performance evaluation of the physical layer of ieee 802.16e standard

Performance Evaluation of the Physical Layer of IEEE 802.16e standard

A Dissertation

Submitted in partial fulfillment of the requirements for the award of the Degree of

MASTER OF TECHNOLOGY In INFORMATION & COMMUNICATION TECHNOLOGY

(Specialization in Wireless Communication & Networks)

Submitted by: VIPIN SHARMA

10-PIT-042

Supervisor: Mr. Sandeep Sharma

Faculty Associate School of ICT, GBU

SCHOOL OF INFORMATION & COMMUNICATION TECHNOLOGY GAUTAM BUDDHA UNIVERSITY

GREATER NOIDA-201308, UTTAR PRADESH, INDIA May, 2012

School of Information and Communication Technology Gautam Buddha University, Greater Noida

Candidate’s Declaration

I hereby certify that the dissertation work embodied in this dissertation report by the roll no. 10-

PIT-042 entitled “Performance Evaluation of the Physical Layer of IEEE 802.16e standard” in

partial fulfillment of the requirements for the award of the degree of M.Tech. in ICT

specialization in Wireless Communication & Networks submitted to the school of ICT, Gautam

Buddha University, Grater Noida is an authentic record of my own work carried out under the

super vision of Mr. Sandeep Sharma.

The matter presented in this work has not been submitted by me in any other

University/Institution for the award of any other degree or diploma.

Vipin Sharma

(10-PIT-042)

The information furnished above is correct to the best of my knowledge and belief.

Date: 12 .May.2012

Place: Gautam Budh Nagar

(Mr. Sandeep Sharma)

Faculty Associate

School of ICT

Gautam Buddha University

Gautam Budh Nagar-201308

iii

Acknowledgements

I would like to acknowledge many people who have help me during the entire time of

dissertation work and supported it in one or another way. First of all, my admiration and

thanks go to my former dean “Dr. Brahmjit Singh.”

I wish to express my gratefulness to my supervisor, Mr. Sandeep Sharma, for his

seasoned guidance. Without his effective suggestions my work could not be completed. I

am deeply indebted to my parents for their inspiration and ever-encouraging moral

support, which enabled me to pursue my studies, I also want to thanks all my friend who

was always appreciate my work.

iv

Abstract WiMAX is given by the Institute of Electrical and Electronic Engineers which is a

standard designated as 802.16d (for fixed wireless user) and 802.16e (for mobile wireless

application) to provide a worldwide interoperability for microwave access. WiMAX has

proved to be a superior technology for BWA (Broadband Wireless Access) that

theoretically covers approx 30 to 50 Km. Physical layer of the WiMAX is based on

OFDM, that is the transmission scheme that’s provide the high-speed data for the video

and multimedia stemming and is used by the variety of commercial broadband technique

systems including DSL, Wi-Fi, and Digital Video Broadcast-Handheld, besides WiMAX.

OFDM is a refined and efficient scheme for high data rate transmission in a non-line-of-

sight and multipath fading radio environment.

WiMAX supports an Adaptive modulation and coding schemes that allows changing the

scheme on a burst-by-burst basis, depending on the channel conditions. Using the channel

quality feedback indicator, the base station can provide the downlink channel quality with

feedback and for the uplink channel quality the base station can estimate the received

signal strength through mobile station. Due to the multipath fading temporal variation in

channel, an AMC technique is beneficial with OFDM that’s minimizing the multipath

effect. This technique consist variety of modulation and channel encoding schemes to

provide the QoS by instantaneously adapting channel SNR variation, that’s provide the

maximizing throughput and improving BER performance at all channel condition.

In this paper we are preparing a model of WiMAX, where we studied different

modulation technique with different coding rate using the MATLAB 7.9.0 (R2009b)

simulink. All the parameter is taken from ETSI & IEEE Standard.

v

Table of Contents

Acknowledgement…………………………………………………………………… iii

Abstract……………………………………………………………………………… iv

List of Figure………………………………………………………………………… viii

List of Table………………………………………………………………………… x

List of Abbreviation.................................................................................................... xi

1. Chapter One

Introduction to WiMAX

1.1. Introduction……………………………………………………………………. 2

1.2. Motivation………………………………………………………...................… 2

1.3. Problem Definition…………………………………………………………… 3

1.4. Methodology.................................................................................................... 3

1.5. Application........................................................................................................ 4

1.6. Thesis Contribution…………………………………………..……………… 5

1.7. Outline of the Thesis………………………………………….……………… 5

2. Chapter Two

Literature Survey

2.1. Introduction..............…………………………………………………………. 9

2.2. Open Challenges and key issue……………………………….....................… 9

2.3. Classification of Methods………………………………………..…………… 16

2.4. Summarry……………….........................……………………….…………… 17

3. Chapter Three

IEEE 802.16: Evolution and Architecture

3.1. WiMAX at a Glance…………………………………………….……………. 19

3.2. Evolution of IEEE Family……………………………………....................… 20

3.2.1. IEEE 802.16 2001................................................................................... 21

3.2.2. IEEE 802.16 a 2002............................................................................... 22

3.2.3. IEEE 802.16c 2003................................................................................. 22

3.2.4. IEEE 802.16 2004.................................................................................. 22

vi

3.2.5. IEEE 802.16e 2005................................................................................ 24

3.3. Technical Overview.....………………………………………..……………… 25

3.3.1. IEEE 802.16 Protocol Layer.................................................................. 25

3.3.2. MAC Layer............................................................................................ 26

3.3.3. PHY Layer............................................................................................. 29

3.4. Physical Layer Adaptation…………………………………………………… 33

4. Chapter Four

Transmitter

4.1. Physical Layer Model.....………………….............………………………….. 35

4.2. Transmitter............. ………………...………………………………………… 35

4.3. Data Source....................................................................................................... 36

4.4. Channel Encoding............................................................................................. 38

4.4.1. Randomization....................................................................................... 38

4.4.2. R-S Encoding......................................................................................... 39

4.4.3. Convolution Encoding............................................................................ 44

4.4.4. Puncturing Process................................................................................. 47

4.4.5. Interleaving............................................................................................ 47

4.5. IQ Mapper......................................................................................................... 49

4.6. Principle of OFDM Transmission..................................................................... 52

5. Chapter Five

Channel

5.1. Radio Channel................………………….............………………………….. 58

5.2. Channel Model..... …………………………………………………………… 59

6. Chapter Six

Receiver

6.1. OFDM De-Mapping......………………….............………………………….. 63

6.2. IQ De-Mapping.... …………………………………………………………… 64

6.3. Channel Decoding............................................................................................. 64

6.3.1. Deinterleaving........................................................................................ 65

6.3.2. Inserting Zero......................................................................................... 65

6.3.3. Viterbi Decoder....................................................................................... 66

vii

6.3.4. R-S decoder............................................................................................. 67

7. Chapter Seven

Result & Analysis

7.1. Performance Evaluation………………………………………………………. 70

7.2. Probability of Symbol Error.............................................................................. 83

7.3. Analysis............................................................................................................. 84

8. Chapter Eight

Conclusion & Future Work

8.1. Conclusion........................................................................................................ 86

8.2. Limitation of Work........................................................................................... 86

8.3. Future Work..................................................................................................... 86

References...................................................................................................................... 87

Appendix A……………………………………………………………..…...........,..... 93

Appendix B……………………………………………………………..…...........,..... 99

viii

List of Figures

Figure 1: Basic Communication System................................................................... 6

Figure 2: Possible Scenario for the development of WiMAX.................................. 20

Figure 3: WiMAX Protocol Stack............................................................................ 26

Figure 4: WiMAX Physical and MAC Layer Architecture...................................... 27

Figure 5: Convergence in wireless communication.................................................. 32

Figure 6: Purpose of Mac Layer in WiMAX .......................................................... 32

Figure 7: Adaptive Modulation Scheme................................................................... 33

Figure 8: Transmitter for the WiMAX system......................................................... 35

Figure 9: Physical Layer Scenario............................................................................ 36

Figure 10: Channel Encoding- Randomizer with Shift Register................................ 39

Figure 11: General process of Reed-Solomon Encoder.............................................. 41

Figure 12: Process of shortening and puncturing of the RS code............................... 42

Figure 13: simulink scenario of the Reed-Solomon encoder of WiMAX.................. 43

Figure 14: simulink implementation of Reed-Solomon encoder of WiMAX............ 44

Figure 15: block diagram of convolution encoder...................................................... 16

Figure 16: Convolutional encoder of binary rate 1/2................................................. 46

Figure 17: Convolutional encoder implementation in simulink................................. 46

Figure 18: BPSK, 4-QAM and 16-QAM constellation map....................................... 51

Figure 19: Rearrangement performed before realizing the IFFT operation............... 53

Figure 20: Delay from front symbol........................................................................... 54

Figure 21: Cyclic prefix insertion.............................................................................. 54

Figure 22: OFDM symbol with the cyclic prefix...................................................... 56

Figure 23: Generating the OFDM symbol using the IFFT......................................... 56

Figure 24: Signal Losses due to three Effects............................................................. 58

Figure 25: Simulink Implementation.......................................................................... 61

Figure 26: Block Diagram of Receiver...................................................................... 63

Figure 27: Block Diagram of channel Decoding........................................................ 65

Figure 28: Simulink implementation of Convolution Decoder.................................. 67

ix

Figure 29: Simulink implementation of R-S Decoder................................................ 68

Figure 30: BER Performance of BPSK with different CP.......................................... 71

Figure 31: BPSK result in term of Signal Strength and constellation diagram......... 72

Figure 32: BER Performance of QPSK(1/2) with different CP.................................. 33

Figure 33: BER Performance of QPSK(5/6) with different CP.................................. 75

Figure 34: QPSK result in term of Signal Strength and constellation diagram.......... 75

Figure 35: BER Performance of 16-QAM (1/2) with different CP........................... 78

Figure 36: BER Performance of 16-QAM (1/2) with different CP............................ 78

Figure 37: 16-QAM result in term of Signal Strength and constellation diagram.... 79



Figure 40: 64-QAM result in term of Signal Strength and constellation diagram..... 82

Figure 41: Probability of symbol error for the different transmitted power.............. 84

x

List of Table

Table 1: Literature Survey................................................................................... 10

Table 2: Comparison of IEEE standard for BWA............................................... 23

Table 3: 802.16-2004 MAC features.................................................................. 28

Table 4: 802.16-2004 PHY features.................................................................... 30

Table 5: Data source for AMC............................................................................ 37

Table 6: Mandatory channel coding per modulation............................................ 40

Table 7: Puncturing Vector for different convolution code................................. 47

Table 8: Normalization factors............................................................................ 50

Table 9: Modulation alphabet for the constellation map...................................... 50

Table 10: Customization Mapping......................................................................... 51

Table 11: BER Performance on various noise levels on different cyclic prefix..... 70



Table 14: BER Performance on various noise levels on different cyclic prefix...... 80

xi

List of Abbreviation Note: All the abbreviation in this thesis has been taken from the standard books

0-9 3G 3rd Generations

A AMC Adaptive Modulation & Coding

ARQ Automatic Repeat Request

ATM Asynchronous Transfer Mode

AWGN Additive White Gaussian Noise

B BER Bit Error Rate

BTC Block turbo coding

BPSK Binary Phase Shift Keying

BS Base Station

BWA Broadband Wireless Access

C

CC Convolution Code

CPS Common Part Sub-layer

CS Convergence Sub-layer

CTC Convolutional turbo coding

CP Cylic Prefix

CPE Customer Premises Equipment

D DES Digital Encryption Scheme

DL Down-Link

DSL Digital Subscriber Scheme

DFS Dynamic Frequency Selection

xii

F FDD Frequency Division Duplexing

FDM Frequency Division Multiplexing

FEC Forward Error Correction

FFT Fast Fourier Transform

G GF Galois Field

I IFFT Inverse Fast Fourier Transform

IP Internet Protocol

ISI Inter symbol Interference

L LOS Line of Sight

M MAC Medium Access Layer

MRC Maximum Ratio Combining

MC Mobile Code

MIMO Multiple Input & Multiple Output

MS Mobile Station

N NIST National Institute of Standard and Technology

N-LOS Non Line of Sight

O OFDM Orthogonal Frequency Division Multiplexing

OFDMA Orthogonal Frequency Division Multiple Access

P PDU Packet Data Unit

PHY Physical Layer

xiii

Q QAM Quadrature Amplitude Modulation

QoS Quality of Services

QPSK Quadrature Phase Shift Keying

R RF Radio Frequency

S SC Single Carrier

SAP Service Access Point

SDU Service Data Unit

SMS Short Messaging Services

SNR Signal to Noise Ratio

STC Space-Ttime Coding

SS Security Sub-Laier

T TDD Time Division Duplexing

TDM Time Division Multiplexing

U UL Uplink

V VoIP Voice over IP

W Wi-Fi Wireless Fidelity

WiMAX Worldwide Interoperability for the Microwave Access

WLAN Wireless Local Area Network

WMAN Wireless Metropolitan Area Network

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Chapter One

“Introduction to WiMAX”

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1.1 Introduction This chapter contains a brief description of the dissertation work along with some open

challenges issues of WiMAX and its mitigation. A short description about the structure of

dissertation is included at the end of this chapter.

1.2 Motivation

Sometimes ago, we were completely dependent on analog system, both the sources,

transmitter and receiver were on analog format but as the advancement of technology it is

made possible to transmit the data in digitize form. Along with the digital advancement,

the computer was getting faster towards fastest, the data carrying capacity and data rate

increased from kilobytes to megabytes. By emerging the concept from wire to wireless

and after investing so much money in researching, engineers became successful to invent

wireless transmitter and receiver for air communication. Applications like voice, Internet

access, e-mail, SMS, paging, file transferring, video conferencing, gaming and

entertainment etc became a part of life.

Mobile phone systems, WLAN, wide-area wireless network systems, ad-hoc wireless

networks satellite systems and the system where the channel interface is air are the

wireless communication systems, all these technology based on wireless technology to

providing higher throughput, vast mobility, wider coverage, robust backbone to thereat.

The vision is seen as a little bit more by the engineers to provide the smooth transmission

of multimedia anywhere on the globe through ubiquitous application and devices that’s

emergence a new concept for the wireless communication which is cheap and easy to

handle to work in all weather condition.

This is to be fact that, Broadband Access through DSL, T1-carrier or cable infrastructure

is not available especially in rural areas. With DSL we can covers only up to 18,000 or

19,000 feet after the 19,000 feet there is huge degradation in speed, this means that many

suburban and rural areas may not served. The Wi-Fi standard broadband connection may

solve this by some mean but not possible in everywhere due to coverage limitations. But

the Wireless Metropolitan-Area standard which is to be known as WiMAX can solve

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these limitations. The wireless broadband connection is much easier to deploy, that have

the capacity to address the long geographical area and have easier to access.

1.3 Problem Definition We know that the physical layer is most unreliable layer in any wireless system which is

responsible for error free delivery, so the error free communication in WiMAX is a

challenging task.

In order to achieve the higher throughput, we are trying to minimize the BER as much

as possible.

So to achieve the minimum BER, we must have the higher SNR.

But the problem is that we can improve the SNR at a certain limit as we are following

the cellular architecture.

Mitigation

So in order to achieve the solution we have to find the alternative solution to achieving

the minimum BER and the solution is, we can achieve the minimum BER by using the

different modulation and coding scheme (BPSK, 4-QAM, 16-QAM, and 64-QAM) with

different channel coding rate.

So, we measure the performance evaluation of Physical Layer of IEEE 802.16e.

SNR BER

1.4 Research Methodology

The Evaluation Methodology of IEEE 802.16e defines a unified method of simulation

models and associated parameters that can be used when introducing new proposals for

IEEE 802.16e or when presenting new research results. The simulation components can

introduce results both from the link-level perspective, when only one base station and one

mobile station exist in the network topology scenario.

The Physical layer which should be consisting of:-

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• Random Source

• Transmitting module

• Channel Module

• Receiving Module

We will use the simulink of MATLAB 7.9.0 (R2009b) environment for the simulation of

physical layer model. On the WiMAX physical layer we are using the channel encoding

for minimizing the error.

1.5 Application As we know WiMAX is the standard for Wireless MAN for BWA user, we are deal with

the Physical Layer which have greater advantage with OFDM that is enable to archive the

throughput in order to save the spectrum apart of this there are several applications some

of these are-

QoS with adaptive Modulation & Coding

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Wider Coverage Greater Throughput (Up to 73 Mbps at 20 MHz Channel) Advance Security Mechanism Lower Bit Rate at all channel condition Radio Resource Management

1.6 Thesis Contribution The goal of this project is to implement and simulate the OFDM Physical layer

specifications of IEEE 802.16e-2005 using Adaptive Modulation Techniques. We are

also analyzing the performance of OFDM physical layer in mobile WiMAX based on the

simulation results of-

Bit-Error-Rate , Signal-to-Noise Ratio and

Probability of Error (Pe).

After achieving the objective we are optimize the overall system by changing the system

parameter and finally we have to analyze that how much we have deal with BER, that’s

tell how our communication is more effective.

1.4 Outline of the thesis

This thesis examines the implementation of a WiMAX Physical layer built with Matlab

Simulink. This simulation is targeted to the n-point FFT. The thesis is organized in seven

chapters, in which a detailed overview of every communication block of the system is

taking into account both the standard and the corresponding theoretical aspects, which are

necessary to understand all the different methods and processes that have been used.

An overview of the WiMAX system and related issue with mitigation and methodology

has already been exposed in the present chapter and in chapter-2 we are describe the open

challenges and issues and classification of methods with relative advantages and

disadvantages.

Whereas the main features of the standard are summarized in chapter-3. To understand

the objectives and the applications of this system, a comparison between WiMAX and

other wireless systems is also included in the chapter.

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The remaining five chapters discuss the implementation and their resul of the WiMAX

simulator.

Like any other communication system, WiMAX has consist of three basic elements first

one is transmitter second is channel which is air interface in wireless communication and

third one is the receiver. The block diagram of a WiMAX communication system is

shown in Figure 1.

Figure 1: Basic communication system.

The transmitter and its component are presented in presented in Chapter 4, from

generating the symbol to be transmitted over the channel. Before sending it, the system

has to be adapted to the channel conditions by using a specific adaptive modulation

coding scheme which have to be more appropriate. As the modulated data is transmitted

through the OFDM transmission, it also needs to generate the OFDM symbol by IFFT

operations, which include a frequency-time transformation and the addition of a guard

period. Then, the information is send through the multicarrier technology over the

channel, discussed in the chapter 4.

Chapter 5 we are discussed about the communication channel. For the WiMAX system, it

is a wireless channel. The performance of any wireless communication system is highly

dependent on the propagation channel, and so, a detailed knowledge of radio propagation

effects, such as path loss, frequency-selective fading, Doppler spread, and multipath

delay spread have to be considered for the optimization of the communication link.

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The receiver is part is discussed in Chapter 6. It collects the signal after passing the

channel and performs the reverse operations of the transmitter to obtain the transmitted

information.

Chapter 7 analyzes the obtained results. Firstly, simulation results using an AWGN with

Multipath Fading channel are discussed and at last discussed the Probability of Error for

the AWGN channel with respect to the transmitted power at the ambient temperature.

Finally, the concluding remarks and Future work are summed up in Chapter 8.

Additionally, this work also includes two appendices that complete the thesis already outlined. Appendix A is intended to give an .m file codes whose output is use for the simulink scenario systems. Appendix B presents a Probability Error.

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Chapter Two

“Literature Review”

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In this chapter contains a brief description of Literature survey which have to be conclude

to find the open challenges in emergence of next generation wireless communication, and

also we are include some of latest research paper which is to be intended for finding the

mitigation in some of open issues.

2.1 Open Challenges and Key Issue

IEEE 802.16 is a set of telecommunications technology standards aimed at providing

wireless access over long geographical area by the various ways - from point-to-point

links to full mobile cellular type access. WiMAX covers a long area of several kilometers

that’s why it is also called WirelessMAN. Theoretically, a WiMAX base station can

covers a in range of up to 50 kms for fixed stations and 5 to 15 kms for mobile stations

with a maximum throughput of up to 73 Mbps [1], [2] compared to 802.11a with 54

Mbps up to several hundred meters, EDGE with 384 kbps to a few kms, or CDMA2000

(Code-Division Multiple Access 2000) with 2 Mbps for a few kms.

IEEE 802.16 standards group has been developing a set of standards for BWA for a

metropolitan area. Since 2001, several amendments are going through of standards that

have been published and are still being developed. Like other standards, these

specifications are also a compromise of various competing proposals and contain many

optional features and mechanisms. The Worldwide Interoperability for Microwave

Access Forum or WiMAX Forum is a group of 400+ service providers, component

manufacturers, networking equipment manufacturer vendors and users that decide which

of the legion options allowed in the IEEE 802.16 standards or not so that equipment from

different vendors are interoperable. Several features such as unlicensed band operation,

60 GHz operation, while specified in the IEEE 802.16 are not a part of WiMAX networks

so that these are not in the standard profiles by the WiMAX Forum. For an equipment to

be certified as WiMAX compliant, the equipment has to pass the inter-operability tests

specified by the WiMAX Forum. For the rest of this paper, the terms WiMAX and the

IEEE 802.16 are used interchangeably.

We we have include some of the latest research paper from the eminent publication-

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Table 1: Literature Review

S.No Title Author Publication Conclusion Platform [1] The

WiMAX 802.16e Physical Layer Model

Muhammad Nadeem Khan and Sabir Ghauri

IET International Conference on Wireless, Mobile and Multimedia Network; Jan 2009

In this paper the authoe prepare a WiMAX PHY layer model for fixed modulation scheme (4-QAM) with 5/6 CC rate and the performance will be based on BER for AWGN channel.

MATLAB simulink

[2] On QoS Aspects with Different Coding and Channel Condition for a WiMAX based Network

Vinit Grewal and Ajay K Sharma

IEEE 2nd International Conference on Advance Computing; March 2010

In this paper author simulate a physical layer scenario under the different modulation & coding scheme the result shall be described in the form of SNR impact on BER for the different channel.

OPNET Modulator

[3] Performance Simulation of IEEE 802.15e WiMAX Physical Layer

Mohamed A. Mohamed , Mohamed S. Abo-El-Seoud and Heba M. Abd-El-Atty

Second IEEE International Conference on Information Management and Engineering; Jan. 2010

Again in this paper author prepare a model for WiMAX PHY and obtaining the performance in term of BER for the different modulation and coding scheme.

MATLAB simulink

[4] An Analytical Approach to Qualitative Aspect if WiMAX Physical Layer

Arathi R. Shanker, Poonam Rani and Suthikshn Kumar

IEEE Second International Conference on Information Technology for Real World Problems;

In this paper the author prepare a model for the WiMAX PHY, the performance has been obtain in term of BER under the Rayleigh and Rician channel and

MATLAB

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June 2010 also evaluated the Pe for the same channel.

[5] A Survey on Next Generation Mobile WiMAX Networks: Objectives, Features and Technical Challenges

Ioannis Papapanagiotou,Dimitris Toumpakaris,Jungwon Lee and Michael Devetsikiotis

IEEE Communication Surveys & Tutorials; Fourth Quarter 2009

In this survey paper the author focused on the emerging trend of next generation mobile especially on WiMAX. In this paper the author also tells about the PHY layer specification with MIMO reception.

----------

[6] Performance Characteristics of an Operational WiMAX Network

James M. Westall and james J. Martin

IEEE Transactions on Mobile Computing, Vol. 10, NO.7, July 2011

In this paper the author evaluate the performance on different parameter of QoS(like throughput, latency ) for different type of traffic which shpuld be classified accordind to their preference all the QoS will check for the Adaptive PHY which have use multiple modulation & coding scheme.

OPNET Modulator

[7] Performance Parameter of Mobile WiMAX: A Study on the Physical Layer of Mobile WiMAX under Different

Omar Arafat and K. Dimyati

IEEE International Conference on Computer Engineering and Applications, Sep. 2010

In this paper the author measure the performance by developing a model, the performance will be evaluated in under the SUI(Stanford university interim ) channel model for

MATLAB

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Communication Channels & Modulation Technique

different SNR and evaluated the BER, the author iterate this process for the different guard time period.

[8] WiMAX Physical Layer: Specifications Overview and performance Evaluation

Mingxi Wang

Second IEEE CCNC Research Student Workshop, Jan. 2011

In this paper, the author given a brief overview of the physical layer specifications of the latest WiMAX standard IEEE 802.16-2009. A simplified simulation system of WiMAX OFDMA PHY with LDPC coded MIMO-OFDM is established For performance evaluation purpose. Simulations show that the Iterative receiver structure can achieve good performance. OFDM is established For performance evaluation purpose. Simulations show that the iterative receiver structure can achieve good performance. Channel should be considered as AWGN.

-

[9] A Nadine Second IEEE In this paper the The

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Comprehensive WiMAX Simulator

Abbas, Hazem Hajj and Ahmad Borghol

CCNC Research Student Workshop, Jan. 2011

author first classified the inbound traffic then classified traffic should be scheduled according to the priority then according to the priority resource will be provided the result is obtain in form of throughput and AMC.

proposed simulator is implemented using Borland C++ builder.

[10] A Physical layer simulator for WiMAX in Rayleigh Fading Channel.

Jamal Mountassir, Horia Balta, Marius Oltean , Maria Kovaci and Alexandru Isar

6th IEEE International Symposium on Applied Computational Intelligence and Informatics , May 19–21, 2011

The Author obtains the performance for the Rayleigh fading channel for non-mobility with physical layer specification.

MATLAB

[11] Simulation of Channel Estimation and equalization for WiMAX Physical layer in Simulink

Onsy Abdel Alim, Nemat Elboghdadly, Mahmoud M. Ashour and Azza M. Elaskary

First International Confrence on Computer Engineering and System; Oct 2007

Comparing the performances of all schemes by measuring bit error rate versus SNR with setup with 16QAM, as modulation scheme and multi-path fading and Doppler shift channels as channel models. Channel estimation based on LS algorithm, with the linear interpolation, the

MATLAB Simulink

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second order interpolation, the spine cubic interpolation and the low-pass interpolation.

[12] Y.Q. Bian,

A.R. Nix, Y.Sun and P. Strauch

Performance Evaluation of Mobile WiMAX with MIMO and Relay Extension

IEEE International Conference on Wireless Communication and Networking,; June 2007

In this Paper the author obtain the performance of mobile Wimax with 2x2 MIMO relay extension for a microcell with some assumption all the parameters are taken for the simulation is carried out from the standard documentation. For an urban macrocell (radius of 1.5km), around 92% of users were seen to experience SNR levels below this threshold, and hence would struggle to exploit Spatial Mutiplexing.

--------------

[13] Link-Level Simulation and Performance Estimation of WiMAX IEEE 802.16e

Wen-an ZHOU, Bing XIE and Jun-de SONG

Second International Conference on Pervasive Computing and Application; June 2009

In this paper the author prepares a Link-level Simulation and Performance Estimation of WiMAX

MATLAB

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IEEE802.16e PHY and obtains performance curves. The simulation results provide a reference value of PUSC gain. And also the whole link performance with QPSK and 16QAM.

[14] Performance of MIMO Antenna Technique IEEE 802.16e

Onsy Abdel Alim and Ahmed E Naggary

ITI 5th International Conference on Information Communication and Technology; June 2007

In this paper the author obtains the performance through the smart antenna technology which includes Beamforcing, space-time diversity code and spatial multiplexing. The author first presented antenna array techniques, which reduce interference and provide the diversity gain that enhances the useful signal SNR. Next, we gave a general description of Multi-Input Multi-Output systems that can be used for various purposes including

ADS Aglient

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diversity gain, and interference reduction.

Key issues of WiMAX Networks

There is some open issues in WiMAX networks that differentiate it from other

metropolitan area wireless access technologies are-

1) Its use of Orthogonal Frequency Division Multiple Access (OFDMA),

2) Scalable use of any spectrum width (varying from 1.25 MHz to 28 MHz),

3) Time and Frequency Division Duplexing (TDD and FDD),

4) Advanced antenna techniques such as beam forming, Multiple Input Multiple

Output (MIMO),

5) Per subscriber adaptive modulation,

6) Error Free Communication

7) Advanced coding techniques such as space-time coding and turbo coding,

8) Strong security and Multiple QoS classes

2.3 Classification of Methods In order to achieve the research objective there are several method, in our dissertation we

are go with the Physical Layer issue so to obtain the performance of WiMAX physical

layer with different channel encoding scheme and also including the OFDM we are

having two scheme as the methodology-

1) Analytical Approach

2) Simulation Approach

With both of scheme there is some pros and cons-

• Analytical Approach

Pros

Result is more accurate

No need of Computer environment

Based on some standard formulation

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Obtain the generalize the result

Cons

Hard to deal with Large Data

Hard to deal with Complex input

Iteration is taking the more time

Finding the error is too hard and time taking

Requirement of Skill workforce

• Simulation Approach

Pros

Result is more scalable

Computer environment save the time of computation

Easy to deal with large data

Computation of complex number is also easy

Iteration is helpful.

To readout the result no skill workforce is require

Cons

Result is not so more accurate

Simulation is bound with limitation

Generalize formulation is hard

2.4 Summary After go through with several research paper and discussed with our supervisor, I am

deciding to go with physical layer issue, because in any wireless environment physical

layer is the most unreliable layer which have to responsible for error free communication

so there is lot of scope.

By changing the parameter like channel encoding scheme, modulation scheme we can

enhance the performance of the overall system and also by iteration the simulation we

can optimize the system also.

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Chapter Three

“IEEE 802.16: Evolution and Architecture”

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This chapter contains the brief discusses of the evolution of the IEEE 802.16 standard for

WMAN. The protocol layer of the standard has been viewed to get the idea of relation

between different layers. This chapter ends with a overview of the IEEE 802.16 based

Physical and MAC layer specification with their Pros and Cons.

3.1 WiMAX at a Glance WiMAX is known as the next generation wireless broadband technology that offers high

transmission rate, secure, QoS sophisticate and last mile access broadband services along

with a cellular concept and Wi-Fi hotspots. The evolution of WiMAX began a few years

ago when engineers and researcher having the need of wireless Interface access and other

internet services which works ubiquitously especially in sub-urban areas or on those areas

where it is hard to establish wired infrastructure and economically not feasible.

IEEE 802.16 is also known as Wireless-MAN standard, explored both licensed and

unlicensed band of 2-66 GHz which is standard for both fixed and mobile broadband

application. WiMAX forum is a private organization which was formed in June 2001 for

the purpose of to coordinate and maintain the equipment and develops the instrument

those will be backward compatible and interoperable. After few years, in 2007, Mobile

WiMAX equipment developed with the standard IEEE 802.16e and got the certification

and they announced to publish the product in 2009 to provide the mobility for nomadic

user.

WiMAX have deputize other broadband technologies contending in the same section and

will get an advantages solution for the BWA in order to deploy the last mile access in

every places where on other hand it is hard to deploy with other technologies, like cable,

DSL, T-1 carrier and where the costs is always matter for the maintenance and

deployment of such technologies. In that way, WiMAX would provide the coverage in

the rural areas and underserved metropolitan areas in developing countries. It can be used

in backhaul for enterprise campus, Wi-Fi hot-spots and for a large institution. WiMAX

provide a excellent solution for these issue because it offers a cost-effective, rapidly

growing deployable solution [2].

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In addition to that, WiMAX will face a grievous competitor of 3G cellular systems with

high speed mobile data specification would be achieved with the 802.16e specification.

Figure 2: Possible scenarios for the deployment of WiMAX

3.2 Evolution of IEEE family of standard for Broadband Wireless

Access (BWA)

At the end of 90’s, many telecom gadgets manufacturers were start to develop the

equipment and offers products for BWA. But the Industry was suffered from an

interoperable problem due to this need of a standard, The U.S. NIST called a meeting to

discuss that topic in August 1998 [1]. The meeting had terminated with a decision to

organize within IEEE 802 standard. The endeavor was welcomed in WiMAX forum that

was leaded to constitution of the 802.16 Working Group. Since then, the Working Group

members have been developing lot of standards for fixed and mobile BWA. IEEE

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Working Group 802.16 on BWA standard is responsible for development of 802.16 and

the included Wireless Man air interface.

The IEEE 802.16 standard contains the of PHY and MAC layer specification. The first

version of the standard IEEE802.16 2001 [2] was release on December 2001 and it has

pass through with many modification to consisting the new features and securities. The

current version of the standard IEEE 802.16 2004 [3], release on September 2004, that

replace the all previous versions of the standards. This standard specifies the air interface

for fixed BWA systems with supporting multimedia services in licensee and unlicensed

spectrum [3]. The Working Group approved the amendment IEEE 802.16e2005 [4] to

IEEE802.16 2004 on February 2006. To understand the development of the standard to

its current stage, the evolution of the standard is presented here.

3.2.1 IEEE 802.16 2001

The first issue of the standard specifies a set of MAC and PHY layer specification that is

dedicated to providing the fixed broadband wireless access in a point-to-point or point-to-

multipoint topology [5]. Single carrier modulation technique is used by the PHY layer at

the 10-66 GHz frequency band.

Transmission slots, durations and modulations schemes are allotted by the BS and shared

with in the network. Subscribers need to stay within the coverage from the base station

that they are connected and do not need to listen any other node of the network. MS have

the ability to negotiate with the BS for bandwidth allocation on a burst by burst basis that

provides scheduling flexibility.

The standard consists of digital modulation scheme such as QPSK, 4-QAM, 16-QAM

and 16-QAM. These can be changed from frame to frame and from SS to SS, depending

on the channel condition. The standard supports both TDD and FDD technique.

Most important ability of 802.16-2001 is its characteristic to provide the QoS at the MAC

Layer. Traffic Flow identification does checks the QoS. Traffic flows are classified by

their QoS parameters, which can be used to specify parameters like low latency and

tolerated jitter [6]. Service flows can be originated either from BS or SS. 802.16-2001

works only for the L-O-S conditions with outdoor CPE.

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3.2.2 IEEE 802.16a 2002

The IEEE 802.16a-2003 is nothing but the some amends of IEEE 802.16-2001 by

enhancing the MAC layer to support various PHY layer properties to providing the

additional physical layer specifications. This was filtered out by WiMAX forum

organization in January 2003[7]. This amendment added physical layer support for 2-

11GHz band for both licensed and unlicensed bands. N-LOS operation becomes possible

due to inclusion of below 11 GHz band. Due to N-LOS operation multipath propagation

becomes a problem. To solve this problem multipath propagation and interference

mitigation features like advanced power management technique and adaptive antenna

arrays were included in the specification [7].The option of employing the OFDM was

included as an alternative.

In this version, some security feature was upgraded while in 802.16-2001 it was not

mandatory; many of security layers became added. IEEE 802.16a support for mesh

topology optimally in place of P-M-P.

3.2.3 IEEE 802.16c 2003

IEEE Standards certified the amendment of IEEE 802.16c [2] in December 2002. In this

amendment the WiMAX forum added the detailed profiles of 10-66 GHz and removes

some errors and incompatibility issues of the first version.

3.2.4 IEEE 802.162004

802.16-2001, 802.16a and 802.16c were consolidated and a new standard was formed

which is known as 802.16-2004. At the starting, it was revised under the name 802.16

REVd, but the changes were so unfeigned that the standard was released under the name

802.16-2004 on September 2004. With this version, the whole family of the standard is

signed and approved.

BER

When number of bits error occurs within one second in transmitted signal then we called

BER. According to some other books Bit Error rate is a type of parameter which used to

access the system which can transmit the digital signal from one end to another end. We

can define BER as follows,

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If transmitter and receiver’s medium are good in a particular time and SNR is high, then

Bit Error rate is very low. In our dissertation the simulation result will be in form of BER

aginst the different set of SNR.

Table 2: Comparison of IEEE standard for BWA

IEEE 802.16

2001

IEEE 802.16a IEEE802.16

2004

IEEE 802.16e

2005

Completed December

2001

January 2003 June 2004 December 2005

Spectrum 10-66 GHz 2-11 GHz 2-11 GHz 2-6 GHz

Propagation

/channel

conditions

LOS NLOS NLOS NLOS

Bit Rate

Up to 134

Mbps

(28 MHz

channelizatio

n)

Up to 75 Mbps

(20 MHz

channelization)

Up to 75 Mbps

(20 MHz

channelization)

Up to 15Mbps (5

MHz

channelization

Modulation QPSK,

16QAM

(optional in

UL),

64QAM

(optional)

BPSK, QPSK,

16QAM,

64QAM,

256QAM

(optional)

256 subcarriers

OFDM, BPSK,

QPSK, 16QAM,

64QAM,

256QAM

Scalable

OFDMA, QPSK,

16QAM,

64QAM,

256QAM

(optional)

Mobility Fixed Fixed Fixed/Nomadic Portable/mobile

Eb/E0

Energy per bit to noise power spectral density ratio is important role especially in

simulation. Whenever we are simulating and comparing the BER performance of

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adaptive modulation technique is very necessary Eb/N0. The normalized form of Eb/N0 is

SNR. In telecommunication, is the form of power ratio between a signal and background

noise.

Here P is mean power. If the signal and the background noise are measured at the same

point and if the measurement will take the same impedance then SNR will be getting by

measuring the square of the amplitude ratio.

BER Vs Eb/E0

The BER defined as the probability of error on the other hand SNR is the term of signal

power ratio between a noise powers. Some variables are described as under,

The error function (erfc)

The energy per bit (Eb)

The noise power spectral density (N0)

The value of error function is different for every modulation intrigue. That’s why every

modulation intrigue performs different behavior with respect to the background noise.

The higher modulation intrigue (like 64-QAM) is not beneficial for noise channel but it

accommodate the more data. On the other hand, the lower modulation scheme (like

BPSK) is more robust for noisy environment but data carrying capacity is too low.

The energy per bit (Eb) is defined by dividing the carrier power to measure of energy (in

joule). Noise power spectral density (N0) is the power per hertz (Joules per second). So, it

is clear from the definition that the dimension of SNR is cancelled. So the conclusion is

that, the probability of error is proportional to Eb/No.

3.2.5 IEEE 802.16e2005

This amendment was included in the current applicable version of standard IEEE 802.16-

2004 in December 2005. This includes the PHY and MAC layer specification to

combined fixed and mobile operation on the licensed band.

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3.3 Technical Overview The WiMAX standard defines the air interface for the IEEE 802.16-2005 specification

working in the frequency band 2-11 GHz. This air interface includes the definition of the

MAC and the physical (PHY) layers.

3.3.1 IEEE 802.16 Protocol Layers

The IEEE 802.16 standard is structured in the form of a protocol stack with well defined

interfaces. As shown in Figure 3, the MAC layer is formed with three sub layers:

Service Specific Convergence Sub-layer (CS)

MAC Common Part Sub-layer (CPS) and

Privacy Sub-layer.

The MAC CS receives higher level data through CS SAP and provides transformation

and mapping into MAC SDU. The WiMAX specification hits the two types of traffic

transportation through IEEE 802.16 networks: ATM and Packets. Thus, interfacing on

various protocols is available for multiple CS specification.

The core part of the MAC layer is CPS. The CPS performs the various function related to

the channelization, duplexing, accessing, framing, network topology and initialization.

This CPS offers the rules and mechanism for accessing the system, resource allocation

and connection maintenance. QoS scheduling and classification decisions are also

performed within the MAC CPS.

The security layer stands between the MAC CPS and the PHY layer. Security is a big

challenge for the wireless networks. MAC sub layer offers the cryptography mechanism

for protecting the information from unauthorized disclosure and is also used for

authorization and key management. Data, physical layer control and statistics are

exchange between the MAC CPS and the PHY through the PHY SAP.

The PHY layer includes multiple modulations and coding scheme, which is help to adapt

the instantaneous variation of the channel. Physical layer flexibility allows the system

designers to sartor their system according to the requirements. The physical layer

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describes the some mandatory profile that implemented with the system including some

optional features.

Figure 3: WiMAX Protocol Stack

3.3.2 MAC layer

Some functions are associated with providing service to subscribers. They have

transmitted the data in form of frames and have the control access of the common

wireless medium. The MAC layer, which is situated above the physical layer, groups the

mentioned functions.

Primarily work of the MAC is increase the performance by to accommodating multiple

physical layer specifications and their services, addressing the needs for different

environments. It is generally designed to work with point-to-multipoint networks,

through a base station that control independently. Access and resource allocation

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algorithms can be capable to carries hundreds of terminals on a single channel, terminals;

that may be shared by multiple users. Therefore, the MAC protocol defines how and

when a BS or a subscriber station may enlighten the transmission. At the time of

downlink there is only one user, and the MAC protocol is quite simple using TDM to

multiplex the data. In uplink, when more than one SS contend for accessing the channel,

then MAC layer protocol provide a mechanism that is a TDMA technique, thus providing

an efficient use of the bandwidth.

Figure 4: WiMAX Physical and MAC layer architecture

The services required by the multiple users are varied, including voice and data, IP

connectivity, and VoIP. In order to support this variety of services, the MAC layer must

accommodate both continuous and busty traffic, adapting the data velocities and delays to

the needs of each service. Additionally, mechanisms in the MAC provide for

differentiated QoS supporting the needs of various applications.

The services required by the multiple users are varied, including voice and data, IP

connectivity, and VoIP. In order to support this variety of services, the MAC layer must

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accommodate both continuous and busty traffic, adapting the data velocities and delays to

the needs of each service. Additionally, mechanisms in the MAC provide for

differentiated QoS supporting the needs of various applications.

Issues of transport efficiency are also addressed. Both modulation and coding schemes

are specified in a burst profile that is adjusted adaptively for each burst to each subscriber

station, making the use of bandwidth efficient, offers maximum throughput, and enhance

the system capacity. The radio resource allocation mechanism is designed to be scalable,

effective, and self- correcting, allowing the system scalability from one to hundreds of

users. Another transmission protocol that enhances the performance is the ARQ that

compatible with mesh topology rather than only point-to-multipoint network

architectures. The main advantage with mesh topology is that subscriber station direct

communication with other SS, so this topology increases the scalability of the system.

The specification also offers the automatic power control, and cryptography mechanisms.

Further detailed information of MAC could be found in [4] and [5].

Table 3: 802.16-2004 MAC features Feature Benefit

TDM/TDMA scheduled uplink/downlink frames

• Efficient bandwidth usage.

Scalable from one to hundreds of subscribers

• Allows cost effective deployments by supporting enough subscribers to deliver a robust business case Connection-oriented • Per connection QoS. • Faster packet routing and forwarding.

QoS support • Low latency for delay sensitive services (TDM, Voice, VoIP). • Optimal transport for VBR6 traffic (video). • Data priorization.

ARQ • Improves end-to-end performance by hiding RF layer induced errors from upper layer

t l Support for adaptive modulation • Enables highest data rates allowed by channel conditions, exploiting system capacity.

Security and encryption (Triple DES) • Protects user privacy.

Automatic power control • Enables cellular deployments by minimizing self-interference.

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3.3.3 Physical (PHY) layer

The IEEE 802.16-2005 standard defines three different PHYs that can be used in

conjunction with the MAC layer to provide a reliable end-to-end link. These PHY

specifications are:

• A single carrier SC modulated air interface.

• A 256-point FFT OFDM multiplexing scheme.

• A 2048-point FFT OFDMA scheme.

While the SC air interface is used for LoS transmissions, the two OFDM-based systems

are more suitable for NLoS operations due to the simplicity of the equalization process

for multicarrier signals. The fixed WiMAX standard defines profiles using the 256-point

FFT OFDM PHY layer specification. Furthermore, fixed WiMAX systems provide up to

5 km of service area allowing transmissions with a maximum data rate up to 70 Mbps in

a 20 MHz channel bandwidth, and offer the users a broadband connectivity without

needing a direct line-of-sight to the base station.

The main features of the mentioned fixed WiMAX are detailed next:

Use of an OFDM modulation scheme, which allows the transmission of multiple

signals using different subcarriers simultaneously. OFDM waveform is composed

of multiple narrowband subcarriers that are orthogonal to each other, frequency

selective fading is affected to a set of subcarriers that are easy to equalize.

Concept of an AMC mechanism that depends on channel conditions. It allows

changing the modulation and coding scheme that is more appropriate for optimum

throughput, thus making a most efficient use of the bandwidth.

WiMAX offers the both time and frequency division duplexing formats to enable

the system to be adapted to the regulations in different countries.

Robust FEC coding, used to minimize the effect errors in order to improve bit

error rate. The FEC scheme is implemented with a Reed- Solomon encoder

concatenated with a convolutional one, and followed by an interleaver. Optional

support of BTC and CTC can be implemented.

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Table 4: 802.16-2004 PHY features

Feature Benefit 256-point FFT OFDM waveform

• Simple equalization of multipath channels in Outdoor LoS and NLoS environments.

Adaptive modulation and variable error correction encoding per RF burst

• Ensures a robust RF link while maximizing the number of bits per second for each Subscriber unit.

TDD and FDD duplexing support • Addresses varying worldwide regulations when One or both may be allowed.

Flexible channel sizes (from 1.25 to 20 MHz)

• Provides the necessary flexibility to operate in many different frequency bands with Varying requirements around the world.

DFS support • Minimizes interference between adjacent Channels.

Designed to support AAS • Smart antennas are fast becoming more affordable, and as these costs come down, their ability to suppress interference and increase system gain is more important to BWA deployments.

TDM and FDM support • Allows interoperability between cellular Systems (TDM) and wireless systems (FDM).

Designed to support MIMO schemes

• Implemented in DL to increase diversity and capacity. • STC algorithms at the transmitter, MRC at the receiver.

Use of flexible channel bandwidths, comprised from 1.25 to 20 MHz, thus

providing the necessary flexibility to operate in many different frequency bands

with varying channel requirements around the world. This flexibility facilitates

transmissions over longer ranges and from different types of subscriber platforms.

In addition, it is also crucial for cell planning, especially in the licensed spectrum.

Optional support of both transmits and receives diversity to enhance performance

in fading environments through spatial diversity, allowing the system to increase

capacity. The transmitter implements STC to provide transmit source

independence, reducing the fade margin requirement, and combating interference.

The receiver, however, uses MRC techniques to improve the availability of the

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system.

Design of a DFS mechanism to minimize interferences.

Optional support of smart antennas, whose beams could be concentrated in a

particular direction or receiver intended directions, and therefore avoiding the

interference between co-channels, and enhance the spectral density and the BER.

Smart antennas are basically of two types, those have multiple beams (directional

antennas), and these are known as adaptive antenna array systems. The first ones

can use either a fixed number of beams; system choosing the most appropriate

beam direction for the transmission to the desired antenna. The second type is

with multi-element antennas with a adaptive beam pattern. These smart antennas

are becoming a good alternative for BWA deployments.

Implementation of channel quality measurements which help in the selection and

assignment of the adaptive burst profiles.

Support of both time and frequency division multiplexing formats (TDM and

FDM), to allow interoperability between cellular systems working with TDM, and

wireless systems that use FDM.

The mobile WiMAX uses the 2048-point FFT OFDMA PHY specification. It provides

service area coverage from 1.6 to 5 km, allowing transmission rates of 5 Mbps in a 1.75

MHz channel bandwidth, and with a user during the mobility. It presents the same

features as those of the fixed WiMAX specification that have been already mentioned.

However, other features such as handoffs and power-saving mechanisms are added to

offer a reliable communication. Battery life and handoff are two critical issues for

mobile applications. On one hand, maximizing battery life implies minimizing the mobile

station power usage. On the other hand, handoff and handovers are necessary to enable

the MS to shift from one cell to another at vehicular speeds without disconnecting the

connection.

Handoff is the main features of the IEEE 802.16 specification, and those of the so-called

fixed and mobile WiMAX, 802.16-2004 and 802.16e respectively, are summarized in the

following chart:[22]

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Figure 5: Convergence in wireless communications.

Sub-layers

WiMAX MAC layer is divided into three sub-layers such as Service Specific

Convergence Sub-layer, Common Part Sub-layer and Security Sub-layer.

Figure 6: Purposes of MAC Layer in WiMAX [32]

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3.4 PHY Layer Adaptation WiMAX technology is an IEEE 802.16 standard, which is responsible for providing the

Broadband Wireless Access (BWA) to the users as an alternative of the wired broadband.

The WiMAX provides fixed, nomadic, portable and mobile wireless broadband

connectivity without having the direct line-of-sight from the base station. It is different

from the previous versions of the WiMAX standard in that manner 802.16e adds the

feature of the mobility to the standard.

WiMAX technology supports adaptive modulation to regulate the Signal Modulation

Scheme which is depends on the SNR state of the radio link. When the radio link is

soaring in quality, the highest modulation scheme is opted which is offering the system to

avail additional capacity. And when the radio link is poor, the WiMAX system can move

to a lower modulation scheme to keep the connection stability [3].

The current channel condition report is send to the BS via reverse signal strength

indicator (RSSI) and, based on this report, a specific coding rate is opted for the data

transmissions thus, users who are having the bad channel condition, will be provided the

optimal coding rate that gives the maximum efficiency and better throughput. This

process is AMC.

Figure 7: Adaptive Modulation Scheme

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Chapter Four

“Transmitter”

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4.1 Physical Layer Model The Model of the WiMAX physical layer is build from the standard documentation [9,

10]. The model prepared in this dissertation is build under the defined parameters.

The modeling is created on MATLAB 7.9.0 (R2009b), Simulink 9 in Windows XP

SP2/Windows 7 operating system. MATLAB 7.9.0 (R2009b) Simulink consist all the

mandatory source blocks as from the standard documents. The Model includes three main

components namely transmitter, channel and receiver. Transmitter consists of channel

coding, modulation and sub-components whereas channel is modulated on AWGN and

Multipath Rayleigh Fading channel.

4.2 Transmitter

This section contains the different steps of the transmitter which should be performs

before transmitting the data. The blocks representations of the WiMAX transmitter

simulator are describe in Figure 9.

Figure 8: Transmitter of the WiMAX system

First of all, the data source is generated from the source is randomized and afterwards,

coded and mapped into QAM symbols. As previously explained in Chapter 1, the

simulator implemented in the thesis works for the Wireless MAN-OFDM physical layer

of WiMAX. This PHY layer uses OFDM with 256 subcarriers. Each OFDM symbol is

composed of 192 data subcarriers, one DC subcarrier, eight pilot subcarriers, and fifty

five guard carriers. So, the procedure of collecting the zero DC subcarrier, data, and

pilots is needed to build the symbols. Moreover, preambles consist of training sequences

Data Source

Channel Encoding

I-Q Mapping

Assembler

Add Zeros

IFFT Add CP

Training

Pilot

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that would be appended at the starting on each burst. These training sequences are used

for analyzing the channel estimation.

Figure 9: Physical Layer Scenario

4.3 Data Source

When we are go for the simulation then we will deal with the random source because in

actual system we can’t predict how much of data the user will used so for that model we

are select the input source by generating the random binary number number or

alternatively we have a choice with Bernoulli Binary block according to the AMC

requirement which is to be putting the simulink as MAC_PDU, standard is taken from

'ETSI TS 102 177 V1.3.2 (2006-03)’,[10] by running this ‘.m’ file we are generating

some parameter which is used as input for the other source, like primitive polynomial as

‘Prim_Poly’, generator polynomial as ‘Gen_Poly’ for R-S encoder, qamconst for M-ary

modulation.

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The number of bits that are generated is specified as frame-based and is calculated from

the packet size. The size of the packet depends on the OFDM symbol which is to be

transmitted and also overall coding rate, as well as the modulation M-ary. In equation 1

calculates the number of transmitted OFDM symbols in one frame. It depends on the total

number of transmitted symbols, NTsym that also consist the symbols used for the

preamble, specified by Ntrain:

NOFDM = NTsym − Ntrain. (1)

Furthermore, the total number of transmitted symbols is defined as

NTsym = . (2)

In the formula, Tsym is the OFDM symbol time, and Tframe denotes the frame duration.

The expression that defines Tsym as well as the possible values specified for the frame

duration, once the number of OFDM symbols is known, the number of bits to be sent by

the source is calculated:

Spacket = NOFDMRNdataMa. (3)

Here, R represents the overall coding rate, Ndata is the number of used data subcarriers,

and Ma defines the modulation alphabet, which is specified by the number of transmitted

bits per symbol.

Table 5: Data source for AMC

Modulation Overall Code Rate Data Source

BPSK 1/2 data_get=randint(11*8,1);

4-QAM 1/2 data_get=randint(23*8,1);






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4.4 Channel Encoding Small-scale link performance could be enhance by adding the redundant bits through the

channel encoding in the transmitting message so that if the data is corrupted by the mean

of instantaneous fading, the destroyed data may recovered at the receiver side. At the

transmitter side, baseband signal’s message sequence is mapped into the specific

sequence which is contain the larger number of bits (that’s called redundant bit, generally

represented by ‘k’) is added with the message, and then the coded message is modulated

for the transmission. [11]

Channel coding is used by the receiver to detect and correct some (or all) of the errors

introduced by the channel in a particular sequence of message bits. Because decoding is

performed after the demodulation portion of the receiver, coding can be consider to be a

post detection technique. The added coding bits lower the raw data transmission rate

through the channel (that is, coding expends the occupied bandwidth for a particular

message data rate). In WiMAX system channel coding is performed in three steps-

[1]. Randomization

[2]. Forward Error Correction

i. R-S Encoding

ii. Convolution Encoding

[3]. Interleaver.

4.4.1 Randomization

Randomization is the first process of the channel coding where the information bits of the

baseband must be randomized after receiving the data packet from the MAC, each burst

of the data is randomized before the transmission. The purpose of using randomizer is to

ignore the long sequence of zeros and ones. Randomization is performed on each burst

of data on a bit by bit basis. Randomization is implemented with the help of Pseudo

Random Binary Sequence generator with XOR gate which use the 15 stage shift register

with generator polynomial of the given equation in feedback configuration as shown in

figure 11. [3]

g(x) =1+x14+x15 (4)

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Figure 10: Channel Encoding- Randomizer with Shift Register

Forward Error Correction

The channel encoder carries out error-control coding for the purpose of protecting

information against error incurred as it progresses through the noise channel. This is

achieved by including additional information such that the channel decoder is able to

accurately recover the source information despite the presence of errors.

Forward Error Correction is applying on both the Uplink and Downlink bursts

which consist of R-S encoding and convolution encoding that improves the Bit Error

Rate (BER) performance. [11]

4.4.2 Reed-Solomon Encoding

The data is encoded by added some bytes through the Reed Solomon Encoder after the

randomization process, the calculation of this addition bits which is be helpful for

correction the baseband on the receiver side is based on Galois Field Computations, to do

obtain the redundant bits. Galois Field is widely used to represent data in error control

coding and is denoted by GF. WiMAX uses a dynamic R-S Encoding technique based on

GF (28) which is denoted as according to the table-.

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Table 6: Mandatory channel coding per modulation

Module AMC Modulation R-S code CC code rate Overall code rate

1 1. BPSK (12,12,0) 1/2 1/2

2 2. 4-QAM (32,24,4) 2/3 1/2

3. 4-QAM (40,36,2) 5/6 3/4

4 4. 16-QAM (64,48,8) 2/3 1/2

5. 16-QAM (80,72,4) 5/6 3/4

5 6. 64-QAM (108,96,6) 3/4 2/3

7. 64-QAM (120,108,6) 5/6 3/4

The purpose of using the Reed-Solomon codes is to minimize the error by scaling the

data using to add the redundancy bit to the data sequence. This redundancy bits provides

the addition helps in correcting the error that’s occur during the transmission. Reed-

Solomon is a coding scheme which works as it first constructing a polynomial from the

data symbols which is to be transmitted instead of the original baseband. The randomized

data are arranged in block format before passing through the encoder and a redundant

byte is appended according to the code rate.

The error correction capability of any RS code is determined by (n − k), the measure of

redundancy in the block. If the location of the corrupted symbols is not known in

advance, then the R-S code can correct up to t symbols. Where

t = (n − k)/2.

n= the total number of code symbols in the encoded block.

k = the number of data symbols being encoded,

(n, k) = (2m - 1, 2m - 1 - 2t)

For WiMAX the Reed-Solomon encoding shall be derived from a systematic R-S (n =

255, k = 239, t = 8) code using a Galois field specified as GF (28).

Where:

N = Number of Bytes after encoding

K = Data Bytes before encoding

41 | P a g e

T = Number of bytes that can be corrected

The primitive and generator polynomials used for the systematic code are expressed as

follows [12, 13]

Code Generator Polynomial-

g(x) = (x+λ0) (x+λ1 ) (x+λ2) (x+λ3) ...... (x+λ2T-1) (5)

Field Generator Polynomial-

p(x) = x8 + x4 + x3 + x2 +1 (6)

Figure 11: General process of Reed-Solomon Encoder

The primitive polynomial is the one used to construct the symbol field and it can also be

named as field generator polynomial. The code generator is used the polynomial to

calculate parity and has the form specified as before, where is the primitive element of

the Galois field array over which the input information is overlap See [9] and [10] for

more information about Reed-Solomon codes.

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Figure 12: Process of shortening and puncturing of the RS code

To make the RS code flexible, i.e. to offer for the variable block sizes and variable

capability of error correction, it is passing through shorting and puncturing process.

When a block is shortened to k bytes, 239−k zero bytes are added as a prefix, and, after

the encoding process, the 239−k encoded zero bytes are deselected. After the shorting

process, the number of symbols goes out from the R-S encoder. With the puncturing,

only the first 2t of the total 16 parity bytes shall be employed. Figure 16 shows the RS

encoding, shortening, and puncturing process.

The input of the RS encoder block defined by Simulink that is specified by a vector

whose length is multiple of an integer of lk, where l the length of the binary sequences

with regarding the Galois field GF(2l), and the output is also specified by a vector whose

length is multiple of an integer. Therefore, the first step in this process is to divide the

message vector in a number of blocks sizes those lengths fits according to the quoted

requirement. On the same time, it has been noticed that the number of message bytes

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before the encoding, k, the number bytes after encoding is n, and the number of message

bytes which is to be corrected is t, are the specified in Table 6, and they change for every

modulation scheme. Thus, the number of blocks used in the Reed-Solomon encoder is

calculated as

NRS = .

A block diagram of the Reed-Solomon encoder implemented in Matlab Simulink is

depicted in Figure 14.

Figure 13: simulink scenario of the Reed-Solomon encoder of WiMAX

First of all output of randomizer is converted to the integer from the binary then all the

integer values are arrange the input data for the RS encoder in a matrix form, the number

of rows is calculated through the block size length before the encoding, k, and the

number of calculated Reed-Solomon blocks, as specified in Equation, determines the

number of columns. Zero padding is added from the beginning to achieve a length of 239

bytes for the R-S encoding block. The "Select rows"-block deals with selecting the

correct amount of bytes after the encoding process. Thus, the zero prefix is discarded, and

data is punctured by taking only the first 2t bytes of the total parity bytes, as previously

explained. To end, all the selected output is again transformed into the binary, and then it

is ready for the convolutional coding.

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Figure 14: simulink implementation of Reed-Solomon encoder of WiMAX

4.4.3 Convolution Encoding

Convolution codes are differ from block codes in that the encoder output is constructed

not from a single input but also using some of the previous encoder input. Convolution

codes are used for correcting the random errors in the data transmission. A convolution

code is a type of FEC code that is specified by CC (m, n, k), in which each m-bit

information symbol to be encoded and is transformed into an n-bit symbol, where the

n≥m and code rate is defined as m/n and the k is function of transformation of the last k

information symbols, where k is the constraint length (which is represent by the shift

register) of the code [11].the most basic diagram of convolutional coding is understand in

the figure.

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In WiMAX PHY RS block is encoded by the convolutional encoder, which has encoded

rate according to the table-1, Convolution encoder has two binary adders X and Y and

uses two generator polynomials, A and B. This generator polynomial is defined as [2, 3]:

A = 171 octal = 1111001 binary for X (7)

B = 133 octal = 1011011 binary for Y (8)

WiMAX uses the native code rate of 1/2, with constraint length of 7 which is show the

length of shift register.

Figure 15: block diagram of convolution encoder

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Figure 16: Convolutional encoder of binary rate 1/2

Figure 17: Convolutional encoder implementation in simulink

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4.4.4 Puncturing Process

Puncturing is done at the output of the convolutional encoder for deleting the additional

bits from the output stream of a convolutional encoder to reduce the length of the

message to be transmitted, thus Output of the convolution encoder is then punctured to

ignore the redundant bits from the encoded burst. The removed bits are dependent on the

code rate used. In order to produce the variable code rate a puncturing operation is done

on the output of the convolution encoder in accordance to Table 7.

Table 7: Puncturing Vector for different convolution code

The purpose of using the puncturing is obtain the variable coding rates. The

different rates that can be used are rate 1/2, rate 2/3, rate 3/4, and rate 5/6. In Table-3

denotes that the corresponding convolution encoder output is used, while “0” denotes that

the corresponding output is not used or deleted. On the receiver end Viterbi decoder is

used to decode the convolution codes.

4.4.5 Interleaving

Data interleaving is generally used to scatter error bursts. its most basic form can be

defined as a randomizer but it is quite different from the randomizer in the manner that it

does not change the state of the bits but it works on the position of bits and thus, reduce

the error concentration to be corrected with the purpose of increasing the efficiency of

FEC by spreading burst errors which is introduced by the transmission channel over a

longer time.

Interleaving is done by spreading the code symbols in time, before the transmission. The

incoming data in the interleaver is randomized done in two step permutations. First

permutation ensures that adjacent bits are mapped onto the non-adjacent subcarriers. The

Rate Puncturing Vector

1/2 [1; 1]

2/3 [1; 1; 0; 1]

3/4 [1; 1; 0; 1; 1; 0]

5/6 [1; 1; 0; 1; 1; 0; 0; 1; 1; 0]

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second permutation maps the adjacent coded bits onto less or more significant bits of

constellation thus avoiding long runs of less reliable bits.

The block interleaver interleaves all encoded data bits with a block size corresponding to

the number of coded bits per OFDM symbol. The number of coded bits depends on the

modulation technique used in the Physical layer. WiMAX 802.1 6 supports 4 modulation

techniques and is adaptive in the selection of a particular technique based on the channel

conditions and data rate. [3]

WiMAX 802.16e defines two permutations for the interleaver.

The first permutation is defined by the formula:

ink =(Ncbps/ 12) * mod(k, 12) + floor(k/ 12) (9)

The second permutation is defined by the formula:

s = ceil (Ncpc/2) (10)

jk = s * floor(mk / s)+(ink + Ncbps - floor(12 x mk / Ncbps ))mod(s) (11)

Where:

Ncpc = Number of coded bits per carrier

Ncbps = Number of coded bits per symbol

k =Index of coded bits before first permutation

mk =Index of coded bits after first permutation

jk =Index of coded bits after second permutation

WiMAX uses an interleaver that combines data using 12 interleaving levels. The effect of

this process can be understood as a spreading of the bits of the different symbols, which

are combined to obtain the new symbols with, rearranged the bits buts on same size. The

interleaving process in the simulator has been deployed in two steps. First, the data go

through a matrix which performs block interleaving through filling a matrix by the input

symbols in row by row, and then it send that matrix content in column manner. The

parameter which is used for this block is the number of rows and columns that compose

the matrix:

Nrows=12, Ncoloums=

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The second step consists of a block interleaver. It rearranges the elements of its input

according to an index vector. This vector is defined as

I= (12)

Where:

• is the total number of coded bits

=

• Ncpc is the number of coded bits per subcarrier, being the same as specified with

the modulation alphabet, Ma,

• Ntx-data is the total number of transmitted data symbols, and

Ntx-data = NdataNOFDM

• S=

4.5 I-Q Mapper

In M-ary PSK modulation, the amplitude of the transmitted signal was remaining

constant, thereby conceding a circular constellation. A new modulation scheme called

quadrature amplitude modulation is obtained when the phase is varying on different

amplitude. In figure 5 shows the constellation diagram of 2-ary, 4-ary and 16-ary QAM.

[11]

The constellation consists of a square lattice of signal points. The general form of an M-

ary QAM signal can be defend as

Si (t) = + (13)

0≤t≤T i= 1, 2… M

The purpose interleaver is to rearrange the data stream and sends the data frame to the IQ

mapper. The function of the IQ mapper is to map the incoming bits from interleaver on to

the constellation. Once the signal has been coded, it enters the modulation block.

Modulation scheme is the primary need of any wireless system to map coded bits on to

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the carrier that can be effectively transmitted over channel. The IQ plot for a modulation

scheme shows the transmitting vector for all combinations of data word. Gray coding is a

method for this allocation so that adjacent points in the constellation only differ by a

single bit.

The adaptive modulation and coding scheme is used in the DL and UL are binary phase

shift keying (BPSK), 4-QAM, and 16-QAM to modulate bits to the constellation points.

The PHY specifies seven combinations of modulation and coding rate, which can be

allocated to each subscriber according to the channel condition, in both UL and DL [9].

There are tradeoffs between data rate and robustness, depending on the channel

conditions.

To achieve equal average symbol power, the constellations described above are

normalized by multiplying all of its points by an appropriate factor Cm. Values for this

factor Cm are given in Table 8.The modulation mapping is built in the simulator by a

Simulink block implemented as a Matlab m-file. The symbol alphabet, As, represents the

coordinate points in the constellation map and is defined in Table 9.

Table 8: Normalization factors

Modulation Scheme Normalization constant for unit average power

BPSK Cm = 1

4-QAM Cm = 1/√2

16-QAM Cm = 1/√10

64-QAM Cm = 1/√42

Table 9: Modulation alphabet for the constellation map

Modulation Scheme Symbol alphabet

BPSK As = (1,−1)

4-QAM As = (1 + j, 1 − j,−1 + j,−1 − j)

16-QAM A = (j, 3j,−j,−3j)

As = (A + 1,A + 3,A − 1,A − 3)

64-QAM A = (j, 3j, 5j, 7j − j,−3j,−5j,−7j)

As = (A + 1,A + 3,A + 5,A + 7,A − 1,A − 3,A − 5,A − 7)

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Figure 18: BPSK, 4-QAM and 16-QAM constellation map

Moreever, an adaptive modulation and coding mechanism which is used for downlink

channel quality through allowing the number of transmitted bits per symbol that is

depending on the channel conditions.

Simulink Implementation

In our model we are use the customized I-Q mapper through the .m file whose output

from workspace is putting on the simulink model, customization is done according to

table-

Table 10: Customization Mapping.

Modulation Scheme Customization Constellation

BPSK

Ry=[+1 -1];

Iy=[0 0];

qamconst=complex(Ry,Iy);

qamconst=qamconst(:);

bitspersymbol=1;

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4-QAM

Ry=ones(2,1)*[+1 -1];

Iy=([+1 -1]')*ones(1,2);


qamconst=qamconst(:)/sqrt(2);

bitspersymbol=2;

16-QAM

Ry=ones(4,1)*[+1 +3 -1 -3];

Iy=([+1 +3 -3 -1]')*ones(1,4);



bitspersymbol=4;

64-QAM

Ry=ones(8,1)*[+3 +1 +5 +7 -3 -1 -5 -7 ];

Iy=([+3 +1 +5 +7 -3 -1 -5 -7 ]')*ones(1,8);



bitspersymbol=6;

4.6 Principle of OFDM Transmission OFDM is a multiplexing technique that divides a channel with a higher relative data rate

into several orthogonal sub-channels with a lower data rate. For high data rate

transmissions, the symbol duration Ts is short. Therefore ISI due to multipath

propagation distorts the received signal, if the symbol duration Ts is smaller as the

maximum delay of the channel. To mitigate this effect a narrowband channel is needed,

but for high data rates a broadband channel is needed. To overcome this problem the total

bandwidth can be split into several parallel narrowband subcarriers. Thus a block of N

serial data symbols with duration Ts is converted into a block of N parallel data symbols,

each with duration T = N×Ts. The aim is that the new symbol duration of each subcarrier

is larger than the maximum delay of the channel, T > Tmax. With many low data rate

subcarriers at the same time, a higher data rate is achieved. In order to create the OFDM

symbol a serial to parallel block is used to convert N serial data symbols into N parallel

data symbols. Then each parallel data symbol is modulated with different orthogonal

frequency subcarriers, and added to an OFDM symbol, [4].

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Using Inverse FFT to Create the OFDM Symbol All modulated subcarriers are added together to create the OFDM symbol. This is done

by an IFFT. The advantage of using IFFT is that the system does not need N oscillators to

transmit N subcarriers.

The IFFT is used to obtain the signal in time domain, after modulation the produce

symbols obtained can be considered the amplitudes of sinusoids in a certain range. Before

applying the IFFT algorithm; each of the discrete samples corresponds to an individual

subcarrier. Apart of maintaining the orthogonality of the OFDM subcarriers, the IFFT is a

rapid way for modulating these subcarriers in parallel, and so, the use of multiple

modulators and demodulators, operation, is avoided. Before deploying the IFFT

operation in simulator, the subcarriers are rearranged. Figure 20 shows the subcarrier

structure that enters the IFFT block after performing the cited rearrangement. As seen in

the following figure, zero subcarriers are kept in the center of the structure.

Before doing the IFFT operation in the simulator, the subcarriers are rearranged. Figure

20 shows the subcarrier structure that enters the IFFT block after performing the cited

rearrangement. As seen in the following figure, zero subcarriers are kept in the center of

the structure.

Figure 19: Rearrangement performed before realizing the IFFT operation.

Cyclic Prefix Insertion

The cyclic prefix is used in OFDM signals as a guard interval and can be defined as a

copy of the end symbol that is inserted at the beginning of each OFDM symbol. Guard

interval is applied to mitigate the effect of ISI due to the multipath propagation. Figure

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21 shows the symbol and its delay. These delays make noise and distort the beginning of

the next symbol as shown.

To overcome this problem, one possibility is to shift the second symbol furthers away

from the first symbol. But existence of a blank space for a continuous communication

system is not desired. In order to solve this problem a copy of the last part of the symbol

is inserted at the beginning of each symbol. This procedure is called adding a cyclic

prefix. Figure 22 shows the insertion of a cyclic prefix. The Cyclic prefix is added after

the IFFT at the transmitter, and at the receiver the cyclic prefix is removed in order to get

the original signal. A detailed mathematical explanation can be found in [4].

Figure 20: Delay from front symbol

Figure 21: Cyclic prefix insertion.

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The robustness of any OFDM transmission is achieved by having a long symbol period to

minimizing the inter-symbol interference against multipath delay spread. Figure 23

depicts one way to perform the cited long symbol period that creating a cyclically guard

interval where each OFDM symbol is introduced by a periodic extension of the signal.

This guard interval is nothing but a copy of the last portion of the data symbol is known

as the cyclic prefix.

Copying the end of a symbol and appending it to the start results in a longer symbol time.

Thus, the total length of the symbol is

Tsym = Tb + Tg, (14)

Where:

• Tsym is the OFDM symbol time,

• Tb is the useful symbol time, and

• Tg represents the CP time.

The parameter G defines the ratio of the CP length to the useful symbol time. When

eliminating ISI, it has to be taken into account that the CP must be longer than the

dispersion of the channel. Moreover, it should be as small as possible since it costs

energy to the transmitter. For these reasons, G is usually less than 1/4:

G = (15)

The OFDM symbol enforces the source symbols to perform the operation into time-

domain. If we chose the N number of subcarriers for the system to evaluate the

performance of WiMAX the basic function of IFFT is to receive the N number of

sinusoidal and N symbols at a time (i.e. it converts the frequency domain signals into

time domain. These time domain signals are then transmitted through the channel.) The

output of IFFT is the total N sinusoidal signals and makes a single OFDM symbol. The

mathematical model of OFDM symbol defined by IFFT which would be transmitted

during our simulation as given bellow:

(16)

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Figure 22: OFDM symbol with the cyclic prefix

Figure 23: Generating the OFDM symbol using the IFFT

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Chapter Five

“Channel”

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5.1 Radio Channel When communicating over a wireless radio channel the received signal cannot be simply

a copy of the transmitted signal that is corrupted by channel. Instead signal fading occur

caused by the time-varying characteristics of the propagation environment. In this way,

random fluctuations caused by signal scattering due to the Non-LOS propagation

environment lead a phenomenon known as multipath fading. Signal that undergo either

flat or frequency-selective fading introduce the time dispersion in its self in multipath

environment. Moreover, the time dispersion is demonstrate by spreading in time of the

modulating symbols that introduced the inter-symbol interference. To avoid ISI, the

cyclic prefix time has to be chosen larger than the maximum delay spread of the channel.

Figure 24: Signal Losses due to three Effects

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5.2 Channel Model In order to measure the performance of the emergence communication system, a precise

description of the wireless channel is required to give its propagation environment. The

radio structure of a communication system plays very important role in the modeling of a

channel. The wireless channel is characterized by:

• Path loss (including shadowing)

• Multipath delay spread

• Fading characteristics

• Doppler spread

• Co-channel and adjacent channel interference

All the model parameters are random in nature and only a statistical characterization of

these parameters is possible in terms of the mean and variance value and these are

dependent upon terrain, tree density, antenna height, beam width (BW), wind speed and

time of the year.

Path loss

Path loss is affected by several factors such as terrain contours, distinct environments like

(urban or rural, vegetation and foliage), propagation medium (dry or moist air), the

distance between transmitter and receiver, height and location of antennas, etc. It has only

effect on the link budget [11] that is why we cannot consider it in the channel modeling.

Multipath Delay Spread

Due to the non NLOS propagation nature of the WMAN OFDM, we have to give

multipath delay spread in our channel model. It results due to the scattering behavior of

the environment. This multipath delay spread is a parameter which is used to signify the

effect of multipath propagation. It totally depends on the terrain, distance, antenna

directivity and other factors. The R.M.S delay spread value can span from tens of nano

seconds to microseconds.

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Fading characteristics

In a multipath propagation environment, the received signal detects fluctuation in signal

amplitude, phase and angle of arrival. The effect of this fluctuation is described by the

term multipath fading. Due to fixed arrangement of transmit and receive antenna, we

have to address the small scale fading in this channel model. Small scale fading gives to

the striking changes in signal amplitude and phase that could be experienced as a result of

small changes (as small as a half wavelength) in the spacial positioning between the

receiver and a transmitter.

Small scale fading is called Rayleigh fading if there are multiple reflective paths which

are large in number and there is no LOS signal component, the envelope of that received

signal is statistically explained by a Rayleigh Pdf. When a dominant non fading signal

component is present, such as a LOS propagation path, the small scale fading envelope is

also obtained by a Rayleigh Pdf [14]. In other words, the small scale fading statistics is

said to be Rayleigh whenever the LOS path is blocked and Multipath otherwise.

Doppler Spread

In a fixed wireless access, a Doppler frequency shift is formed on the signal due to

movement of the tiny objects in the environment. Doppler spectrum of wireless channel

differs from the exits mobile channel [12]. It has derived that the Doppler spectrum is in

the 0.12 Hz frequency range for fixed wireless channel. The shape of this spectrum is

also different than the classical Jake's spectrum for mobile channel.

With the above channel parameters, coherence distance, co-channel interference, antenna

gain reduction factor are addressed for channel modeling.

The primary requirements for that channel model, we have two options to go with. First,

we can use a mathematical model for each of them and second we can choose an

empirical model that is needed of the above requirements.

Description of the fading channel

The realistic wireless radio environment, a single received signal is composed of a

number of scattered waves, caused by the reflection and diffraction of the original

transmitted signal by objects in the surrounding geographical area. These multipath

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waves are combined at the receiver to give a resultant signal that can widely vary in

signal amplitude and phase. The Physical factors which are influencing the characteristics

of the fading experienced by the transmitter that are multipath propagation, mobility of

the reflecting objects and scatterers, and the relative motion between transmitter and

receiver. The presence of these reflecting objects and scatterers in the wireless channel

causes a change in the propagation environment and this changing environment also

alters the signal energy in amplitude, phase, and time and as a consequence, multipath

propagation occurs causing signal fading. The transmitted signal arrives at the receiver

through the multiple propagation paths, each of which has an associated time delay.

Because the received signal is spread with time due to the multipath scatterers are at

different delays, so that channel is said to be time dispersive. The difference between the

largest and the smallest among these delays introduce the maximum delay spread. On the

other hand, whenever the receiver and the transmitter are in relative motion, the received

signal is subjected to a constant frequency shift is called the Doppler shift. Therefore, as

it occurs in the time domain, the Doppler spread is defined as the difference between the

largest and the smallest among frequency shifts.

Fig. 25: Simulink Implementation

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Chapter Six

“Receiver”

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As seen in Figure 27, the receiver basically performs the reverse operation as the transmitter as well as channel estimation necessary to reveal the unknown channel coefficients. This section explains the different steps performed by the receiver to reconstruct the transmitted bits.

Figure 26: Block Diagram of Receiver

6.1 OFDM De-mapping

Firstly, the CP is removed and the received signal is converted to the frequency domain

using, in this case, the FFT algorithm. As it has been previously Section, an OFDM

symbol is composed by guard bands, data, pilots and the DC subcarrier. So a process is

requiring separating all the subcarriers. So in this order, at the decoder side first the guard

band is removed then to achieve pilots, data, and trainings disassembling is performed.

The training sequence is used to estimate the channel, through which manipulate the

channel coefficients. The calculated channel coefficient is used at the demapper side to

perform an equalization process and so this compensates the fading on the multipath

propagation channel. Once the data has been demapped, it go for the decoding process.

Fast Fourier Transform algorithm

The IFFT algorithm represents a rapid way that modulated parallel subcarriers. The FFT

or the IFFT are the pair of linear processes, so t is require converting the signal again to

the frequency domain by the mean of FFT.

Remove CP

FFT Disassembler

Demapper Decode Derandomizzer

Channel Estimation

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Removing the guard bands

When removing the subcarriers corresponding to the guard bands, the frequency structure

has been taken into account. Although zero padding appended at the end of the subcarrier

which is acting as a guard band is perform at the transmitter end, subcarriers is rearrange

when performing the IFFT operation, as display in Figure 27. Thus, the guard bands are

discarded at the middle of the OFDM symbol that is where they are allocated after the

arranging process.

Disassembler

The disassembler deals with the task of separating the signal, either in time or in

frequency domain, to get data, training, and pilots. These three different symbol streams

form the output of the disassembler.

6.2 IQ De-mapping At the receiving end of the communication link the demapper allowing the interface

between the channel and the functions that estimates the transmitted data bits for the user.

Moreover, the demapper operates on the received waveform that produces a set of

numbers that represent an estimatation of a transmitted binary for M-ary symbol. Thus,

the demapping process is used for making decision metrics about which bit is "zero" or

which bit is “one". This decision metric can be as simple decoded with hard decision, and

more complex, with soft decision.

With hard demapping the output of a hard decision has the function of the input, and this

form of output is application-dependent. However, the output of a soft decision

demapping is a real number, in form of a log-likelihood ratio. This is the logarithm ratio

between the likelihood of target produced the input and the likelihood of non-target

produced the input. In contrast, this form of output is application-independent in the

sense that this likelihood ratio output can theoretically be used to make optimal decisions

for any given target prior.

6.3 Channel Decoding The final stage of receive processing is the decoder. A block diagram of the decoder is

depicted in Figure-

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Figure 27: Block Diagram of channel Decoding

The decoder accepts the sequence of bits from the demapper process for next in

accordance with the encoding method. As the encoder block, the decoder is deployed in

four steps, which perform opposite operations with the purpose of retrieve the

information done by the encoder.

6.3.1 Deinterleaving

The deinterleaver rearranges the bits from each burst in the right manner by ordering

them serially before the interleaving process. Deinterleaving is of two types, a general

block deinterleaver and a matrix deinterleaver. Both of them work similarly as the ones

used interleaveing process according to the pair of transmitter and receiver. In general

block deinterleaver the elements of its input are rearranges according to the index vector.

The parameters used in both transmitter and receiver are the same as those ones used in

the interleaving process.

6.3.2 Inserting zeros

The block named "Insert Zeros" deals with the task of reversing the process performed by

the "Puncture" block. The puncturing process is used to deleting bits from the data

stream. The receiver did not know the position of the deleted bits but it could be know

their position through the puncturing vectors. Thus, zeros are used to fill the

corresponding vacancy of the stream in order to achieve the same code rate as before the

puncturing process. The puncturing can also be viewed as erasures from the channel.

They have no influence on the metric calculation of the succeeding Viterbi decoder

described in the following section.

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6.3.3 Viterbi decoder

The Viterbi algorithm reduces the manipulation overhead by taking the advantage of the

of the trellis code. Another advantage is its complexity, which is not the function of the

number of symbols. The Viterbi decoder performs approximate maximum likelihood

decoding. It involves calculating a measure of distance between the received signal at

time ti, and all the trellis paths entering each state at the same time.

The algorithm performs by discarding those trellis paths that could not possibly be part

for the maximum likelihood choice. When two paths enter the same state, the one is

chosen as the "surviving" path that has the best metric. The selection of the dissimilar

"surviving" paths is performed for all the states. The decoder continues perform in this

way to deeper into the trellis by making decisions through eliminating the least likely

paths. The early rejection of unlikely paths is avoiding the complexity. The goal of

selecting the optimum path can be expressed as choosing the codeword with the

maximum likelihood metric, or as selecting the codeword with the minimum distance

metric.

Moreover, the delay is introduced at the decoding process has been taken into account.

The rejection of possible paths does not process again until the third step in the

representation of trellis diagram. This is due to the fact that two branches cannot have

converged in one state so no decision can be made. This delay effect is considered in a

parameter called trace-back depth, which specifies how many symbols may precede the

beginning of the algorithm. For code rates of 1/2, a typical value for the trace-back depth

is about five times the constraint length of the code.

Another parameters of the Viterbi decoder block in the Simulink are used the trellis

structure for decoding the convolutional encoder, the decision type for decoding and the

operation mode for performing the process are defined as under:

• The types of signals that can support the Viterbi decoder are based on the decision

type parameter. The decision parameter can be of three types that have offered by

the simulink: unquantized, hard-decision and soft-decision.

• As the decision process that has been deployed in the demapper, the last kind of

decision is "unquantized", is one of them that are used by our simulator. It accepts

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real numbers on decoder block. The positive numbers are indicates as a logical 0,

and the negative number gives the logic 1. Whenever the decision parameter is set

to "soft-decision", the entries of this block are integers between 0 (most confident

decision for logical zero) and 2b (most confident decision for logical one), where

b is the number of soft-decision bits.

• The operation mode controls which method the block uses for transitioning. The

"truncated" mode, in this mode each frame is process independently and the

traceback depth parameter lye between starts at the state with the best metric and

the ends in the all-zeros state.

• Other values for this parameter are the "continuous" and "terminated" modes.

Figure 28: Simulink implementation of Convolution Decoder

6.3.4 Reed-Solomon decoder

The last part of the decoding process is the Reed-Solomon decoding. It processes the

mandatory operations to retrieve the signal and obtain at the end. As in the entire in

receiver blocks, the RS decoder performed the opposite operation corresponding to the

encoding block, explained in previously. Thus, the RS decoder takes codeword’s of

length n, and, after decoding the signal, it returns messages with length of k being n =

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255 and k = 239, the same as in the RS encoder. Therefore the implementation for the RS

decoder has been performed with a Matlab simulink and s-function using the m-file. The

block diagram of the RS decoder is depicted in Figure 30.

Figure 29 Simulink implementation of R-S Decoder

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Chapter Seven

“Result & Analysis”

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7.1 Performance Evaluation

Based on the model presented in this dissertation, and tests carried out, the performance

was established based on 10 thousand symbols in each case. The performance is

displayed in the following figure in terms of the BER versus SNR logarithmic plot, time-

scatter plots for each module; Signal-to-Noise Ratios, time-scatter plot for the output

from the transmitter and FFT scope diagram for the transmitted signal.

The BER plot obtained in the performance analysis showed that model works well on

according to the channel condition. The time-scatter plots demonstrate the scattering of

the transmitted and received signals at different values of the Signal-to-Noise Ratios. It

also shows that at very low SNR the symbols are very difficult to recognize.

Module-I

Parameter (BPSK- 1/2)

• Modulation scheme:: BPSK

• Source:: Random Number (randint(11*8,1); )

• R-S Coding Rate:: No Need (12,12,0)

• Convolution Encoding:: 1/2

• Interleaving:: [1; 1]

• FFT Size:: 256

• Channel:: 16

• Simulation:: 50,000 bits

• Noise:: Multipath Rayleigh + AWGN

Result

Table 11: BER Performance on various noise levels on different cyclic prefix

BPSK-1/2

SNR BER

1/4 1/8 1/16 1/32

1 0.0011 0 0 0

2 0 0 0 0

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5 0 0 0 0

7 0 0 0 0

10 0 0 0 0

12 0 0 0 0

15 0 0 0 0

17 0 0 0 0

20 0 0 0 0

22 0 0 0 0

25 0 0 0 0

27 0 0 0 0

30 0 0 0 0

Figure 30: BER Performance of BPSK with different CP

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Figure 31: BPSK result in term of Signal Strength and constellation diagram

Result discussion

After the iteration of simulation we are obtain the result in term of signal-strength by

which we can see that how the signal is fade after passing the channel, constellation

diagram shows that inter symbol interference.

We know that in AMC concept when the channel is more noise than the WiMAX is adapt

the lower modulation technique now the general question is arise why the system not

going with higher modulation whereas the higher modulation technique gives the

freedom of sending the more data as compare to lower modulation technique.

My dissertation result shows that why the higher modulation technique is not appropriate

for the noise channel in table we can clearly see that when SNR is too low then the BER

is nearly negligible, that’s why BPSK is useful for noise channel.

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Module-II

Parameter (QPSK- 1/2)

• Modulation scheme:: QPSK


• R-S Coding Rate:: (32,24,4)


• Interleaving:: [1; 1; 0; 1]

• FFT Size:: 256

• Channel:: 16



Parameter (QPSK- 3/4)

• Modulation scheme:: QPSK




• Interleaving:: [1; 1; 0; 1; 1; 0; 0; 1; 1; 0]

• FFT Size:: 256

• Channel:: 16



Result


4-QAM 1/2 4-QAM 3/4

SNR BER BER

1/4 1/8 1/16 1/32 1/4 1/8 1/16 1/32

1 0.1803 0.2428 0.2203 0.1639 0.3607 0.3545 0.3446 0.3277

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2 0.0942 0.1105 0.0797 0.0053 0.3598 0.3089 0.3607 0.3241

5 0 0 0.0018 0 0.2241 0.1982 0.2598 0.3018

7 0 0 0 0 0.0205 0.0491 0.0125 0.1018

10 0 0 0 0 0 0 0 0

12 0 0 0 0 0 0 0 0

15 0 0 0 0 0 0 0 0

17 0 0 0 0 0 0 0 0

20 0 0 0 0 0 0 0 0

22 0 0 0 0 0 0 0 0

25 0 0 0 0 0 0 0 0

27 0 0 0 0 0 0 0 0

30 0 0 0 0 0 0 0 0

Figure 32: BER Performance of QPSK(1/2) with different CP

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Figure 33: BER Performance of QPSK (5/6) with different CP

Figure 34: QPSK result in term of Signal Strength and constellation diagram

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Result discussion

In module-2 we see that 4-QAM with code rate of 1/2 have the greater capability for find

and corection the errors through R-S encoding scheme in 4-QAM with 1/2 code rate the

error correcting capability is 2t=8, where 4-QAM with code rate of 3/4 is 2t=4. So we can

see that the BER performance of 4-QAM with code rateof 1/2 is better than 4-QAM 3/4.

When the channel condition is some what good than uppar modulation technique

can be opt with choice of different code rate. The main advange with higher modulation

technique is that we can impose he ore number of bits on a same carrier cycle, so we are

gatting the higer throuhput.

Module-III

Parameter (16-QAM- 1/2)

• Modulation scheme:: 16-QAM




• Interleaving:: [1; 1; 0; 1]

• FFT Size:: 256

• Channel:: 16








• Interleaving:: [1; 1; 0; 1; 1; 0; 0; 1; 1; 0]

• FFT Size:: 256

• Channel:: 16

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Result


16-QAM 1/2 16-QAM 3/4

SNR BER BER

1/4 1/8 1/16 1/32 1/4 1/8 1/16 1/32

1 0.3236 0.3191 0.3236 0.3573 0.2500 0.2412 0.2588 0.2386

2 0.3218 0.2996 0.3050 0.3777 0.2526 0.2306 0.2518 0.2553

5 0.2846 0.3112 0.2890 0.3218 0.1136 0.2526 0.2544 0.2412

7 0.1543 0.1924 0.2004 0 0.2403 0.2500 0.2500 0.2386

10 0.0195 0.0168 0.0443 0 0.2245 0.2474 0.2482 0.2474

12 0 0 0 0 0.2280 0.2456 0.2280 0.1857

15 0 0 0 0 0 0.0449 0 0

17 0 0 0 0 0 0 0 0

20 0 0 0 0 0 0 0 0

22 0 0 0 0 0 0 0 0

25 0 0 0 0 0 0 0 0

27 0 0 0 0 0 0 0 0

30 0 0 0 0 0 0 0 0

Result discussion

In module-3 we see that 16-QAM with code rate of 1/2 have the greater capability for

find and corection the errors through R-S encoding scheme in 16-QAM with 1/2 code

rate the error correcting capability is 2t=16, where 16-QAM with code rate of 3/4 is 2t=8.

So we can see that the BER performance of 16-QAM with code rateof 1/2 is better than

16-QAM 3/4.

The question is what is need of 3/4 code rate whereas 1/2 is available which is more

efficient so the answer is when the signal is fluctuate for the less amount of nose level

then we have the choice uder the less SNR level.

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Figure 35: BER Performance of 16-QAM (1/2) with different CP


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Figure 37: 16-QAM result in term of Signal Strength and constellation diagram

Module-IV






• Interleaving:: [1; 1; 0; 1; 1; 0]

• FFT Size:: 256

• Channel:: 16



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• Interleaving:: [1; 1; 0; 1; 1; 0; 0; 1; 1; 0]

• FFT Size:: 256

• Channel:: 16



Result


64-QAM 2/3 64-QAM 3/4

SNR BER BER

1/4 1/8 1/16 1/32 1/4 1/8 1/16 1/32

1 0.2625 0.2539 0.2388 0.2336 0.2625 0.2582 0.2436 0.2465

2 0.0277 0.2632 0.2440 0.2421 0.0277 0.2564 0.2360 0.2447

5 0.2461 0.2467 0.2513 0.2566 0.2461 0.2523 0.2588 0.2523

7 0.2408 0.2395 0.2539 0.2612 0.2408 0.2395 0.2471 0.2512

10 0.2230 0.2184 0.2316 0.2507 0.2230 0.2436 0.2377 0.2582

12 0.2329 0.2157 0.1941 0.2349 0.2329 0.2325 0.2360 0.2782

15 0.1678 0.1704 0.1625 0.1829 0.1678 0.2284 0.2319 0.2658

17 0.0500 0.0631 0.0493 0.1211 0.0500 0.2412 0.2068 0.2389

20 0.0450 0.0638 0 0 0.0450 0.2202 0.1530 0.2348

22 0 0 0 0 0 0.1343 0.0625 0.2179

25 0 0 0 0 0 0.0608 0 0

27 0 0 0 0 0 0 0 0

30 0 0 0 0 0 0 0 0

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Result discussion

In last module we can see that when the SNR is high then we get the perfect

communication, on the other hand we can see that the BER is also depending on the FEC

scheme when the error correcting coding is more efficient then the BER is minimum.

The result shows that the higher rate (when more bits are sending on same time of

interval) is only possible when the channel condition is good as we are saying in AMC.

So it is clear that there is a tradeoff between the throughput and BER on the constant

SNR.


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Figure 40: 64-QAM result in term of Signal Strength and constellation diagram

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7.2 Probability of Symbol Error

Probability of Error (Pe) is important to find out the error rate in a system because it

affects fading and noise in a channel at transmitting and receiving end. From the

following formula Probability of Error for M-array PSK has been calculated.

From the following formula Probability of Error for M-array PSK has been calculated.

(16)

Probability of Error for M-array QAM has been calculated through this formula which is

as follows,

(17)

Where:

erfc= error function

M=M-array Modulation

Es= Energy per symbol (Joules)

N0=Noise Power Spectral density

Due to fading and Doppler shift effect, the Probability of Error of the system increased

resulting the physical layer performance degrades. At this circumstance, we used channel

model as a Rayleigh distribution which is mentioned in chapter one. We presented the

different error probability in figure for all adaptive modulation schemes. In this section

we have shown the probability of error for all mandatory modulations with AWGN.

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Figure 41: Probability of symbol error for the different transmitted power

7.3 Analysis

After getting the result of two modules under the AMC, we have to find that there is a

tradeoff between BER and Modulation Scheme, i.e. when the channel condition is good

then the system can opt the higher modulation scheme so that we can impose the more

data without losing the bits but while we are opt the higher modulation scheme on the

poor channel condition then we should deal with higher BER.

So the result shows that the lower modulation scheme is give the higher efficiency

on the poor channel condition.

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Chapter Eight

“Conclusion & Future Work”

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8.1 Conclusion

In this dissertation we have prepared a simulation model of the physical layer of IEEE

802.16e. The performance is measure for different modulation technique with different

coding rate in terms of BER. We know that fading is one of the main aspects of wireless

communication. At the starting of our simulation, we used AWGN channel and got same

results using Rayleigh fading and AWGN. After obtaining the result it was found that

with the same channel condition the lower modulation technique gives the lower BER

and lower transmission efficiency where higher modulation technique like 16-QAM give

higher BER with better transmission efficiency. This model is very useful for analysis the

effect of different modulation technique, and also this model helps to optimize the overall

system.

And also by getting the probability of symbol error (Pe) we see that at lower power the

probability of occurring the error is low for a constant bandwidth and at ambient

temperature.

8.2 Limitation of Work In our dissertation we are obtain the result in term of BER and probability of error, we are

trying to add the MAC layer component like scheduling, radio resource allocation and

security but our simulator does not provide the freedom to include of them.

8.3 Future Work In future we try to include MIMO and Higher modulation technique (like 64-qam and

128-qam) in the system and also trying to introduce the MAC layer functionality to

provide the QoS for the classified traffic.

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References

[1] Ghosh, A.; Wolter, D.R.; Andrews, J.G.; Chen, R., “Broadband wireless access

with WiMax/802.16: current performance benchmarks and future potential”,

Communications Magazine, IEEE, Vol.43, Iss.2, Feb. 2005, PP: 129-136

[2] “IEEE Standard 802.16 for Global Broadband Wireless Access,”

http://ieee802.org/16/docs/03/C8021603_14.pdf” last accessed 15.05.07

[3] IEEE Std 802.162001,”IEEE Std. 802.162001 IEEE Standard for Local and

Metropolitan area networks Part 16: Air Interface for Fixed Broadband Wireless

Access Systems”, December 2001

[4] IEEE Std 802.16e2005 and IEEE Std 802.162004/Cor 12005 (Amendment and

Corrigendum to IEEE Std 802.162004), ”IEEE Standard for Local and metropolitan

area networks Part 16: Air Interface for Fixed and Mobile Broadband Wireless

Access Systems Amendment 2: Physical and Medium Access Control Layers for

Combined Fixed and Mobile Operation in Licensed Bands and Corrigendum 1”,

February 2006

[5] IEEE Std 802.16a2003(Amendment to IEEE Std 802.162001), “IEEE Standard for

Local and metropolitan area networks Part 16: Air Interface for Fixed Broadband

Wireless Access Systems Amendment 2: Medium Access Control Modifications

and Additional Physical Layer Specifications for 211 GHz”, January 2003

[6] WiMAX Forum, “Mobile WiMAX – Part 1: A Technical Overview and

Performance Evaluation”, August 2006.

[7] Johnston D., Walker J., “Overview of IEEE 802.16 Security”, IEEE Computer

Society, 2004.

[8] IEEE 802.16e-2005, “IEEE Standard for Local and Metropolitan Area Networks,

part 16, Air Interface or Fixed and Mobile Broadband Wireless Access Systems”,

IEEE Press, 2006.

[9] http://www.wimaxforum.org

[10] Gazi Faisal Ahmad Jubair; “Performance Evaluation of IEEE 802.16e (Mobile

WiMAX) in OFDM Physical Layer”, ME Thesis of Blekinge Institute Of

Technology 2009.

88 | P a g e

[11] Ghosh, D. R. Wolter, J. G. Andrews, and R. Chen, “Broadband Wireless Access

with WiMAX/802.16: Current performance benchmarks and future potential,” in

IEEE Commun. Mag., vol. 43, no. 2, pp. 129-136, Feb. 2005.

[12] K. Etemad, “Overview of Mobile WiMAX Technology and Evolution.” in IEEE

Commun. Mag., vol. 46, no. 10, pp. 31–40, Oct. 2008.

[13] IEEE Std 802.16e-2005, “IEEE Standard for local and metropolitan area networks,

part 16: air interface for fixed broadband wireless access systems, amendment 2:

physical and medium access control layers for combined fixed and mobile operation

in licensed bands,” Feb. 2006.

[14] D. Tse, and P. Viswanath, “Fundamentals for Wireless Communication,”

Cambridge University Press, 2005.

[15] Amalia Roca; “Implementation of WiMAX Simulator in Simulink”, M.S. Thesis

Feb. 2007.

[16] Data over Cable Service Interface Specification (DOCSIS 3.0), III generation

transmission systems for interactive cable television services- IP cable modems,

ITU-T Recommendation J.222.

[17] B. Li, Y. Qin, C. P. Low, and C. L. Gwee, “A Survey on Mobile WiMAX,” in IEEE

Commun. Mag., vol. 45, no. 12, pp. 70–75, Dec. 2007.

[18] M. Cudak, ed., “IEEE 802.16m System Requirements Document, draft IEEE

802.16m-07/002r9,” Sep. 2009.

[19] S. Hamiti, ed., “IEEE 802.16m System Description Document, draft IEEE

802.16m-09/0034r2,” Sep. 2009.

[20] Mohammad Azizul Hasan; “Performance Evaluation of WiMAX/IEEE 802.16

OFDM Physical Layer”, MS Thesis of HELSINKI UNIVERSITY OF

TECHNOLOGY 2009.

[21] R. Srinivasan, ed., “IEEE 802.16m Evaluation Methodology Document (EMD),

draft IEEE 802.16m-08/004r5,”vol.49,ppno.145-149, Jan. 2009.

[22] D. J. Love, R. W. Heath, V. K. N. Lau, D. Gesbert, B. D. Rao, and M. Andrews,

“An Overview of Limited Feedback in Wireless Communication Systems,” in IEEE

J. Select. Areas Commun., vol. 26, no. 8, pp. 1341–1365, Oct. 2008.

89 | P a g e

[23] D. Tse, and P. Viswanath, “Fundamentals for Wireless Communication,”

Cambridge University Press, 2005.

[24] H. Weingarten, Y. Steinberg, and S. Shamai, “The Capacity Region of the Gaussian

Multiple-Input Multiple-Output Broadcast Channel,” in IEEE Trans. Inform.

Theory, vol. 52, no. 9, pp. 3936–3964, Sep. 2006.

[25] G. Dimic, and N.D. Sidiropoulos, “On Downlink Beamforming with Greedy User

Selection: Performance Analysis and a Simple New Algorithm,” in IEEE Trans.

Signal Processing, pp. 3857–3868, vol. 53, no.10, Oct. 2005.

[26] T. Yoo, and A. Goldsmith, “On the Optimality of Multi antenna Broad- cast

Scheduling Using Zero-Forcing Beamforming,” in IEEE J. Select. Areas Commun.,

pp. 528–541, vol. 24, ppno. 3, Mar. 2006.

[27] WiMAX Forum, “WiMAX Forum Mobile System Profile Release 1.0,” rev. 1.5.0,

Nov. 2007.

[28] IEEE 802.16 Broadband Wireless Accesses WG, “IEEE802.16e Evaluation

Methodology,” Dec. 2007.

[29] F. Wang et al., “IEEE 802.16e System Performance: Analysis and Simulations,”

16th Annual IEEE PIMRC, 2005.

[30] F. Wang et al., “WiMAX System Performance with Multiple Transmit and Multiple

Receive Antennas,” IEEE VTC, vol.34, pp.134-136, Apr. 2007.

[31] C. Sankaran, A. Ghosh, and F. Wang, “Performance Study of a Fractional

Frequency Reuse (FFR) Scheme for an 802.16e Based WiMAX System,”vol.19,pp

.24-28, 2008, preprint.

[32] F. Hsieh, F. Wang, and A. Ghosh, “Link Performance of WiMAX PUSC,” IEEE

WCNC, Apr. 2008.

[33] R. Srinivasan, ed., “IEEE 802.16m Evaluation Methodology Document (EMD),

draft IEEE 802.16e-08/004r5,” Jan. 2009.

[34] Nuaymi Loutfi, , WiMAX Technology for Broadband Wireless Access, Wiley,

London 2007

[35] What is WiMAX, http://www.wimax.com/education/wimax/what_is_wimax

[36] Dave Wisely; IP for 4G, Pub. WILEY Press London, 2009

90 | P a g e

[37] Samsung Corp., “Downlink MIMO for EUTRA, R1-060335,” 3GPP TSG RAN

WG1 Meeting #44, Denver, USA, Feb 2006.

[38] S. Saur, H. Halbauer, A. Rueegg, and F. Schaich, “Grid-of-Beams (GoB) Based

Downlink Multi-User MIMO, IEEE C802.16m-08/487,” May 2008.

[39] Part 16:Air Interface for Broadband Wireless Access Systems, IEEE Std

802.16TM-2009, May. 2009.

[40] W. C. Wong, and S. Talwar, “Interference mitigation using downlink transmit

beamforming with nulling techniques, IEEE C802.16e-08/653r2,” Jul. 2008.

[41] H. Kwon, and B. G. Lee, “Distributed Resource Allocation through Noncooperative

Game Approach in Multi-Cell OFDMA Systems,” in Proc. IEEE Int. Conf.

Commun. (ICC), Istanbul, June 2006.

[42] IEEE Std 802.16j-2006, “IEEE Standard for local and metropolitan area

networks, part 16: air interface for fixed broadband wireless access systems, Air

Interface for Fixed and Mobile Broadband Wireless Access Systems - Multihop

Relay Specification,” March 2006.

[43] S. W. Peters and R. W. Health Jr. “The future of WiMAX: Multihop Relaying with

IEEE 802.16j,” in IEEE Commun. Mag., vol. 47, no. 1, pp. 104–111, Jan. 2009.

[44] S. Ahson and M. Ilyas, “The WiMAX Handbook. Vol: “Standards and Security,”

CRC Press, Taylor & Francis Group, 2007.

[45] J.-F. Cheng, “Coding Performance of Hybrid ARQ schemes,”, in IEEE Trans.

Commun., vol. 54, no. 6, pp. 1017–1029, June 2006.

[46] D. Toumpakaris, J. Lee, A. Matache, and H.-L .Lou, “Performance of MIMO

HARQ under Receiver Complexity Constraints,” in Proc. IEEE Global com 2008,

New Orleans, USA, Dec. 2008.

[47] J. Lee, D. Toumpakaris, H-L. Lou, E. W. Jang, and J.M. Cioffi, “Transceiver

Design for MIMO Wireless Systems Incorporating Hybrid ARQ,” in IEEE

Commun. Mag., vol. 47, no. 1, pp. 32–40, Jan. 2009

[48] Z. Ding, and M. Rice, “Hybrid-ARQ code combining for MIMO using

multidimensional space-time Trellis codes,” in Proc. IEEE ISIT ’07, Glasgow,

Scotland, UK, Jun. 2007.

91 | P a g e

[49] G.S. Paschos, I. Papapanagiotou and T.M. Bohnert, “Power Saving Mechanisms in

IEEE 802.16e Wireless Networks,” Chapter in “WiMAX Networks Planning and

Optimization,” Auerbach Publications, CRC Press, 2009.

[50] H-H. Choi and D-H. Cho, “Mobility Support for IEEE 802.16e System,” Chapter in

“WiMAX Standards and Security,”vol.34, pp. 103–128, CRC Press, 2008.

[51] IEEE 802.16-2006: "IEEE Standard for Local and Metropolitan Area Networks -

Part 16: Air Interface for Fixed Broadband Wireless Access Systems"2009

[52] ETSI TS 102 177 Version 1.3. 1, February 2006, "Broadband Radio Access

Networks (BRAN); HiperMAN; Physical (PHY) Layer"

[53] Practical Applications for Wireless Networks, Paris, lET Workshop 2006,

https://netfiles.uiuc.edu/prkumar, 10 October 2006.

[54] WiMAX and Mesh Networks, London, lEEE Seminar 2005,

https://netfiles.uiuc.edu/prkumar, 14-15 June 2005

[55] Nuaymi Loutfi, WiMAX Technology for Broadband Wireless Access, Wiley,

London, 2007.

[56] WiMAX Network Reference Model, http://www.tutorialspoint.com/wimax/wimax

network model.htm

[57] Simulation of WiMAX Physical Layer: IEEE 802.16e IEEE 802.16 Network

Architecture, http://www.csie.ndhu.edu.tw/~robert/Wimax/ WiMax-

Architecture.pdf ,2003.

[58] Eugene Crozier (System Architect, SR Telecom); Allan Klein (VP System and

Technology, SR Telecom, “WiMAX Technology for LOS and NLOS

Environments”, WiMAX forum, http://www.wimaxforum.org/technology

/downloads/WiMAXNLOS general-versionaug04.pdf , 2009

[59] Mobile WiMAX Base Station, Japan Radio Co. LTD, Japan,

http://www.jrc.co.jp/eng/ whatsnew/20080206/index.html , 2003.

[60] Mobile WiMAX CPE, Shenzhen Natural Technologies Co. LTD, China, http://

www.naturalteck.com/product.asp?class=364

[61] Introduction to FDM, OFDM, OFDMA and SOFDMA , OFDM and OFDMA

Symbol Structure, http://www.conniq.com/WiMAX/fdm-ofdm-ofdma-sofdma-

03.htm, 2001.

92 | P a g e

[62] Omar Arafat and K. Dimyati, “Performance Parameter of Mobile WiMAX : A

Study on the Physical Layer of Mobile WiMAX under Different Communication

Channels & Modulation Technique,” IEEE Second International Conference,

vol.2,vppno. 245-256, April 2010.

[63] Mohamed A. Mohamed, Mohamed S. Abo-El-Seoud and Heba M. Abd-El-Atty,

“Performance Simulation of IEEE 802.16e WiMAX Physical Layer,” IEEE Second

International Conference, vol.2,April 2010,ppno. 274-279,Feb. 2009.

[64] Wen-an ZHOU, Bing XIE and Jun-de SONG, “Link-level Simulation and

Performance Estimation of WiMAX IEEE802.16e,” IEEE Second International

Conference, vol.2, pp.245-247, April 2010.

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Appendix A MATLAB CODE FOR WiMAX SIMULINK SCENARIO clear clc BW=input('Required channel bandwidth in MHz(max 20 MHz)= '); disp('choose cyclic prefix to overcome delays spreads') disp('1/4 for longest delay spread ,') disp('1/8 for long delay spreads ,') disp('1/16 for short delays spreads ,') disp('1/32 for very small delay spread channels') G=input('= '); channels=[1.75 1.5 1.25 2.75 2.0]; oversampling=[8/7 86/75 144/125 316/275 57/50 8/7]; for i=1:5 y(i)=rem(BW,channels(i)); if y(i)==0 n=oversampling(i); end end y=(y(1))*(y(2))*(y(3))*(y(4))*(y(5)); if y~=0 n=8/7; end if ((G~=1/4)&(G~=1/8)&(G~=1/16)&(G~=1/32)) error('u have choosed a guard period thats not valid in the ieee 802.16') end Nused=200; Nfft=256; fs=(floor((n*BW*1e6)/8000))*8000; %sampling freqency freqspacing= fs/Nfft; %freqency spacing Tb= 1/freqspacing; %usfel symbol time Tg= G*Tb ;%Guard time Ts=Tb+Tg ;%symbol time samplingttime= Tb/Nfft; %adaptive encoding and decoding depending on the channel SNR genpoly=gf(1,8); for idx=0:15 genpoly=conv(genpoly,[1 gf(2,8)^idx]);

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end primepoly=[1 0 0 0 1 1 1 0 1]; convvec=poly2trellis(7,[171,133]); cSNR=input('Enter the channel SNR in dB(it should be above 1 dB)= '); if cSNR<1 error('not a valid channel for transmission ,use another channel with better SNR') end %BPSK 1/2 if (1<=cSNR&cSNR<9.4) inputsize=88; seqafterrand=inputsize+8; shortening=[1:12]; shorteningRx=[1:11]; punvec=reshape([1 , 1],2,1);%convolutional of rate 1/2 Ncbps=192;%selctor of RS 12*8 k=0:Ncbps-1; mk=(Ncbps/12 )*mod(k,12)+floor(k/12); s=ceil(Ncbps/2); jk=s*floor(mk/s)+mod(mk+Ncbps-floor(12*mk/Ncbps),s); [x,int_idx]=sort(jk); Ry=[+1 -1]; Iy=[0 0]; qamconst=complex(Ry,Iy); qamconst=qamconst(:); bitspersymbol=1; CPsel=[(256-G*256+1):256 1:256]; CPremove=[(256*G+1):(256+G*256)]; coderate=1/2; disp('Modulation scheme is chosed for that particular SNR is BPSK with Coding rate 1/2'); elseif (9.4<=cSNR&cSNR<11.2) inputsize=184; seqafterrand=inputsize+8; shortening=[1:32]; shorteningRx=[1:23]; punvec=reshape([1 0 , 1 1],4,1);%convolutional of rate 2/3 Ncbps=384; %selctor of RS 48*8 k=0:Ncbps-1; mk=(Ncbps/12 )*mod(k,12)+floor(k/12); s=ceil(Ncbps/2);

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jk=s*floor(mk/s)+mod(mk+Ncbps-floor(12*mk/Ncbps),s); [x,int_idx]=sort(jk); Ry=ones(2,1)*[+1 -1]; Iy=([+1 -1]')*ones(1,2); qamconst=complex(Ry,Iy); qamconst=qamconst(:)/sqrt(2); bitspersymbol=2; CPsel=[(256-G*256+1):256 1:256]; CPremove=[(256*G+1):(256+G*256)]; coderate=1/2; disp('Modulation scheme is chosed for that particular SNR is QPSK with Coding rate 1/2'); elseif (11.2<=cSNR&cSNR<16.4) inputsize=280; seqafterrand=inputsize+8; shortening=[1:40]; shorteningRx=[1:35]; punvec=reshape([1 0 1 0 1, 1 1 0 1 0],10,1);%convolutional of rate 5/6 Ncbps=384; %selctor of RS 48*8 k=0:Ncbps-1; mk=(Ncbps/12 )*mod(k,12)+floor(k/12); s=ceil(Ncbps/2); jk=s*floor(mk/s)+mod(mk+Ncbps-floor(12*mk/Ncbps),s); [x,int_idx]=sort(jk); Ry=ones(2,1)*[+1 -1]; Iy=([+1 -1]')*ones(1,2); qamconst=complex(Ry,Iy); qamconst=qamconst(:)/sqrt(2); bitspersymbol=2; CPsel=[(256-G*256+1):256 1:256]; CPremove=[(256*G+1):(256+G*256)]; coderate=3/4; disp('Modulation scheme is chosed for that particular SNR is QPSK with Coding rate 3/4'); elseif (16.4<=cSNR&cSNR<18.2) inputsize=376; seqafterrand=inputsize+8; shortening=[1:64]; shorteningRx=[1:47]; punvec=reshape([1 0 , 1 1],4,1);%convolutional of rate 2/3

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Ncbps=768; %selctor of RS 96*8 k=0:Ncbps-1; mk=(Ncbps/12 )*mod(k,12)+floor(k/12); s=ceil(Ncbps/2); jk=s*floor(mk/s)+mod(mk+Ncbps-floor(12*mk/Ncbps),s); [x,int_idx]=sort(jk); Ry=ones(4,1)*[+1 +3 -1 -3]; Iy=([+1 +3 -3 -1]')*ones(1,4); qamconst=complex(Ry,Iy); qamconst=qamconst(:)/sqrt(5); bitspersymbol=4; CPsel=[(256-G*256+1):256 1:256]; CPremove=[(256*G+1):(256+G*256)]; coderate= 1/2; disp('Modulation scheme is chosed for that particular SNR is 16-QAM with Coding rate 1/2'); elseif (18.2<=cSNR&cSNR<22.7) inputsize=568; seqafterrand=inputsize+8; shortening=[1:80]; shorteningRx=[1:71]; punvec=reshape([1 0 1 0 1, 1 1 0 1 0],10,1);%convolutional of rate 5/6 Ncbps=768; %selctor of RS 96*8 k=0:Ncbps-1; mk=(Ncbps/12 )*mod(k,12)+floor(k/12); s=ceil(Ncbps/2); jk=s*floor(mk/s)+mod(mk+Ncbps-floor(12*mk/Ncbps),s); [x,int_idx]=sort(jk); Ry=ones(4,1)*[+1 +3 -1 -3]; Iy=([+1 +3 -3 -1]')*ones(1,4); qamconst=complex(Ry,Iy); qamconst=qamconst(:)/sqrt(5); bitspersymbol=4; CPsel=[(256-G*256+1):256 1:256]; CPremove=[(256*G+1):(256+G*256)]; coderate= 3/4; disp('Modulation scheme is chosed for that particular SNR is 16-QAM with Coding rate 3/4'); elseif (22.7<=cSNR&cSNR<24.4) inputsize=760;

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seqafterrand=inputsize+8; shortening=[1:108]; shorteningRx=[1:95]; punvec=reshape([1 0 1 , 1 1 0 ],6,1);%convolutional of rate3/4 Ncbps=1152; %selctor of RS 144*8 k=0:Ncbps-1; mk=(Ncbps/12 )*mod(k,12)+floor(k/12); s=ceil(Ncbps/2); jk=s*floor(mk/s)+mod(mk+Ncbps-floor(12*mk/Ncbps),s); [x,int_idx]=sort(jk); Ry=ones(8,1)*[+3 +1 +5 +7 -3 -1 -5 -7 ]; Iy=([+3 +1 +5 +7 -3 -1 -5 -7 ]')*ones(1,8); qamconst=complex(Ry,Iy); qamconst=qamconst(:)/sqrt(21); bitspersymbol=6; CPsel=[(256-G*256+1):256 1:256]; CPremove=[(256*G+1):(256+G*256)]; coderate= 2/3; disp('Modulation scheme is chosed for that particular SNR is 64-QAM with Coding rate 2/3'); elseif 24.4<=cSNR inputsize=856; seqafterrand=inputsize+8; shortening=[1:120]; shorteningRx=[1:107]; punvec=reshape([1 0 1 0 1, 1 1 0 1 0],10,1);%convolutional of rate 5/6 Ncbps=1152; %selctor of RS 144*8 k=0:Ncbps-1; mk=(Ncbps/12 )*mod(k,12)+floor(k/12); s=ceil(Ncbps/2); jk=s*floor(mk/s)+mod(mk+Ncbps-floor(12*mk/Ncbps),s); [x,int_idx]=sort(jk); Ry=ones(8,1)*[+3 +1 +5 +7 -3 -1 -5 -7 ]; Iy=([+3 +1 +5 +7 -3 -1 -5 -7 ]')*ones(1,8); qamconst=complex(Ry,Iy); qamconst=qamconst(:)/sqrt(21); bitspersymbol=6; CPsel=[(256-G*256+1):256 1:256]; CPremove=[(256*G+1):(256+G*256)]; coderate= 3/4;

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disp('Modulation scheme is chosed for that particular SNR is 64-QAM with Coding rate 3/4'); end

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Appendix B MATLAB CODE FOR PROBABILITY OF SYMBOL ERROR (PE) FOR AWGN CHANNEL

clc; clear; BW=input('enter channel bandwidth in MHz(max 20 MHz)= '); TP=input('enter the transmitted power(in mW)= '); M=input('select M-arry modulation= '); No=-174; %No=KT(K=Boltzman’s constant ant T=Ambient temperature =290K) Et=(TP/BW)*(10^-6); dbm =10*log10(Et); Es=dbm-120; %where -120dB is channel attenuation SNR=Es+174; Eb_by_No=SNR-(10*log10(M)); Pe=(2*(1-(1/sqrt(M))))*erfc(sqrt(3*Es/(2*(M-1)*No)));

performance evaluation of the physical layer of ieee 802.16e standard

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