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International Journal of Emerging Technology and Advanced Engineering

Website: www.ijetae.com (ISSN 2250-2459, Volume 2, Issue 8, August 2012)

437

Capacity Enhancement of WiMAX System Using Adaptive

Modulation and Code Rate

Varsha Birla1, Prof. Rupesh Dubey2

ME Scholar, Specialization in Electronics and Communication, IESIPS Academy, Indore (M.P.) India

2

Head & Associate Professor (Dept. of Electronics and Communication Engg.) IESIPS Academy, Indore (M.P.) India

Abstract - This paper presents capacity enhancement of WiMAX system using adaptive modulation and code rate in Matlab. This paper focusing on the physical layer design that is modulation (BPSK, QPSK, 8QAM, 16QAM, 32QAM,64QAM are used in this work) and convolution codes(CC) with ½, ⅔ codes. Here various used modulation types will be implemented in a single Matlab function that can be called with the appropriate coefficient. This work examines the benefits and performance enhancement made possible by of using adaptive modulation with convolution code ½, ¾ code rate based on simulation results of bit error rate(BER) Vs SNR and channel capacity Vs SNR under the AWGN channel. Simulation results proved that the adaptive system performance with convolution coding is better than other modulation alone. Simulation result also show the flexibility of the adaptive system to operate with different desired BER.

Index Terms – Adaptive modulation, AWGN, BER, Convolution coding (CC), SNR, WiMAX.

I. INTRODUCTION

Future wireless networks such as 4G system will support high data rate and multimedia services including facsimile, video teleconferencing, file transfer by consuming less bandwidth such as high-speed Internet accesses [1].The IEEE WiMAX/802.16 is a promising technology for broadband wireless metropolitan areas networks (WMANs) as it can provide high throughput over long distances and can support different qualities of services [2].

The fundamental limitations of wireless communication system are limited channel bandwidth, time varying channel fading make it a difficult problem to provide a high QoS. The traditional wireless communication systems are designed to provide good quality of services at the worst channel conditions. As the result inefficient utilization of the full channel capacity [3]. One of the efficient techniques to overcome to this problem is known as adaptive modulation and coding (AMC).

The idea behind to adaptive modulation is to dynamically adapt and adjust the transmission parameters such as modulation and coding scheme based on the channel quality information notice by the receiver and fed back to the transmitter so as to achieve the highest spectral efficiency at all times[4].These techniques provide many parameters including transmitted power level, symbol rate, coding scheme, constellation size, or any combination of these parameters can be vary according to the time varying nature of wireless channel[5].

II. SYSTEM DESCRIPTION

In our system we investigated the behavior of adaptive modulation technique of WiMAX system. Adaptive modulation is effectively increasing the channel capacity of time varying wireless channel while maintain the desired bit error rate. In adaptive modulation technique modulation scheme and convolution code rate are varied according to the variation in the communication channel. The transmitter can choice the appropriate modulation scheme and code rate is depend upon the SNR (signal to noise ratio) threshold such that it guarantees a BER (bit error rate) below the desired BER [6].The SNR thresholds are obtained from the BER Vs SNR characteristics of a modulation schemes. The probability of BER for different modulation scheme in the AWGN channel are given by [7].

…… (1)

…… (2)

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International Journal of Emerging Technology and Advanced Engineering

Website: www.ijetae.com (ISSN 2250-2459, Volume 2, Issue 8, August 2012)

438

Where Q = complementary error function, γb = Signal to

noise ratio, Ma = is order of modulation.

The Capacity for different modulation scheme in the AWGN channel are given by [4].

C = R (1-BER) log2M bps/Hz …. (4)

Where C = Channel capacity, R = code rate

BER = Bit error rate, M = no. of points in the constellation

In order to decide the proper level from this plot, we have to decide our desired BER are 10-2, 10-3, 10-4 and calculate the SNR threshold in each desired BER perform following steps:

1. SNR range is split into K+1 region where K is no. of modulation and coding scheme here K=12.

2. Assign a modulation coding scheme to operate within a particular region can be described as :

M1 if 0 ≤ SNR ≤ α1

M2 if α1 < SNR ≤ α2

Mmod = M3 if α2 < SNR ≤ α3

:

MK if αK-1< SNR ≤ ∞ …. (5)

Where Mmod, mod=1, 2, 3… K is modulation coding schemes.

III. System Architecture

A. WiMAX system architecture

[image:2.612.331.556.468.726.2]

Figure 1. Shows the block diagram of Physical layer of WiMAX system [8] [9].

Figure 1. Physical layer of WiMAX System

A short description of the physical layer of WiMAX system is listed below:

1. Generate the information bits randomly.

2. Encode the information bits using convolutional encoder with specified generator matrix.

3. Encoded information bits are then punctured to create the variable coding rates to reduced amount of data to be transmitted.

4. Encoded information bits are then interleaved to arrange data in a non-contiguous way to increase performance. 5. Use BPSK, QPSK, 8QAM, 16QAM, 32QAM, 64QAM modulation to convert the binary bits, 0 and 1, into complex signals.

6. Performed serial to parallel conversion. 7. Use IFFT to generate OFDM signals. 8. Performed cyclic prefix insertion. 9. Performed serial to parallel conversion.

10. The signals are transmitted over an AWGN channel . 11. At the receiver side, perform reverse operations to decode the received sequences of information bits.

11. Count the number of specious bits by comparing the decoded bit sequences with original one.

12. Calculate the Bit Error Probability (BER) and Capacity as a function of against different values of signal to noise ratio (SNR) and plot it accordingly.

[image:2.612.51.289.540.702.2]

The OFDM parameters used in WiMAX system are listed in Table I.

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International Journal of Emerging Technology and Advanced Engineering

Website: www.ijetae.com (ISSN 2250-2459, Volume 2, Issue 8, August 2012)

439 B. Adaptive Modulation System Architecture:

[image:3.612.52.286.218.383.2]

Figure 2. Shows the block diagram of Adaptive Modulation System.

Figure 2.-Adaptive Modulation System

The main parts of system are:-

1) DATA IN: Here is where the information bits are randomly produced.

2) Adaptive Modulation Switch: This is the logic that decides which modulation scheme to apply the bits generated from DATA IN. For do this work it requires information from the channel measures block. In can also send the adaptive modulation information to the receiver.

3) Transmitter: Transmitter is responsible for transmitting the data over a AWGN Channel. Transmitter can adopt different types of modulation scheme is depend upon the output of the adaptive modulation switching block.

4) Channel: AWGN channel is applied to the transmitted signal.

5) Receiver: Receiver is responsible for data reception and demodulation of the received data.

6) Channel Measures: Channel measures can determine the quality of the channel and information is then sent back to the adaptive modulation switch for adaptation decisions.

7) Data Out: Here the BER and capacity are calculated when data is received and demodulated.

IV. SIMULATION RESULTS

In this section the performance of Adaptive modulation BER and capacity results are presented using fixed WiMAX simulator in the AWGN channel. The used OFDM parameters are listed in Table I. Simulation result based on Adaptive modulation technique. In adaptive modulation technique modulation scheme and convolution code rate are varied according to the variation in the communication channel. The transmitter can choice the appropriate modulation scheme and code rate is depend upon the SNR (signal to noise ratio) threshold . Table II. shown the switching threshold levels of SNR for BER 10-2, 10-3, 10-4.

Table II. Switching thresholds levels

[image:3.612.325.563.347.634.2]
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International Journal of Emerging Technology and Advanced Engineering

Website: www.ijetae.com (ISSN 2250-2459, Volume 2, Issue 8, August 2012)

[image:4.612.56.283.136.348.2]

440

Figure 3. BER performance of different modulation schemes (BPSK, QPSK, 8QAM, 16QAM, 32QAM, 64QAM) with code rate ½ , ¾

[image:4.612.328.561.208.443.2]

Figure 4. Shows the capacity variation with SNR for different modulation schemes (BPSK, QPSK, 8QAM, 16QAM, 32QAM, 64QAM) with code rate ½ , ¾ in the AWGN channel evaluated by plotting the Capacity Vs SNR characteristics.

Figure 4. Capacity variation with SNR for different modulation schemes (BPSK, QPSK, 8QAM, 16QAM, 32QAM, 64QAM ) with

code rate ½ , ¾

Figure 5, 6 and 7 display the performance of BER versus SNR for Adaptive modulation system at desired BER 10-2, 10-3, 10-4 respectively. These results show the effectiveness of Adaptive modulation to keep a BER lower than the desired BER .

[image:4.612.328.559.208.678.2]

Figure 5.BER performance of Adaptive modulation at desired BER 10-2

[image:4.612.61.276.458.654.2]
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International Journal of Emerging Technology and Advanced Engineering

Website: www.ijetae.com (ISSN 2250-2459, Volume 2, Issue 8, August 2012)

[image:5.612.325.560.136.331.2]

441

Figure 7.BER performance of Adaptive modulation at desired BER 10-4

Figure 8, 9 and 10 display the performance of capacity versus SNR for Adaptive modulation system at desired BER 10-2,10-3, 10-4 respectively. These results show the variation of capacity of Adaptive modulation for different values of desired BER (10-2, 10-3, 10-4).

Figure 8.Capacity of Adaptive modulation at desired BER 10-2

[image:5.612.61.278.155.391.2]

Figure 9.Capacity of Adaptive modulation at desired BER 10-3

Figure 10.Capacity of Adaptive modulation at desired BER 10-3

V. CONCLUSION

[image:5.612.326.560.371.567.2] [image:5.612.54.288.494.677.2]
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International Journal of Emerging Technology and Advanced Engineering

Website: www.ijetae.com (ISSN 2250-2459, Volume 2, Issue 8, August 2012)

442

At the higher SNR value the 64-QAM is preferred because at the higher SNR it give the higher capacity value but at the lower SNR value it have high BER. At further increment the SNR value is utilized to improve the capacity by changing the code rate.

REFERENCES

[1] Chengzhi Li Hao Che Sanqi Li “QUALITY OF SERVICE AWARE ADAPTIVE MODULATION AND CODING FOR NAKAGAMI FADING CHANNELS” Department of Computer Science and Engineering Department of Electrical and Computer Engineering University of Texas at Arlington University of Texas at Austin Arlington, TX 76019, USA Austin, TX 78712, USA.

[2] M.A. Mohamed 1 , F.W. Zaki1, R.H. Mosbeh 2,“Simulation of WiMAX Physical Layer: IEEE 802.16e” 1

Faculty of Engineering-Mansoura University-Egypt , 2 New Damietta Higher Institute of Engineering

and Technology- Egypt.

[3] Dr. H. T. Ziboon & Zeinah Tariq Naif “Design and Implementation of Adaptive Modulation Modem Based on Software Defined Radio(SDR) for WiMAX System”

[4] Hadj Zerrouki

1

, Mohamed Feham

2

“High Throughput of WiMAX MIMO-OFDM Including Adaptive Modulation and Coding”Laboratoire de Systèmes de Technologies de l'Information et de Communication (STIC) University Abou Baker Belkaid, Tlemcen, Algeria.

[5] Amalia Roca “Implementation of a WiMAX simulator in Simulink”.

[6] Raymond Chan “CHANNEL PREDICTION FOR ADAPTIVE MODULATION IN WIRELESS COMMUNICATIONS” Master of Science thesis In Electrical Engineering R. Michael Buehrer, ChairBrian WoernerTim Pratt July 16, 2003.

[7] Hrudananda Pradhan “BLOCK TURBO CODE AND ITS APPLICATION TO OFDM FOR WIRELESS LOCAL AREA NETWORK" Master of Technology In Electronic systems and Communication.

[8] Sami H. O. Salih, Mamoun M. A. Suliman “Implementation of Adaptive Modulation and Coding Technique using”.

[9] M. K. GUPTA1, VISHWAS SHARMA2 “TO IMPROVE BIT ERROR RATE OF TURBO CODED OFDM TRANSMISSION OVER NOISY CHANNEL”.1Department of Electronic

Figure

Figure 1.  Physical layer of WiMAX System
Figure 2.-Adaptive Modulation System
Figure  3. BER performance of different modulation schemes (BPSK,  QPSK, 8QAM, 16QAM, 32QAM, 64QAM) with code rate ½ , ¾
Figure 7.BER performance of Adaptive modulation at desired BER  10-4

References

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