Master Thesis Computer Science Thesis no: MCS-2010:08 Dec 2009

The Performance Evaluation of OFDM Based WLAN (IEEE 802.11a and 802.11g)

Kamil Mohiuddin Shaikh

This thesis is submitted to the School of Computing at Blekinge Institute of Technology in partial fulfillment of the requirements for the degree of Master of Science in Computer Science.The thesis is equivalent to 20 weeks of full time studies.

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School of Computing Blekinge Institute of Technology Box 520 SE – 372 25 Ronneby Sweden

Contact Information: Author(s): Kamil Mohiuddin,Shaikh E-mail: Kam ohiuddin@gmail.com il.m

University advisor(s): Dr. Guohua Bai School of Computing

Internet : www.bth.se/tek Phone : +46 457 38 50 00Fax : + 46 457 102 45

ABSTRACT

In the past decade there has been a steady growth in development and implementation of

wireless

ccess technology in the Local Area Network (LAN) world.

Mostly

iplexing OFDM has been adopted by IEEE 802.11’s

standard

of WLAN standards. 802.11a and

802.11g

n that 802.11a provides high speed throughout the entire coverage area and long

term sol

demodu

ion Multiplexing (OFDM), IEEE 802.11s family, Wireless

Local Area Networks and emerged as in the largest sectors of the telecommunication

industry. Wireless local area network (WLANs) provides connectivity, mobility, and much higher

performance and achievable data rate.

WLAN is a new medium of a

WLAN applications are used in public sectors such as airports, banks, hotels, offices, city

centres because of the flexibility of the people.

Orthongonal Frequency Division Mult

as a transmission technique for high data rate in WLANs.

Now IEEE 802.11 standard has been expanded to a family

both are used Orthongonal Frequency Division Multiplexing (OFDM) but operate in different

frequency bands.

It is show

ution however it does not provide better solution in most cases as compared to IEEE 802.11g.

Matlab Simulation model based on IEEE 802.11a/g using different modulation and

lation techniques such as BPSK, QPSK and QAM to analysis the best performance of IEEE

802.11a/g with implementation of OFDM.

Keywords: Orthongonal Frequency Divis

Local Area Network, Simulation, MATLAB.

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Somewhere, something incredible is waiting to be known.”

American Astronomer, Writer and Scientist,

“

Dr. Carl Sagan

1934-1996

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DEDICATIONS

To my father and mother whose kindness always prays for me.

Kamil Mohiuddin Shaikh

Also dedicate this to my family and friends.

I am really proud all of them.

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ACKNOWLEDGEMENT

my dre puter Science. Conducting

H, the most Beneficent, and the most Merciful who

tily thanks to my family for giving me such a support while I

my friends who provide me such circumstance which were always

ke to thanks and it is justified to say that it would have been impossible to work and

amil Mohiuddin Shaikh

This Master thesis is s

am and last nail to achieve MSc degree in Comuch a research work was luxury because I was allowed to do everything as I wish. I was expected to

do everything as good as possible within a time. Firstly I would like to thanks to Almighty ALLAgive me strength to complete this task. After that, I would like to offer my hearwas 7-seas away from them but they did not make me feel about it and the courage and strength I needed to complete my goals. I would like to thank all of favorable to me. Finally, I would lisubmit this thesis without the assistance and support of my respectable advisor Dr. Guohua Bai, to whom I owe the most overwhelming debt of gratitude. Words are inadequate to express my thanks. KDec 2009

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CONTENTS

Abstract …………….....………………………………………….................................…….......2

Dedication......................................................................................................................................4

Acknowledgements....................................................................................................................5 Table of contents ……......…………………………………......................................................6

List of Figures...............................................................................................................................8

List of Tables.................................................................................................................................9

Abbreviation..................................................................................................................................10

Chapter 1: Introduction…………….......................…......……………....…..........................11 1.1 Background …………………………………….............................................................11 1.1.1 IEEE 802.11 Wireless Local Area Network............................................................12 1.1.2 IEEE 802.11a...........................................................................................................12 1.1.3 IEEE 802.11b...........................................................................................................12 1.1.4 IEEE 802.11g...........................................................................................................13 1.2 IEEE 802.11 Wireless LAN Architecture................................................................14 1.2.1 Stations......................................................................................................................14 1.2.2 Access Point (AP).....................................................................................................14 1.2.3 Wireless Medium.......................................................................................................14 1.2.4 Basic service set (BSS)..............................................................................................15 1.2.5 Distribution System (DS)...........................................................................................16 1.2.6 Extended Service Set (ESS).......................................................................................16 1.3 Motivation........................................................................................................................17

Chapter 2: Problem definition/Goals................................................................................18

2.1 The Problem......................................................................................................................18 2.1.1 Interference ..................................................................................................................18 2.1.2 Multipath Environment.................................................................................................19 2.2 The Suggestion.................................................................................................................20 2.3 The Solution.....................................................................................................................20

Chapter 3: Methodology..........................................................................................................22 3.1 Literature Review..............................................................................................................23 3.2 Questionnaire.....................................................................................................................24 3.3 Simulation.........................................................................................................................25

Chapter 4: The IEEE 802.11 Protocol..............................................................................26

4.1 IEEE 802.11.....................................................................................................................26 4.1.1 THE INFRARED (IR)..............................................................................................26 4.1.2 Frequency hopping spread spectrum (FHSS)...........................................................26 4.1.3 Direct Sequence Spread Spectrum (DSSS)..............................................................27

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4.1.4 Orthogonal Frequency Division Multiplexing................................................................27 4.2 IEEE 802.11a PHY LAYER............................................................................................28 4.3 OFDM PLCP Sublayer of IEEE 802.11a.........................................................................28 4.4 IEEE 802.11g....................................................................................................................29 4.5 Performance and Capacity................................................................................................30 4.6 Deployment Considerations for IEEE 802.11g ................................................................30

CHAPTER 5: SIMULATION MODEL AND RESULTS.....................................31

5.1 Methodology and Simulation Model.....................................................................................31 5.2 OFDM MODULATION TECHNIQUES Using IEEE 802.11a/g.........................................32 5.2.1 Binary Phase Shift Keying.............................................................................................32 5.2.2 Quadrature Phase Shift Keying (QPSK)........................................................................34 5.2.3 16 Quadrature Amplitude Modulation ..........................................................................36 5.2.4 64 Quadrature Amplitude Modulation ..........................................................................36 5.3 Additive white Gaussian Noise...........................................................................................37 5.4 Bit Error Rate (BER)...........................................................................................................37 5.5 Signal-to- Noise Ratio (SNR)...............................................................................................38 5.6 Simulations for IEEE 802.11a IEEE 802.11g Using OFDM...............................................39 5.7 Simulation Bit Error Rate curve BPSK................................................................................39 5.8 Results and Conclusions......................................................................................................41 5.9 Simulation Bit Error Rate curves for 16 QAM....................................................................41 5.10 Simulation Bit Error Rate curves for 64 QAM....................................................................42 5.11 Results and Conclusions......................................................................................................43 Chapter 6: Summary and Future work....................................................................44

6.1 Summary...................................................................................................................................44

6.2 Future Work..............................................................................................................................44

References..................................................................................................................................45

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LIST OF FIGURES Figure 1.1: Basic Service Set [7] ...............................................................................................15 Figure 1.2: Independent Basic Service Set [7]...........................................................................15 Figure 1.3: Extended Service Set [16].......................................................................................16 Figure 2.1: Multipath Propagation.............................................................................................19 Figure 3.1: Research work Methodology...................................................................................22 Figure 3.2: Methodology for the literature.................................................................................23 Figure 3.3 Methodologies for Questionnaire.............................................................................24 Figure 4.1 (a): Frequency hopping spread spectrum (FHSS)..........................................................26 Figure 4.1 (b): Frequency hopping spread spectrum (FHSS)...........................................................27 Figure 4.2: OFDM PLCP Preamble, Header and PSDU [6] .....................................................28 Figure 5.1: Binary Shift Keying (a) Block Diagram (b) Constellation......................................33 Figure 5.2: QPSK (a) Block Diagram (b) Constellation............................................................34 Figure 5.3: QPSK Constellation Scatter Plot..............................................................................35 Figure 5.4: 16 QAM Constellations............................................................................................36 Figure 5.5: 64 QAM Constellations............................................................................................36 Figure 5.6: Received Signal through an AWGN channel...........................................................37 Figure 5.7 Theoretical and Simulated curves of BER for BPSK (10000 symbols)...................39 Figure 5.8 Theoretical and Simulated curves of BER for BPSK (1000 symbols).....................40 Figure 5.9 Theoretical and Simulated curves of BER for 16 QAM..........................................41 Figure 5.10 Theoretical and Simulated curves of BER for 64 QAM..........................................42

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LIST OF TABLES

Table: 1.1 Summarized IEEE Standard.......................................................................................13 Table: 4.1 Rate bits [7]..................................................................................................................25 Table 5.1 Rate-dependent parameters of 802.11a/g [19].............................................................28 Table 5.2 Timing-related parameters of 802.11a [19].................................................................29 Table 5.3 Statistical Data of Bit Error Rate curve BPSK (10000 symbols)................................40 Table 5.4 Statistical Data of Bit Error Rate curve BPSK (1000 symbols)..................................40 Table 5.5 Statistical Data Bit Error Rate for 16 QAM................................................................42 Table 5.6 Statistical Data Bit Error Rate for 64 QAM................................................................43

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ABBREVIATIONS

AIEE American Institute of Electrical Engineers AP Access Point BSS Basic service set BPSK Binary Phase Shift Keyed CCK Complementary Code Keying CDMA Code Division Multiple Access DSP Digital Signal Processing DS Distribution System DQPSK Differential Quadrature Phase Shift Keying DSSS Direct Sequence Spread Spectrum DFT Discrete Fourier Transform ESS Extended Service Set FHSS Frequency Hopping Spread Spectrum FFT Fast Fourier Transform FDM Frequency Division Multiplexing FCC Federal Communications Commission GPS Global Positioning System IEEE Institute of Electrical and Electronics Engineers MSDU MAC Service Data Unit MAC Multiple Access Control NIC Network Interface Card OFDM Orthongonal Frequency Division Multiplexing PAM Pulse Amplitude Modulation PMD Physical Medium Dependent PLCP Physical Layer Convergence Procedure QAM Quadrature Amplitude Modulation QPSK Quadrature Phase Shift Keyed STA Station SNR Signal-to- Noise Ratio Wi-Fi Wireless Fidelity

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CHAPTER 1: INTRODUCTION

In the recent year, the word PORTABLE is the most common word in today’s life. Everyone needs everything should be portable. Wired communication networks can provide the connectivity and performance but not mobility. WLAN provides the solution for portability with connection of mobility as well as performance. There is incredible hype in the field of Wireless technology which is commonly known as wireless fidelity (Wi-Fi).

Institute of Electrical and Electronics Engineers (IEEE) is the foundation of WLAN product implemented IEEE standard 802.11 in 1997. IEEE 802.11’s family has become very popular in every different environment due to their simplicity, low cost, easy installation, location freedom and high data rate. It provides easy way to configuration of computer network using without complex wiring infrastructure. WLAN deals with local area networking where the communication done over the air between the connected devices those are within the range. There is a famous saying “Nothing is constant but change”, likewise, every days demands in high speed and data rate produce some technical demands one of them is the demand of high date rates that’s why multi carrier transmission has been implemented in IEEE 802.11’s family.

The IEEE 802.11 standard defines both a Multiple Access Control (MAC) protocol and physical layer implementations at MAC layer; IEEE 802.11 supports both infrastructure and ad hoc networks [1].

Orthogonal Frequency Division Multiplexing (OFDM) is a special form of multicarrier transmission, where a single data stream is transmitted over a number of lower rate subcarriers (SCs). It is either a modulation or multiplexing technique because OFDM is to raise robustness against frequency selection fading or narrowband interference. In a single carrier system, a single fade or interferer can cause the entire link to fail, but in a multicarrier system only a small percentage of the SCs will be affected [2].

Today’s 802.11 family is divided into much more substandard but in this thesis it will be an overview of IEEE 802.11a, 802.11 b and 802.11 g. Further discuss, WLANs have a high-rate data issues and identify some key research for future of WLAN on basics of OFDM and comparison performance between 802.11a and 802.11g.

1. Background

In 1963 the "American Institute of Electrical Engineers (AIEE)" and the "Institute of Radio Engineers (IRE)" merges together now it’s called the "Institute of Electrical and Electronics Engineers (IEEE)". Today, the IEEE is leading authority for every field such as aerospace, computers, telecommunication, biomedical engineering, electrical power and much more. IEEE is playing a very vital role not only in industry field but also in education field. More than 1430 student branches at colleges and universities in 80 countries prove IEEE's presence in the research community. [3]

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Currently there are 22 working Group (WGs) in IEEE 802 and each and every WGs can be divided into subgroup these subgroup are referred to as Task Group (TGs).The most popular WGs are following:

• 802.0, wireless Coordination Active Group • 802.1, Higher Layer Local Area Network(LAN)Protocols • 802.3, Ethernet • 802.11, Wireless Local Area Network (WLAN) • 802.15, Wireless Personal Area Network (WPAN) • 802.16, Wireless Metropolitan Area Network (WMAN) • 802.17, Resilent Packet Ring • 802.20, Mobile Broadband Wireless Access (MBWA) • 802.22, Wireless Regional Area Network (WRAN)

This thesis will focus more on 802.11 and its family.

1.1.1 IEEE 802.11 Wireless Local Area Network

In 1997 IEEE implemented 802.11 Wireless LAN standards. IEEE 802.11’s family has become very popular in every different environment due to their simplicity, low cost, easy installation, location freedom and high data rate. It provides easy way to configuration of computer network using without wiring complexity.

IEEE 802.11 standard defined that WLANs can be implemented either optical or radio

technologies for the transmission of the signals through the air. Firstly the original standard defined rates of 1 Mbps and 2 Mbps. The radio technology is used in WLANs known as Spread Spectrum modulation. Basically there are two types of spread spectrum modulation techniques which are: Frequency Hopping Spread Spectrum (FHSS) and Direst Sequence Spread Spectrum (DSSS). [4] The main issue of 802.11 was slow data rate mostly in business environment. The later revision of 802.11 can be more classified into three categories.

• IEEE 802.11a • IEEE 802.11b • IEEE 802.11g

1.1.2 IEEE 802.11a

IEEE standard 802.11a has been approved in July 1999 include with a new specification. It operates in the 5 GHZ spectrum. The 802.11a standard was designed for better scalability and higher bandwidth application rather than 802.11b include with the data rates of 6, 9, 12, 18, 24, 36, 48, 54 Mbps using orthogonal frequency division multiplexing (OFDM) modulation.

1.1.3 IEEE 802.11b

IEEE 802.11b extends the original IEEE 802.11 direct sequence spread spectrum (DSSS) standard to operate up to 11 Mbps in the 2.4-GHz unlicensed spectrum using complementary code keying (CCK) modulation. The four data rates of 1, 2, 5.5, and 11 Mbps are specified on up to three non- overlapping channels and the lowest two rates are also allowed on up to 13 overlapping channels

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[5]. The main disadvantage of the 802.11b is the frequency band is common and interference from the other networking technology such as Bluetooth, 2.04GHz cordless phone and so on.

1.1.4 IEEE802.11 g

The IEEE's 802.11g standard has been ratified in June 2003. The 802.11g standard provides optional higher-bandwidth up to 54 Mbps. IEEE 802.11g used two technology DSSS and OFDM at the 2.4 GHz ISM band.

802.11 802.11a 802.11b 802.11g

Standard Approved

July 1997 September 1999 September 1999 Completion expected in 2002

Available Bandwidth

83.5 MHz 300 MHz 83.5 MHz 83.5MHz

Frequency of operation

2.4-2.4835 GHz

DSSS,FHSS

5.15-5.35 GHz OFDM

5.725-5.825 GHz OFDM

2.4835GHz

DSSS

2.4-2.4835GHz

DSSS, OFDM

Data Rate per channel

2.1Mbps 54,48,36,24,18,12,9,6 Mbps

11,5.5,2,1

Mbps

54, 36, 33, 24, 22,

12, 11, 9, 6, 5.5, 2,

1 Mbps

Modulation Type

DQPSK (2 Mbps DSSS)

DBPSK (1 Mbps DSSS)

4GFSK (2 Mbps FHSS)

2GFSK (1Mbps FHSS)

BPSK (6,9 Mbps)

QPSK (12,18 Mbps)

16-QAM (24,36 Mbps)

64-QAM (48,58 Mbps)

DQPSK/CCK

(11,5.5 Mbps)

DQPSK(2 Mbps)

DBPSK(1 Mbps)

OFDM/CCK (6,9,12,18,24,36,48,54)

OFDM (6,9,12,18,24,36,48,54)

DQPSK/CCK (22, 33, 11, 5.5 Mbps)

DQPSK (2 Mbps)

DBPSK (1 Mbps

compatibility 802.11 Wi-Fi 5 Wi-Fi Wi-Fi at 11Mpbs & below

Table 1: Summarized IEEE Standard.

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1.2 The IEEE 802.11 Wireless LAN Architecture

The architecture of the IEEE 802.11 WLAN is designed to support network where most decision making is distributed to the mobile STAs (station). The IEEE 802.11 architecture consists of several components and services [6]:

• Station(STA) • Access Point (AP) • Wireless Medium • Basic service set (BSS) • Distribution System(DS)  • Extended service set(ESS)

IEEE 802.11 architecture defines nine services. These services can be divided into two groups

which are STAs services and distribution services. STAs services contain authentication, de-authentication, Privacy, and delivery of the data and distribution services consist of association, re-association, disassociation, distribution and integration.

1.2.1 Stations

The Station is basic components of the wireless network which is used to connect wireless network medium. In the other hand it does not provide access to a distribution system. Stations are computing device that contain IEEE 802.11 specification MAC and PHY interface to wireless network. Generally the 802.11 functions are implemented either software or hardware of Network adapter or network interface card (NIC). Station may be work station, laptop, and mobile.

1.2.2 Access Point (AP)

An Access Point is a device provides the point of interconnection wireless station to the wired network or wireless network at the same time or either. Access point performs so many functions but bridging function is the most important function. Access point functions were put into standalone devices, though several newer products are dividing the 802.11 protocol between "thin" access point and AP controllers [7].

1.2.3 Wireless Medium

Wireless Medium is used to move frame from one station to another station. There are multiple physical layers is to develop to support the 802.11 MAC. [8]

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Figure 1.1: Basic Service Set [7]

1.2.4 Basic service set (BSS)

The BSS is a collection of Stations that able to communicate with each other within 802.11 wireless local area network then they form a BSS. BSS is also called a cell. There should be at least two stations, if all stations in the BSS are mobile stations and there is no any connectivity to wired LAN network, the BSS called an Independent BSS (IBSS).Independent BSS is also called ad-hoc network.

IBSS does not support relay function. IBSS stations directly communication one and another (peer to peer) and unable to connect with any BSS. Sometime it is possible that each every mobile station may not communicate with each other because of limitation of coverage area all mobile stations should be within a range to communicate. While a BSS includes an access point and one station, the BSS is not an Independent BSS. It is called an infrastructure BSS or simply as BSS.

Figure 1.2: Independent Basic Service Set [7]

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1.2.5 Distribution System (DS)  

The distribution system (DS) is the fixed wired infrastructure used to connect a set of BSSs to create an extended service set (ESS). The IEEE 802.11 distribution services enable a wireless terminal to roam freely within ESS and also allow an 802.11 WLAN to connect to the wired LAN Infrastructure. The IEEE 802.11 standard also defined a portal as a logical point at which non 802.11 packet enter an ESS [9]. 

1.2.6 Extended Service Set (ESS)

Extended service set(ESS) consists of multiple IEEE 802.11 BSSs forming single subnet work where the access point communicate each other to forward traffic from one BSS to another and provide facility to move mobile stations from one BSS to other.

ESS configuration is a collection of multiple BSS cells that can be connected by either wired LAN or wireless LAN and used the same channel. The access point performs this communication through the distribution system. [10]

Extentened Service Set

BSSBSS

Access Point

Station 1

Station 2

Station 4

Station 3

Access Point

Station 1

Station 2

Station 4

Station 3

Distribution Systerm

Figure 1.3: extended service set [16]

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1.3 Motivation

When I was in school I read the article of DR, Philips. He is inventor of cordless phone he said that "Radio Waves are picked up from the air". I always thinks that how can I pick waves from the air. Now I am fully understand what the mean of this sentences is? The best thing in this thesis is that Wireless technology growing rapidly in all sectors it will help me in future to find a job in this field.

In the recent years, there are large numbers of wireless transmission technology available. These technologies depend on different network families such as PAN, WLAN, WMAM, and WAN. Main focus of Wireless communication is to provide data transmission with higher rates. Multipath propagation is a main problem in WLAN which motivates me to research in this area. Currently, there is solution in IEEE 802.11standard.

This thesis will focus on WLANs having a high-data rate issues and identify some key research for future of WLAN on the basis of OFDM and comparison performance between 802.11a and 802.11g. This thesis report consists of six chapters.

Chapter No.1 fully described introduction and backgrounds of the IEEE 802.11 family, OFDM as well as IEEE 802.11 Wireless LAN Architecture.

Chapter No. 2 of this thesis consists of Problem in the research medium and goals.

Chapter No. 3 includes the research methodology (qualitative and quantitative) approach adopted in the thesis and how research study carried out.

Chapter No.4 provides the depth detail of IEEE 802.11 PHY Layer and THE IEEE 802.11 protocol and different transmission techniques.

Chapter No.5 describes the simulation model and simulation results based on Matlab.

Chapter NO 6 consists of the conclusion of thesis and future work.

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CHAPTER 2: PROBLEM DEFINITION/GOALS 2.1 The Problem

Since last decade, there has been increasingly demand of wireless communication network. There is a very famous saying "Necessity is the mother of all inventions", but I will rather modify it by saying "Problem is the mother of all inventions". Always new technology raises new problems but best way to find out the solution is to use them without their issue. There are so many WLAN techniques available today but there is still some technical problem remains unsolved such as security, increase in mobility, flexibility, short range, demand of high data rates and data transmission from one destination to another destination.

Mostly IEEE 802.11 standard WLANs used radio waves at the frequency band of 2.4 GHz also known as industrial scientific and medical (ISM) band, sometimes it create interference problem with other communication equipment where two signals are close to each other at the same time and same frequency because one signal may be louder and overcome the other signal, such as Bluetooth and Microwave Ovens. Furthermore there are several problems arises with the different kind of WLANs. There are most common issues regarding Wireless LANs.

• Wireless standards are varying more quickly rather than Wired LAN because it require to upgrading for provide higher performace to customers of WLAN, it means also have to replace the wireless equipment such as Wireless network interface cards (NICs) and access points (APs).

• The devices are operated at a limited distances from APs. To increase the signal requires more APs which also increases the overall cost.

• The data rate will be dropped if the user moves further away from APs.

• The growing of wireless network also growing the risk of security attacks.

• Multipath.

• Interference.

• Fading.

2.1.1 Interference

Interference is a main problem in wireless communication when two or more signals is close to each other at the same time and same frequency interference each other if one signal is louder then overcome the other signal, they will be conflict each other. This problem is very common in home environment where so many APs work.

Loss of signal strength due to signal decrease caused by walls and obstacles is common even human body in the way for transmitters can decrease signal strength. AP standing low close the floor

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or having obstacle in close range decreases as well signal strength. Bit Error Rate (BER) rises as signal loose strength [31].

2.1.2 Multipath Environment

RF signal will turn into wider whilst spread farther, during the transmission between the radio frequency signal and the receive object. In the process, the RF signal supposed to come across the item which may reflect or deter the signal. Due to the newest duplicated wave fronts, consequently, the receiver encounters the multiple wave fronts. The RF reaching the target through various ways can be regarded as multipath propagation. Some signal arrives to the target directly, however, the rest getting the aim with overcoming the obstacle, Hence, leading to a relative longer way before getting to the destination. Since the path from the receiver up to the transmitter owns more paths over one, multipath distortion would be given birth to. This takes place around the surface of the walls, metalwork and so forth.

Figure 2.1: Multipath Propagation.

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The items posed below can be considered as WLAN with a higher possibility of multipath interference:

• Airport hangars • Ceilings • Racks • Shelving • Other metallic items

2.2 The Suggestion

In today’s world, The WLAN standard is being accepted rapidly in every environment particularly in business and educational institutions. The demand of bandwidth increases because of wire-free technology. Customer satisfaction is fundamental rule for any business. WLAN customers have a right to choose flexible, interoperable solutions from multiple seller and low prices high-speed throughout small enterprise, large enterprise and home market. Following are the basic services which are very important to provide WLANs customers:

• Performance • Connectivity • Mobility • High data rates

There are many more issues in WLAN has to be resolved. Some of them are hidden node, multipath, fading and WLAN configuration.

2.3 The Solution

The IEEE 802.11 standard has been improved the performance of Wireless Local Area Networks, while providing low cost and high-speed data capability. The WLAN performance may also be improved by using fragmentation option that divides the 802.11 data frames into smaller pieces sent separately to destination [12], and there is a need of higher data rates to obtain desirable performance of wireless LANs. IEEE802.11WLAN standard allows large Wireless networks connect with multiple access points.

Orthogonal Frequency Division Multiplexing (OFDM) tried to overcome the multipath problem through divided bandwidth into many sub-bands of frequency. The adjacent sub-bands in this system are kept orthogonal from each other so that they do not interfere with each other [30].

IEEE 802.11 b network is easily influenced to multipath propagation because in operation in DSSS but IEEE 802.11a and IEEE 802.11g uses OFMD technology, it transmits information in multiple sub channels hence, reduces the impacts of multipath.

This thesis is to explore and identify the methods for high data rate and data transmission issue with the help of two different techniques, IEEE 802.11a and IEEE 802.11g and to make a conclusion which offers best performance and result based on OFDM technology.

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The simulations implemented in MATLAB 7.01. Simulation result proved the performace of IEEE 802.11a/g PHY using different techniques BPSK, QPSK, 16 QAM and 64 QAM with an AWGN channel and OFDM techniques. The purpose of this thesis is to:

• Provide an overview of existing IEEE 802.11’s family. • Performance between IEEE 802.11a and IEEE 802.11g based on OFDM. • Evaluation of WLAN, particularly the IEEE 802.11a and IEEE 802.11g standard.

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CHAPTER 3: METHODOLOGY

The way to do research is normally called methodology and it is very importance to conduct any research work, because it provides method that researcher use to get knowledge and solve the problem and give thought before start the research. There are commonly three research methodologies or approaches used are:

1. Qualitative Research Approach 2. Quantitative Research Approach 3. Mixed Research Approach

Normally, most of the researcher use more than one methodology approach to answering their research questions which makes their result more appropriate and suitable to their discussed problems. In this thesis both of qualitative and quantitative approaches are used which is called mixed approach. The purpose of adopting mixed approach is to collect and reviewing available research work, literature and retrieve the simulation result in the field of Wireless LAN. Following figure describes both qualitative and quantitative methodology use in this thesis.

1. Literature Review 2. Questionnaire 3. Simulation

Figure 3.1: Research work Methodology

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3.1 Literature Review

The research has been carried out in multiple phases. In the beginning phase, to collect literatures from different resources and database which is available free of cost for Blekinge Institute of Technology student for research and study purpose. Most used resources are as follow:

• IEEE Explorer • ACM Digital Library • Google search engine • e-brary

Literature review is a method consists of review research publication, books,  magazines, conference papers and other journals relevant information to Wireless Local Area Network.

Relevant Literature

N0

Search Literature

Literature Review

Summarize Literature

Yes

Fundamental Concept 

Literature study done

Figure 3.2: Methodology for the literature

Literature review helps us to provide information about research area, what has been done in the past and what will be happened in future. The figure 3.2 shows the systematic approach has been adopted to search the literature. If the literature is relevant in the research area then it will be summarized otherwise all these steps will be repeated until to find related literature.

Before starting of this research work, I had some fundamental concept about the topic which helps to find out good journals and research papers. To complete literature study is to understand fact and figure out the WLANs issue and WLAN standards.

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3.2 tionnaire Ques

Informal Questionnaire is designed on the basis of current issues and compares performance between IEEE 802.11a and 802.11 g and current problem with using Wireless Local Area Network. Questionnaire is sent through email and informal face to face discussion with fellows, students, PhD students and Lab Assistants and other certified professionals in the same research field. Mostly questions and informal discussions conduct in Hamlstad University because there is Cisco academy and Cisco certified instructor.

The main objective of the questionnaire is to get the current data and issue which normally occurred in home or organisation. To understand the problem area and gain the current information issue qualitative approach was used.  Meanwhile I started study some manuals for simulation to investigation the performance and comparison of OFDM based Wireless Local Area Network IEEE 802.11a and IEEE 802.11g standards. Figure 3.3 shows that procedure which is followed in designing the questionnaire.

Figure 3.3 Methodologies for Questionnaire

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3.3 Simulation

In the end the computer simulation is very useful when researcher cannot evaluate theories in real world. MATLAB is a high level language which is used to perform numerical computing task much faster than other programming language such as C, C++, and etc. Furthermore Matlab also can be used to wide range of applications, including signal and image processing, communications.

Matlab simulation technique is adopted to analyze and verify and validate the appropriate results. The system model tested through different modulation schemes such as BPSK, QPSK, 16QAM and 64 QAM with an AWGN channel and OFDM modulator and demodulator. The object of this thesis is to find out the solution to IEEE 802.11a and IEEE 802.11g which offers best performance and result based on OFDM technology.

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CHAPTER 4: THE IEEE 802.11 PROTOCOL 4.1 IEEE 802.11

The IEEE 802.11 protocol is growing rapidly worldwide and become the most mature technology for WLANs. The IEEE 802.11 standard consists of detailed specifications for both the medium access control (MAC) and three physical layers (PHY). [14] The PHY layer selects the correct modulation scheme that provides spread spectrum in channel accessibility, data rate as well as the necessary bandwidth. The IEEE 802.11 physical layer uses basically four types of wireless data exchange techniques:

• Infrared (IR) • Frequency hopping spread spectrum (FHSS) • Direct sequence spread spectrum (DSSS). • Orthogonal Frequency Division Multiplexing (OFDM)

The infrared technique operates at the baseband but FHHS and DSSS operates in radio frequency techniques at the 2.4 GHz band. Generally WLAN proffered radio frequency technology because IR has a limitation of medium. These techniques support 1 Mbps and 2 Mbps data rates. Later on 802.11 revised and implemented (orthogonal frequency-division multiplexing) modulation techniques in IEEE 802.11a.

4.1.1 THE INFRARED (IR)

IR transmission operate at wavelength near 850nm.The IR signal is produced either by semi-conductor laser diodes or LEDs with the former being preferable because their electrical to optical conversion behaviour is more liner[15]. The infrared technology is not successfully commercialized.

4.1.2 Frequency hopping spread spectrum (FHSS)

Frequency hopping spread spectrum (FHSS) is to divide the allocated frequency band into a number of channels. Each channel has an equal bandwidth and is determined by the target data bit rate and the modulation scheme used. A transmitter sends data from each channel for a fixed amount of time called the dwell time. There are two types of frequency hopping slow frequency hopping and fast frequency hopping. The main advantage of frequency hopping over DSSS is its flexibility to use and alternative channel within the allocation band [16].Typically there are 22 hop patterns and 79 no overlapping frequency channels with 1 MHz channel spacing.

150 mW

902 MHz Frequency 928 MHz

Figure 4.1 (a): Frequency hopping spread spectrum (FHSS) [29]

26  

Figure 4.1(b): Frequency hopping spread spectrum (FHSS) [29]

4.1.3. Direct Sequence Spread Spectrum (DSSS)

Direct Sequence Spread Spectrum (DSS) is modulation techniques in which a message signal is spread over a bandwidth that is typically much greater than that required for reliable communications. [17]. DSSS PHY is the part of PHY layer works on 2.4 GHz frequency band. Data transmission is run through the DSSS PMD sub layer. The DSSS PMD get binary bits information from the PLCP protocol data unit (PPDU) then change into RF signals for the wireless medium by the help of carrier modulation and DSSS techniques. The PLCP preamble and PLCP header send 1 Mbps with differential binary phase shift keying (DBPSK) and MPUD send at either 1Mbps or 2Mpbs both uses differential quadrature phase shift keying (DQPSK) modulation techniques [18]. DSSS techniques also use in cellular network (CDMA), Global Positioning System (GPS).

4.1.4 Orthogonal Frequency Division Multiplexing (OFDM)

OFDM is a multi-carrier modulation technique which is used to transmitted single data stream over a number of lower rate subcarrier either modulation or a multiplexing technique. IEEE 802.11’s standard adopted OFDM technology because of transmission high-rate wireless local area networks (WLANs).The main reasons to merged OFDM in IEEE 802.11 is to increase the robustness against frequency selective fading and narrow interference. [11]

There are some more features concerned with the OFDM technology are:

• High spectral efficiency • Great flexibility • Confirmation to available channel bandwidth

4.2 IEEE 802.11a PHY LAYER

IEEE 802.11a PHY uses an orthogonal frequency Division Multiplex(OFDM) radio which provide eight different PHY layer with data rate of 6,9,12,18,24,36,48 and 54 Mbits in the 5GHZ unlicensed National information structure(U-NII) band. The band divided into 52 subcarriers. [19] The Federal Communications Commission (FCC) allows all 3 bands for unlicensed transmission in the United States but in the Europe only the low and middle bands are free. IEEE 802.11a physical

27  

layer divides into two sub layers, Physical Medium Dependent (PMD) layer and Physical Layer Convergence Procedure (PLCP) layer. [27] IEEE 802.11a PHY is to transforms PSDU frames at several data rates up to 54 Mbps for Wireless LAN. The IEEE 802.11 PHY is as same as OFDM PHY specification of ETSI-HPPERLAN II.

4.3 OFDM PLCP Sublayer of IEEE 802.11a

IEEE 802.11a PLCP Sublayer includes its own PPDU frame standard. PPDU is a combination of OFDM preamble, signal and data. The PHY Sublayer Service Data Units (PSDU) of the 802.11a is transformed a PLCP Protocol Data Unit. The PLCP hold the interface with MAC layer it is not necessary which medium is used. The PLCP converts the data from MAC layer to PMD sub layer. The PPDU consists of several fields in protocol unit and OFDM frame forced through the Medium Access Control (MAC) Layer.

The IEEE 802.11a PPDU format is shown in figure 4.2 and it includes:

R A T E4 b i t s

R e s e r v e d1 b i t

L e n g th1 2 b i t s

P a r i ty1 b i t

T a i l6 b i t s

S e r v ic e1 6 b i t s

P S D UT a i l

6 b i t sP a d

P L C P P r e a m b le1 2 S y m b o ls

S ig n a l1 O F D M s y m b o l

D a taV a r ia b le n u m b e r o f O F D M s y m b o ls

P P D U

P L C P - H e a d e r

C o d e d - O F D M

B P S K R a t e = 1 /2

C o d e d - O F D M

R a te in d ic a te d b y s ig n a l s y m b o ls

Figure 4.2: OFDM PLCP Preamble, Header and PSDU [6]

PLCP Preamble –The PLCP preamble consists of 10 short OFDM symbols and two long symbols. The purpose of short OFDM symbols is to train the receiver to tune AGC (automatic gain control) and refine estimate of the carrier frequency as well as channel. The long OFDM symbols are used to fine-tune during data transmission. There are 12 subcarriers for short OFDM symbols and 53 for the long. The transmission of preamble time is 16μs.The coding rate of R = 1/2 using BPSK at a data rate of 6 Mbps. [20]

Rate-This field is used to encode the data rate. The 4 bit rate is used to encode the data rate. There are 8 possible available rates are: 6, 9, 12, 18,24,36,38 and 54 Mbps. Table 4.1 shows the bits used to encode each data rates.

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Date rate(Mbps)

Bits (Transmission Order)

6 Mbps 1101

9 Mbps 1111

12 Mbps 0101

18 Mbps 0111

24 Mbps 1001

36 Mbps 1011

48 Mbps 0001

54 Mbps 0011

Table 4.1: Rate bits [7]

Reserved- The reserved must be set to a logic zero and can be reserved for future use.

Length- A 12 bits field specify the number of octets in the PSDU enclose with the Mac frame. It is used to send least significant bit (LSB) to most significant bit (MSB).

Parity- Parity is base on values of the Rate, Reserved, and Length fields and contains a single-bit value that is used to provide even parity for error checking.

Tail- 6 bits is set to “0” for the tail signal.

Services: The final field is the 16 bit services field. The 0-6 bits are set to 0 to initialize the scramble. The remaining bits 7-15 reserved for future use.

4.4 IEEE 802.11g

The IEEE 802.11g for wireless LAN was formed in September 2000 which is now extends the data rate of the IEEE 802.11b to 54 Mbps from its current level of 11 Mbps. According to the Stuart Kerry, "By extending the IEEE 802.11b PHY to 54 Mbps, IEEE 802.11g will create data-rate parity at 2.4 GHz with IEEE standard 802.11a (TM), which allows for a 54 Mbps rate at 5 GHz," [13]

By using OFDM, IEEE 802.11g increase wireless LAN speed up to 54 Mbps. The IEEE 802.11g specification is also compatible with the widely deployed IEEE 802.11b standard. The parallel operation capability of 802.11g enables mixed network operation. Mixed operation also allows 802.11b devices to operate at 11Mbps on the same network while new 802.11g devices operate at 54Mbps. This compatibility provides consumers a clean path to upgraded performance when in a mixed network. The combination of higher performance and backward compatibility of 802.11g is

29  

similar in concept to the wildly successful 100-Mbps Fast Ethernet standard from the wired LAN world. [28]

Access to fixed-network LANs and internetwork infrastructures has been improved in 802.11g and it create higher performing ad-hoc networks but 802.11g is also limited to the same three non-overlapping channels as 802.11b.

4.5 Performance and Capacity

Due to the Hidden Node Problem, The 802.11g standard provides an option called CTS/RTS (Clear-To-Send/ Request-To-Send) to Self, which provides greater throughput when in mixed-cell mode. As we know that wavelength is inversely proportional to range, a signal transmitted in a lower frequency spectrum will carry further than a signal travel in a higher frequency band.

In addition, longer waveform tends to propagate better through solid mediums (like walls glass, trees, etc.) which will transmitted in lower in the frequency spectrum and 802.11g operates in the same 2.4 GHz portion of the radio frequency spectrum as 802.11b does. As the rule of thumb, range will decreases as the data rate increases. 802.11b uses DSSS to support data rates of 11, 5.5, 2 and 1 Mbps each, with correspondingly longer ranges as the data rates decrease and on the other side OFDM is used by 802.11g to support 54, 48,36,24,18,12,9 and 6 Mbps each.

According to the researchers statistics DSSS is not that much efficient than OFDM in the means of transmission because it support lower data rate than OFDM-based data rates. When comparison performance between both the latest technologies another factor which is to be considered is transmit power and receive sensitivity, because selection of transmission type of either DSSS or OFDM has an effect on the max power the transmitter can use as well as the capability of the receiver especially at higher data rate.[26]

EVM (Error Vector Magnitude) is a phenomenon when the higher power coming from the radio’s transmitter tends to desensitize which results counterintuitive effects. On the other hand increasing transmits power results to decrease the range of the device at higher data rate.

4.6 Deployment Considerations for IEEE 802.11g

As it discussed earlier 802.11g is considered as the superset of 802.11b because it provides all the backward compatibility with 802.11b with higher performance with OFDM transmission. There is another considerable factor which is important that 802.11g heavily relies on earlier 2.4 GHz technology, which provides significant cost reduction in engineering and economical scale which results in increasing in production of 802.11g products although the final cost is almost same for both products.

802.11a leverages 802.11g in the same way 802.11g leverages 802.11b technology. The production of 802.11g products is high although the final cost is almost same for both products. 802.11 radios has 3 major parts which are MAC, PHY and RF. MAC layer is common in all three 802.11a, 802.11b and 802.11g. OFDM and DSSS transmission types are in PHY layer and RF is the part of radio that sends and receives signals accordingly the specific frequency band. [26]

30  

CHAPTER 5: SIMULATION MODEL AND RESULTS

5.1 Methodology and Simulation Model Simulation is a powerful tool because it provides accurate result without implementation on

real world and tells us how the system will work. This simulation was implemented in Matlab 7.01. The performance of the system model tested through different modulation schemes such as

BPSK, QPSK, 16QAM and 64 QAM with an AWGN channel and OFDM modulator and demodulator are used in the MATLAB. Theoretically, IEEE 802.11a and IEEE 802.11g operates in same PHY layers specification as well as similar Bit Error Rate (BER) performance of the simulation over Additive White Gaussian Noise (AWGN). IEEE 802.11a/g PHY used OFDM modulation with the combination of different modulation schemes and convolution coding rates. There are eight operation modes which provide data rates between 6 Mbps and 54 Mbps.

The OFMD cyclic prefix and Symbol Interference (ISI) has been adopted for modulation techniques in this Matlab simulation. In other to investigate the performance of the OFDM based WLANs IEEE 802.11a/g standard. Table: 5.1 Show the IEEE 802.11a specifications OFDM modulation Rate dependent parameters. These parameters can also be used for IEEE 802.11g.

Data rate (Mbps)

Modulation

Coding rate (R)

Coded bits per subcarrier (NBPSC )

Coded bits per OFDM symbol (NCBPS )

Data bits per OFDM symbol

(NDBPS )

6 BPSK 1/2 1 48 24

9 BPSK 3/4 1 48 36

12 QPSK 1/2 2 96 48

18 QPSK 3/4 2 96 72

24 16 QAM 1/2 4 192 96

36 16 QAM 1/2 4 192 144

48 64 QAM 2/3 6 288 192

54 64 QAM 3/4 6 288 216 Table 5.1: Rate-dependent parameters of 802.11a/g [19]

31  

Table 5.2 describes the list of timing related parameters the IEEE 802.11a OFDM

Parameter

Value

NSD : Number of data subcarriers 48

NSP : Number of pilot subcarriers 4

NST : Number of subcarriers, total 52 (NSD + NSP )

ΔF : Subcarrier frequency spacing 0.3125 MHz (=20 MHz/64)

TFFT : IFFT/FFT period 3.2 µs (1/ΔF )

TPREAMBLE : PLCP preamble duration 16 µs (TSHORT + TLONG )

TSIGNAL : Duration of the SIGNAL BPSK-OFDM symbol 4.0 µs (TGI + TFFT )

TGI : GI duration 0.8 µs (TFFT /4)

TGI2 : Training symbol GI duration 1.6 µs (TFFT /2)

TSYM : Symbol interval 4 µs (TGI + TFFT )

TSHORT : Short training sequence duration 8 µs (10 × TFFT /4)

TLONG : Long training sequence duration 8 µs (TGI2 + 2 × TFFT ) Table 5.2: Timing-related parameters of 802.11a [19]

5.2 OFDM MODULATION TECHNIQUES Using IEEE 802.11a/g

OFDM is a frequency-division multiplexing (FDM) scheme utilized as a digital multi-carrier modulation method. The main feature of OFDM modulation in IEEE 802.11 standard is to provide modes with different code rates and modulation schemes due to good performance on highly dispersive channels which are selected through link adaptation [21]. There are different modulation techniques using IEEE 801.11a/g as follows:

• Binary Phase Shift Keying (BPSK) • Quadrature Phase Shift Keying (QPSK) • 16 Quadrature Amplitude Modulation (16QAM) • 64 Quadrature Amplitude Modulation (64QAM)

5.2.1 Binary Phase Shift Keying

The phase of the carrier is varied to represent binary ones and zeros which is used to transmit data via changing and modulating of carrier wave is called Phase Shift keying and if the phase shift uses two phases differing by 180 degree to represent binary digits, the modulation is called BPSK.  

32  

Figure 5.1 (b) shows the constellation of BPSK and I-axis and Q-axis is component as an orthogonal or in quadrature which is separated by 90 degrees. The principle equation of BPSK as following:

s t           5.1

cos 2                                 1cos 2                        0cos 2                                1cos 2                             0 

Where

A = constant = the carrier frequency

t = the bit duration

(a) (b)

Figure 5.1: Binary Shift Keying (a) Block Diagram (b) Constellation

33  

5.2.2 Quadrature Phase Shift Keying (QPSK)

QPSK is also known as quaternary PSK, 4-PSK or 4-QAM. Each symbol consists of two bits and signal transmits among the phases that are separated by 90 degrees but used only one bit per channel. The constellation contains four points but the decision make in two bits. The figure 5.2 (a) and (b) describes the mechanism for QPSK modulation techniques and constellation. The principle equation of QPSK as following:

 

s t   cos 2 3 /4cos 2 3 /4

      5.2 

   

cos 2 /4           11cos 2 3 /4         01

        00       10

   

   

 

(a) (b)

Figure 5.2: QPSK (a) Block Diagram (b) Constellation

34  

Figure 5.3: QPSK Constellation Scatter Plot

In the simulation constellation consists of 4 points but decision is to be taken in two bits. Real is I channel and Imaginary is Q channel. Input bits {0, 1} to be mapped into QPSK symbols and output complex values of QPSK symbols is X 0.7071 and Y 0.7071.

35  

5.2.3 16 Quadrature Amplitude Modulation

This is also called 16-state quadrature amplitude modulation which means four different phases and 4 different amplitudes are used for 16 symbols because 2 4 = 16. In this mechanism every symbol represents 4 bits.

Figure 5.4: 16 QAM Constellations

5.2.4 64 Quadrature Amplitude Modulation

64 QAM as same as 16-QAM except it is 64 possible signal combinations with each symbol represent six bits(26 =64). 64 QAM is a complex modulation technique but gives high efficiency.

Figure 5.5: 64 QAM Constellations

36  

5.3 Additive White Gaussian Noise

Additive white Gaussian noise (AWGN) is the commonly used to transmit signal while signals travel from the channel and simulate background noise of channel. The mathematical expression in received signal r(t) = s(t) + n(t) is shown in figure 5.1 that passed through the AWGN channel where s(t) is transmitted signal and n(t) is background noise.[22]

Figure 5.6: Received Signal through an AWGN channel

5.4 Bit Error Rate (BER)

IEEE 802.11 standard has ability to sense the bit error rate (BER) of its link and implemented modulation to data rate and exchange to FEC which is used to set the BER as low error rate for data applications.[23] BER measurement the number of bit error or destroy within a second during transmitting from source to destination.

The figure 5.3 is shown comparison between the simulated BPSK BER with OFDM 802.11a/g parameter model and theoretically. It is simulated BER performance of the system in AWGN and generated random signal whenever noise occurs then obtains values of BER. Mathematically BER can be defined as follows.

BER =    

       

There are some more factors that affect on BER. If the transmission speed and transmission medium are good in a particular time but Signal-to-Noise (SNR) is high then BER will be very low.

37  

5.5 Signal-to- Noise Ratio (SNR)

Signal to noise ratio (SNR) is an indicator commonly used to evaluate the quality of a communication link [24]. There are several techniques available to measure SNR such as OFDM and QPSK. The SNR mathematically can be expressed as fellows.

SNR=10 log10 (   

) dB [25]

38  

5.6 Simulations for IEEE 802.11a IEEE 802.11g Using OFDM

modulated through binary or quadrature phase shift keying (BPSK). The 16QAM, 64-QAM with a coding rate of 1/2, 2/3, or ¾ and 10000 n

comparison between computer system simulation BER and theoretical BER for serial and sim

nsform (FFT) size is equal to = 64

0MHz

us

PSK

Figure 5.7 Theoretical and Simulated curves of BER for BPSK (10000 sym ols)

In the simulation part there are 52 subcarriers which are

umbers of symbols is used.

All the simulation results aresystems. It has been proved through simulation results that theoretical BER

ulated BER under AWGN are good agreement with each other.

Parameters Used are:

• Fast Fourier Tra• Number of pilot subcarriers 4 • Number of data Subcarriers = 48 • Fast Fourier Transform (FFT) = 2• Spacing used for subcarriers = 312.5 kHz • Duration cyclic prefix is = 0.8 us • Duration data symbol is = 3.2 us • Total used symbol duration is = 4 • 10000 number of symbols • 64 constellation size for 64 QAM

QAM • 16 constellation size for 16

5.7 Simulation Bit Error Rate curve B

b

0 1 2 3 4 5 6 7 8 9 1010

-5

10-4

10-3

10-2

10-1

100

Bit to Noise ratio, dB

Bit

Erro

r Rat

e

Simulation BR curve BPSK using OFDM(IEEE 802.11a/g)

Theoretical BR (AWGN)BER-Simulation

39  

SNR  BER0  0.0077911  0.056682  0.03753  0.023044  0.012735  0.0058946  0.0024127  0.00081739  0.00001788  3.846e‐005

istical Data of Bit Error Rate curve BPSK (10000 symbols)

Figure 5.8 Theoretical and Simulated curves of BER for BPSK (1000 symbols

Table 5.3 Stat

0 1 2 3 4 5 6 7 8 9 1010-5

10-4

10-3

10-2

10-1

100

Bit to Noise ratio, dB

Bit

Erro

r Rat

e

Simulation BR curve BPSK using OFDM(IEEE 802.11a/g)

Theoretical BR (AWGN)BER-Simulation

)

SNR  BER0  0.080121  0.056122  0.022673  0.012174  0.0056355  0.0026926  0.00078857  0.00017319  3.846e‐005

Table 5.4 Statistical Data of Bit Error Rate curve BPSK (1000 symbols)

40  

5.8 Results

HZ to +10MHz and subcarriers ±26/64*20MHz are used. It means the signal energy is spread over a 20 MHz Bandwidth. BPSK modulation added AWGN

and Conclusions

In these scenario bandwidth from -10M

channel to correspond BER expressions of OFDM system. BPSK bit 0 represent -1 and bit 1 represent +1. In the figure 5.7 the result calculated almost 10000 symbols and figure 5.8 result calculated almost 1000 symbols to find average BER. The coding rate is   and can be increased through simulation code. In the code SNR define as:

SNR = BNRdB + 10*log10 (data_subc/FFT) + 10*log10 (fft/SD);

c= 52 FT = 64

duration is 80 samples) ix size = 16

of OFDM under an AWGN channel using QPSK modulation technique has been proved theoretically and simulated.

.9 Simulation Bit Error Rate curves for 16 QAM

Figure 5.9 Theoretical and Simulated curves of BER for 16 QAM

Where Data_subFSD= 80 (symbolCyclic pref

The above figures show the performance

5

0 5 10 1510-5

10-4

10-3

10-2

10-1

100

Eb/No, dB

Bit

Erro

r Rat

e

Simulation BR curve for 16-QAM modulation

Theoretical 16 QAM16 QAM (BER) Simulation

41  

SNR  BER0  0.14151  0.11922  0.097793  0.0078034  0.058625  0.041926  0.02787  0.016859  0.009210  0.00450511  0.00163512  0.000607513  0.00013514  1.75e‐005

Table 5.5 Statistical Data Bit Error Rate for 16 QAM

5.10 Simulation Bit Error Rate curves for 64 QAM

Figure 5.10 Theoretical and Simulated curves of BER for 64 QAM

0 5 10 15 20 25 3010-5

10-4

10-3

10-2

10-1

100

Es/No, dB

Bit

Erro

r Rat

e

Simulation BR curve for 64-QAM modulation

theoretical 64 QAM64 QAM Simulation

42  

SNR  BER0  0.8695  0.719810  0.424215  0.0903420  0.0009725  0.04192

Table 5.6 Statistical Data Bit Error Rate for 64 QAM

.11 Results and Conclusions

shows the simulation result of 16 QAM and 64 QAM constellations are distance between I and Q points if the point on constellation are much closer to each other th

5

Figure 5.9 and figure 5.10

e data error can be reduced as well as transmission easily influenced to noise. 64 QAM is much better than 16 QAM when BER decrease SNR will be increase because signal is stronger than noise. 64QAM modulation need higher bandwidth and gives an excellent data rates as compared to 16 QAM

43  

Chapter 6 Summary and Future work 6.1 Summary

The objective of this research is to examine the performance of the IEEE 802.11a and IEEE

802.11g WLAN comparing through OFDM modulation techniques. It is found that IEEE 802.11a/g

provides similar quality except IEEE 802.11g provides wider range but range is the controversial

topic in WLAN medium.

In the other hand IEEE 802.11a provides more channels in 5 GHz bands as well as have a

good enough signal qualities but there is range limitation factor. Range limitation in the enterprise and

public sectors can be adjusting through installations more APs.

The main disadvantage of the 802.11g is the frequency band is common and interference from

the other networking technology such as Bluetooth, 2.04 GHz cordless phone and IEEE 802.11a

avoid this interference because its operate in 5.GHz bands.

Consequently, all the simulation is a comparison between simulated BER for a computer system and theoretical BER for serial systems it has been proved through simulation results that theoretical BER and simulated BER under AWGN are good agreement with each other. It means that I and Q points on constellation are much closer to each other the data error can be reduced as well as transmission easily influenced to noise. 64 QAM modulations are much better than 16 QAM when BER decrease SNR will be increase because signal is stronger than noise. 64 QAM modulations need higher bandwidth and give an excellent data rates as compared to 16 QAM.

6.2 Future Work

Future research work will consider in IEEE 802.11 standard. The performance analysis of the IEEE 802.11g and IEEE 802.11n because high data rate is a main issue of Wireless Network and IEEE 802.11n uses Multiple-Input Multiple-Output (MIMO) and 40 MHz channel and latest version of MATLAB will be considered.

.

44  

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[5] White paper 802.11g-WP104-R www.54g.org visited 10 November 2009

[6] Bob O'Hara, Al Petrick, “IEEE 802.11 handbook: a designer's companion” page # 5-6,

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45  

[20] Tung T. Ly, “Shipboard Wireless Network Applications”, June 2001

[21] Mohinder Jankiraman, “Space-time codes and MIMO systems”, pages #217-220, ISBN 1-58053-865-7

[22] Ahmer Ali Bajwa, Junaid Anwar Awan “Performance study of IEEE 802.16d (Fixed WiMAX) Physical layer with Adaptive Antenna System”,October 2008

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[24] Franc¸ois-Xavier.S, Abdeldjalil A¨ıssa-El-Bey, S´ebastien. H “Non Data-Aided SNR Estimation of OFDM Signals”, November 2009

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[26] “Capacity Coverage, and Development Consideration for IEEE 802.11g”, 2005 Cisco Systems, http://www.cisco.com visited on 5th December 2009

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BIBLIOGRAPHY

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