wimax with different modulation techniques and code rates

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IJITT,Vol. 3, Issue 1, Feb. 2011ISSN:0976-5972

International Journal of Information and Telecommunication Technologywww.sriste.com

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WiMax with Different Modulation Techniques and Code RatesManinder Singh

1, Prof. R.S.Uppal

2and Jaspal Singh

1

1Department of ECE, R.I.E.I.T. Railmajra2Department of ECE, BBSBEC, Fatehgarh [email protected],

[email protected][email protected]

A R T I C L E I N F O : A B S T R A C T

Article history:

Received : September 26, 2010Revised :October 8, 2010

Available online : February 11, 2011

With the advent of WIMAX we can visualize the world of internet reaching very far off

places. WIMAX provides wireless connectivity in the last mile thereby providing highspeed voice, video and data speeds to the customer. IEEE specifies the different

modulation techniques which should be used in WIMAX namely BPSK, QPSK, 4-QAM,

16 QAM and 64 QAM. The aim of this paper is to analyse the Bit error rate Vs SNR

and Block error rate Vs SNR curves using QPSK, 16 QAM and 64 QAM in an AWGN

channel. Further WIMAX system uses Reed Solomon (RS) encoder and in this paper

the above parameters are analysed for different code rates. From the analysis it has

been concluded that greater the number of symbols transmitted per block, the

transmission quality decreases .It rises from the very fact that at the time of

transmitting if a value has greater no of options for mapping then at the same time the

chances of making a wrong value in the process also increases . 2010 Sriste. All rights reserved.

Keywords:

IEEE 802.16e (WiMax)

Modulation

Code Rate

Bit Error Rate

Block Error Rate

I. INTRODUCTIONSome fifteen years back very few people realized that

internet will become The Backbone of the society. It gotjustified now when we see that Internet has made our lives soeasy. It revolutionalised our lives to such an extent that things

which we were able to do in days are now possible at a clickof a button. But the Expansion of internet to far off placeswas always a problem. Conventional high-speed Broadbandsolutions such as Digital Subscriber Line (DSL) are based onwired access technology and this type of service is verydifficult to deploy in remote rural areas. Furthermore they donot provide the user mobility feature. Mobile Broadband

Wireless Access (BWA) offers a flexible and cost effectivesolution to these problems

The IEEE WiMax -802.16 is a solution to all thesesproblems. It forms the basis of Broadband WirelessMetropolitan Area Network (WMANs) and can provide highthroughput over long distances and can support differentqualities of service. It incorporates the wireless connectivityand mobility at the last mile. It provides a wireless backhaul

network that enables high speed Internet access to residential,small and medium business customers, as well as Internet

access for WiFi hot spots and cellular base stations. Itsupports both point-to-multipoint (P2MP) and multipoint-to-multipoint (mesh) modes. In this way, WiMax will connect

rural areas in developing countries as well as underservedmetropolitan areas. It can even be used to deliver backhaul

for carrier structures, enterprise campus, and Wi-Fi hot-spots.WiMax offers a good solution for these challenges because itprovides a cost-effective, rapidly deployable solution

In addition to this WiMax will provide a stiff competitionto 3G (Third Generation) cellular systems as high speedmobile data achieved through WiMax is a way greater thanthat of 3G technology.

Mobile WiMax supports full mobility, nomadic and fixedsystems. It addresses the following major issues therebyreducing the digital divide:-

1) It is cost effective2) It offers high data rates in the order of five Mbps.3) It supported the backwards compatibility thereby

providing fixed, nomadic and mobile applications.

4) Very easy to deploy5) Architecture is quite flexible and robust.6) It supports Interoperability with other networks.


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It is aimed at being the first truly a global wirelessbroadband network.

II SIMULATION MODEL

Figure (1) corresponds to the physical layer ofWiMax/IEEE 802.16e wireless MAN OFDM air interface.The system is modelled or defined as per the IEEE 802.16e

standard and is there after analysed The definition of themodel means to construct the model from basic elementsconstructed previously, as, mathematical operators, signals,connectors, visualizers and others. The analysis of the modelmeans to realize the simulation, linearization and todetermine the point of balance of a model as was defined.

Fig. 1 IEEE 802.16e physical layer implementation

Figure shows simulation model of the physical layer of thenetwork WiMax that is used for different modulations

techniques namely QPSK, 16- QAM and 64-QAM. Thismodel consists of two parts: the transmission and the

reception. A random data (test data as provided by IEEE

802.16e standard) is modulated and is transmitted byemploying Orthogonal Frequency Division Multiplexing(OFDM) technique. The reverse processes goes at thereceiver end and same data is retrieved at the output. Thedifferent errors in transmitted data and received data were

compared.The type of modulation and codification that were used in

the simulation of the physical layer of WiMax are as under:-

Modulation

Un-codedBlockSize

(Bytes)

CodedBlockSize(Bytes)

OverallCodingRate

RS (ReadSolomon)Code

CC(ConvolutionCoding

) CodeRate

QPSK 24 48 (32,24,4) 2/3

QPSK 36 48 (40,36,2) 5/6

16QAM

72 96 (80,72,4) 5/6

64QAM

108 144 (120,108,6)

5/6

The input data as per the IEEE 802.16e standard is a 35byte data ([45 29 C4 79 AD 0F 55 28 87 AD B5 76 1A 9C

80 50 45 1B 9F D9 2A 88 95 EB AE B5 2E 03 4F 09 14 6958 0A 5D].This data when fed to Integer to bit converter ismapped into 8 bits corresponding to each whole number.Randomness of data is maintained when it is given to PNsequence generator. Further zeros are attached to it and theirnumber depends upon the type of modulation used. The totalnumber of bits should be:-

QPSK =36 bytes * 8 bits = 28816QAM = 72 bytes * 8 bits = 57664QAM= 108 bytes * 8 bits = 864

RS Encoder, encodes the message in the input vector usingan (N,K) Reed-Solomon encoder with the narrow-sensegenerator polynomial. The input must be a frame-based

column vector with an integer multiple of K elements. Eachgroup of K input elements represents one message word to beencoded. Each symbol must have ceil (log2 (N+1)) bits. ReedSolomon code should works as per the standard which

specifies following for a code rate of 5/6:-

QPSK = (40, 36.2) [240:243,204:239]16QAM = (80,72,4) [240:247,168:239]

64QAM = (120,108,6) [240:251,132:239]

The block data is then fed to Convolution Encoder whichconvolutionally encode the binary data. It uses the oly2trellisfunction to create a trellis using the constraint length, code

generator (octal) and feedback connection (octal). Togenerate two codes, output denotes the function poly2trellisfor which:-

First output: X: 171OCT

Second Output: Y: 133OCT

The data goes through the Puncture code checkbox which

punctures the encoded data for all other operation modes.Thefollowing data shows the code vector obtaining rate:

Coding Rate

Rate 2/3 5/6 7/8

O/PX

1 10 101 10101 1000101

O/PY

1 11 110 11010 1111010

XY X1Y1

X1Y1Y2

X1Y1Y

2X3X1Y1Y2X3Y4X5

X1Y1Y2X3Y

4X5Y6X7

Then the bits are fed to General Block Interleaver whichallows placing of transmitted bits in a vector to be acceptedby the modulator. The Modulator Block modulates the data.Before feeding to a modulator the bits should be convertedinto Integers. The Bit to Integer Converter works as

Tpye RS Code No of bits per integer

QPSK (40,36,2) 2

16 QAM (80,72,4) 4


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64 QAM (120,108,6) 6

Further The output of modulator should be normalized into

order to send it over the channel after employing OFDMmodulation technique. The gain of the normaliser Block asper the standard is:

Type Gain

QPSK 1/216 QAM 1/1064 QAM 1/42

After modulating the signal data is send over a AWGNchannel. The SNR values of AWGN channel is varied so asto find out the best modulation technique. In this paper thevalues are varied from 2 dB to 36 dB.

III ERROR RATE CALCULATIONS FOR CODE RATE

Bit Error Rate (BER) is the ratio of number of bits lost tothe number of bits transmitted. It defines the quality oftransmission. Another parameter directly related to BER isthe Block Error Rate (BLER) which is given as:-BLER = 1 - (1 - BER) NWhere N is the size of the word.

Table obtained from the simulation process for code rate with is as:

Modulation: - QPSK, Uncoded Block Size: - 36Coded Block Size: - 48, RS Code Rate: (40,36,2), CC CodeRate :- 5/6

TABLE I

BER and BLER FOR DIFFERENT SNR VALUES FOR QPSK

SNR Time BER BLERNo ofErrors

2 350000 0.5000457 1.0000000 49004479

6 350000 0.4999221 1.0000000 48992366

10 350000 0.4773375 1.0000000 46779075

14 350000 0.1112854 1.0000000 10905969

18 350000 0.00093325 0.2357815 91459

20 350000 0.0000099 3.96E-05 970

24 350000 0 0 0

30 350000 0 0 0

36 350000 0 0 0

Modulation: - 16 QAM, Uncoded Block Size: - 72Coded Block Size: - 96, RS Code Rate: (80,72,4), CC CodeRate :- 5/6, Overall Coding Rate :-

TABLE 2

BER and BLER FOR DIFFERENT SNR VALUES FOR 16 QAM

SNR Time BER BLER No of Errors

2 350000 0.500531 1.0000000 49010000

6 350000 0.4999982 1.0000000 48999824

10 350000 0.4998886 1.0000000 48989083

14 350000 0.4960679 1.0000000 48614654

18 350000 0.384681 1.0000000 37698738

20 350000 0.1628115 1.0000000 15955527

24 350000 0.00356286 0.8720188 349160

30 350000 0.00000004 0.0000230 4

36 350000 0 0 0

Modulation: - 64 QAM , Uncoded Block Size :- 108Coded Block Size: - 144 , RS Code Rate : (120,108,6), CCCode Rate :- 5/6, Overall Coding Rate :-

TABLE 3

BER and BLER FOR DIFFERENT SNR VALUES FOR 64 QAM


2 350000 0.50009 1.0000000 49010000

6 350000 0.499959 1.0000000 48995982

10 350000 0.49975 1.0000000 48975500

14 350000 0.497349 1.0000000 4874019218 350000 0.4959 1.0000000 48598200

20 350000 0.487764 1.0000000 47800852

24 350000 0.340215 1.0000000 33341021

30 350000 0.001479 0.7216559 144953

36 350000 0 0 0

IV SIMULATION RESULTS

The above readings have been plotted and graphs werefurther analysed in order to derive the results. As shown onthe next page Fig 2 specifies the bit error rate versus thesignal to noise ratio for three type of modulations with a coderate of . Fig 3 specifies the block error rate versus the signal

to noise ratio for QPSK,16 QAM and 64 QAM modulationtechniques.

FIG.2Bit Error Rate Vs Signal to Noise Graph for code rate


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FIG.3Block Error Rate Vs Signal to Noise Graph for code rate

V ERROR RATE CALCULATIONS FOR CODE RATE

Modulation: - QPSK, Uncoded Block Size: - 24

Coded Block Size: - 48, RS Code Rate: (32,24,4)CC Code Rate: - 2/3, Overall Coding Rate: -

TABLE 3

BER and BLER FOR DIFFERENT SNR VALUES FOR QPSK


2 350000 0.4992 1.0000000 48921600

6 350000 0.4466836 1.0000000 43774993

10 350000 0.1698244 1.0000000 16642791

14 350000 0.0001175 0.0332758 11515

18 350000 0.00000001 0.0000029 1

20 350000 0 0 0

24 350000 0 0 030 350000 0 0 0

36 350000 0 0 0

VI SIMULATION RESULTS

FIG.4Bit Error Rate Vs Signal to Noise Graph for code rate

FIG.5Block Error Rate Vs Signal to Noise Graph for code rate

VII CONCLUSIONSA performance analysis of a WiMax (Worldwide

Interoperability for Microwave Access) system adopting

concatenated Reed-Solomon and Convolutional encodingwith block interleaver has been carried out. The BER curveswere used to compare the performance of differentmodulation techniques and coding scheme. In the graphsobtained one can see that the greater the number of symbolstransmitted per block, the transmission quality decreases.This is because that at the time of mapping while

transmitting, if each value has a greater number of options ofmapping then at the same time the chances of making awrong value in the process, also increases .

It also shows that for QPSK with code rate (CR) of and, transmission is best for . But this further implies that forevery two bits transmitted one is useful and the other is

redundant and in some applications it might not be asoptimal. Hence rate represents a better option to takeadvantage of the channel because it has only one bitredundant for every 3 useful bits.

REFERENCES[1] Mai Tran, George Zaggoulos, Andrew Nix and Angela Doufexi,

Mobile WiMAX: Performance Analysis and Comparison with

Experimental Results 2nd IEEE International Symposium on Wireless

Vehicular Communications 21 - 22 September 2008Telus Convention

CenterCalgary, Canada

[2] M. Nadeem Khan, S. Ghauri, The WiMAX 802.16e Physical LayerModel,IET International Conference on Volume, 2008, pp.117 120.

[3] Kaveh Pahlavan and Prashant Krishnamurthy, Principles of WirelessNetworks, Prentice-Hall, Inc., 2006.

[4] Yang Xiao,"WiMAX/Mobile MobileFi: advanced Research andTechnology",Auerbach Publications,2008

[5] 802.16 IEEE Standard for Local and metropolitan area networks. Part16: Air Interface for Fixed Broadband Wireless IEEE Computer

Society and the IEEE Microwave Theory and Techniques Society. 8

April, 2002

[6] WiMAX Forum, Fixed, Nomadic, Portable and Mobile Applicationsfor 802.16-2004 and 802.16e WiMAX Networks, November, 2005.

[7] ETSI TS 101 475, Broadband Radio Access Networks (BRAN);HIPERLAN Type 2; Physical (PHY) layer, April 2000

[8] Mohammad Azizul Hasan , Performance Evaluation of WiMAX/IEEE802.16 OFDM Physical Layer by Master's thesis, 2007.

wimax with different modulation techniques and code rates

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