cell plans must be verified by means of predictions to ensure that interference does not
become a problem. Nevertheless, the first cell plan based on hexagons, the nominal cell
plan, provides a good picture of system planning.
2.2.12 Handover
As a mobile station moves away from its serving BTS towards the coverage area of
neighboring BTSs, the mobile station measurement reports will show a gradual decrease in
signal strength from its serving BTS while showing an increase in measured signal strength
from one or more neighboring BTSs. It is the responsibility of the serving BSC to analyze
the measurement reports from the mobile station and to decide when a handover should be
performed.
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Chapter 2 Radio Access Network
Figure 2.21: The handover process
Figure 2.21 shows that as MS moves from cell ‘a’ to cell ‘b’, RSL of MS decreases
gradually. When RSL drop down to minimal RSL level (i.e. less than -100dBm) it hand over
to neighboring BTS.
2.2.12.1 Handover types
The type of handover procedure executed depends on what level of switching must be
performed in order to move the call from the serving BTS to the new candidate BTS.There
are basically four types of handovers:
i. Internal or intra-BSS handover, which can be:
Intra-cell handover
Inter-cell handover.
ii. External or inter-BSS handover, which can be:
Intra-MSC handover
Inter-MSC handover.
If the serving and candidate BTSs reside within the same BSS, the BSC for the BSS can
perform the handover without the involvement of the MSC; thus termed internal or intra-
BSS handover. This type of handover can also be sub-divided into intra-cell and inter-cell
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Chapter 2 Radio Access Network
handovers. An intra-cell handover is an intra-BSS handover within the same BTS. An inter-
cell handover is a handover between different BTSs.
If the serving and candidate BTSs do not reside within the same BSS, then an inter-BSS
handover is performed, which requires the MSC to coordinate and switch facilities
(handover the call) between the serving BTS and the candidate BTS. This type of handover
can also be divided into intra-MSC and inter-MSC handovers.
2.2.13 Power control
Power Control enables the mobile station and/or the BTS to increase or decrease the
transmission power on a radio link. Power Control is separately performed for the uplink
and downlink. In both cases the BSC is responsible for initiating Power Control. The mobile
station and the BTS adopt transmit power according to the BSC power control commands.
Reasons for Power Control - While a mobile station is active on a call, it has the
responsibility of providing measurement report about the performance of the air-interface
periodically to its serving BTS so that the serving BSC can decide if a power control should
be performed. Reason of power control is to save mobile station battery power. The main
reason for power control is improving the carrier-to-interference ratio within the cellular
network.
2.3 Radio Access Network Design
GSM system network planning undergoes extensive modification so as to fulfill the ever-
increasing demand from operators and mobile users with issues related to capacity and
coverage. In order to meet the requirements of the mobile services, the radio network must
offer sufficient coverage and capacity while maintaining the lowest possible deployment
costs. The designing of Radio Access Network (RAN) consists of mainly three stages that
are:
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Chapter 2 Radio Access Network
Fig 2.22: Stages of RAN Design
The Radio Access Network designing begins with traffic and coverage analysis. The
analysis should produce information about the geographical area and the expected capacity
(traffic load). The types of data collected are:
Cost of network
Capacity & Coverage of Network
Grade Of Service (GOS)
Available frequencies
Speech quality
System growth capability
The simplified radio network planning process is shown in Figure 2.23:
Figure 2.23: Radio network planning process
2.3.1 Coverage Planning
Coverage in a cell is dependent upon the area covered by the signal. The distance traveled
by the signal is dependent upon radio propagation characteristics in the given area, since it
is important for the interference management to correctly estimate the situation of the
propagation from the base station. Radio propagation varies from region to region so
predictions are different for both coverage and capacity. The radio wave propagation loss
varies greatly depending on the incidence of buildings and the population density in the
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Chapter 2 Radio Access Network
area. The propagation loss can be estimated either by statistical or deterministic
techniques. The prime requirement is that the network design should cover 100% of the
area. Fulfilling this requirement is usually impossible, so efforts are made design a network
that covers all the regions with no ‘holes’. The whole land area is divided into five major
classes – dense urban, suburban, industrial, residential and rural – based on human-made
structures and natural terrains. The cells (sites) that are constructed in these areas can be
classified as outdoor and indoor cells. Outdoor cells can be further classified as macro-
cellular, micro-cellular or pico-cellular (see Table 2.3).
2.3.2 Capacity Planning
Capacity can be understood in simplest terms as the number of mobile subscribers a BTS
can cater for at a given time. The greater the capacity, the more mobile subscribers can be
connected to the BTS at a given time, thereby reducing the amount of base stations in a
given network. This reduction would lead to an increase in the operation efficiency and
thereby profits for the network operator. Capacity planning is a very important process in
the network rollout. Capacity plans are made in the preplanning phase for initial estimations,
as well as later in a detailed manner. The number of base stations required in an area
comes from the coverage planning, and the number of transceivers required is derived from
capacity planning as it is directly associated with the frequency re-use factor. The minimum
frequency re-use factor calculation is based on the C/I ratio. As soon as the C/I ratio
decreases, the signal strength starts deteriorating, thereby reducing the frequency re-use
factor.
Another factor is the antenna height at the base station. If the antenna height is too high
then the signal has to travel a greater distance, so the probability that the signal causes
interference becomes greater. The average antenna height should be such that the number
of base stations (fully utilized in terms of their individual capacities) is enough for the
needed capacity of the network. There are three essential parameters required for capacity
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Chapter 2 Radio Access Network
planning: estimated traffic, average antenna height, erlang calculations, busy hour and
frequency usage.
Average Antenna Height - The average antenna height is the basis of the
cellular environment (i.e. whether it is macro-cellular or micro-cellular). If the
average antenna height is low, then the covered area is small in an urban
environment. This will lead to the creation of more cells, and hence increase the
number of times the same frequency can be re-allocated. Exactly the opposite is the
case in a macro-cellular environment. Here the coverage area would be more, so
the same frequency can be reallocated fewer times. All these calculations are based
on the interference analysis of the system as well as the topography and
propagation conditions.
Frequency Usage and Re-use - Frequency usage is an important concept
related to both coverage and capacity usage. Frequency re-use basically means
how often a frequency can be re-used in the network. If the average number of the
transceivers and the total number of frequencies are known, the frequency re-use
factor can be calculated. Example :If there are 3 TRX that are used per base station
and the total number of frequencies available is 27, then the total number of
frequencies available for re-use is 27/3 = 9.
2.3.3 Frequency Planning
In the radio planning process, the maximum utilization of the available frequencies is known
as frequency planning. Capacity and frequency planning go hand-in-hand. A good
frequency plan ensures that frequency channels are used in such a way that the capacity
and coverage criteria are met without any interference. This is because the total capacity in
a radio network in terms of the number of sites is dependent upon two factors: transmission
power and interference. Frequency plan must ensure that C/I > 12 dB and C/A > -12 dB
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Chapter 2 Radio Access Network
(GSM recommendation).The re-use of the BCCH TRX (which contains the signalling time
slots) should be greater than that of the TCHs, since it should be the most interference-free.
2.3.4 Quality
The quality of the radio network is dependent on its coverage, capacity and frequency
allocation. The quality of the network is dependent upon the parameter settings. Most of
these are implemented during the rollout of the network and are based on measurements.
Once there are measurements available from the initial launch of the network, these
parameters then can be fine-tuned. This process becomes a part of the optimization of the
radio network. Most of the severe problems in a radio network are attributed by signal
interference. When interference exists in the network; the source needs to be found. The
entire frequency plan is checked again to determine whether the source is internal or
external. The problems may be caused by flaws in the frequency plan, in the configuration
plans (e.g. antenna tilts), inaccurate correction factors used in propagation models, etc.
2.4 Cell Planning
2.4.1 Introduction
The Cell Planning process consists of three phases, preliminary tasks, design and
implementation. This section describes these activities and the links between them.
The first phase’s main objective is to gather hypotheses (antenna heights and technical
data such as terrain database, link budget calculation, traffic dimensioning, and propagation
model) in order to start the cell planning design.
The second phase objective is cell planning (target site locations, frequency planning, TRX
planning, and propagation modeling).
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Chapter 2 Radio Access Network
The third phase covers the cell planning implementation (final site locations, coverage
concession, frequency planning, TRX planning, network engineering support, radio
acceptance support).
These phases are named as preliminary tasks, design and implementation and are
described below in detail.
2.4.2 Preliminary Tasks
Before starting this project several assumptions were made. The objective of preliminary
tasks is to summarize the required inputs for the design activities into the cell planning. This
phase is further divided into several parts which are shown below.
Figure 2.24: Preliminary Tasks of Cell Planning process
2.4.2.1 Hypotheses Gathering
Most of assumptions are derived from the RFQ (Request for Quotation), from meetings with
the customer or from vendor decisions (products used). Hypotheses gathering consist of
collecting data from various sources that are required for cell planning (coverage target,
BTS equipment information, site constraints, existing sites, traffic information, frequency
information). This information was provided for this project.
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Chapter 2 Radio Access Network
2.4.2.2 Terrain Database Selection and Improvement
Digital Terrain Map (DTM) is a mandatory input for cell planning. Purchase of a terrain
database is a deal between cost, delay and accuracy. Then, it is required to perform several
checks on the terrain database data (heights, clutters, and vectors, geographical continuity)
to validate it. The objective of DTM with appropriate accuracy in regards to cost and delay is
to check the database consistency and updating using results of RF survey.
2.4.2.3 Link Budget
The link budget calculation specifies for each type of environment (urban, suburban, rural
and other clutters), each type of product (indoor BTS, outdoor BTS, coupling system,
antennas type) and RF design assumptions, a maximum cell radius based on the Quality of
Service requirements (quality of coverage). These radius are used to produce cell counts
that give an idea of the number of sites required to meet requirements.
2.4.2.4 Traffic Dimensioning
The objective for this activity is to identify area where traffic is more constraining than
coverage, like in urban areas; and to determine BTS maximum configuration to be used for
each traffic area.
2.4.2.5 Cell Count
This activity consists of calculation of the number of cell sites required to both fulfill traffic
and coverage requirement, in relation with choice of equipment. The cell count may be
performed before design phase, to work out the number of cell sites that will be positioned.
For this project cells which were required to fulfill the requirement was found to be above 70
cells.
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Chapter 2 Radio Access Network
2.4.2.6 Model Design
This activity includes the choice of a propagation model, its calibration to focus on the major
cell planning requirements linked to a contract. The propagation modeling process assumes
that the terrain database is validated. The propagation model is specific to a terrain
database. Propagation model which is used in this project is Okumara - Hata.
2.4.3 Design
The main task of design is Site determination activity. Model tuning, frequency planning and
TRX planning may be part of this phase but not necessarily. Pictorial illustration for this
phase is shown in the figure
.
Figure 2.25: Design phase of Cell Planning
2.4.3.1 Site Determination
This activity consists in determination of each site position and characteristics to achieve
compliance with coverage and traffic requirement. Coverage maps are used to represent
the result of this design step. The objective for this is to evaluate the number of sites and
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Chapter 2 Radio Access Network
their potential locations and to predict the service area. This prediction shows and distinct
the number of sites deployed in different clutters.
2.4.3.2 Model Tuning
This activity is not mandatory but may occur during the design or the implementation phase.
The model tuning might be required if the level of confidence in the terrain database or in
the model is not high enough. The objective for this activity is to check the validity of radio
measurements; and to verify consistency between existing propagation model and radio
measurements.
2.4.3.3 TRX Planning
Based on the contract subscriber profiles and contract products, the traffic planning
specifies the TRX configuration for each site. If the required capacity cannot be provided by
a site location then cell splits may be necessary. A new site determination step might have
to be done. The main objective for this is to determine (or confirm) the number of TRXs per
cell needed to satisfy the customer's traffic requirements.
2.4.3.4 Frequency Planning
Assign frequencies according to the available RF channels in order to minimize the
interference. A C/I (Carrier to Interference) map is created to determine the levels of
interference. These two activities (frequency allocation and C/I analysis) are repeated until
the frequency plan is acceptable.
Once the cells have been positioned and the number of TRXs per cell has been set (or
confirmed by the TRX Plan), frequencies must be allocated to each cell in a way which
minimizes interference using tilts and azimuths. The ARFCN which have been allotted for
this project are 27 which make the total bandwidth of 5.4MHz
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Chapter 2 Radio Access Network
2.4.4 Implementation
The last phase for cell processing is of implementation. Objective of the project is planning
of access part not implementation. Last phase is included to give an overview of complete
Cell planning process.
Theoretical site locations specified during the site determination activity represent target.
SAQ (Site Acquisition) tries to find real locations which are the best matching with site
location criteria. The figure 2.26 illustrates the implementation phase.
Figure 2.26: Implementation phase
2.4.4.1 Site Selection
The purpose for this activity is described below:
Choose a single real location per theoretical site, this location is supposed to be the
best among the proposed ones.
Share data (site location, antennae height, azimuths, and tilts) between cell
planning, site acquisition, and transmission teams.
Maintain the cellular planning tool site database up to date.
2.4.4.2 Coverage Concessions
The purpose for this activity is to:
Keep track of coverage problems.
Propose solutions to solve coverage holes.
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Chapter 2 Radio Access Network
Maintain an accurate communication link with customer project management to
deal with cell planning problems.
2.4.4.3 Radio Data fill
Radio data fill is an iterative process which defines the radio parameters (TRX plan,
frequency plan). It has an objective to:
Provide updated values for TRX plan, frequency plan, and BSIC plan.
Provide neighboring cell definition.
Provide initial LAC definition
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Chapter 3 BSS Planning
CHAPTER 3
BSS Planning
3.1 Introduction
The main aim of radio network designing is to provide a cost-effective solution for the radio
network in terms of coverage, capacity and quality. The network design criteria vary from
region to region depending upon the dominating factor or priority, which could be capacity
or coverage. Our task was to completely plan the site using 27 ARFCN when its generally
done with the help of 37 ARFCN.
This chapter illustrates the procedure followed for designing the radio access network for
the given area taking under consideration all the parameters, resources allocated and
standards mentioned by HUAWEI.
3.2 Steps of Designing Process
The approach adopted to accomplish designing of radio access network is broken down in
different steps as shown in figure 3.1. According to project design, fig 3.1, planning steps
are divided in two phases which are initial planning and System growth.
Figure 3.1: Project Design
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Chapter 3 BSS Planning
The phase of initial or pre-planning starts from first step of “traffic and coverage analysis”
goes till “System design”. The specifications and targets given by HUAWEI are:
Network cost: 10 Million $ ARFCNS: 27
Cost per BTS: 0.2 Million $ Number of users: 7,000
GoS : 2%
3.2.1 STEP 1: Traffic and Coverage Analysis
The aspect of network’s coverage includes defining the coverage areas,
terrain profile and related signal strength. In this project the area allocated is
“Super Highway”, the signal strength of -70dBm is the outdoor acceptance
level required by the HUAWEI.
It is mandatory to calculate number of sites required to fulfill the coverage and capacity
requirement. As per budget for this project, maximum sites that can be placed are 80.
These sites have to be placed in such a way to give an optimum coverage and capacity.
There are coverage-driven areas and capacity-driven areas in a given network region. The
average cell capacity requirement per service area is estimated for each phase of network
design, to identify the cut-over phase where network design will change from a coverage-
driven to a capacity-driven process. While the objective of coverage planning in the
coverage-driven areas is to find the minimum number of sites for producing the required
coverage. It is necessary to experiment with both coverage and capacity, as due to the
capacity requirements the number of sites may have to be increased resulting in a more
effective frequency usage with minimal interference.
The definition of capacity include the number of subscribers and traffic profile in the region,
information on the radio access system and the antenna system performance associated
with it. Traffic is classified in two types
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Chapter 3 BSS Planning
Offered Traffic: It is defined as traffic which user attempt to originate .
Carried Traffic: It is the traffic actually successfully handled by the system.
There are basically two approaches to perform the calculation of network’s capacity and
required equipment.
1. Theoretical approach
2. Practical approach
3.2.1.1 Theoretical Approach
The theoretical approach is the empirical method to perform the capacity calculations. The
steps involved during the capacity calculations using the data and assumptions are
mentioned below:
i. Choose sectorization that satisfies the desired Signal-to-Noise ratio.
ii. Calculate number of voice channels for the given area
iii. Calculate traffic density
iv. Find the traffic per sector using Erlang B chart
v. Cell area and number of cell.
i. Sectorization
Sectorization scheme is chosen first for pre-planning. The standard Signal-to- Noise ratio is
12dB. Following formulas are used to calculate Signal to Noise ratio.
For Omni
3.1
For Sector
3.2
Where γ = path loss value in dB q =√3N
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Chapter 3 BSS Planning
ii. Voice channels (m)
The number of voice channels for city and highways are calculated using eq 3.3. Voice
channels are used to estimate the number of TRX required in particular area.
3.3
Where;
BW = Total bandwidth ; Channels BW=200 kHzSpeech/RF = voice channels ; N = reuse factor
iii. Traffic density (TD)
Traffic density of the city is calculated using eq 3.4. TD has unit of Erlang/km².
3.4
Where;
E = Traffic per subscriber ; Pop = PopulationPene = Market penetration ; ROT = Roll out time/yearShare = Market share ; Growth = Annual Population growth
iv. Traffic per sector (TS)
For a given GoS of 2%, traffic on each sector is calculated using Erlang-B chart for six
different terrains.
v. Number of cells
Area of a single cell is calculated using eq 3.5. Cell area has unit of ‘km²’ and it is
used to calculate minimum number of cells required to cover given area
Cell Area = TS × Sector TD
3.5
Number of Cells = Total Area Cell Area
3.6
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Chapter 3 BSS Planning
3.2.1.2 Calculations:
Area Radio Planning(A case to Study)
Given Data:
Site specifications system scenario:
Signal Strength = -70dBmSite Configuration = S333Out door HighwayFrequency band = 900MHzEnviroment = rural area (semi-open)
Financial Specifications:
Cost per BTS = 0.2 Million $Network Cost = 2 Million $
Technical Limitations:
Total BW = 5.4MHzChannel BW = 200 kHzPath loss = -156 dBGoS = 2%
Statistical Analysis:
Traffic per subscriber = [25mEr occupy the resource/channel for 90 seconds (standard)]Penetration (pene) = 7% [Next year 7% of the net population will be added to network]Roll out time/year = 15 days Annual population growth = 20%Number of Users (PoP) = 16000Market share = 90% [How much share our network (N) will hold in total telecom market]Number of Interference Cell (j) = for Omni: j = 1, for Sector: j = 3 Total area = 100 x 7 km2
*If X operators in sum carry Y% of total population, our market share will be = (N/X) * Y
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Chapter 3 BSS Planning
Capacity Planning:
Number of sites:
It is mandatory to calculate number of sites required to fulfill the coverage and capacity
requirement. As per budget for this project, maximum sites that can be placed are 10.
These sites have to be placed in such a way to give an optimum coverage and capacity.
2 Million $ = 10 sites (Maximum)
0.2
That means we can install up to 10 sites to provide coverage.
Busy-hour traffic: A is the maximum traffic on the busiest hour of system or line. A= a * b * t. .a = is everyday call times (originating and terminating) per user . b = is busy-hour to day ratio( busy-hour traffic divided by daytime traffic. t = is average call duration
Area Topographic features
DenseUrban
Average height of surrounding buildings is more than 30 metres (over 10 storey) and average distance between buildings is 10-20 metres. Usually the buildings are crowded around the site with the height of 10-20 stories and the ambient roads are not considerablly wide.
Urban
Average height of surrounding buildings is about 15-30 metres (5-9 storey) and average distance between buildings is 10-20 metres. The buildings are evenly distributed around the site. Mostly are below 9 stories and some are over 9 stories and the ambient roads are not considerably wide.
suburb
Average height of surrounding buildings is about 10-15 metres (3-5 storey) and average distance between buildings is 30-50 metres. The buildings are evenly distributed around the site. Mostly are 3-4 stories and some are over 4 stories. Roads around are wide.
ruralAverage height of surrounding buildings is below 10 metres. They are dispersed and mainly are 1-2 storey high. There are spacious space between.
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Chapter 3 BSS Planning
a) Theoretical Approach:
(i) Sectorization:
Where q =√3N and γ = path loss value in dB = -156 dB q = 3N = 3
Therefore SIR = -886.3 dB for sector
(ii) Voice Channels (m)
Where;
BW = Total bandwidth ; Channels BW=200 kHz Speech/RF = voice channels
N = reuse factor = no. of channels x no. of sites 27 x 9 = 3 Total no. of TRX 81Since
Total BW = 5.4MHzSpeech/Rf = 8 (since full rate) [Note: At Half rate Speech/Rf is taken 16]Channels BW = 200 kHzN = 3
Therefore, m = 23
Total available Channels = Total BW divide by Channel BW = 5.4 MHz/ 200kHz = 27 ARFCN
Since
m = 23Therefore, 27-23 = 4 controls channels
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Chapter 3 BSS Planning
(iii) Traffic Density (TD):
OR Where;
E = Traffic per subscriber = 25m ; Pop = Population = 16000Pene = Market penetration = 0.07 ; ROT = Roll out time/year = 15Share = Market share = 0.14 ; Growth = Annual Population growth = 0.2
TD = 25m x 16000 x 0.07 x (1 + 0.2)15 x 0.90 = 0.97 Er/ km2 100 x 7 km2
(iv) Traffic per sector (TS):
One site has 3 sectors. Each sector has 3 Radios and each radio has 8 channels/slots so we have 24 slots per sector, 3 slots per sector are used for other purposes like signaling, broadcast, and data traffic so we are left with 21 slots per sector.
Our GOS is 2 %. Now using ErlangB table we can find out how much traffic one sector of a site can carry it turns out to be 14.03 Erlangs, Total trafic a site can carry is 42.09 Erlangs
Total traffic for that area is 0.9 Er/kmsq x 400 kmsq = 360 Erlangs
Total sites required = Total traffic = 360 = 8.5 (app 9 sites) Traffic per site 42.09
(v) Number of Cells:
Cell area has unit of ‘km²’ and it is used to calculate minimum number of cells required to
cover given area
Cell Area = TS × Sector TD
Cell Area = 14.03 × 3 = 46.76 m2 0.9
Number of Cells = Total Area Cell Area
Number of Cells = 400 = 8.5 sites (app 9 sites) 46.7
TD = 25m x Population x market share Area
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Chapter 3 BSS Planning
b) Practical Method:
The maximum configuration stated by customer for this project is S333. It means that each
of the three sectors has 3 TRX in it. From the Erlang B table the traffic carried by this
configuration is 14.03 Erlang/ sector.
Site traffic it calculated as:
Traffic Carried by Site = Traffic carried by a cell × number of cell in that Site
= 14.03* 3 = 42.09 Erlang/ Site.
Total Erlang which is offered by the target population can be found as:
Total offered traffic in Erlang = Number of total users * traffic offered by a user
= 16000 * 25mErlang
= 400 Erlang
No. of sites = 16000 * 25mErlang = 8 sites (approx 24 sectors)
(14.03*3)
Comparison between Theoretical and practical approachesNumber of sites in Theoretical = 9
Number of sites in Practical = 8
Frequency hopping and Frequency Reuse – Frequency hopping and tighter reuse plan
also helped in accommodating capacity requirements. This approach allows more
transceivers to be deployed in the network, gradually enhancing traffic capacity.
Fractional Load Guide
□ For 1 x 1 schemeFractional Load = 16 %
■ For 1 x 3 schemeFractional Load = 50 %
Fractional Load = No of hopping radios = 50 % (Since we are using 1 x 3 scheme) 2x
Where 2x = No. of frequencies in each MAL list Therefore, x = 2 if we want 50 % OR 2x = 4
(In other words, 4 frequencies will be assign to each MAL list)
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Chapter 3 BSS Planning
Duplex Sub bands of width = 25 MHz – Duplex Spacing 45 MHzUplink Sub band = 890 – 915 MHzDownlink Sub band = 935 – 960 MHzFrequency Spacing between carriers = 200 kHz (0.2 MHz)
One acrrier is used for guard band, giving:
Total number of carriers (ARFCN) = (25 – 0.2)/0.2 = 124
Uplink frequencies: Fu(n) = 890 + 0.2n MHz where 1 < n < 124Downlink Frequencies: Fd(n) = Fu(n) + 45 MHz
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Chapter 3 BSS Planning
Frequency allocation Data Sheet:
NCC: 2, 3BCC: 0-7BSIC combinations: 20, 21, 22, 23, 24, 25, 26, 27, 30, 31, 32, 33, 34, 35, 36, 37MAL frequencies for sector A 1, 4, 7, 10MAL frequencies for sector B 2, 5, 8, 11MAL frequencies for sector C 3, 6, 9, 12MAIO for sector A: 0, 2MAIO for sector B: 1, 3MAIO for sector C: 0, 2Guard frequency = 20BCCH = 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26Guard Frequency for Next operator = 27HSN: 0-63
SD Calculation:
SITE VIEW:13/4 BCCH distribution scheme
400 kilo meter
1517
21
16
19
14
23
19
25
24
26
18
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Chapter 3 BSS Planning
Since no. of slots per sector = 21 and GoS = 2%, From ErlangB TS = 14.03
Therefore ¼ * 14.03 = 3.5 (app 4) SD Time Slots i.e 32 channels
Total no. of subscribers per sector = TCH traffic per sector = 14.03 Traffic per subscriber 25m
= 561 subscribers
Actual traffic = Total – SDCCH usageSDCCH traffic = no.of subscribers per sector *no.of sectors*SD traffic/sub SDCCH traffic on each site = (561 *3) x 3.56 m erlang = 5.9 erlangSo actual traffic = 42.09 – 5.9 = 36.09 erlang
We can also refer to the standard table for SD traffic per sector
CGI:
Where MCC (Mobile country code) = 092, MNC (Mobile network code) = 01 LAC (Location area code) = 1234CI = Cell Id (given to each cell)
E1 Calculations:
Our one site contains data = 16 kbps x 8 time slots x 9 TRX = 1.152 Mbps
However one E1 carries = 32 slots x 64 kbps
= 2.048 Mbps (which is greater than 1.152 Mbps)
Therefore, only one E1 will be enough for communication between HUB site and BTS
MNC CILACMCC
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Chapter 3 BSS Planning
BCCH
14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25,
26
SD = 2 time slots
BCCH
14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25,
26
SD = 2 time slots
TRX Radio#1
BCCH
14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25,
26
SD = 2 time slots
TRX Radio#1
TRX Radio#1
Hopping
14710
MAIO (0)
Hopping
14710
MAIO (2)
TRX Radio#3
TRX Radio#2
Hopping
25811
MAIO (1)
Hopping
25811
MAIO (3)
TRX Radio#3
TRX Radio#2
Hopping
36912
MAIO (0)
Hopping
36912
MAIO (2)
TRX Radio#3
TRX Radio#2
S333 Sector A
S333 Sector B
S333 Sector C
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Chapter 3 BSS Planning
Site 1
Site Name = HihfrmALongitude = 67.27448Latitude = 24.97918CI = 123BSIC = 27HSN = 59MAL = 1, 4, 7, 10BCCH = 16
Site 2:
Site Name = GothoreA Longitude = 67.37873Latitude = 25.02176CI = 113BSIC = 35HSN = 16MAL = 1, 4, 7, 10BCCH = 15
Site 3:
Site Name = Taj_GothA Longitude = 67.5621Latitude = 25.0731CI = 116BSIC = 23HSN = 50MAL = 1, 4, 7, 10BCCH = 23
Site 4:
Site Name = BismillahA Longitude = 67.61521Latitude = 25.12002CI = 119BSIC = 31HSN = 31MAL = 1, 4, 7, 10BCCH = 24
Site 5
Site Name = HihfrmB Longitude = 67.27448Latitude = 24.97918CI = 111BSIC = 27HSN = 59MAL = 2, 5, 8, 11BCCH = 19
Site Name = HihfrmCLongitude = 67.27448Latitude = 24.97918CI = 112BSIC = 27HSN = 59MAL = 3, 6, 9, 12BCCH = 14
Site Name = GothoreBLongitude = 67.37873Latitude = 25.02176CI = 114BSIC = 35HSN = 16MAL = 2, 5, 8, 11BCCH = 17
Site Name = BismillahB Longitude = 67.61521Latitude = 25.12002CI = 120BSIC = 31HSN = 31MAL = 2, 5, 8, 11BCCH = 18
Site Name = Taj_GothB Longitude = 67.5621Latitude = 25.0731CI = 117BSIC = 23HSN = 50MAL = 2, 5, 8, 11BCCH = 19
Site Name = Taj_GothC Longitude = 67.5621Latitude = 25.0731CI = 118BSIC = 23HSN = 50MAL = 3, 6, 9, 12BCCH = 25
Site Name = BismillahC Longitude = 67.61521Latitude = 25.12002CI = 121BSIC = 31HSN = 31MAL = 3, 6, 9, 12BCCH = 26
Site Name = GothoreC Longitude = 67.37873Latitude = 25.02176CI = 115BSIC = 35HSN = 16MAL = 3, 6, 9, 12BCCH = 21
Site Name = NoriabadB Longitude = 67.68612Latitude = 25.16189CI = 123BSIC = 24HSN = 9MAL = 2, 5, 8, 11BCCH = 19
Site Name = NoriabadC Longitude = 67.68612Latitude = 25.16189CI = 124BSIC = 24HSN = 9MAL = 3, 6, 9, 12BCCH = 14
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Chapter 3 BSS Planning
Site Name = NoriabadA Longitude = 67.68612Latitude = 25.16189CI = 122BSIC = 24HSN = 9MAL = 1, 4, 7, 10BCCH = 16
Site 6
Site Name = FayyakunA Longitude = 67.8019Latitude = 25.1433CI = 125BSIC = 30HSN = 2 MAL = 1, 4, 7, 10BCCH = 15
Site 7
Site Name = AlAhmedALongitude = 67.79743Latitude = 25.15303CI = 128BSIC = 26 HSN = 21MAL = 1, 4, 7, 10BCCH = 23
Site 8
Site Name = HajeramA Longitude = 67.79402Latitude = 25.1672CI = 131BSIC = 32HSN = 5MAL = 1, 4, 7, 10BCCH = 24
3.2.1.3 General Problems and their Remedies:
Site Name = HajeramC Longitude = 67.79402Latitude = 25.1672CI = 133BSIC = 32HSN = 5MAL = 3, 6, 9, 12BCCH = 26
Site Name = AlAhmedB Longitude = 67.79743Latitude = 25.15303CI = 129BSIC = 26HSN = 21MAL = 2, 5, 8, 11BCCH = 19
Site Name = AlAhmedC Longitude = 67.79743Latitude = 25.15303CI = 130BSIC = 26HSN = 21MAL = 3, 6, 9, 12BCCH = 25
Site Name = HajeramB Longitude = 67.79402Latitude = 25.1672CI = 132BSIC = 32HSN = 5MAL = 2, 5, 8, 11BCCH = 18
Site Name = FayyakunB Longitude = 67.8019Latitude = 25.1433CI = 126BSIC =30HSN = 2MAL = 2, 5, 8, 11BCCH = 17
Site Name = FayyakunCLongitude = 67.8019Latitude = 25.1433CI = 127BSIC = 30HSN = 2MAL = 3, 6, 9, 12BCCH = 21
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Chapter 3 BSS Planning
i) Coverage Problems:
The terrain configuration and human-made structures are different on different locations
resulting in different area-area predictions. The measurements made in dense urban areas
are different from those made in urban, sub-urban and other areas. During coverage
planning optimum level of RSL (i.e. -65dBm) was not achieved at distinct locations due to
propagation losses. Following approaches are used at cell site to increase the coverage.
Increasing the Transmitted Power - Increasing the transmitted power of each affected cell
results in coverage of a large area. When power level is doubled, gain increases by 3dB.
Increasing Cell-Site Antenna Height – To fill the coverage holes, cell-site antenna’s
height is increased. The effective antenna height is dependent on the location of Site and
MS. Sometimes, doubling the actual antenna height results in a gain increase of less than
6dB and sometimes more.
High-Gain Antennas at Site – The high gain antennas are also used to increases the
coverage especially in dense urban areas, because coverage is generally found to be less
at farthest part of the network
Selecting Cell-Site Location – Coverage area is also increased by selecting proper site
location for actual antenna height and transmitted power. For better coverage purposes,
high site is selected for minimizing the impact of interference.
Antenna Pattern - Problem is solved by immediate scrutiny of the deployed antennas
pattern and tilts. Such problems are usually sorted out by moving the antenna positions and
altering the tilting of the antennas.
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Chapter 3 BSS Planning
ii) Capacity Problems:
Efficient designing of Radio Access Network is all about building high-capacity networks in
the most economical way, and therefore, GSM radio network capacity solutions are
becoming increasingly important. Following techniques are used to cater the allocated
number of users.
Small Cell Size – Controlling the radiation pattern results in reduction of cell size and
increases the traffic capacity. This approach is based on the assumption that all mobile
units are identical.
Increasing the Number of Radio Channels in Each Cell – Requirement of capacity is
met by increasing the number of radio channels in each cell. This is done by increasing
number of TRX at each site resulting in increase of TS.
Frequency hopping and Frequency Reuse – Frequency hopping and tighter reuse plan
also helped in accommodating capacity requirements. This approach allows more
transceivers to be deployed in the network, gradually enhancing traffic capacity.
iii) Performance Aspects:
Apart from achieving capacity and coverage, the two main parameters that are considered
when building a network are monetary cost and time—the actual cost of each solution is
market-dependent, since the costs associated with cell sites (site acquisition, site
preparation, rental costs) and transmission vary from market to market. Over dimensioning
of the network causes too much cost, traffic revenue gets too low to support cost of
network, very poor economic efficiency. Similarly, under dimensioning of the network
causes blocking probability to increase, has poor technical performance (in other words
interference), capacity for billable revenue become low, revenue gets lower due to poor
quality and very poor economic efficiency
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Chapter 3 BSS Planning
Remedy – The solution to above mention problem is to deploy more transceiver on a cell
site or tighter frequency reuse plan. A third option is to introduce micro cells as it is easier
and less expensive to acquire sites for them. While designing trade off should be made
between resources and requirements to avoid both over and under dimensioning.
3.2.2 STEP2: Nominal cell planning
A nominal cell plan is produced from the data compiled from traffic and coverage analysis.
The nominal cell plan is a graphical representation of the network and looks like a cell
pattern on a map. First cell plan is laid which formed the basis for further planning. The
nominal plan is made by taking under consideration the following parameters and methods
which help to predict the path losses, make efficient use of available frequency band and
cater the interference.
i. Radio propagation
ii. Frequency reuse
iii. Interference
i. Radio propagation
To predict the signal strength and path losses of the radio wave or transmitted signal many
propagation models are analyzed. The Okumura-Hata model is chosen as the prediction
model .The radio propagation is highly dependent on clutter profile and the terrain assigned
for planning. The Okumura - Hata model is best suited for its loss predictions. Losses due
to clutter profile, shadowing, multi-path fading and vertical diffraction losses are catered
(see figure 5.4 and table 5.3).
ii. Frequency reuse
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Chapter 3 BSS Planning
Based on the traffic calculations, the cell pattern and frequency re-use plan are worked out
not only for the initial network, but also for future demands.
The re-use patterns recommended for GSM are the 4/12 and the 3/9 pattern. Selected
reuse pattern is 3/9.
iii. Interference
Co-channel Interference (C/I) - Cellular networks are more often limited by problems
caused by interference rather than by signal strength problems.
The criteria of C/I used for designing the radio network is as follow:
C/I >= 12dB
Where, C is carrier frequency
I is interfering frequency
Adjacent channel interference (C/A) - The main focus is made to mitigate C/A in the
same cell during the planning. The C/A in neighboring cell is given the second priority as it
does not affect the communication. Here, the criteria of C/A used for designing the radio
network is as follow:
C/A>= 3db
Where, C is carrier frequency
A is adjacent frequency
These criterions are chosen after consultations with experienced personals and vendors. As
GSM standards are C/I greater then 9db and C/A greater than -9db, these criterions taken
here are well above the acceptance levels.
3.2.3 STEP3: Surveys
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Chapter 3 BSS Planning
When the pre-planning phase is completed, the site search process starts. Based on the
coverage plans, prospective sites location is identified for specific areas. The process of site
selection, from identifying the site to site acquisition, is very long and slow therefore it is
worked out in conjunction with transmission planners, installation engineers and civil
engineers to make this process faster. A good site is a place that does not have high
obstacles around it and has a clear view for the main beam. The responsibilities of site
acquisition, civil works and engineering teams are discussed below:
Site Acquisition
The Site Acquisition process is performed in close co-operation with the Civil Works. It
consists of the following activities:
Searching for sites and gaining a site appraisal.
Outlining the site design and evaluating the cost.
Negotiating and signing leasing contracts.
Handling permits and arranging the hand-over to the Engineering personnel.
Civil Works
The Civil Works process consists of the following activities:
Preparing a detailed civil works design of the site.
Updating the costs for the site construction.
Arranging the site construction.
Engineering
The Engineering process begins when the Site Acquisition process and ends when Civil
Works process are complete. It consists of the following activities:
Measuring and collecting information about the sites.
Designing the antenna and radio configuration and producing cable drawings.
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Chapter 3 BSS Planning
Making drawings showing the position of antenna and RBS equipment.
“Radio measurements” are performed to adjust the parameters used in the planning tool to
match the real situations. That is, adjustments are made to meet the specific site climate
and terrain requirements. A test transmitter is mounted on a vehicle, and signal strength is
measured while driving around the site area. Afterwards, the results from these
measurements can be compared to the values the planning tool produces when simulating
the same type of transmitter. The planning parameters can then be adjusted to match the
actual measurements.
Model Tuning Process
In these steps model tuning of Okumra - Hata model is described.
1. The model tuning starts by selection of the propagation model, Okumura-Hata
model is selected for signal loss prediction. The equation is;
L=A + Blog(f) – 13.82log(hbts) – a(hms) + (C – 6.55log(hbts))logd
Where,
A,B,C =Constant
d = distance
hbts = Effective height of BTS
hms = Effective height of MS
2. The measurement reports are prepared. The amount of measurements depend on
a.) Resolution of digital map provided
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Chapter 3 BSS Planning
b.) The size of target area
3. The results of model tuning measurement report are imported in “the planning
system software and alignment with the digital map of the given area is made. This
alignment is made to minimize the GPS-SA effect or inaccuracies in coordinate
conversion parameters.
4. In Okumura-HATA model there are many unassailable parameters. At first the slope
of Okumura-Hata model is tuned by changing the factor “C”. In the equation of the
model. It can be seen that first three terms are independent of distance “d”. As
log(d) has the coefficient “C – 6.55log(h)”, by changing the factor “C” model has
been tuned. The values of this very factor depends on the clutter, which is
Lower for rural environment
Higher for Urban environment
The correction by factor “D” affects the effect of antenna height on prediction of losses. As
the Okumura- Hata model is suitable for cells that have antenna installed well above roof
tops ( in other words the lattice towers ). If the antenna is installed near the roof-top then
factor “D” in the equation is used for improving the accuracy of the predictions. The height if
mobile antenna is not considered for correction as the correction factor is 0db (given in
Okumura - Hata profile).
3.2.4 STEP 4: System Design
In system designing, dimensioning plays a vital role on cost of a network. Dimensioning is
used to identify the equipment and the network type required in order to cater for coverage
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Chapter 3 BSS Planning
and quality requirement. Network must be planned that capacity needs are fulfilled for next
3-5 years. The inputs that are required for the dimensioning include:
The geographical area to be covered
The estimated traffic in each region
The minimum requirement of power in each region and blocking criteria
Path loss
The frequency band to be used and frequency re-use.
With above parameters, number of base stations is calculated for estimated number of
users (Table 3.2) in different clutters. Initially all sites deliver equal power (i.e. -43dBm).
Variation in power is dependent on level of interference.
3.2.5 STEP 5: System Implementation
Implementation and deployment completes the 2G-network design process by realizing the
projected site locations, service target requirements and time to service. It takes into
account the solution adopted for the network deployment, e.g. sharing sites with existing
base stations and evolution of core network elements or a complete new overlay network. It
will also take into account the hierarchy of the network, i.e. the macro- and micro layers
where applicable. When deploying in the macro-cell environment the implementation will
take into account the coverage dependency on the transmission rates and technology
availability in terms of antenna configuration and interference minimizing features. Thus, the
four steps outlined above do have an iterative process.
3.2.6 STEP 6: System Tuning
Networks need to operate at full efficiency with a minimal amount of maintenance; a high
degree of quality and with enough capacity according to the traffic demand. Once the
system has been installed, it is continuously monitored to determine how well it meets
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Chapter 3 BSS Planning
demand. This is called system tuning. It involves checking whether the final cell plan was
implemented successfully, evaluating customer complaints, monitoring the network
performance, changing parameters accordingly and taking other signal measurements, if
necessary.
Drive testing is used for system tuning. It analyzes the current performance of network and
analysis measurable objectives in terms of quality, capacity and cost. TEMS, Test Mobile
System, is a tool for investigations and maintenance of Cellular networks: to ensure
coverage, quality or to pinpoint problem areas. Drive Tests are used to capture the
throughput at lower layers over the air interface, measure radio conditions, and monitors
signaling messages between the terminal and the network. Drive Testing assist in detecting
specific problems in the network and performing trouble shooting. This tool composes of
one mobile terminal with special firmware and software that collect information from the
radio interface. Typical information that is achieved from Drive Tests is:
Information about system serving cell: Cell Id, frequency, broadcast information,
etc.
Measurement of radio quality: Received power (RXLEV), signal to interference
ratio, RQUAL, Cell selection (C1) and Cell Re-selection (C2), TXPOWER, Call
Status, neighbor information, block error rate, etc.
Through put and delay on radio interface.
Signalling messages
Drive test tools also use GPS (Global Positioning System) in order to correlate the
measurement with different locations.
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Chapter 4 Quick Budget
CHAPTER 4
Quick Budget
4.1 Introduction
The post processing RF tools enables the RF engineers to predict the effect of their
designed network or changes they make to the network will have on the perceived
coverage and quality. Thus expensive problems can be avoided and trouble spots can be
identified early and fixed quickly. These tools basically provide the visualizing the radio
access network for any specific terrain. The combination of the map, ground profiles and
the 3D view can save engineers visiting sites as a lot of information can be deduced by
viewing the database maintained by post processing tools.
This chapter provides a description of Quick Budget working and its back programming.
Quick Budget is a software application that is intended to lend a hand in designing,
operating and optimizing a cellular radio network. Its database is used to store all the
relevant information on sites, base stations and cell parameters, and from this Quick
Budget.
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Chapter 4 Quick Budget
This is a screenshot of our link budgeting software that has been uploaded on the following
link www.fyp.awardspace.com. For further details, visit the above mentioned link.
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Chapter 5 Optimization
Chapter 5
Optimization
5.1 Introduction
Every alive Network needs to be under continues control to maintain/improve the
performance. Optimization is basically the only way to keep track of the network by
looking deep into statistics and collecting/analyzing drive test data. It is keeping an eye
on its growth and modifying it for the future capacity enhancements. It also helps
operation and maintenance for troubleshooting purposes.
Successful Optimization requires:
• Recognition and understanding of common reasons for call failure
• Capture of RF and digital parameters of the call prior to drop
• Analysis of call flow, checking messages on both forward and reverse
links to establish “what happened”, where, and why.
Optimization will be more effective and successful if you are aware of what you are
doing.
5.1.1. Purpose and Scope of Optimization
The optimization is to intend providing the best network quality using available
spectrum as efficiently as possible. The scope will consist all below;
• Finding and correcting any existing problems after site implementation and
integration.
• Meeting the network quality criteria agreed in the contract.
• Optimization will be continuous and iterative process of improving overall
network quality.
• Optimization can not reduce the performance of the rest of the network.
• Area of interest is divided in smaller areas called clusters to make optimization
and follow up processes easier to handle.
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Chapter 5 Optimization
5.2. Optimization Process
Optimization process can be explained by below step by step description:
5.2.1. Problem Analysis
Analyzing performance retrieve tool reports and statistics for the worst performing BSCs
and/or Sites.
Viewing ARQ Reports for BSC/Site performance trends
Examining Planning tool Coverage predictions
Analyzing previous drive test data
Discussions with local engineers to prioritize problems
Checking Customer Complaints reported to local engineers
5.2.2. Checks Prior to Action
Cluster definitions by investigating BSC borders, main cities, freeways, major roads
Investigating customer distribution, customer habits (voice/data usage)
Running specific traces on Network to categorize problems
Checking trouble ticket history for previous problems
Checking any fault reports to limit possible hardware problems prior to Test
5.2.3. Drive Testing
Preparing Action Plan
Defining drive test routes
Collecting RSSI Log files
Scanning frequency spectrum for possible interference sources
Re–driving questionable data
5.2.4. Subjects to Investigate
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Chapter 5 Optimization
Non–working sites/sectors or TRXs
In–active Radio network features like frequency hopping
Disabled GPRS
Overshooting sites – coverage overlaps
Coverage holes
C/I, C/A analysis
High Interference Spots
Drop Calls
Capacity Problems
Other Interference Sources
Missing Neighbors
One–way neighbors
Ping–Pong Handovers
Not happening handovers
Accessibility and Retainability of the Network
Equipment Performance
Faulty Installations
5.2.5. After the Test
Post processing of data
Plotting RX Level and Quality Information for overall picture of the driven
area
Initial Discussions on drive test with Local engineers
Reporting urgent problems for immediate action
Analyzing Network feature performance after new implementations
Transferring comments on parameter implementations after new changes
5.2.6. Recommendations
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Chapter 5 Optimization
Defining missing neighbor relations
Proposing new sites or sector additions with Before & After coverage plots
Proposing antenna azimuth changes
Proposing antenna tilt changes
Proposing antenna type changes
BTS Equipment/Filter change
Re–tuning of interfered frequencies
BSIC changes
Adjusting Handover margins (Power Budget, Level, Quality, Umbrella
HOs)
Adjusting accessibility parameters (RX Lev Acc Min, etc..)
Changing power parameters
5.3 TEMS Software
Example of Bad FER
73
Chapter 5 Optimization
Example of FER is OK
Collusion of MA list causing low C/I
74
Chapter 5 Optimization
RX_Level
75
Chapter 5 Optimization
Late Handovers
Ping-Pong Handovers
76
Chapter 5 Optimization
Missing Neighboring relation
Drop call due to low signal level
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Chapter 5 Optimization
Drop call due to bad RX_Quality
Call drop due to interference
78
Chapter 6 Results & Discussions
CHAPTER 6
RESULTS AND DISCUSSIONS
6.1 Introduction
The radio access network design being a complex process has been accomplished in eight
discrete steps. Each step has its separate problems, which can be tackled in a number of
ways. The choice of a solution depends on the scenario, priority and resources at hand. In
this chapter the final results of each step are stated and the solutions to mitigate the
problems faced during the designing process are discussed in adequate detail.
6.2 Results and Discussion
6.2.1 Step1: Traffic and coverage Analysis
The final coverage and capacity is as follow:
The phase of initial or pre-planning starts from first step of “traffic and coverage analysis”
goes till “System design”. The specifications and targets given by HUAWEI are:
Network cost: 2 Million $
ARFCNS: 27
Cost per BTS: 0.2 Million $
Number of users: 7,000
GoS: 2%
Radio network capacity solutions can be divided into three solution categories:
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Chapter 6 Results & Discussions
i) Cell capacity solutions - These solutions consist of methods and features that permit
more transceivers per cell. Factor that has the greatest influence on cell capacity is
frequency reuse. Cell capacity is thus determined by different methods and functions to
enhance frequency reuse. Two common methods are
• Multiple Reuse Pattern (MRP); and
• Fractional Load Planning (FLP).
The Multiple Reuse Pattern, which is based on base-band frequency hopping, yields the
best results for network composed mainly of filter combiners. The primary transceiver
carries the broadcast control channel (BCCH) and must therefore have a relatively loose
reuse pattern (explanation: a handset must listen to the information broadcast on the BCCH
before it can make calls in a cell). Where as; due to the frequency hopping gain, all
remaining transceivers in the network can have a successively tighter reuse pattern.
Compared to a non-hopping network, the MRP solution can be more than double cell
capacity. The requirements of MRP are that it requires
• Considerable spectrum (greater than 5 MHz)
• At least three transceivers per cell for good performance.
Fractional Load Planning is based on synthesized frequency hopping, which requires the
use of hybrid combiners. In FLP, the gain from frequency hopping is not dependent on the
number of transceivers in a cell, since each transceiver can hop on every frequency
allocated to the cell. Notwithstanding, due to the characteristics of synthesized frequency
hopping, the BCCH transceiver cannot hop frequencies.
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Chapter 6 Results & Discussions
ii) Network capacity solutions - These solutions focus on adding different kinds of cells
and make most of cell capacity by distributing traffic as efficiently as possible.
In addition to improving cell capacity, operators can introduce micro cells, since site
acquisition for micro cells is usually easier and less expensive than when adding regular
cells. Traffic management is an important issue in a network composed of cells of different
sizes. With multilayered hierarchical cell structures, cells can be divided in up to eight layers
and traffic can be prioritized and distributed between these layers. There are also numerous
add-on functions, such as
• Cell load sharing, which distributes traffic within layers.
• Assignment to another cell, which redirects traffic to other cells when
congestion occurs during call setup.
• Handling of fast-moving mobiles, which moves calls to higher layers when
there are too many handovers within a given interval. This function reduces
the number of handovers, thereby increasing voice quality.
iii) Channel capacity solutions - These solutions center on ways of using the available
throughput of the channels in the air in a more efficient manner, for example half-rate voice
channels and GPRS.
In the context of circuit-switched traffic, the channel capacity is about half-rate voice
channels and the way they are managed as shown in the figure 5.1. Since the half-rate
technique reduces the quality of voice, it has not been widely deployed. However, operators
are now beginning to use this technique more and more, since it can be allocated on a
dynamic basis during traffic peaks as shown in figure 5.1.
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Chapter 6 Results & Discussions
Figure5.1: Dynamic half-rate allocation
6.2.1.1 Capacity Planning Approaches
For comparative analysis purpose capacity planning is done using two approaches.
i. Cell based approach
i) Cell based Approach
During the cell based capacity planning of the Global System for Mobile Communications
(GSM) network, traffic measurements are of significant importance. Because of false
predictions, the capacity planning of a cell may be done inaccurately. If the capacity of the
cell is not adequate to handle all of the busy-hour requests, the requests are not granted a
channel and users are blocked. Thus, when the blocking ratio is high, the cellular capacity
should be re-planned.
6.2.2 STEP2: Nominal cell planning
The result of nominal cell planning is shown in the figure 5.2 which is the cell pattern on
map. The densely polluted areas have cells with small radii and others have comparatively
larger radii. The small radius cells are enabling greater number of traffic channels in the
respective area, thus more users can be catered in densely polluted areas.
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Chapter 6 Results & Discussions
The following results are achieved from the three under considered parameters while
making the nominal plan.
i) Radio propagation – The prediction model Okumura-Hata is selected. The
figure 5.3 shows the coverage prediction of a site by using Okumura- Hata.
Figure 6.3: Coverage Prediction by Okumura-Hata
ii) Interferences
Reduction of co channel interference in a cellular mobile system is always a
challenging problem. A number of methods are considered to overcome this
problem, such as
a) Increasing separation between two co channel cells
b) Using directional antennas at BTS
c) Lower antenna height at BTS
Method ‘a’ is not advisable because as number of frequency-reuse cells increases,
the system efficiency, which is directly proportional to the number of channels per
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Chapter 6 Results & Discussions
cells increases, decreases. Method ‘c’ is not recommended either because such an
arrangement also weakens the RSL at mobile unit.
Method ‘b’ is a good approach, because the use of directional antennas in each cell
serves two purposes:
Further reduction of co channel interference when it is not eliminated by
a fixed separation of co channel cells
Increasing the channel capacity when traffic increases.
Initially the co-channel interference was 60%, which is reduced to 10% by using one
of the following methods:
Designing of Antenna Pattern - By designing an antenna that emit strong signals
in a particular direction and no signal in other direction, co channel interference can
be significantly reduced.
Tilting Antenna Pattern – Co-channel interference is minimized by confining the
energy within small area. This is achieved by downward tilting of directional
antenna.
Reducing Antenna Height – This method is used because minimal interference is
more important than radio coverage.
Reducing the Transmitted Power – In certain circumstances, reducing transmitted
power is more effective in eliminating interference than reducing height of antenna
Four conditions are used to compare the co channel interference results:
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Chapter 6 Results & Discussions
If Carrier to interference ratio C/I is greater than 15 dB throughout the
network, system is properly designed for capacity.
If C/I is greater than 12 dB and Carrier to Noise ratio C/N is greater than
18dB in some areas, there is a co channel interference
If both C/N and C/I are greater than 3dB and C/N = C/I in a particular area,
there is a coverage problem
If both C/N and C/I are greater than 3 dB and C/N > C/I in particular area,
there is a coverage problem and co channel interference.
6.2.3 STEP3: Site surveys
The “site surveys” were conducted for all sites and following are the results of checked
parameters.
Exact location – Most of the site’s locations were mono pol. These sites are
displaced to acceptable location such that it doesn’t affect the coverage to
considerable level.
Space for the BTS equipment- The equipments used is HUAWEI BSC-6000.
The HUAWEI BSC-6000 belongs to the BSC family of HUAWEI. Its a 10
Transceiver (TRX) radio base station for outdoor applications. The HUAWEI
BSC-6000 is a high coverage base station and configured for three sectors
site.
Antennas – The 25dBi gain antennas are used, one for each sector. It has
zero electrical polarization and 4 to 5 degree mechanical down tilt where
ever there was requirement of more capacity.
The radio measurement is done to find the corrections in prediction model. The quality of a
network plan is dependent on the accuracy of the propagation model used to predict
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Chapter 6 Results & Discussions
coverage pattern. The model tuning of Okumura-Hata resulted in modified area curves as
under.
Figure6.4: Okumura-Hata Correction curves
Due to the model tuning, the prediction gets better as in figure 5.3, which shows the
coverage pattern of same site as in figure 5.4. These graphs are being provided by external
advisor for calculation purposes
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Chapter 6 Results & Discussions
Figure 6.5: Coverage prediction by Tuned Okumura-Hata
6.2.4 STEP4: System Design
Once the planning parameters have been adjusted to match the actual measurements,
dimensioning of the BSC is performed and the final cell plan produced. As the name
implies, this plan can then be used for system installation. New coverage and interference
predictions are run at this stage, resulting in Cell Design Data (CDD) documents containing
cell parameters for each cell. In [1], Dimensioning of BSC includes:
i. Calculation of number of E1 (trunk circuits) at each site.
ii. Total number of Erlang supported by BSC.
iii. Determination of the kinds of links.
iv. Distribution of microwave links.
v. Assigning the BTS sites to appropriate BSCs.
vi. Link Capacities calculations.
vii. Total num4ber of radio required.
viii. Bandwidths for radio links.
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Chapter 6 Results & Discussions
i. Calculation of E1s
For calculations of E1s at each site it is mandatory to calculate the traffic carrying capacity
of each Site.
Data rate of 1 Time slot of E1 = 64 Kbps
Traffic channel on E1 = 30
Data rate of 1 Time slot of TRX = 16 Kbps.
Data rate of 1 TRX = 16 Kpbs × 8 = 128 Kbps.
Traffic carrying capacity of 1 cell = 3 × 128 Kpbs = 384 Kbps.
Traffic carrying capacity of 1 Site = 384 Kbps × 3 = 1152 Kbps
Required time slot for carrying traffic of S333 site = 1152 / 64 = 18 TS of E1s
Results show that one E1 is required by each site for supporting S333 configuration. So
total number of required E1 in the network is equal to total number of sites deployed. In total
79 E1 are required.
ii. Capacity of BSC :
Total number of Erlang supported by BSC is dependent on type and size of BSC. Here,
capacity of BSC is given to be 900 Erlangs.
iii. Determination of kind of link:
The determination of link is dependent on real site location and neighboring sites. This
parameter is calculated during installation and integration phase.
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Chapter 6 Results & Discussions
iv. Assigning BTSs to BSCs :
The assignment of BTSs to a particular BSC is dependent on amount of traffic and location
of site. In this project, four BSCs have been deployed each is linked to 8 BTSs.
6.2.5 STEP5: System tuning
The system tuning is done by drive testing using TEMS.
Beside drive testing the system tuning also include:
a.) Eliminating equipment failures
b.) Improving network operation indicators, such as radio completion rate, call
drop rate, the worst cell, handover success rate and congestion rate, etc.
c.) Improving voice quality, such as balancing the traffic between the cells
inside the network.
d.) Network balancing, such as signalling load balancing, equipment load
balancing and link load balancing, etc.
e.) Adjusting the network resources reasonably, for example, improving
equipment and spectrum utilization and adjusting the traffic in each channel.
f.) Creating and maintaining a long term network optimization platform, and
creating and maintaining network optimization archives.
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CHAPTER 7
CONCLUSION
7.1 CONCLUSION
It can be concluded that radio access network designing requires a thorough
analysis of resources, geographical area and required standards. A fine line or trade
off is to be made at different stages, depending on the circumstances. This very
project provided an opportunity of grasping the concepts of RAN, understanding the
procedure of its designing, resolving different encountered problems and studying
diverse solutions. It also granted a juncture, to interact with professionals of the
telecommunication industry.
This project provides an individual with intrinsic details of BSS planning and radio
access network. The analysis made between the theoretical and practical
approaches is based on professional consultancy, theory mentoring and real
environment testing. Thus this project provides information about working in the
field. The radio access network is developed in four distinguished steps, which can
assist an individual in developing a clear idea of the complex process of designing of
RAN.
The proposed design is enabling an optimum service of 94%. The required stages of
coverage, capacity, and frequency planning are well accomplished in the designed
RAN and the frequency planning has been taken to the next level, called transceiver
planning for all the sites which contributes in mitigating the problem of interferences.
The coverage prediction and loss estimations are improved by model tuning and
drive testing. The outcome of model tuning is implemented. The surveys and site
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visits gave a clear idea of hardware requirements, its limitations and cost which
assisted in increasing the real environment realization of the designed RAN.
The designed RAN is a cost effective design, it can be said so as the cost of
network is 1.6 million$ (cost per site is 0.2 million $ and total sites are 8). The total
given budget for the network was 2 million$, thus 0.4 million$ have been saved. This
RAN also has the dispensation of easy implementation because of likeness between
sites of a clutter or defined traffic density.
Although the designed RAN is fulfilling the given target but it can be improved in a
number of ways. The shortcomings of few stages of designing are as follows. In the
stage of coverage planning, the loss and gain factors to cater open qausi terrain
could not be found due to clandestine company data. 100% service could not be
enabled in the given city. Thus, efforts can be made to further improve the tuning of
applied model. In the second stage of capacity planning, the concept of cell
hierarchy can be applied to improve the user catering, as it will classify the outdoor,
indoor, moving and stationary users.
The designed RAN in this project is for a 2G technology (GSM), as its currently
deployed all over Pakistan and license of 3G has not been provided by PTA. Yet 3G
is the future of mobile communication technology. The foremost and major
recommendation is to make this network for the 3G technologies (like WCDMA or
WIMAX); developing a RAN will provide an opportunity to be distinctive and gain
latest knowledge. The second recommendation is the application of quality planning
in the proposed design. This stage is not implemented as it was not a requirement of
HUAWEI but it can make the network resource utilization efficient. The quality
planning will also satisfy the customer’s needs more appropriately.
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GLOSSARY
ARFCN: Absolute Radio Frequency Channel Number
BSC: Base Station Controller
BSIC: Basic Station identity controller
BSS: Base Station Subsystem.
BSSMAP: BSS Management Application Part
BTS: Base Transceiver Station.
dTRX: double Transceiver Unit
CCH: Control Channel
CDD: Cell Design Data.
CDU: Combiner Distribution Unit.
CM: Control Module.
EIR: Equipment Identity Register
FDMA: Frequency Division Multiple Access.
FLP: Fractional Load Planning.
GoS: Grade of Service
GSM: Global System for Mobile communications.
HLR: Home Location Register
ISDN: Integrated Services Digital Network
LAC: Location Area code
LAPD: Link access Protocol on Data channel
LAPDm: Link access Protocol on Data modified channel
MAP: Mobile Application Part
MRP: Multiple Reuse Pattern
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MS: Mobile Station.
MSC: Mobile Switching Centre
MTP: Message Transfer Part
NSS: Network Switching Subsystem
PSU: Power Supply Unit
PTT: Postal Telephone and Telegraph
RAN: Radio Access Network
RBS: Radio Base Station.
RIL3: Radio Interface Layer 3
RSL: Received Signal level
RSM: Radio Subsystem Management
TRAU: Transcoding Rate and Adaptation Unit.
TRM: Transmission Module.
TRX: Transceiver Unit.
TDMA: Time Division Multiple Access.
TCH: Traffic Channel
TCAP: Transaction Capabilities Application Part
SAQ: Site acquisition
SCCP: Signaling Connection Control Part
Um: User mode
VLR: Visitor Location Register
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REFERENCES
[1] “Modern Approaches in Modeling of Mobile Radio Systems Propagation
Environment”,
http://www.comsoc.org/livepubs/surveys/public/3q00issue/neskovic.html;
access date: 18/06/07
[2] Wireless and cellular wireless communications, 3rd Edi by Willian C.Y.LEE
[3] atlas.cc.itu.edu.tr/~pazarci/WandelGoltermann_gsm.pdf
[4] “COST 231 Walfisch- Ikegami Model”
http://www.ee.bilkent.edu.tr/~microwave/programs/wireless/prop/costWI.htm; access
[5] Wireless Network by Jeffery Wheat
[6] End-to-End Quality of Service Over Cellular Networks: Data Services ...
By Gerardo Gomez, Rafael Sánchez
[7] Principles and Applications of GSM by Vijay k. Garg and Joseph E. Wilkey
[8] en.wikipedia.org/wiki/GSM
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