Ijecet 06 10_006

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International Journal of Electronics and Communication Engineering & Technology
(IJECET)
Volume 6, Issue 10, Oct 2015, pp. 53-65, Article ID: IJECET_06_10_006
Available online at
http://www.iaeme.com/IJECETissues.asp?JType=IJECET&VType=6&IType=10
ISSN Print: 0976-6464 and ISSN Online: 0976-6472
© IAEME Publication
A COMPARATIVE SURVEY ON PAPR
REDUCTION TECHNIQUES FOR OFDM
PERFORMANCE IMPROVEMENT
Rimpi Datta
Dept. of Electronics and Communication, Narula Institute of Technology, India
Anirban Bhar
Dept. of Information Technology, Narula Institute of Technology, India
Arpita Barman Santra
Dept. of Electronics and Communication, Narula Institute of Technology, India
Sohan Ghorai
Dept. of Electronics and Communication, Narula Institute of Technology, India
ABSTRACT
The Orthogonal Frequency Division Multiplexing is one of the modulation
techniques widely used in the broadband wireless technology. One of the main
problems of this technology is the high peak-to-average power ratio of
transmission signal due to the superposition of many subcarriers. This paper
presents a comparative studies of peak-to-average power ratio reduction
technique, which compares among the selective mapping method, clipping
method and Tone reservation techniques for PAPR reduction. The paper
presents the performance of these different PAPR reduction techniques and
compares it with unreduced PAPR.
Key words: PAPR, OFDM, Selective Mapping Algorithm, Clipping, Tone
Reservation.
Cite this Article: Rimpi Datta, Anirban Bhar, Arpita Barman Santra and
Sohan Ghorai. A Comparative Survey on PAPR Reduction Techniques for
OFDM Performance Improvement, International Journal of Electronics and
Communication Engineering & Technology, 6(10), 2015, pp. 53-65.
http://www.iaeme.com/IJECET/issues.asp?JType=IJECET&VType=6&IType=
10
1. INTRODUCTION
Orthogonal Frequency Division Multiplexing (OFDM) scheme is a popular standard
for next generation mobile radio communication system [2]. In OFDM system, serial

2. Rimpi Datta, Anirban Bhar, Arpita Barman Santra and Sohan Ghorai
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data stream is multiplexed into a large number of orthogonal sub-channels producing
a bandwidth efficient signal spectrum. As it is robust against multipath fading, the
orthogonal frequency division multiplexing system can transmit high-speed data using
a number of orthogonal sub-carriers [4]. Various studies show that when OFDM sub-
carriers are added with the same phase [4], it produces a high peak to average power
ratio (PAPR). PAPR is the ratio between the maximum power of a sample OFDM
signal and the average power of that OFDM symbol. High PAPR introduces signal
distortion in the nonlinear region of power amplifier and the signal distortion
introduces the degradation of bit error rate [2]. Major study has been carried out on
effect of PAPR in OFDM and study shows that PAPR depends on the SNR for
Channel with signal and noise. The effect has been tested with introducing a Gaussian
noise in OFDM system.
1.1. OFDM System
OFDM has been developed as the modulation method in the new wireless
technologies. It mitigates the serious problem of multipath propagation, which causes
massive data errors, and loss of signal in the microwave and UHF spectrum. OFDM is
a broadband multicarrier modulation technique that gives very good performance and
it is very beneficial over single-carrier modulation methods as it fits better with
today’s high-speed data requirements and operation in the UHF and microwave
spectrum [1]. The main Features of OFDM systems are processing on the source data,
the symbols are modulated onto orthogonal sub-carriers, orthogonally is maintained
during channel transmission, Synchronization, Demodulation of the received signal
by using FFT, Channel equalization, Decoding and de-interleaving. In the OFDM
system, Inverse Fast Fourier Transform/Fast Fourier Transform (IFFT /FFT)
algorithms are used in the modulation and demodulation of the signal [6, 3]. The
length of the IFFT/FFT vector determines the resistance of the system to errors caused
by the multipath channel [6]. OFDM is generated by firstly choosing the spectrum
required, based on the input data and modulation scheme used. Each carrier to be
produced is assigned some data to transmit. The required amplitude and phase of the
carrier is then calculated based on the 3 modulation scheme (typically differential
BPSK, QPSK, or QAM) [6, 1]. Then, the IFFT converts this spectrum into a time
domain signal. The FFT transforms a cyclic time domain signal into its equivalent
frequency spectrum. Finding the equivalent waveform, generated by a sum of
orthogonal sinusoidal components, does this. The amplitude and phase of the
sinusoidal components represent the frequency spectrum of the time domain signal.
OFDM signal has high peak-to-average-power ratio (PAPR) value.
Figure 1 OFDM Spectrum

3. A Comparative Survey on PAPR Reduction Techniques For OFDM Performance
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1.2. Peak to Average Power Ratio (PAPR)
Let us consider a data block of length N as a vector
where N denotes the number of sub-carriers. The duration of a symbol in X is T.
Each symbol in X modulates one of a set of subcarriers where
{ }. The modulation scheme taken either quadrature amplitude
modulation (QAM) or quadrature phase shift keying (QPSK) by definition. The
subcarriers are orthogonal to each other, that is, , where and NT
is the duration of OFDM [8] data block X. The complex envelop of the OFDM signal
is expressed as
, (1)
PAPR is defined as the ratio of the maximum divided by the average power of the
signal [4]. Now the PAPR of the signal expressed in (6) can be defined as
(2)
The effects of PAPR need to be studied for a continuous time OFDM signals, as
the cost and power dissipation of the analog components dominated by this factor.
Reducing the value of PAPR dramatically increases the performance of OFDM
system and reduces the cost of system. However, most existing PAPR tuning methods
can only be implemented on discrete time OFDM signals [9]. For better calculation of
true PAPR, the OFDM signal samples are obtained by oversampling equation (6) by a
factor of L to approximate the PAPR of the true OFDM signals better [9]. The L-
times oversampled time domain samples can be obtained by an LN-point inverse
discrete fourier transform (IDFT) of the data block with zero padding [8]. It
was shown in [7] that is sufficient to get . Therefore,
I have considered for my numerical calculation in this paper [9].
One of the major drawbacks of the OFDM system. Drawback is high PAPR
(PeakTo Average Power ratio). PAPR means randomly sinusoidal leads occurred
during transmission of the OFDM signal. So in this chapter we discuss basics of
PAPR, why it is created & what the proposed solution are for reduce it. So as per the
introduction of PAPR we can judge that to reduce the PAPR is most important point
in the OFDM system. Because of when we are talking about the high speed data
communication in real life like video calling, high speed internet access, and also
main point is that high speed data access up to 2mbps while moving on the vehicle at
100km/h, digital video broadcasting (DVB), Microwave terrestrial television, Digital
audio broadcasting (DAB), 4G system, hyper LAN. So this most type of
communication systems required high data rate. But problem occurs like PAPR in
OFDM system prevent these types of facilities in the real life. So to reduce it is most
important. Various studies show that when OFDM sub-carriers are added with the
same phase [2], it produces a high peak to average power ratio (PAPR). PAPR is the
ratio between the maximum power of a sample OFDM signal and the average power
of that OFDM symbol. High PAPR introduces signal distortion in the nonlinear
region of power amplifier and the signal distortion introduces the breakdown of bit
error rate [4]. Extensive study has been carried out on effect of PAPR in OFDM
system and it shows that PAPR depends on the SNR for Channel with signal and
noise. The effects of PAPR need to be studied for a continuous time OFDM signals,
as the cost and power dissipation of the analog components dominated by this factor.
Reducing the value of PAPR dramatically increases the performance of OFDM

4. Rimpi Datta, Anirban Bhar, Arpita Barman Santra and Sohan Ghorai
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system and reduces the cost of system. So we want to reduce the PAPR in the OFDM
system by using different reduction technique algorithms for PAPR in the OFDM
systems and make a comparative analysis of these techniques and want to get OFDM
signal with improved higher bit error rate. MATLAB based simulation results are
included.
1.3. PAPR Reduction Techniques
Researchers have been proposed several PAPR reduction Techniques. These
techniques can be divided into two groups. There are signal scrambling techniques
and signal distortion techniques. Block coding techniques selected mapping (SLM),
partial transmit sequence (PTS) etc. are signal scrambling techniques. Signal
distortion techniques are peak windowing, envelope scaling, peak reduction carrier
and clipping and filtering. In this paper we discuss about the techniques signal
scrambling techniques and signal distortion techniques.
2. LITERATURE REVIEW
2.1. Selective Mapping
The SLM technique is developed from the idea of symbol scrambling. In this
technique, a set of candidate signals are generated to represent the same information,
the signal with lowest PAPR is selected and transmitted. The information about the
selection of these candidate signals need to be explicitly transmitted along with the
selected signal as side information. Selected mapping needs to transmit the
information to the receiver, about the selected signal, as side in formation. If there is
an error in the received side information, then it is very difficult for the receiver to
recover the information from the transmitted selected signal. That is the reason why a
strong protection against transmission errors is needed regarding side information.
Once the receiver has these side information then the decoding process is very simple.
SLM can be employed for larger number of sub carriers with moderate complexity.
The technique uses codes only for PAPR reduction and does not include error
correction capabilities of codes. The complexity is increased due to the multiple
numbers of IFFT operations. The need for transfer of side information to the receiver
without any margin for transmission errors is very crucial under the fading channels.
Under such noisy channels, the side information is distorted to result in BER
degradation in the OFDM systems. Hence, the side information affected the system
performance and its bandwidth efficiency.
Figure 2 Transmitter Block Diagram with SLM technique
The transmitter side [10] of an OFDM system with SLM technique is shown in
figure 1. In the SLM technique, a set of U different, distinct sequences-

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(0,2π), n=0,1,………N-1, u=1,2,……….U must be defined. At first, the input
information is divided into OFDM data block X, which consists of N symbols, by the
serial-to parallel (S/P) conversion and then data block X is multiplied carrier wise
with each one of the U different phase sequences P(u), resulting in a set of U different
OFDM data blocks
n=0,1,……..N-1, u=1,2……..U Then all U alternative data blocks are transformed
into time domain to get transmit OFDM symbol-
The sequence with minimum PAPR is selected for transmission. The receiver
block diagram is shown in fig.3.
Figure 3 Receiver Block Diagram
To recover the data sequence X at the receiver, SLM needs to transmit the
information on the selected phase sequence as side information , which results in
some loss of transmission efficiency. If each phase sequence is –P(u)
n generated as the
cyclically shifted version of the previoussequence, the information needed to transmit
will be less to reconstruct the data. The BER performance will not be affected due to
the presence of this technique because the original information is transformed into a
different sequenceand we can rebuild the information from the selected phase
sequence itself.
2.2. Clipping
The simplest approach for reducing the PAPR of OFDM signals is clipping [11,12].
But this technique comes under the distortion based category. In this technique, the
high amplitude peaks of the signal are clipped to a predetermined threshold value
which limits the peak envelope of the input signal. Since the clipping is done on the
actual information itself, there is a possibility to loose the data. So there will be a
trade-off between the clipping and the BER performance. Let x[n] denote the pass
band signal and x˛[n] denote the clipped version of x[n],which can be expressed as
(3)

6. Rimpi Datta, Anirban Bhar, Arpita Barman Santra and Sohan Ghorai
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Where A is the pre-specified clipping level. This technique has some drawbacks
which causes in band signal distortion, resulting in Bit Error Rate performance
degradation. It also causes out-of-band radiation, which imposes out-of-band
interference signals to adjacent channels. This out-of-band radiation can be reduced
by filtering. This filtering of the clipped signal leads to the peakregrowth. That means
the signal after filtering operation may exceed the clipping level specified for the
clipping operation.
2.3. Tone Reservation
Tone Reservation (TR) is one of the well-known methods for PAPR reduction of
Orthogonal Frequency Division Multiplexing (OFDM) systems. In this method some
sub carriers are reserved for PAPR reduction and the symbols in these sub carriers are
selected such that the PAPR of the OFDM frame is minimized. This technique
contains some set of reservation of tones. By using this technique reserved tones can
be used to minimize the PAPR. This method is used for multicarrier transmission and
also shows the reserving tones to reduce the PAPR. This technique is depend on
amount of complexity. When there is number of tones is small reduction in PAPR
may represent non negligible samples of available bandwidth. Advantage of this tone
reservation is very positive that no process is needed at receiver end. And also do not
need to transmit the side information along with the transmitted signal. in this data
block is added to the time domain signal to reduce the peak leads.
3. SIMULATION RESULTS
Simulation has been performed using MATLAB and compared with various
algorithm.
3.1. Selective mapping algorithm
Simulation has been performed using MATLAB In selective mapping algorithm as
reduction technique for PAPR in OFDM systems, here we consider 16 subcarriers.
Here we use phase rotation by multiplying all the subcarriers in the sum by different
phases to create a new data vector, not only that but also as we don't know the
optimum phases to give the best PAPR we now create more than one vector and then
select the optimum value. Now the selector should test the PAPR for the data vectors
and select the one with the least PAPR to use in transmission. Here we can see the
Performance analysis using selective mapping.
Table 1Selective PAPR Comparison Chart for Different PAPR Selection
Selective PAPR PAPR Values
PAPR 29.2900
PAPR1 22.0610
PAPR2 31.2678
PAPR3 31.3918

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Figure 4 'PAPR against different phase shifts'
3.2. Clipping and Filtering as a PAPR reduction techniques
when OFDM signal pass through power amplifier system the signal distort. The
effects of the nonlinear distortions introduced by a High Power Amplifier (HPA) on
the system performance are evaluated in terms of the Bit Error Rate (BER). So a need
of technique which reduces PAPR and amplitude clipping is one of the techniques
used to reduce PAPR .In amplitude clipping, a threshold value of the amplitude set
and any subcarrier having the amplitude more than that value is clipped or that
subcarrier is filtered to bring out a lower PAPR values. By using this techniques we
can investigates the effects of high power amplifier and the channel noise on the
OFDM signals and then introduces clipping as a PAPR reduction method to reduce
the PAPR effect. Firstly select parameters- QPSK signal constellation having 128 data
points, size of each OFDM block-8 and assigns the length of cyclic prefix. Then
Generate 1 x 128 vector of random data points, Perform QPSK modulation then
perform IFFT for each block. Make the serial stream a matrix where each column
represents a pre-OFDM block). Firstly we have to find out the number of columns
that will exist after reshaping then secondly Create empty matrix to put the IFFT's
data next Operate column wise .After that Compute and append Cyclic Prefix.
Append the CP to the existing block to create the actual OFDM block then Convert to
serial stream for transmission. Now we get actual OFDM signal. Now by using
clipping techniques reduce the PAPR. To show the effect of the PAPR simply we add
random complex noise when the power exceeds the avg. value, otherwise it add
nothing.

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Figure 5.1 x 128 vector of random data points
Figure 6 Transmitted data and phase representation
Figure 7 OFDM signal representation

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Figure 8 Clipped Signal Representation
Figure 9 OFDM Signal after High Power Amplifier (HPA)
Figure 10 clipped Signal after High Power Amplifier (HPA)

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Figure 11 Received data phase representation
Figure 12 Received Data clipped representation
3.3. Tone reservation as PAPR techniques
There we use the 12 information subcarriers (BPSK modulated). Now consider the 4
reduction carriers we will map different combinations from them by changing the
reduction subcarrier case (positive or negative). Let us dedicate r1,r2,r3 and r4 as peak
reduction carriers and transmit on x1:x12 so when x1:x12 summation creates a peak, a
combination from r1,r2,r3 and r4 creates an anti-peak but not the exact anti-peak or
the output would be a flat signal from which data can be retrieved. Then the total sum
should have less peaks, but we have noted that even if it has less peaks but sometimes
the value of these peaks are twice the original peaks. So that we must take both
criteria into consideration the number of peaks and its values. Now calculate the
PAPR.

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Table 2 Tone Reservation Performance
Tone Reservation PAPR PAPR Values
PAPR 26.6393
PAPR1 29.2900
PAPR2 25.8413
PAPR3 25.4080
PAPR4 21.6240
PAPR5 21.7348
PAPR6 25.4585
PAPR7 24.3934
PAPR8 23.6455
PAPR9 24.5452
PAPR10 22.8342
PAPR11 26.3100
PAPR12 25.7989
PAPR13 26.0764
PAPR14 23.2783
PAPR15 22.1395
PAPR16 23.4401
Figure 13 Representation of sum with no peak reduction carriers (PRC)

12. Rimpi Datta, Anirban Bhar, Arpita Barman Santra and Sohan Ghorai
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Figure 14 Sums with no peak Figure 15 Sum with no
peak Reduction carriers (PRC) Reduction carriers (PRC)
Figure 16 Sum with no Peak reduction Carriers (PRC)
4. CONCLUSION
The evaluation of PAPR performance is done by CCDF parameters. In this literature
several PAPR reduction technique has been discussed. I found that tone reservation is
a good technique for PAPR reduction but it needs side information to receiver to
recover original data block that increases algorithmic complexity. Also the above.

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Also they are less immune to dynamic noise. In future a pre-coder will be combined
with a neuro-fuzzy algorithm to reduce time complexity and increase performance.
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