implementation of turbo coded ofdm for papr reduction...

ISSN: 2278 – 1323

International Journal of Advanced Research in Computer Engineering & Technology (IJARCET)

Volume 2, Issue 10, October 2013

2687

All Rights Reserved © 2013 IJARCET

Implementation Of Turbo Coded OFDM For

PAPR Reduction using Modified Selective Mapping

Technique

RAVI MOHAN SUMIT SHARMA MOHAMMAD SUHEL

Abstract— Multi-carrier modulation is an attractive

technique for fourth generation wireless

communication.Orthogonal Frequency Division Multiplexing

(OFDM) is an efficient method of data transmission for high

speed communication systems. However, the main drawback of

OFDM system is that, it exhibits high Peak to Average Power

Ratio (PAPR) of the transmitted signals. Many techniques have

been proposed to mitigate the PAPR problem. Except for the

signal distortion techniques such as clipping, peak windowing

and companding and so on. The redundancy based PAPR

reduction techniques include selective mapping, partial transmit

sequence, tone reservation, tone injection and coding,etc

information The undesired effects occurring to the distortion

techniques can be alleviated with the penalty of the reduced

transmission rates due to introduction of redundancy. In a turbo

coded orthogonal frequency-division multiplexing (TCOFDM)

system, low peak-to-average power ratio (PAPR) can be achieved

by selective-mapping (SLM).OFDM consist of large number of

independent subcarriers, as a result of which the amplitude of

such a signal can have high peak values. The .Selected Mapping

(SLM) and turbo coding is one of the promising PAPR reduction

techniques for OFDM.In a turbo coded orthogonal frequency-

division multiplexing (TCOFDM) system, low peak-to-average

power ratio (PAPR) can be achieved by selective-mapping

(SLM). In this thesis, the issue of PAPR in OFDM is discussed.

Two new methods are proposed to reduce the PAPR .first

method is carried out by selecting mapping, the input sequence

properly using a Hamming code and second method by turbo

code using convolution encoder. These two methods provide less

PAPR and also reduce BER.

Keywords—PAPR,BER,OFDM,SLM,TCOFDM

INTRODUCTION

Much of the research focuses on the high efficient

multicarrier transmission scheme based on "orthogonal

frequency" carriers. In 1971 Weinstein and Ebert applied the

discrete Fourier transform (DFT) to parallel data transmission systems as part of the modulation and demodulation process.

The spectrum of the individual data of the sub channel.The

OFDM signal, multiplexed in the individual spectra with a

frequency spacing equal to the transmission speed of each

subcarrier. The center frequency of each subcarrier, there is

no crosstalk from other channels. Therefore, if we use DFT at

the receiver and calculate correlation values with the center of

frequency of each subcarrier we recover the transmitted data

with no crosstalk. In addition, using the DFT-based

multicarrier technique, frequency-division multiplex is

achieved not by band-pass filtering but by baseband

processing.[9] Moreover, to eliminate the banks of subcarrier

oscillators and coherent demodulators required by frequency-

division multiplex, completely digital implementations could

be built around special-purpose hardware performing the fast

Fourier transform (FFT), which is an efficient implementation

of the DFT. Recent advances in very-large-scale integration

(VLSI) technology make high-speed, large-size FFT chips commercially affordable. Using this method, both transmitter

and receiver are implemented using efficient FFT techniques

that reduce the number of operations from N2 in DFT down to

N log N. In the 1980s, OFDM was studied for high-speed

modems, digital mobile communications, and high-density

recording. One of the systems realized the OFDM techniques

for multiplexed QAM using DFT and by using pilot tone,

stabilizing carrier and clock frequency control and

implementing trellis coding are also implemented. Moreover,

various-speed modems were developed for telephone

networks. [11]

ALGORITHM

Step 1: Generate input data stream.

Step 2: Parallel to serial conversion.

Step 3: Map the input signal to available substitute.

Step 4: Take the IFFT of selected samples.

Step 5: Calculate the PAPR of the selected samples.

Step6: Check the calculated PAPR with reference.

Step 7: If the PAPR > Reference, go to step 3 ,else go to step

8.

Step 8: Transmit the data to receiver side.

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5.4 BLOCK DIAGRAMS

Fig 5.2 Block Diagram Of Transmitter Side[10]

Data stream generated basically mimic’s the data generator

which supplies the randomly generated bit stream for

simulation s/p block used as serial to parallel convertor

because block coder needs data in parallel. Hamming code is

a linear block code. Here we are using hamming Code as a

replacement matrix which is used to replace the consecutive

ones and zeros with non consecutive ones and zeros sequence.

turbo coder here we are using turbo encoder .encoder is based on the convolution Technique.

The basic idea of turbo codes is to use two convolutional

codes in parallel with some kind of interleaving in between

Convolutional codes can be used to encode a continuous

stream of data, but in this case we assume that data is

configured in finite blocks - corresponding to the interleaver

size. The frames can be terminated - i.e. the encoders are

forced to a known state after the information block. The

termination tail is then appended to the encoded information

and used in the decoder. IFFT is used for modulation. Then it

goes to transmitter.

fig 5.3 Block Diagram Of Receiver Side

FFT of the signal is done after it is made to pass

through a serial to parallel converter. A demodulator is used

to get back the original signal. The bit error rate and the signal

to noise ratio is calculated by taking into consideration the un-

modulated signal data and the data at the receiving end.

Demodulation is the technique by which the original data (or a

part of it) is recovered from the modulated signal which is received at the receiver end.[14]

RESULT & OUTPUT SCREENS-

6.1.1BER Performance-

Figure 6.1 shows the simulated results of proposed

algorithm in terms of BER ,for different values of AWGN

channels where the AWGN is varying from 0 to 20 dB ,the

total simulation is performed for 10000 bits with signal

modulated by BPSK & the code rate of,1/2 the FFT length of

Subcarrier are 4. (the value offer SNR of 1dB drops to zero

for 10000 bits, Hence the curve ends at this point.)

INPUT DATA SCREEN-

Source bit stream generated using normal distribution.

Modified

Selective

Mapping

Turbo

Coder IFFT Transmitter

Serial to

parallel

Data

Stream

FFT Modified

Selective

Mapping

Turbo

Decoder

Parallel to

Serial Output

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Fig6.3 s/p block used as serial to parallel convertor

because block coder needs data in parallel

The input serial is divided into 4 parallel stream for the

IFFT operation.

Fig 6.4 Subcarriers Amplitudes Graph for OFDM

without noise

In this figure we are using IFFT for modulation.Frequency

Domain to Time Domain Conversion (sub-carrier generation)

of the input stream by taking IFFT of the parallel 4 bit stream.

am by taking IFFT of the parallel 4 bit stream.

Fig 4.6 Demodulation by FFT

Received bit stream

Figure shows the four parallel bit steams received from for

sub-carrier is converted into signal bit stream, it was

originally.

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Received Sub-carrier Power

In this figure the sum of power of all subcarriers for each

parallel bit sample upto 100 such measures are shown which

reprenst the power variation at transmitting side.

Simulated BER for OFDM with different codes under

AWGN Channel

In this Graph we are compare the Proposed and previous

technique for BER .the comparison shows the improvement in

BER of proposed technique is 0.25 for 0dB and 00.398 for 1

dB .

Comparision of PAPR for different code

We can easily shows the comaprison of PAPR for different

technique.here we are using total five techniuqe one simple

Ofdm technique ,second technique is OFDM using

Hammming(7,4),third is OFDM with Hamming (11,15) and

fourth with OFDM with turbo codes and is proposed technique.we can easily shows proposed technique

provied better result

Received Subcarrier Power for different codes

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6.2 COMPARISION TABLES

1) PAPR, Comparison of Different Methods in

OFDM: In Table no., we can shown PAPR is 1.756

Modified Technique.

CONCLUSION-

OFDM is a very attractive technique for multicarrier

transmission and has become one of the standard choices for

high speed data transmission over a communication channel.

It has various advantages; but also has one major drawback: it

has a very high PAPR. In this project, the different properties of an OFDM System are analyzed and the advantages and

disadvantages of this system are understood.

OFDM consist of large number of independent

subcarriers, as a result of which the amplitude of such a signal

can have high peak values. The .Selected Mapping (SLM) and

turbo coding is one of the promising PAPR reduction

techniques for OFDM. In a turbo coded orthogonal frequency-

division multiplexing (TCOFDM) system, low peak-to-

average power ratio (PAPR) can be achieved by selective-

mapping (SLM).In this thesis, the issue of PAPR in OFDM is

discussed. Two new methods are proposed to reduce the

PAPR .first method is carried out by selecting mapping,the

S.No Methods 0

dB

1 dB 2 3 4 5

1. Simple

OFDM

0.25 0.19953 0.12589 0.05012 0.001 0.00079

2. OFDM

with

Hamming

(7,4)

0.25 0.15849 0.03162 0 0 0

3. OFDM

with

Hamming

(15,11)

0.25 0.12589 0 0 0 0

4. OFDM

with

Turbo

codes

0.25 0.19953 0 0 0 0

5. OFDM

with

Modified

Selective

Mapping

and

Turbo

codes

0.25 0.00398 0 0 0 0

S.No.

Methods

Calculated

PAPR

1. Simple OFDM 2.004

2. OFDM with Hamming( 7,4) 2.0237

3. OFDM with Hamming (15,11) 2.0287

4. OFDM with Turbo Codes 2.0156

5. OFDM with modified Selective

Mapping and Turbo code

1.7564

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input sequence properly using a Hamming code and second method by turbo code using convolution encoder. These two

methods provide less PAPR and also reduce BER.

The simulation results shows that the proposed technique

reduces the PAPR is reduced to 1.75 when compare with

turbo coding which provide a PAPR of 2.016. Hence it can be

said that proposed method provide better result. It also shows

that BER of proposed is reduced to 0.003 from 0.19, hence it

can be concluded that the technique is an efficient way of

reducing the PAPR with enhancing the error correcting

properties of turbo codes.

REFERENCES-

1 Ms. V. B. Malode1, PAPR Reduction Using Modified Selective Mapping

Technique Int. j Advance Networking and

Applications 626 Volume:02, Issue: 02, Pages:626-630 (2010)

2 Yung-Chih Tsai, Student Member, IEEE, Shang-Kang Deng, Student

Member, IEEE, Kuan-Cheng Chen,and Mao-Chao Lin, Member, IEEE,

Turbo Coded OFDM for Reducing PAPR and Error Rates, IEEE

TRANSACTIONS ON WIRELESS COMMUNICATIONS, vol. 7, no. 1,

January 2008

3 Sang-Woo Kim, Jin_Kwan Kim and Heung-Gyoon Ryu., A computational

complexity Reduction scheme using Walsh Hadamrd sequence in SLM

method., IEE 2006, pp. 762-766

4 Yang Jie, Chen Lei, Liu Quan and Chan De, .A Modified selected mapping

technique to reduce the Peak to Average Power Ratio of OFDM signal.,

IEEE transaction on consumer Electronics, Vol53, No.3,pp.846-851, August

2007

5 Dae-Woon Lim, Seok-Joong Heo," A New PTS OFDM Scheme with Low

Complexity for PAPR Reduction," IEEE transactions on broadcasting, vol.

52, no. 1, pp. 166-169, march 2006.

6 A. D. S. Jayalath and C. Tellambura, “SLM and PTS Peak-Power

Reduction of OFDM Signals Without Side Information,” IEEE Trans.

Wireless Commun., vol. 4, no. 5, pp. 2006–2013, Sept.2005.

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8 Abdulla A. Adouda, .PAPR Reduction of OFDM signal using Turbo

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10 Carson, N. and Gulliver, A., "Peak-to-average power ratio reduction of

OFDM using repeat-accumulate codes and selective mapping" Proc. ISIT

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Sons nc.2001

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reduce the peak-to-average power ratio of an OFDM signal,” Proc. IEEE

GLOBECOM, Nov. 2000, vol. 1, pp. 82–86

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Communications Letters,VOL.5, No.6, pp.239-241,JUNE 2001

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and Wireless. Norwell, MA: Kluwer Academic Publishers, 2000

15 Takeshita, O.Y., Costello, D.J., Jr., “New deterministic interleaver designs

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pp. 1988–2006, September 2000

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edition.

AUTHOR’S PROFILE

RAVIMOHAN has completed his B.E. in

Electronics & Telecommunication Engineering

form GEC Jabalpur and received his Master’s

degree in Communication System from GEC

Jabalpur. Currently he is pursuing PHD and

working as H.O.D. in PG courses at Shri Ram

Institute of Technology Jabalpur M.P.

SUMIT SHARMA has received B.E. in

Electronics & Telecommunication Engineering

and M.Tech in image processing and is currently

working as H.O.D. in EC dept. at Shri Ram

Institute of Technology, Jabalpur M.P.

MOHAMMAD SUHEL has completed B.E.

in 2010 from Guru Ramdas khalsa Institute

of Sciencee and Technology, Jabalpur and at

present he is pursuing M.E. in Electronics and

Communication from Shri Ram Institute of

Technology , Jabalpur M.P.

implementation of turbo coded ofdm for papr reduction...

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