implementation of turbo coded ofdm for papr reduction...
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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.
ISSN: 2278 – 1323
International Journal of Advanced Research in Computer Engineering & Technology (IJARCET)
Volume 2, Issue 10, October 2013
2688
All Rights Reserved © 2013 IJARCET
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
ISSN: 2278 – 1323
International Journal of Advanced Research in Computer Engineering & Technology (IJARCET)
Volume 2, Issue 10, October 2013
2689
All Rights Reserved © 2013 IJARCET
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.
ISSN: 2278 – 1323
International Journal of Advanced Research in Computer Engineering & Technology (IJARCET)
Volume 2, Issue 10, October 2013
2690
All Rights Reserved © 2013 IJARCET
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
ISSN: 2278 – 1323
International Journal of Advanced Research in Computer Engineering & Technology (IJARCET)
Volume 2, Issue 10, October 2013
2691
All Rights Reserved © 2013 IJARCET
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
ISSN: 2278 – 1323
International Journal of Advanced Research in Computer Engineering & Technology (IJARCET)
Volume 2, Issue 10, October 2013
2692
All Rights Reserved © 2013 IJARCET
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.
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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.