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Aalborg University

Diploma thesis

Physical Layer measurements in3GPP LTE

Author:

Rasmus Birkelund Nielsen

Mauritio B. G. M. Nielsen

Supervisors:

Kim Hjgaard-Hansen

February 3, 2012


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Institut for Elektroniske SystemerElektronik & ITFredrik Bajers Vej 7

9220 Aalborg

Telefon 99 40 86 00

http://es.aau.dk

Titel:

Physical Layer measurements in 3GPPLTE

Tema:Kommunikationssystemer

Projektperiode:3. november 2011 3. februar 2012

Forfattere:Mauritio Birk Georg Musil NielsenRasmus Birkelund Nielsen

Vejleder:Kim Hjgaard-Hansen

Oplagsantal: 4

Sideantal: 97

Bilagsantal: 1 praktikrapport

Afsluttet: 3. februar 2012

Synopsis:

Denne rapport beskriver throughputmlinger p udrullet 3GPP LTEnetvrk. Disse mlinger skal benyttestil at undersge hvorledes dmpn-ing og intermodulations forvrngningpvirker andre UEs i nrheden.For at undersge disse aspekter er derforetaget en rkke live mlinger p eti forvejen udrullet LTE netvrk, hvorder i den frste mling foretages en sim-pel undersgelse ved at dmpe down-link signalet vha. attenuatorer. Denanden mling blev foretaget ved at sam-menkoble signalet modtaget p UE,med at stj-signal fra en SMIQ 06b Vec-tor Signal Generator.Det kunne ses fra resultaterne at dertydeligvis var en effekt ved at udstteen UE for disse stj niveau. Desvrre,er de foretagede mlinger ikke nok isig selv, og der br foretages yderligeremlinger. Forslag til hvilke aspekter derbr fokuseres p, er angivet i perspek-tiveringen.

Rapportens indhold er frit tilgngeligt, men offentliggrelse (med kildeangivelse) m kun ske efteraftale med forfatterne.
http://es.aau.dk/http://es.aau.dk/


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Department of Electronic SystemsElectrical EngineeringFredrik Bajers Vej 7

9220 Aalborg

Telefon 99 40 86 00

http://es.aau.dk

Title:

Physical Layer measurements in 3GPPLTE

Subject:Communication Systems

Project period:November 3rd, 2011 February 3rd, 2012

Authors:Mauritio Birk Georg Musil NielsenRasmus Birkelund Nielsen

Supervisors:Kim Hjgaard-Hansen

Copies: 4

Page count: 97

Appendix: 1 internship report

Completion of project: February 3rd, 2012

Synopsis:

This report describes throughput mea-surements performed on a deployed3GPP LTE network. The measure-ments are to be utilised to examinehow attenuation and intermodulationdistortion affects other UEs in the vicin-ity.Inorder to examine these aspects, anumber of live measurements were per-formed on a deployed LTE network,where in the first measurement, a sim-ple examination is made by attenuat-ing the downlink signla with attenua-tors. The second measurement was per-formed by combining the signal receivedon the UE with a noise signal generatedfrom a SMIQ 06b Vector Signal Gener-ator.It could be seen from the results thatthere was clearly an effect, by exposingthe UE for these noise levels. Unfor-tunately, the performed measurementsare not enough, in the sense that thereshould be proformed additional mea-

surements. Some proposals as to whichaspects should be investigated further,and are given in the Perspective chap-ter.

The contents of the report is freely available however, publication (with reference) may only happenper agreement with the author(s).
http://es.aau.dk/http://es.aau.dk/


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Chapter 1

Preface

This project has been made by Rasmus Birkelund Nielsen and Mauritio BirkGeorg Musil Nielsen, as part of the diploma thesis in Electronic Engineeringat Aalborg University. The overall theme of the project is based on Com-munication Systems, and was conducted over the period from November3rd, 2011 to February 3rd, 2012.

The supervisor for this project is Kim Hjgaard-Hansen, ph.d studentat Networking & Security, associated with School of Information andCommunication Technology, at Aalborg University. Futhermore, the groupwould like to give a special credit the employees at Agilent Technologies,

Aalborg for their help and guidance throughout the internship and on thisproject.

Rasmus Birkelund Nielsen Mauritio Birk Georg Musil Nielsen

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Contents

1 Preface vii

2 Introduction 1

3 Project Goal 3

I Analysis 4

4 Long Term Evolution System Overview 54.1 Network architecture . . . . . . . . . . . . . . . . . . . . . . . 54.2 Protocol architecture . . . . . . . . . . . . . . . . . . . . . . . 6

5 LTE Physical Layer 105.1 Introduction To The Physical Layer . . . . . . . . . . . . . . 105.2 Architectural Overview . . . . . . . . . . . . . . . . . . . . . 10

5.2.1 Frame And Slot Structure . . . . . . . . . . . . . . . . 105.3 Modulation Scheme and Coding. . . . . . . . . . . . . . . . . 16

5.3.1 Adaptive Modulation and Coding (AMC) . . . . . . . 165.3.2 Downlink: Orthogonal Frequency Division Multiple

Access (OFDMA) . . . . . . . . . . . . . . . . . . . . 175.3.3 Uplink: Single-Carrier Frequency Division Multiple

Access (SC-FDMA) . . . . . . . . . . . . . . . . . . . 185.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

6 Concepts Of Interference 216.1 Noise. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

6.1.1 Johnson-Nyquist noise . . . . . . . . . . . . . . . . . . 216.1.2 Gaussian noise . . . . . . . . . . . . . . . . . . . . . . 226.1.3 Signal-to-Noise ratio . . . . . . . . . . . . . . . . . . . 22

6.2 Interference . . . . . . . . . . . . . . . . . . . . . . . . . . . . 236.2.1 Co-Channel Interference . . . . . . . . . . . . . . . . . 236.2.2 Intersymbol interference . . . . . . . . . . . . . . . . . 23

6.3 Intermodulation. . . . . . . . . . . . . . . . . . . . . . . . . . 23

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6.4 In Denmark . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

6.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

II Measurements 27

7 Introduction 287.1 Throughput measurement . . . . . . . . . . . . . . . . . . . . 287.2 Intermodulation Distortion measurement. . . . . . . . . . . . 28

7.2.1 Directional coupler . . . . . . . . . . . . . . . . . . . . 287.3 Case: Downlink blocks Uplink. . . . . . . . . . . . . . . . . . 297.4 Key Performance Indicator (KPI). . . . . . . . . . . . . . . . 30

8 Initial test 338.1 Setup and test procedure . . . . . . . . . . . . . . . . . . . . 338.2 Observations . . . . . . . . . . . . . . . . . . . . . . . . . . . 358.3 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

9 Intermodulation Distortion test 409.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . 409.2 Setup and test procedure . . . . . . . . . . . . . . . . . . . . 409.3 Observation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

9.3.1 13-01-2012. . . . . . . . . . . . . . . . . . . . . . . . . 419.3.2 14-01-2012. . . . . . . . . . . . . . . . . . . . . . . . . 46

9.3.3 15-01-2012. . . . . . . . . . . . . . . . . . . . . . . . . 509.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

III Assesment 56

10 Final conclusion 57

11 Perspective 59

IV Appendices 63

A MIMO 64

B Duplexing and Multiplxing 66

C Channel Access Methods 68C.1 Basic Channel Access Methods . . . . . . . . . . . . . . . . . 68C.2 OFDM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69

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D Modulation schemes 70

D.1 BPSK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70D.2 QPSK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70D.3 QAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

E Attenuation measurement report 72E.1 Purpose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72E.2 Requirements and equipement. . . . . . . . . . . . . . . . . . 72E.3 Test setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73

E.3.1 Connectivity setup . . . . . . . . . . . . . . . . . . . . 73E.3.2 Location. . . . . . . . . . . . . . . . . . . . . . . . . . 73

E.4 Performing the measurement . . . . . . . . . . . . . . . . . . 73

E.5 Results 08-12-2011 . . . . . . . . . . . . . . . . . . . . . . . . 74E.5.1 Summary . . . . . . . . . . . . . . . . . . . . . . . . . 76

E.6 Results 11-12-2011 . . . . . . . . . . . . . . . . . . . . . . . . 77E.6.1 Summary . . . . . . . . . . . . . . . . . . . . . . . . . 79

E.7 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80

F Blocker measurement report 81F.1 Purpose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81F.2 Requirements and equipement. . . . . . . . . . . . . . . . . . 81F.3 Test setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82

F.3.1 Connectivity setup . . . . . . . . . . . . . . . . . . . . 82

F.3.2 Location. . . . . . . . . . . . . . . . . . . . . . . . . . 82F.4 Performing the measurement . . . . . . . . . . . . . . . . . . 83F.5 Results from the 13-01-2012 . . . . . . . . . . . . . . . . . . . 84

F.5.1 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . 88F.6 Results from the 14-01-2012 . . . . . . . . . . . . . . . . . . . 89

F.6.1 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . 91F.7 Results from the 15-01-2012 . . . . . . . . . . . . . . . . . . . 92

F.7.1 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . 96

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List of Abbreviations

3GPP 3rd Generation Partnership Project

ACK Acknowledgement

AMC Adaptive Modulation and Coding

ARQ Automatic Repeat Request

AS Access Stratum

AWGN Additive white Gaussian noise

BER Bit Error RatioBLER Block Error Ratio

BPSK Binary Phase-Shift Keying

CCI Co-Channel Interference

CDM Code-Division Multiplexing

CDMA Code-Division Multiple Access

CP Cycle Prefix

CQI Channel Quality Indicator

eNB evolved-Node B

EPC Evolved Packet Core

EPS Evolved Packet System

FDD Frequency-division Duplexing

FDM Frequency-Division Multiplexing

FDMA Frequency-Division Multiple Access

FEC Forward Error Correction

GP Guard Period

GSM Global System for Mobile Communications

HARQ Hybrid Automatic Repeat Request

ISI Inter-Symbol Interference

KPI Key Performance Indicator


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LTE Long Term Evolution

MAC Medium Access Control

MME Mobility Management Entity

MCS Modulation and Coding Scheme

MIMO Multiple Input-Multiple Output

NACK Negative Acknowledgement

NAS Non-Access Stratum

OFDMOrthogonal Frequency Division Multiplexing

OFDMA Orthogonal Frequency Division Multiple Access

P-GW Packet Data Network Gateway

PAPR Peak-to-Average Power Ratio

PDCP Packet Data Convergence Protocol

pdf probability density function

PDN Packet Data Network

PDU Packet Data Unit

PHY Physical layer

PSK Phase Shift Keying

QAM Quadrature Amplitude Modulation

QPSK Quadrature Phase-Skift Keying

RAN Radio Access Network

RB Ressource Block

RLC Radio Link Control

RRC Radio Resource Control

RSRP Reference Signal Receive Power

RSRQ Reference Signal Receive Quality

RSSI Received Signal Strength Indicator

RV Redundancy Version

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S-GW Serving Gateway

SC-FDMA Single-Carrier Frequency Division Multiple Access

SAE System Architecture Evolved

SDM Space-Division Multiplexing

SDMA Space-Division Multiple Access

SDU Serving Data Unit

SINR Signal-to-Interference plus Noise Ratio

SNR Signal-to-Noise RatioTDD Time-division Duplexing

TDM Time-Division Multiplexing

TDMA Time-Division Multiple Access

UE User Equipment

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List of Figures

4.1 The network architecture in Long Term Evolution (LTE),showing how the system is split and interconnected. . . . . . 6

4.2 The protocol stack in the user plane. It consists of 3 layers.Layer 1 is the Physical layer, Layer 2 consisting of 3 sublayers;Medium Access Control (MAC), Radio Link Control (RLC),Packet Data Convergence Protocol (PDCP), and Layer 3 asthe Radio Resource Control (RRC) layer. . . . . . . . . . . . 7

4.3 The protocol stack for the control plane. It functions exactlyas in the user plane, however serves mainly as a carrier forcontrol messaging from the RRC which may contain Non-Access Stratum (NAS) messaging, rather than user data. . . 8

4.4 Overview of the ideal system. The main focus of themeasurements will be on the physical layer downlink side. . . 9

5.1 Frame structure for type 1 for FDD mode. (Rumney 2009). . 115.2 Frame structure for type 2 for TDD mode. (Rumney 2009) . 115.3 Orthogonal Frequency Division Multiplexing (OFDM) sym-

bol structure for normal cyclic prefix case. (Rumney 2009) . . 125.4 OFDMsymbol versus cyclic prefix +OFDMsymbol . . . . . 125.5 Ressource grid for 1 uplink slot (a) and 1 downlink slot (b) . 135.6 Subcarrier allocation in OFDM and OFDMA. By assigning

different OFDM sub-channels, Frequency-Division MultipleAccess (FDMA) is achieved. . . . . . . . . . . . . . . . . . . . 18

5.7 Transmission of a series of QPSK symbols in both OFDMA

and SC-FDMA . . . . . . . . . . . . . . . . . . . . . . . . . . 195.8 Simplified signal generation of SC-FDMA and OFDMA . . . 20

6.1 Intermodulation distortion from third order product . . . . . 246.2 intermodulation interference . . . . . . . . . . . . . . . . . . . 25

7.1 The basic construction of a -20dB directional coupler . . . . 297.2 Block diagram of how the user case is assumed. . . . . . . . . 29

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7.3 UE reporting CQI to the eNB, which afterwards sends a

request of which modulation and coding the UE should usenext. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

8.1 Test setup for measurement the impact of different attenua-tion while downloading in the 1800 MHz band. . . . . . . . . 34

8.2 Throughput from Meas-1. Throughput is measured in kbit/s. 358.3 Measured SINR from Meas-1. . . . . . . . . . . . . . . . . . . 358.4 Reported CQI index from Meas-1. . . . . . . . . . . . . . . . 368.5 Measured RSSI in Meas-1. . . . . . . . . . . . . . . . . . . . . 368.6 Throughput from Meas-2. It is measured in kbit/s. . . . . . . 378.7 SINR from Meas-2. . . . . . . . . . . . . . . . . . . . . . . . . 37

8.8 Reported CQI index, from Meas-2. . . . . . . . . . . . . . . . 378.9 Resource block allocation in Meas-2 . . . . . . . . . . . . . . 388.10 Resource block allocation in Meas-1 . . . . . . . . . . . . . . 388.11 Measured RSRQ from Meas-2. . . . . . . . . . . . . . . . . . 398.12 Measured RSRQ from Meas-1. . . . . . . . . . . . . . . . . . 39

9.1 Test setup for measurement the intermodulation on 1800 MHzband . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

9.2 Throughput in 1869.7 MHz . . . . . . . . . . . . . . . . . . . 429.3 Throughput in 1870.2 MHz . . . . . . . . . . . . . . . . . . . 429.4 RSRQ in 1869.7 MHz . . . . . . . . . . . . . . . . . . . . . . 439.5 RSRQ in 1870.2 MHz . . . . . . . . . . . . . . . . . . . . . . 439.6 Resource Block in 1869.7 MHz . . . . . . . . . . . . . . . . . 449.7 Resource Block in 1870.2 MHz . . . . . . . . . . . . . . . . . 449.8 SINR in 1869.7 MHz . . . . . . . . . . . . . . . . . . . . . . . 449.9 SINR in 1870.2 MHz . . . . . . . . . . . . . . . . . . . . . . . 459.10 Received signal strength indication in 1869.7 MHz . . . . . . 459.11 Received signal strength indication in 1870.2 MHz . . . . . . 459.12 channel quality indicator in 1869.7 MHz . . . . . . . . . . . . 469.13 channel quality indicator in 1870.2 MHz . . . . . . . . . . . . 469.14 Intermodulation distortion on TELIAs 1800 MHz band

starting at the center frequency and move 8 steps with 1 MHzeach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

9.15 Throughput with different modulation on the intermodulateddistorted signal . . . . . . . . . . . . . . . . . . . . . . . . . . 47

9.16 RSRQ with different modulation on the intermodulateddistorted signal . . . . . . . . . . . . . . . . . . . . . . . . . . 48

9.17 Resource Block with different modulation on the intermodu-lated distorted signal . . . . . . . . . . . . . . . . . . . . . . . 48

9.18 SINR with different modulation on the intermodulateddistorted signal . . . . . . . . . . . . . . . . . . . . . . . . . . 49

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9.19 RSSI with different modulation on the intermodulated

distorted signal . . . . . . . . . . . . . . . . . . . . . . . . . . 499.20 channel quality indicator with different modulation on the

intermodulated distorted signal . . . . . . . . . . . . . . . . . 499.21 Intermodulation distortion on TELIAs 1800 MHz band . . . 509.22 Throughput with -40dB attenuation . . . . . . . . . . . . . . 519.23 Throughput with -60dB attenuation . . . . . . . . . . . . . . 519.24 RSRQ with -40dB attenuation . . . . . . . . . . . . . . . . . 519.25 RSRQ with -60dB attenuation . . . . . . . . . . . . . . . . . 529.26 Resource Block with -40dB attenuation . . . . . . . . . . . . 529.27 Resource Block with -60dB attenuation . . . . . . . . . . . . 529.28 SINR with -40dB attenuation . . . . . . . . . . . . . . . . . . 53

9.29 SINR with -60dB attenuation . . . . . . . . . . . . . . . . . . 539.30 RSSI with -40dB attenuation . . . . . . . . . . . . . . . . . . 539.31 RSSI with -60dB attenuation . . . . . . . . . . . . . . . . . . 549.32 channel quality indicator with -40dB attenuation . . . . . . . 549.33 channel quality indicator with -60dB attenuation . . . . . . . 54

A.1 Simplified MIMO. Transmitter (Tx0,Tx1), Receiver (Rx0,Rx1) 64A.2 Multipath with signal diversity. Transmitter (Tx0,Tx1),

Receiver (Rx0,Rx1) and obstacles (A,B,C,D) . . . . . . . . . 65

C.1 Channel access using FDMA, TDMA, and CDMA in relationto each other. (Flintoff et al. 2000) . . . . . . . . . . . . . . . 68

C.2 Multiple modulated OFDM subcarriers with constant ampli-tude. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69

D.1 1-bit signal . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70D.2 QPSK modulated signal, which comprises of 2-bit symbols. . 71D.3 The two QAM schemes. 1) shows 16 QAM while 2) shows 64

QAM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

E.1 Measurement test setup for determining the impact ofdifferent attenuation while downloading, in the 1800 MHzband. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73

E.2 Location of UE and eNB. The measurement was performedapproximately at position A), while the eNB is locatedapproximately at position B). . . . . . . . . . . . . . . . . . . 74

E.3 Throughput is measured in kbit/s. . . . . . . . . . . . . . . . 75E.4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76E.5 Throughput is measured in kbit/s. . . . . . . . . . . . . . . . 78E.6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79

F.1 Test setup for measurement the impact of different attenuatorsize while downloading in the 1800 MHz band . . . . . . . . . 82

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F.2 Location of UE and eNB. The measurement was performed

approximately at position A), while the eNB is locatedapproximately at position B). . . . . . . . . . . . . . . . . . . 83

F.3 TP in kbit/s, RSRQ and RB with different level of attenuation 85F.4 SINR in dB, MCS index, RSSI in dB and CQI with different

level of attenuation . . . . . . . . . . . . . . . . . . . . . . . . 86F.5 TP in kbit/s, RSRQ and RB with different level of attenuation 87F.6 SINR in dB, MCS index, RSSI in dB and CQI with different

level of attenuation . . . . . . . . . . . . . . . . . . . . . . . . 88F.7 Every 1 minute the frequency was increased by 1 MHz. The

extra time was to insure that the interference signal was outof range. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89

F.8 TP in kbit/s, RSRQ and RB with different frequencies . . . . 90F.9 SINR in dB, MCS index, RSSI in dB and CQI with different

frequencies . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91F.10 Every 30 sec. the frequency was increased by 1 MHz. The

bandwidth was 10 MHz and the extra time was to insure thatthe interference signal was out of range. . . . . . . . . . . . . 92

F.11 TP in kbit/s, RSRQ and RB . . . . . . . . . . . . . . . . . . 93F.12 SINR in dB, MCS index, RSSI in dB and CQI . . . . . . . . 94F.13 TP in kbit/s, RSRQ and RB . . . . . . . . . . . . . . . . . . 95F.14 SINR in dB, MCS index, RSSI in dB and CQI . . . . . . . . 96

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Chapter 2

Introduction

Over the last few decade, wireless telecommunication have increaseddramatically, especially after the introduction of the cellular phone, whichnow can not only transmit voice, but as well receive e-mail, browse theWorld Wide Web, and much more. In wireless telecommunication differentstandards are used in order to provide connectivity for the user in the rapidgrow in the usage of the frequency spectrum. With the fusion of usage in thewireless telecommunication that include the same task as before only waspossible in the normal wired communication(modem, ADSL, broadband anda lot more), the demand for speed and availability from the daily user havebecome increasingly real. This is seen especially in studies which have shown

that up to 88 % of danish families have at least one household computer,and with 86 % of these families having internet access (og Telestyrelsen2011). Thus the introduction of LTE. With this new technology, a widerange of improvements are brought forward, such as improved connectivityand availibility, as well as higher speeds.In some countries,LTEis still under deployment, however in most Westerncountries it is currently available by Telecom Service Providers. In Denmark,LTE is provided on two frequency bands. One of these are the 1800 MHzbandwidth, which as of May 1st, 2011, was released for commercial usewith other telecommunication technologies, other than Global System forMobile Communications (GSM). This enables LTE to use this frequency

band. The 1800 MHz frequency is divided into two sub frequency bands.1710-1785 MHz is dedicated to uplink, and 1805-1880 MHz is dedicated todownlink (og Telestyrelsen 2009c).This project deals with the use of Telia Nttjnster Norden ABs1761.3-1773.1 MHz uplink and 1856.3-1868.1 MHz downlink. SinceTelia bought Orange A/S in 2004, Telia was able to increase their1800 MHz band to 1761.3-1784.9 MHz uplink and 1856.3-1879.9 MHzdownlink (og Telestyrelsen 2009b).The focus of this project is primarily to examine how poor signal strength

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and intermodulation in Real life measurements affects throughput. At the

same time the modulation of the network will be analysed.

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Chapter 3

Project Goal

The purpose of this project is to examine how LTEs physical layerthroughput is affected by disturbances, such as noise and interference,from other communication technologies in the same frequency band. Thesedisturbances are seen from a user applications point of view, by introducingnoise in various ways into the channel. This may be done either directly intothe channel or by introducing distortion from third order intermodulationproducts, over the channel bandwidth, afterwhich the effects on the systemare analysed.During the project, this report will include;

A pre-analysis of the physical layer in the LTE standard, frompreliminary experiments

with focus onLTEs adaptive modulation mechanism

A theoretical inference of how physical throughput is affected bydifferent levels of Signal-to-Noise Ratio (SNR).

Experiments on deployed LTE networks with the introduction indifferent levels ofSNR.

A comparison of theoretical and experimental results.

This project will mainly focus on the 1800 MHz frequency area.

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Part I

Analysis

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Chapter 4

Long Term Evolution System

OverviewThe LTE system architecture is designed with the goal of supporting apacket-switched networking paradigm. This allows a highly simplifiedarchitecture in which there only exists two types of nodes. The basestation, also known as evolved-Node B (eNB) and the Mobility ManagementEntity (MME).This chapter serves as a brief discussion on the LTE system architecture,inorder to give a quick overview, before going into depth with the physicallayer. First is a description of the network architecture, and afterwards the

protocol architecture is briefly described.

4.1 Network architecture

System Architecture Evolved (SAE) is the core network architecture of3rd Generation Partnership Project (3GPP)sLTEwireless communicationstandard. It allows for a more simplified architecture, with support forhigher throughput/low latency to non-3GPP networks and for a bettermobility between 3GPP legacy systems. All network interfaces are basedon IP protocols, where the eNBs are interconnected by means of an X21

interface, and the to MME through an S12

interface. Figure 4.1 on thefollowing pageshows how theeNBs andMMEare interconnected.

1The X2 interface is a communication protocol, by which the eNBsare interconenctedwith.

2The S1 interface, connects the eNB to the Evolved Packet Core (EPC).

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Figure 4.1: The network architecture in LTE, showing how the system issplit and interconnected.

The functional split between theeNBand theMMEresults in two logicalgatway entities being defined. The Serving Gateway (S-GW) acts as alocal mobility anchor for the user plane, during handovers and anchoringLTEand other3GPPtechnologies, while at the same time forwarding andreceiving, user data packets. The Packet Data Network Gateway (P-GW)allows interfacing with other external Packet Data Networks (PDNs) suchas the Internet, along with other IP functions. Furthermore, the P-GWacts as an anchor between3GPPand non-3GPPtechnologies, like WiMAX.TheeNBfunctions mainly by performing header compression, ciphering andproviding a reliable delivery of packets.

4.2 Protocol architecture

Besides SAE are the NAS protocols. These form the highest stratum ofthe control plane between the User Equipment (UE) and MME. TheNAS performs functions such as Evolved Packet System (EPS) bearermanagement, authentication and security control.

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In figure4.2, is the user plane protocol stack.

Figure 4.2: The protocol stack in the user plane. It consists of 3 layers.Layer 1 is the Physical layer, Layer 2 consisting of 3 sublayers; MAC, RLC,PDCP, and Layer 3 as the RRClayer.

The protocol stack is divided into three layers, where Layer 2 issubdivided into three sublayers, namely theMAC,RLC and PDCP.Figure 4.3 on the following page shows the protocol stack for the control

plane. MAC, RLCand PDCPbehave exactly as they do in the user plane,however they function mainly to carry control messaging from the RRC.

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Figure 4.3: The protocol stack for the control plane. It functions exactly asin the user plane, however serves mainly as a carrier for control messagingfrom theRRCwhich may containNASmessaging, rather than user data.

As mentioned before, Layer 2 consists of the three sublayers. Themain functions of the MAC layer is to perform multiplexing of data fromlogical channels, which are then to be delivered to the physical layer via the

transports channels. Moreover, the MAC performs error correction fromHARQ, and diciding which UEs will be allowed to send or receive data onthe shared physical resource (Rumney 2009).TheRLCacts as an interface between the higher layers of the stack and theMAClayer. Basically it acts more as a router, since its main purpose is tointerface and buffer because the MAC has no buffer capabilities (Rumney2009).Next is the PDCP layer. This layer performs functions such as headercompression, and decompression, ciphering and passing Serving Data Units(SDUs) and Packet Data Units (PDUs) (Rumney 2009).Finally, is the Physical layer (PHY). This is the lowest layer in the LTE

protocol and covers the downlink transmission from the eNB to the UE,and the uplink transmission from the UEto eNB. The physical layer is ofparticular interest, and it is in this layer that will be primarily focused on.In figure4.4 on the next pageis a simple overview of the system.

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Figure 4.4: Overview of the ideal system. The main focus of themeasurements will be on the physical layer downlink side.

It is the physical layer KPIs that are of main interest. ThePHYlayerwill be discussed in further detail in chapter5.

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Chapter 5

LTE Physical Layer

In order to better understand the principles in LTE, it is neccessary tounderstand how the lowest layer of LTE, the Physical layer, works. Duringthis chapter an introduction to the Physical layer will be given, as well as anoverview of how the Physical layer is constructed. This chapter is primarilybased onRumney(2009), except where stated otherwise.

5.1 Introduction To The Physical Layer

The Physical layer of LTE covers the downlink and uplink tranmissionbetween theUEand the eNBbase transceiver station. The Physical layersupports two multiple access schemes. These multiple access schemes areOFDMA and SC-FDMA, which will be discussed in detail later in thischapter. Addtionally to OFDMA and SC-FDMA, both paired and unpairedspectra are supported by using Frequency-division Duplexing (FDD) andTime-division Duplexing (TDD), respectively.

5.2 Architectural Overview

There are defined two types of Physical layer channels. These two types are;the physical channels, which carry information from the higher layers, as well

as data, and the physical signals, which are generated in the physical layerfor cell identification, radio channel estimation, and system synchronization.Two types of frames are also defined in the Physical layer; type 1 for FDDand type 2 for TDD.

5.2.1 Frame And Slot Structure

The frame structure defines frame, subframe, slot and symbol in the timedomain. Each time length is defined in units ofTS = 1/(15000 2048) =32.55 ns.

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Figure 5.1: Frame structure for type 1 for FDD mode. (Rumney 2009)

The frame structure seen in figure 5.1is frame type 1 defined for FDD

mode. Each frame consistes of 10 subframes, which consists for 2 slots. Oneradio frame is 10 ms long. In FDD mode, both the uplink and downlinkscheme use the same frame structure however, they uses different spectra.Frame structure type 2 is defined for TDD mode, and is seen in figure5.2.

Figure 5.2: Frame structure for type 2 for TDD mode. (Rumney 2009)

Frame structure type 2 is also defined for 7 different configurations,

where each radio frame is 10 ms long and consists of two half frames.Futhermore, each half frame consists of 5 subframes, which are 1 ms long.The 7 configurations of frame structure type 2 can be seen in table 4.2-2 in3GPP(2011b).

Inter-Symbol Interference (ISI) and cyclic prefixing

In OFDM systems, as well as SC-FDMA in this context, one of the keyadvantages is the introduction of a Guard Period (GP) between each symbol.This GP gives the ability to protect against multipath delay spread, and thus

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eliminatesISI. If theGPis longer than the delay spread in the channel, and

each OFDM symbol is cyclically extended into the GP, then the ISI canbe completely removed. In figure 5.3, an example of an OFDM symbolstructure can be seen.

Figure 5.3: OFDMsymbol structure for normal cyclic prefix case. (Rumney

2009)

By cyclic prefixing, the symbol will be prefixed with a repetition of thesymbol sequence itself (Haykin 2000). Thus by introducing cyclic prefixing,OFDMandSC-FDMAsystems are able to protect against multipath spreadsof up to 10 km. In figure 5.4the last part of theOFDMsignal is added inthe beginning if theOFDMsignal. The length of the cyclic prefix is chosento accommodate the wireless channels maximum delay spread.

Figure 5.4: OFDMsymbol versus cyclic prefix +OFDMsymbol

It should be noted that delay spreads represent the variation in pathdelay, and can be interpreted as the difference in time of arrival betweenextreme multipath components, i.e. earliest and latest component.

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Resource elements and blocks

Within the Physical layer, a resource element is the smallest unit andextends over one symbol (OFDM or SC-FDMA) in the time domain, andone subcarrier in the frequency domain.

(a) (b)

Figure 5.5: Ressource grid for 1 uplink slot(a) and 1 downlink slot (b)

The Ressource Block (RB) is the smallest unit, that can be scheduled.It physically occupies 180 kHz in frequency, and 0.5 ms in time. Thus fora channel bandwidth of 10 MHz (including guardspaces, etc.), a maximumof 50RBs can be alotted. For the full channel bandwidth of 20 MHz, thereare 100RBs available.In most systems the transmission bandwidth is fixed, however OFDM

systems enables the possibilty for flexible bandwidths. Subcarrier spacingis determined by an inverse of the FFT intergration time, thus giving LTEthe flexibility of having six different transmission bandwidth configurationsto choose from. The different transmission bandwidth configurations can beseen in table5.1 on the following page

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Channel bandwidth [MHz] 1.4 3 5 10 15 20

Configuration in MHz 1.08 2.7 4.5 9 13.5 18Configuration in RB 6 15 25 50 75 100

Table 5.1: Transmission bandwidth configuration. (3GPP 2011a)

The channel bandwidth which is defined in MHz, represents the nominaloccupied channel. Basically, this is the bandwidth which the operator, suchas Telia, provides. In Denmark, Telia provides LTE with 10 MHz bandwidth,whereas Telenor has 20 MHz. The transmission bandwidth which is definedin units ofRB and represent the maximum ofRB that can be transmitted,

for any given channel bandwidth.The architectural overview, however, does not only cover the the physicalallocation of resource blocks and the frame structure of theLTEframe. Nextcomes the physical layer signalling, which is a key part of the Physical layer,since it contains different error correction methods, among other aspects.

Physical layer signalling

Besides the physical carriers of data, which are RBs there are two keymeasures of performance in communications systems; throughput andlatency. Throughput is the actual amount of data being tranmitted, and isusually measured in bit per second. In comparison, shipping a box of DVDsovernight would result in a superb throughput. Therefore, high throughputis desired if a user wishes to download large files. However, in the shippingexample, the delay would not be acceptable, since the user would have towait some time before recieving his shipment. In this case, it would result inhigh latency, because a low latency is desired to inorder to guarantee quickresponses to a users requests, in applications such as VoIP, internet gaming,etc.To counteract low throughput and high latency, LTE employs a numberof mechanisms in the physical layer. Two of these mechanisms are HybridAutomatic Repeat Request (HARQ) andAMC. AMCwill be discussed insection5.3 on page 16 along with the modulation schemes.In order to ensure that data is sent reliably from one node to another,Automatic Repeat Request (ARQ) is used. This is an error detectionmechanism, which requests a retransmission from the receiver, incase ofa timeout. HARQis a combination ofARQ,and Forward Error Correction(FEC) which is error correction technique by adding redundancy into thetransmitted signal (Haykin 2000). A simple example ofFEC can be seen intable5.2 on the facing page.

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Triplet received Interpreted as

000 0 (error free)001 0010 0100 0111 1 (error free)110 1101 1011 1

Table 5.2: Example of Forward Error Correction. Adding redundancy byreceiving triplets of the symbol, reduces the possibility of errors.

Given the instance that the binary sequence 1012 is to be transmitted,then by usingFECinstead of transmitting a single bit at a time, at triplet ofthe bit is transmitted. Thus the sequence 1012 would result in 1110001112.The added redundancy allows an error in any of the three samples to becorrected.There exists two types ofHARQ. Type IHARQwhich is the simplest formof HARQ,and Type II HARQ,whereas it is the Type II which is used inLTE. On the first transmission of the packets life, a subset of the codedbits are transmitted with enough information for the receiver to decode

the original information of the packet and the CRC, with only a smallamount of redundancy, thus resulting in high efficiency under good channelconditions. However, if the packet is not decoded correctly, a retransmissionis triggered. Where the benefits of HARQ comes into light is rather re-sending the same data, the HARQchooses another set of encoded bits, stillrepresenting the original information bits and the destination node addsthis new information to what was received earlier. This HARQprocess is astop-and-wait protocol, meaning that once the HARQprocess has sent itspacket, it stops and waits for an ACK/NACK from the destination, beforesending the next packet.The different transmitted packet versions from the HARQprocess contains

different mixes of redundancy and systematic bits. These versions are calledRedundancy Versions (RVs). These RVs er sequenced through in LTEbythe HARQprocess, until the packet has either been received correctly, orthe maximum of retransmissions have been reached, in which case HARQdeclares a failure and hands it over to the ARQrunning in theRLClayer.At this pointAMC takes over.

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5.3 Modulation Scheme and Coding

LTEintroduces the use of different modulation schemes, depending on theuplink and downlink. In appendixC on page 68,OFDMandSC-FDMAwillbe discussed more thoroughly. In this section the two modulations schemesandAMC are described.

5.3.1 AMC

WhenHARQhas declared a failure in retransmissions, it hands the packetover toARQandAMCtakes over. It attempts to match the transmissionsfrom the HARQ process to the channel conditions in order to choose theappropriate coding. During good channel conditionsAMC would employ ahigher modulation, such as 64-Quadrature Amplitude Modulation (QAM)which uses less redundancy in the transmission. This would results in alarger transport block to be carried in the allocated channel. However,if the channel suffers from poor conditions, AMC would choose a lowerorder of modulation. Such a modulation would be Quadrature Phase-SkiftKeying (QPSK). With QPSK more redundancy bits would be sent to inorder to improve the probability of reception, but then employing a smallertransport block. If the packet error rate is very low, it would imply the themodulation depth is to high or to much redundancy is used. This resultsin a smaller transport block size, and thus ultimately reduces throughput.Moreover, if the packet are large, then the packet error rate would be high,and again result in reduced throughput.In order for AMC to work it is required that the eNB is informed aboutthe channel quality, seen by the UE. This is done through Channel QualityIndicator (CQI) information, reported by the UE in the uplink. TheCQIindex and its corresponding modulation scheme can be seen in table5.3 onthe facing page.

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Figure 5.6: Subcarrier allocation in OFDM and OFDMA. By assigning

differentOFDMsub-channels,FDMAis achieved.

5.3.3 Uplink: Single-Carrier Frequency Division MultipleAccess (SC-FDMA)

Two of the main concerns to the LTE uplink, however, was the powerconsumption in the UE terminals, as well as high Peak-to-Average PowerRatio (PAPR) which is a comparison of the peak power detected overa period of samples at the time period. SC-FMDA can be seen asa DFT-spread OFDMA by using the time domain data signals andtransform it to frequency domain by a DFT before parsing through OFDMA

modulation. This techniques reduce the instantaneous transmit powerimplying increase power-amplifier efficiency, low-complexity and flexiblebandwidth assignment. Using SC-FDMA allows the usage of a singlecarrier transmission system such asGSMand Code-Division Multiple Access(CDMA). These types of systems have a low PAPR. SC-FDMAutilizes asingle-carrier transmitting signal in contrast to OFDMA that use a multi-carrier transmission scheme. In5.7 on the next pagea graphical comparisonof OFDMA and SC-FDMA are shown.

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Figure 5.7: Transmission of a series of QPSK symbols in both OFDMA andSC-FDMA

In SC-FDMA, signals are built up in units of 12 subcarriers. Howeverin figure 5.7 there are only four subcarriers used over two symbol periodsrepresented byQPSKmodulation. The obvious difference between OFDMAand SC-FDMA is that OFDMA transmit the four QPSK data symbol inparallel, while SC-FDMA transmit the four QPSK data symbols in series.

An overall model of how the data bits get through SC-FDMA andOFDMA is to find in figure 5.8 on the next page. Both the SC-FDMAand OFDMA techniques is represented. First the data gets and transformsto a time domain waveform. By using a DFT the signal gets to the frequencydomain and map one more time. This time the same same is existing in theOFDMA that the symbols gets map to subcarriers. Then the IFFT gets the

subcarriers back in a time domain to be unconverted for the transmission.When received the inverse process take place.

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Figure 5.8: Simplified signal generation of SC-FDMA and OFDMA

5.4 Summary

In this chapter details of the Physical layer has been described. At firstan architectural overview of the physical layer in LTE has been given.The Physical Layer consists of several error correction mechanisms, whichenables the opportunity for a low probability of error. The use of bothOFDMA for downlink and SC-FDMA for the uplink is only possible sincethe introduction of powerful and small DSP(Digital signal processor). Thisgive a range of improvement by access mode seen in OFDMA and low power

consumption as in SC-FDMA.

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Chapter 6

Concepts Of Interference

In this chapter, some concepts of interference will be discussed. Interferencecan be found everywhere in a communication system, and can cause errorsstemming from transmitted symbols interfering with eachother or from anoisy channel resulting in a receiver having trouble with distinguishingbetween wanted signal and background noise.In the following sections, noise and interference will be discussed, andafterwards some aspects on intermodulation, and what influences if makeson a communication system.

6.1 NoiseOne way that interference can be regarded as, is noise. Noise comesin different forms and can be defined as an unwanted and randomsignal or disturbance. It can originate from different places, and givena communication system, can be introduced either before or after thedecoder/encoder. In this section, two types of noise will be considered.These are Johnson-Nyquist noise and Gaussian noise.

6.1.1 Johnson-Nyquist noise

Thermal noise, which it is also known as, arises from the random motion of

electrons in a conductor. Thermal noise is expressed as

PdB = 10 log10(kB T f 1000) (6.1)

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where,

Pis the noise power, [dBm]

kB is Boltzmanns constant,

J

K

Tis the absolute temperature [K]

fis the frequency bandwidth [Hz]

6.1.2 Gaussian noise

Another type of noise is Gaussian noise in which its probability densityfunction (pdf) is equal to that of the normal distribution. The normal

distribution has a bell-shaped pdf, and is regarded as one of the mostprominent probability distributions in statistics due to its applicability asa simple model on complex systems. A special form of this type of noiseis white Gaussian noise, in which all values in any pairs are uncorrelated.However, Gaussian noise is most commonly used in applications as additevewhite noise, in order to yield additive white Gaussian noise.

Additive white Gaussian noise

The Additive white Gaussian noise (AWGN) channel model which is widelyused in communications (Land and Fleury 2007). Having a transmitted

signal X(t), then X(t) will be superimposed by a stocastic noise signalW(t), in such a way that the transmitted signal will be received as,

Y(t) =X(t) + W(t) (6.2)

This means that some noise signal will be directly added to the transmittedsignal.

6.1.3 Signal-to-Noise ratio

A way of measuring noise can be donw through SNR. SNRis a measure ofcomparing the level of desired signal to the level of background noise, and

is defined as the power ratio between signal and noise.

SNR=PsignalPnoise

(6.3)

where P is the average power. SNRis also most often expressed in decibels.Thus in dB,SNR is defined as,

SNRdB= 10 log10

PsignalPnoise

(6.4)

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6.2 Interference

When dealing with communication systems interference will always occur,in some way or another. It can be anything in which alters, modifies ordisrupts the signal as it travels along a channel. In this section, mainlyCo-Channel Interference (CCI) and Inter-Symbol Interference (ISI) will beregarded.

6.2.1 Co-Channel Interference

CCI, also known as crosstalk stems from when two different tranmittersattempst to transmit using the same frequency. Since the frequencyspectrum over the last decade has become more and more crowded dueto other technologies, it is becoming increasingly more difficult to dividethe different frenquency bands required for these technologies. In mobilecommunications, the frequency spectrum is divided into non-overlappingcells. However, due to the crowded spectrum, it is neccessary to reusefrequencies. It is here where CCI arises. Even though two cells using thesame frequency and situated far away from eachother, a signal from theundesired transmitters may still arive. This will lead to the signal from faraway will be received and interfere with closer and correct signals.

6.2.2 Intersymbol interference

In contrast toCCI, ISIis a form of interference where one transmitted signalis blended with subsequent symbols. This is an unwanted effect, since it canbe catagorised as noise, and making communication unreliable. And since,ISI is usually caused by a multipath propagation in a environment proneto reflections, it is especially evident in Multiple Input-Multiple Output(MIMO) systems. A method of counteractingISIis by separating symbolswith guard periods, as mentioned in section5.2 on page 10

6.3 Intermodulation

In non-linear systems, all signals will produce second and third orderproducts around their centerfrequencies. Given two frequencies f1 andf2, these will produce second order products at 2f1, f1+ f2, 2f2 and theinverse. However, since the second order product are situated far away fromtheir main frequencies, they will no immediate significance, and can thusbe filtered away. On the other hand, with second order products removed,third order products are still in range of the signal of interest. Figure 6.1on the next pageshows how the problem of third order products still are ineffect.

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Figure 6.1: Intermodulation distortion from third order product

Having third order products close to the main frequencies is notdesired, since they will influence whatever signal may recide on the mainfrequency, and thus results in Intermodulation Distortion. In table6.1theintermodulation products which are produced in the 1800 MHz area, arelisted.

RX2 TX1 1710 1720 1730 1740 1750 1760 1770 17851805 1900 1890 1880 1870 1860 1850 1840 18251815 1920 1910 1900 1890 1880 1870 1860 18451825 1940 1930 1920 1910 1900 1890 1880 18651835 1960 1950 1940 1930 1920 1910 1900 18851845 1980 1970 1960 1950 1940 1930 1920 19051855 2000 1990 1980 1970 1960 1950 1940 19251865 2020 2010 2000 1990 1980 1970 1960 19451880 2050 2040 2030 2020 2010 2000 1990 1975

Table 6.1: Intermodulation distortion in the 1800 MHz band

All frequencies that are in red, are those of interest. From the tableit can be seen that in the case of having a TX1 in 1730-1785 MHz, andat the same time having an RX2 at 1805-1825 MHz, will directly resultsin third order intermodulation distortion on the RX1. In figure6.2 on thefacing pagethe two times downlink from a second provider RX2 minus oneuplink from first provider TX1, will create intermodulated interference onthe downlink of first provider. This is in contrast to figure 6.1 where theentire 1800 MHz downlink becomes intermodulated with the uplink area inthe 1700 MHz frequency area.

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Figure 6.2: intermodulation interference

In the figure 6.2 the case of intermodulation distortion is shown. Forthis to happen it is a requirement that,

2 RX2low band-edge 1 TX1high band-edge (6.5)

is met.This means that intermodulation distortion will directly occur on the highband-edge of RXs downlink area, given the case that some signals are gen-erated on the high band-edge of the frequency area dedicated to uplink, atthe same time with a signal on the low band-edge on the frequency areadedicated to downlink.

6.4 In Denmark

With Hi3G and TDC together, offeringLTEdownlink on 1805.1-1836.9 MHz (og Telestyrelsen2009a,2010), and Telia having the downlink on 1856.3-1879.9 MHz (og Telestyrelsen2009c) and uplink on 1761.3-1784.9 MHz, this phenomenon is very much ev-ident.

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RX2 Telia TX 1750 1760 1770 1785

Hi3G 1805 1860 1850 1840 1825Hi3G 1815 1880 1870 1860 1845TDC 1825 1900 1890 1880 1865TDC 1835 1920 1910 1900 1885

Table 6.2: Intermodulation distortion in Telias 1800 MHz band

In table6.2the direct impact of the twos providers downlink frequenciesis highlighted in read. In the case where a number ofUEs are in the samecell, the Telia users downlink throughput is significantly impaired, if there

are a number of TDC and/or 3 users uploading large amounts of data. Theexpectation is to reproduce this phenomenon with different signals level andmodulation to see the impact of intermodulation distortion in a real lifemeasurement. A range of different frequencies will be used to observe theeffect of intermodulation distortion.

6.5 Summary

In this chapter, different aspects of noise and interference, has beendiscussed. It can be seen that inorder to be able to perform more indicativemeasurements it is neccessary to include the these different aspects of noise

and interference. In the following chapters, two types of measurements willbe performed. The basis of these measurements are introducing noise to thechannel. However, the type of noise that will be used is based on insertingsome attenuation. A more optimum way of doing this would be to introducea better defined noise or interference channel, such as superimposing aAWGNchannel model, or emulateCCI or ISI.Moreover, during a previous internship at Agilent Technologies, it wasnoticed that a phenomenon indicative of Intermodulation Distortion maybe present. Through the analysis seen in section6.3 on page 23showed thattheorethically this could occur. Thus creating a basis for an IntermodulationDistortion measurement.

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Part II

Measurements

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Chapter 7

Introduction

Two main types of measurements were performed. The initial tests weremade in order to establish what channel condition which are being dealtwith, as well as to confirm that the network responds as expected. Thesecond type of measurement was made to determine what would happen incase some unwanted signal would move in on the center frequency and crossit.

7.1 Throughput measurement

The purpose of this measurement is to give a preliminary indication asto which KPIs may be of special interest, as well as examine how LTEreacts to a simple attenuation of the downlink signal, seen from the UE.Additionally, this measurement will be able to give an indication as to whatfollow up measurements could be perforemed. However, the main focus ofthe measurement will be to give a basic idea as to what happens in the LTEsystem, when a channel becomes more an more impaired.

7.2 Intermodulation Distortion measurement

A blocker is a connection in which an unwanted signal is superimposed on

the desired signal, by using a directional coupler.

7.2.1 Directional coupler

The directional coupler work by having two transmission lines close to eachother see figure7.1 on the next page. These closely align transmission linespassing energy through the one that is not block in the end.

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Figure 7.1: The basic construction of a -20dB directional coupler

7.3 Case: Downlink blocks Uplink

In figure7.2 is graphical representation of the User Case can be seen.

Figure 7.2: Block diagram of how the user case is assumed.

It shows the specific phenomenon which the final measurement is based

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on. By first determining an initial measurement inorder to gain a standpoint

on what to do next, the attenuation measurement was performed. Thismeasurement gave indications that in accordance to the background theoryfrom chapter5 on page 10some changes in throughput should be seen, whensome distortion is added to the channel.Afterwards, the Intermodulation Distortion measurement was set up. Basedon the analysis in section6.3 on page 23the following case study is asserted.

Is it possible to measure the effects of intermodulation distortion in a real

life environment, based on the assumptions given in section6.3 on page 23.

Since the measurement is performed in a reallife environment the neccesityof testing theLTEsystem is an important step.

7.4 Key Performance Indicator (KPI)

RB

RBs are the physical amount of bandwidth which can be scheduled on theeNBand are allocated to theUE. These were discussed in further detail inchapter5 on page 10.

Physical Throughput

Physical throughput can be defined as the actual throughput of data beingtransmitted in the physical layer. It is measured in kbit/s.

Reference Signal Receive Power (RSRP)

RSRP is the most basic of the Physical layer measurements. It is anexpression of the linear average of the downlink Reference Signals, in watts,across the channel bandwidth. Providing theUEwith knowledge of absoluteRSRP,is essential, since it provides information about the strength of cellsfrom which path loss can be calculated, and afterwards used in optimizationalgorithms. However, the measure ofRSRPgive no indication of the signal

quality.

Received Signal Strength Indicator (RSSI)

RSSIrepresents the entire recieved power, which is radiated onto the UE,including wanted power from the serving cell, as well as all other co-channelpower and noise.

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Reference Signal Receive Quality (RSRQ)

Given RSRP and RSSI, the RSRQ is an important measure, since it isdefined as a ratio betweenRSRPand RSSI. A mathematical expression ofRSRQcan be seen in equation7.1

RSRQ= #RBdB+RSRP

RSSI (7.1)

= 10 log10(50) + (RSRPdB RSSIdB) (7.2)

Signal-to-Interference plus Noise Ratio (SINR)

SINRis a measure which calculates the ratio between the wanted signal and

levels of interference and noise. It can be expressed mathematically as,

SINR= P

I+N (7.3)

where,

Pis the signal power,

I is interference power

Nis the noise power

CQI

TheCQIreport, uses measurements performed on the downlink conditions,inorder to report to the scheduler on which combination of modulation andcoding would have resulted in a 10 % Block Error Ratio ( BLER), if thiscombination had been used. In figure7.3the method how the UEreportsCQIto theeNB is shown.

Figure 7.3: UE reporting CQI to the eNB, which afterwards sends a requestof which modulation and coding the UE should use next.

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Modulation and Coding Scheme (MCS)

After the CQIhas been reported, the eNB responds with an MCS index.MCS is an index from 0 to 31 which indicates to the UE, what themodulation and coding it should transmit on next.In figure 7.3 on theprevious page the UE receives the MCS index and on the basis of thisinformation, the data can be transmitted back with the chosen modulationand coding.

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Chapter 8

Initial test

Before being able to determine how LTEwill react when the connection isintroduced to a blocker, it is neccessary to determine how it reacts whenLTEbegins to suffer from a bad channel conditions. Therefore it is neccessary tofind out, a method of introducing noise in the channel. One way to do this,is by attenuating the signal from the base station to the UE. Doing thiswill hopefully result inLTEattempting to perform rate adaption, by eitherchanging the modulation scheme, requesting retransmission or in some othermanner, inorder to sustain a reliable and stable conenction.The goal with this initial measurement is to gain some insight into the effectson throughput, SNR, and RSSI among others. Especially identify what

happens, when some attenuation is introduced into the communicationspath.Inorder to realise this measurement, some different equipments andmeasurement tools are needed. In table8.1, an overview of the equipmentwhich has been utilised is listed.

Device AAU-nr. Note

Attenuators 3 dB attenuator 6 dB attenuator 10 dB attenuator 20 dB attenuator1800 MHz IFA antenna Optimised only for downlink

Table 8.1: List of equipment for initial measurements.

8.1 Setup and test procedure

Figure 8.1 on the next page shows the test setup. To perform thismeasurement, the attenuation in the communication path was increased

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with 10 dB intervals, except at the maximum attenuation. At this point the

total attenuation was 39 dB.

Figure 8.1: Test setup for measurement the impact of different attenuationwhile downloading in the 1800 MHz band.

With the attenuators in place, what this means is that generally lesspower which is radiated on the antenna will be transferred to the dongle.To perform these measurements it is neccessary to create some traffic,because it is imperative to make sure that as many ressource blocks areallocated, since the resource blocks aloocates the amount of bandwidthavailable. Basically, it is neccessary, to attempt to force theeNBto scheduleas many resources as possible. When a connection has been established,the measurements are performed. The first measurement is made with noattenuation. This is to have control measurment as a comparison to theones made with attenuation.

Two sets of measurements with the attenuators were performed over thecourse of two days. They were performed in 2011 on December 8th andDecember11th, and will be referred as Meas-1 and Meas-2, accordingly.Common for all plots in the following chapter, is that the time in minutesare plotted on the X-axis.In Meas-1, a simple explanation as to why each measurement run stands out,regarding to time duration is that during the measurements it was deemedthat a 4 minute measurement was more then enough. So inorder to havetime for other measurement they were shortened. Since these were statictest, it seemed not to make any difference. Of course, this goes against

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common measurement practice, and in hindsight probably should have done

otherwise, these measurements were preliminary tests, meant to be used asa basis for planning future measurements. Meas-2, which was performed afew days later, are based on experiences from Meas-1.In Meas-2, a second control measurement was performed.

8.2 Observations

After performing the measurement 1 it could be seen from figure 8.2, thatthe attenuators clearly had some effect.

Figure 8.2: Throughput from Meas-1. Throughput is measured in kbit/s.

An interesting part of these results are that between the measurement

runs with 0 dB and 10 dB are some very distinct similarities. Throughput for0 dB and 10 dB both stabilise at around 25Mbit/s , whereas SINRandCQI,which can be seen in figures8.3 and 8.4 on the following page. However, itis also noted that in theSINRandCQIplots, also remains high for the 20dB measurement.

Figure 8.3: Measured SINR from Meas-1.

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Figure 8.4: Reported CQI index from Meas-1.

In the meantime, it is also evident that as more attenuation is inserted,theCQIindex falls. This is expected, since UE reports aCQIindex whichtheUEbelieves is neccessary to withhold less then 10 % BLER. It can beseen in figure8.4,that theUErequests a lower modulation, since theCQIindex falls between every measurement run, which can be seen by comparingthe results to table 5.3 on page 17. When no attenuation is inserted, theUErequests 64-QAM, while theUErequests aQPSKwhen the maximumattenuatation is inserted.At the same time theRSSI, differs with approximately 10 dB between everyrun, as seen in figure 8.5, which clearly indicates that the attenuators arelowering radiated power.

Figure 8.5: Measured RSSI in Meas-1.

However, looking at the otherKPIs, they show that perhaps only 10 dBattenuation does not force LTEas far down the BLERcurve, in order toforceLTEto attempt to uphold the connection, by performing rate adaption.The same can seen as well in the results from Meas-2. In figure8.6 on thefacing pagecan the throughput from Meas-2 be seen.

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Figure 8.6: Throughput from Meas-2. It is measured in kbit/s.

By looking at plots of SINR in figure 8.7 and CQI in figure 8.8 fromMeas-2, most of the same observations can be made, as those seen in Meas-1.

Figure 8.7: SINR from Meas-2.

Figure 8.8: Reported CQI index, from Meas-2.

Just as in Meas-1, it can be seen that SINRis approximately the samelevel for 0 dB and 10 dB, with the same going for CQI. A note on Meas-2is as mentioned earlier, that a second 0 dB measurement was performed.This measurement is a control measurement, whose main purpose is makesure that channel condition before and after the Meas-2 are the same. Ofcourse, this is no guarantee, since conditions could have changed betweenthe two 0 dB measurements, and change back. Inorder to be sure that tis

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would not occur, the control measurement should have been done another

way. This will be discussed in the final conclusion in chapter10 on page 57.However, when looking at figure8.8 on the preceding page, one may noticethat suddenly around 3 minutes into the measurement theCQIindex beginsto rise. Recalling figure8.6 on the previous page,throughput begins to fall,around the same time. This may seem unexpected, but when looking at theRBs in figure8.9,drops significantly to slightly above an average of 40 RBs.

Figure 8.9: Resource block allocation in Meas-2

While the same goes for the RB allocation in Meas-1 which is seenfigure8.10.

Figure 8.10: Resource block allocation in Meas-1

This indicates that less bandwidth is scheduled to the user. Preciselywhat causesRBs to drop, is unsure. Perhaps some network issue occurs, or

another UE with better condition is accessing the basestation. Now drawingthe attention over toRSRQin figure8.11 on the facing pageone may noticethat the receive quality for is infact better.

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Figure 8.11: Measured RSRQ from Meas-2.

According toRSRQthe receive quality is much better then the others,so even though less bandwidth is available, theUEincreases the modulationas seen by theCQIindex in figure8.8 on page 37perhaps due to the betterreceive quality. RSRQfrom Meas-1 can be seen in figure 8.12.

Figure 8.12: Measured RSRQ from Meas-1.

In this figure it can be seen thatRSRQalmost does not differ betweeneach measurement run, in contrast to figure 8.11from Meas-2.

8.3 Summary

In summary of the observations in the attenuations measurements, be

concluded that a clear affect on Physical layer throughput can be measured,when introducing attenuation into the channel. By adding attenuation of0dB,10dB and 20dB the performance is close to each other. 30dB and39dB attenuation decreases the throughput drastically and some of thecorrelations between the RSSI, RSRP, CQI and SINR is striking.

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Chapter 9

Intermodulation Distortion

test

9.1 Introduction

In section of intermodulation distortion6.3 on page 23 it has been shownhow certain frequencies affect the upper 1800 MHz band. In this sectionthe purpose is to investigate the effect of intermodulation distortion byadding a intermodulated distorted signal with different level of attenuationand modulation to the traffic. The SMIQ 06b is an signal generator ableto produce a 5MHz signal with a range of different modulation appliedto the signal. In these test the focus was to see; first the effect of theintermodulation distortion and subsequently to see the impact of the levelof attenuation of these intermodulated distortion signals in LTE.

9.2 Setup and test procedure

In figure9.1 on the next pagethe test setup. The setup was only performedin a SISO configuration due to lack of coupler. This is an very importantaspect in this measurement case since this half of the throughput. In goodsignal condition we might theoretical be able to see throughput of 20Mbit/s.

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Figure 9.1: Test setup for measurement the intermodulation on 1800 MHzband

9.3 Observation

In this section three measurement will be evaluated and compared withthe theory of LTE Physical layer from chapter 5 on page 10. All theinformation that is being used in the following subsection can be foundin the measurement journal at the end of Appendix chapter.

9.3.1 13-01-2012

By selecting two frequencies 1869.7 MHz and 1870.2 MHz the impactof intermodulation distortion was measured. The only variable in these

measurement was the attenuation on the signal (that used 1869.7 MHz and1870.2 MHz) generated from the SMIQ. The intermodulated signal from theSMIQ was set to a level of attenuation of -80dB from the start and everyminute decreased by -20dB ending with -40dB after 5 minutes.

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Figure 9.4: RSRQ in 1869.7 MHz

Figure 9.5: RSRQ in 1870.2 MHz

The same observation that was made during throughput can be seen inRSRQ in figure9.4. First after -60dB the RSRQ value decreased to -13. Butin figure9.5the RSRQ decrease later in the measurement and drops down to-25dB. Since RSRQ is a relation between RSRP and the RSSI the conclusionis that the reference signal power dos not vary in contrast to RSSI. In RSSIon figure 9.11 on page 45 the increase of received signal strength is morethan 10dB. This decrease the quality of the channel by almost the sameamount.

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Figure 9.6: Resource Block in 1869.7 MHz

Figure 9.7: Resource Block in 1870.2 MHz

Resource block from figure9.6and figure9.7is stable on the 49 resourceblocks. This indicates that the above fading was not because of some otherUE was using the same eNB. From table 5.1 on page 14it is seen that themaximum of resource block is 50.

Figure 9.8: SINR in 1869.7 MHz

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Figure 9.9: SINR in 1870.2 MHz

In the beginning of the SINR measurement see figure9.8 on the facingpage and figure 9.8 on the preceding page the signal to interference and

noise ratio is positive at a level of 15. After two minute at -60dB the SINRdecrease to almost -15. This indicates that the interference and noise ratiohas increased in both the measurement.

Figure 9.10: Received signal strength indication in 1869.7 MHz

Figure 9.11: Received signal strength indication in 1870.2 MHz

In figure 9.10 and figure 9.10 RSSI starts at -58dB to -56dB and byincreasing the intermodulated distortion signals power, the total receivedsignal strength increase to.

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Figure 9.12: channel quality indicator in 1869.7 MHz

Figure 9.13: channel quality indicator in 1870.2 MHz

Channel quality indicator in figure 9.12 and figure 9.12 reports the

strength of the signal that the UE has to the eNB. In these two measurementwe see how the channel quality decrease when increasing the intermodulationdistortion signal. In figure 9.12 the decease is much greater ranging from64-QAM and to QPSK, according to table 5.3 on page 17. However, infigure9.12the increase at the end comes from the RSRQ index that rise inlevel at the end.

9.3.2 14-01-2012

In this measurement setup the goal was to see if the modulation of theintermodulation distortion signal from the SMIQ 06B signal generator, had

any impact on the performance on the network. The center frequency inTelias 1800 MHz ban is1868.2 and it was used to start the measurement bymoving the intermodulated distorted signal from the center of the frequencyand out of the range of Telias bandwidth. Every minute the intermodulateddistorted signals was moved 1 MHz up in the frequnecy band with 8 steps.All the steps was performed with a -40dB on the intermodulated signal.Figure 9.14 on the next page illustrate the concept in this measurement.After 8 step with 1 MHz each the intermodulated distorted signal is out ofthe bandwidth of Telias downlink frequency.

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Figure 9.14: Intermodulation distortion on TELIAs 1800 MHz bandstarting at the center frequency and move 8 steps with 1 MHz each

Figure 9.15: Throughput with different modulation on the intermodulateddistorted signal

In the first measurement figure9.15the throughput decrease by all types

of modulation. The only difference is that the higher modulation order16QAM and 64QAM has a slighter greater throughput but is affected bythe intermodulated distorted signal seeing an increase of the throughput atthe end of the measurement. In section Intermodulation6.3 on page 23thedirect effect of the distortion on the Telia downlink frequency is seen.

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Figure 9.16: RSRQ with different modulation on the intermodulateddistorted signal

RSRP level in figure 9.16 show in this measurement that both the16QAM and 64QAM modulation has a higher level.

Figure 9.17: Resource Block with different modulation on the intermodu-lated distorted signal

The Resource Block number stays relative stable on the maximumnumber that this 10 MHz bandwidth can provide. The different modulationsform did not cause any unexpected drops in the Resource Block count sincethe only disturbance is on the UE.

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Figure 9.18: SINR with different modulation on the intermodulateddistorted signal

In the SINR on figure 9.18 the first real indication on that the type of

modulation on the intermodulated distorted signal has no effect. The SINRis only effected by the moving of the intermodulated distorted signal througthe half bandwidth. At the end of grafe the SINR value increase above zeroand increase almost to 10. This shows that the signal strength is better thanthe interference and noise that is present.

Figure 9.19: RSSI with different modulation on the intermodulated distortedsignal

By moving the intermodulated distorted signal through the upper Telia1800 MHz band the received signal strength increase to see figure 9.19.This is the result of intermodulation distortion. Both the -60dB and theintermodulated distorted signal strength in merge together.

Figure 9.20: channel quality indicator with different modulation on theintermodulated distorted signal

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In figure9.20 on the previous pageboth BPSK and QPSK stays together

and decrease from 8 and down to 3 and up again. 16QAM and 64QAM moreor less independent on each other. The range from 16QAM starts at 5 CQIand decrease down to 3 and moves up to 8. 64QAM stays in the range of 8to 5.

9.3.3 15-01-2012

This measurement is an semi reproduction of the measurement above (14-01-2012). In figure 9.21 the basic of the measurement setup is displayed.In this measurement the whole bandwidth of 10 MHz is affected by the

intermodulated distorted signal. This gives a range from 1863.21873.2MHzthat the intermodulated signal is moved through. The x-axis increase in1 MHz every 30sec. This was don because of the length of the measuredrange of 16 MHz and to ensure that the 5 MHz modulated distorted signalof 5 MHz was out of the 10 MHz bandwidth from Telias downlink range.The measurement was executed in to level of attenuation -40dB and -60dB.

Figure 9.21: Intermodulation distortion on TELIAs 1800 MHz band

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Figure 9.22: Throughput with -40dB attenuation

Figure 9.23: Throughput with -60dB attenuation

The throughput from both figure 9.22 and figure 9.23 decrease whenthe intermodulated distorted signal is crossing the Telias downlink 10 MHzrange. At the end of both the measurement the throughput increase to1314Mbit/s

Figure 9.24: RSRQ with -40dB attenuation

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Figure 9.25: RSRQ with -60dB attenuation

RSRQ in figure 9.24 on the previous page and in figure 9.24 on thepreceding page dos not give any indication on how the modulation andattenuation level effect the measurement.

Figure 9.26: Resource Block with -40dB attenuation

Figure 9.27: Resource Block with -60dB attenuation

The only interrested thing in figure 9.26 and figure 9.27 is that infigure9.27 the BPSK measurement (red) dos not stay at the 49 Resourceblocks. The eNB can have some other UE using the channel and therefore

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only in this time period down crease the Resource blocks.

Figure 9.28: SINR with -40dB attenuation

Figure 9.29: SINR with -60dB attenuation

The SINR value in figure 9.28 and figure 9.29 differ from each other.In -40db the interference and noise level is hight and therefore the ratiobetween the signal strength and the disturbances from interference and noiseis influencing the measurement. At the end of figure9.28 with -40dB theSINR value increse to 15. The -60dB in figure 9.29

Figure 9.30: RSSI with -40dB attenuation

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Figure 9.31: RSSI with -60dB attenuation

The RSSI in figure 9.30 on the preceding page indicate the strengthof the added intermodulated distorted signal. In contrast to this is in

figure9.31the signal strength from the intermodulated distorted signal nota contributor to the increase of all the received signal strength.

Figure 9.32: channel quality indicator with -40dB attenuation

Figure 9.33: channel quality indicator with -60dB attenuation

Both in figure 9.32 and figure 9.33 there is no direct effect on whichmodulation type is used and the level of noise and interference that thereceiver is experienced. Both is decreasing and increase after leaving theTelia bandwidth.

9.4 Summary

In the results from the 13-01-2012 the attenuation level of the intermod-ulated distorted signal influence the measurement significantly. Both in

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1869.7 MHz and in 1870.2 MHz the throughput decrease while increasing

the signal power from the SMIQ 06B to the LTE dongle. RSRQ decrease(in 1870.2 dramatically) while RB stays untouched at 49. SINR moves fromapproximately +15dB to -15dB. MCS index increase in both measurementop to 20 and stabilising.From the results 14-01-2012 the no major impact on the difference modula-tion types that was use on the intermodulated distorted signal affected theLTE signal. Only the level of the intermodulated distorted signal affectedthe performance on the network. The power level of the intermodulatedsignal was visible in the RSSI measurement.In the last measurement form the 15-01-2012 the whole Telia 10 MHz band-width was used to cross with the intermodulated distortion signal from the

SMIQ. Two levels of attenuation on the intermodulated distortion signalwas used and the impact of the signal was visible both in throughput andin SINR

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Part III

Assesment

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Chapter 10

Final conclusion

The goal of this project was to examine how LTEs physical layer through-put was affected by outside disturbance on the channel. These disturbancescould stem from different sources, and was in this project regarded as distur-bances from noise and interference from other communication technologies,present in the same frequency band.

During this project two main sets of measurements were orchestrated inorder to examine the effects onLTEphysical layer throughput, as could beseen in chapters8 on page 33and 9 on page 40.

From the initial test in chapter8 on page 33it could overall be concludedthat adding attenuation directly in to the channel had a real affect on howLTE adapts to poor channel quality. In figures 8.2 on page 35 and 8.6on page 37, it could clearly be seen that when adding more attenuationinto the channel, physical throughput fell, between every measurement run.Experiences from the initial measurement, were the basis on the followingmeasurement, with the blocker circuit.

During initial studies it was noticed that in the case stated in section7.3on page 29, is indeed real, and can be approximated in real-life on a deployedLTE network. This can directly be seen in figure9.12 on page 46. As the

attenuation of the blocking signal decreases, it can clearly be seen that theCQIindex falls from what appears to be a 16-QAMmodulation, and as theblocking signal becomes more distinct,CQIindex drops to a level indicatingQPSKor the like. E.g. a lesser efficient modulation.

A better understanding on how to perform real-life measurements ondeployed communication networks, mostly due to learning-by-doing-aspectof performing the measurements. However, it should be noted that to beable to actually find the phenomenon it was based on knowledge gained from

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a prior internship at Agilent Technologies.

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Chapter 11

Perspective

The project started by focusing on other aspect than measuring intermod-ulation. This progress in learning by doing has led to some of the problemsseeing in this project by different kind of measurement. There has beenmany initialize measurement leading to this project goal. Usually whenmaking measurements a plan for how it should be done is produced firstand then the measurement could be produced. In our case this was most ofall not possible since the shorten of equipment. This lead to measurementperformed with no goal. One of the main improvement to perform these kindof measurement with both more precision and reliable data is by selectingthe level of attenuation on a smaller scale than the -10dB intervals. The

measurement of the impact with modulation was only produced since thepost processing was after that the equipment had to be delivered back threeday after borrowing it. Since it was over a weekend some of the questionshad to be resolved after the measurement and then it was to late. One of theinteresting aspect in this case studies is that the intermodulated distortedsignal did not react on the modulation but only in the level of attenuation.In further studies the smaller interval on attenuation in a intermodulateddistorted signal interference could show some more accurate data collection.But at the same time the real life measurement is a dangerous area to per-form measurement on since a wide range of variable has to be under controlor needed to be suppress. All the measurement was performed sequential

while the network performance varies in time and in the end all the mea-surement was placed above each other (look like parallel). This is one of themain risk which one must consider before stating the measurement. Theseuncertainties makes the measurement hard to reproduce and can only beenas a case study. Laboratories measurement would eliminate these uncertain-ties and give a wider control to all of the variables that is not under controlin a real life measurement. This project only focus on real life measurementsince the experiences from Agilent Technologies internship.

In the future the use of MIMO will increase since the performance of the

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network only will be better. LTE supports an 4x4 MIMO connection and

this will increase the throughput dramatically in urban environments sincethe best condition of multipath.

The use of IFA antenna in the measurement is maybe a problem torepresent a standard UE since the design of the IFA direct emphasizedownload frequencies in the 1800 MHz band. Normally this would not bethe case and other antenna designs would be used to accommodate tx andrx antenna in the big range of 17001800 MHz band on one antenna. Byusing the IFA antenna only the downlink communication is preferred anddos not reflect an

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