Implementation Of Turbo Coded OFDM For PAPR Reduction using Modified Selective Mapping Technique

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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 selectingmapping, the input sequence

properly using a Hamming code and second method by turbo

code usingconvolution 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.

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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

[image:2.612.27.294.70.241.2]

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

[image:2.612.314.540.515.705.2]

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because block coder needs data in parallel

[image:3.612.49.282.69.291.2]

The input serial is divided into 4 parallel stream for the IFFT operation.

Fig 6.4 Subcarriers Amplitudes Graph for OFDM without noise

[image:3.612.50.290.375.522.2]

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

[image:3.612.312.556.422.642.2]

Received bit stream

Figure shows the four parallel bit steams received from for sub-carrier is converted into signal bit stream, it was

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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

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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

dB

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

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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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Sons nc.2001

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17 Rudra Pratap. “MATLAB PROGRAMMING",2 nd 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.