PAPR Reduction in OFDM using New Hybrid Techniques

International Journal of Trend in Scientific Research and Development (IJTSRD)
Volume 3 Issue 5, August 2019 Available Online: www.ijtsrd.com e-ISSN: 2456 – 6470
@ IJTSRD | Unique Paper ID – IJTSRD27820 | Volume – 3 | Issue – 5 | July - August 2019 Page 1703
PAPR Reduction in OFDM using New Hybrid Techniques
Vikas kumar1, Preeti Sondhi2
1,2M.Tech Scholar, Universal Institute of Engineering and Technology, Lalru, Punjab, India
How to cite this paper: Vikas kumar |
Preeti Sondhi "PAPR Reduction in OFDM
using New Hybrid Techniques" Published
in International
Journal of Trend in
Scientific Research
and Development
(ijtsrd), ISSN: 2456-
6470, Volume-3 |
Issue-5, August
2019, pp.1703-
1707,
https://doi.org/10.31142/ijtsrd27820
Copyright © 2019 by author(s) and
International Journal ofTrend inScientific
Research and Development Journal. This
is an Open Access article distributed
under the terms of
the Creative
Commons Attribution
License (CC BY 4.0)
(http://creativecommons.org/licenses/by
/4.0)
ABSTRACT
With the advancement in age and its growing demands, there has been fast
production in the field of communication system. Signals, which were sent at
the beginning in the analog form, are being sent more and more in the digital
form now in these days. For improved transmission, even singlecarrier waves
are being recouped by multi carriers’ waves. Multi carrier systems like CDMA
and OFDM are now a days being implementedcommonly. IntheOFDMsystem,
orthogonally placed subcarriers areused tosend thedata fromthetransmitter
end to the receiver end. Presence of guard band in this communicationsystem
deals with the ISI issues and noise is mitigated by larger number of sub
carriers. But the large PAPR (Peak to Average Power Ratio) of these signals
have some unsuitable effects on the communication system. In this research
work we have focused on the OFDM System and have implemented various
techniques to reduce the PAPR in the OFDM system so that this system can be
used more commonly and energetically.
KEYWORDS: PAPR, BER, OFDM, PAPR reduction techniques
1. INTRODUCTION
With the ever-growing demand of this generation, need for high speed
communication has become an utmost priority. Various multicarrier
modulation techniques have evolved in order to meet these demands, few
notable among them being Code Division Multiple Access (CDMA) and
Orthogonal Frequency Division Multiplexing (OFDM).
Orthogonal Frequency Division Multiplexing is a frequency–
division multiplexing (FDM) scheme utilized as a digital
multi – carrier modulationmethod.Alargenumberofclosely
spaced orthogonal sub – carriers is used to carry data. The
data is divided into several parallel streams of channels,one
for each sub – carriers. Each sub – carrier is modulated with
a conventional modulation scheme (such as QPSK) at a low
symbol rate, maintaining total data rates similar to the
conventional single carrier modulation schemes inthesame
bandwidth. Orthogonal Frequency Division Multiplexing
(OFDM) is a Multi-Carrier Modulation technique in
which a single high rate data-stream is dividedintomultiple
low rate data-streams and is modulated using sub-carriers
which are orthogonal to each other. OFDM is a “Multi-
Carrier Transmission Scheme.” ODFM is a good solution
for high speed digital communications. In this the data to
be transmitted is spreaded over a large number of
orthogonal carriers, each being modulated at a low rate.The
carriers can be made orthogonal by appropriately
choosing the frequency spacing between them. Orthogonal
frequency division multiplexing (OFDM) is a widely used
modulation and multiplexing technology, whichhas become
the basis of many telecommunications fields. Therefore,
OFDM is an advanced modulation technique which is
suitable for high-speed data transmission due to its
advantages in dealing with the multipath propagation
problem, high data rate and bandwidth efficiency. OFDM
have several attractive features which make it more
advantageous for high speed data transmission over other
data transmission techniques. These features include
 High Spectral Efficiency
 Robustness to channel fading
 Flexibility
 Easy equalization
But in spite of these benefits there are some
disadvantages in using OFDM:
 OFDM signal exhibits very high Peak to Average Power
Ratio (PAPR)
 Very sensitive to frequency errors (Tx. & Rx. offset)
 Inter carrier Interference (ICI) between the subcarriers
OFDM have got certain disadvantages also. One of the major
disadvantages of OFDM is high PAPR associated with the
transmitted signal. Large PAPR leads to both in-band
distortion and out of band radiation. It also increases the
complexity of the analog-to-digital and digital-to analog
converter and reduces the efficiencyoftheRadio-Frequency
(RF) power amplifier used. Therefore, it is useful to reduce
the PAPR of the OFDM system. In this paper we are studying
different techniques to reduce PAPR in OFDM system.
Fig1. Simple block diagram of OFDM system
IJTSRD27820

International Journal of Trend in Scientific Research and Development (IJTSRD) @ www.ijtsrd.com eISSN: 2456-6470
2. PAPR
The PAPR is the relation between the maximum power of a
sample in a given OFDM transmit symbol divided by
the average power of that OFDM symbol. PAPR occurs
when in a multi-carrier system, the different sub-carriers
are out of phase with each other. At each instant they
are different with respect to each other at different
phase values. When all the points achieve the
maximum value simultaneously; this will cause the output
envelope to suddenly shoot up which causes a 'peak' in the
output envelope. Due to presence of large number of
independently modulated sub-carriers in an OFDM system,
the peak value of the system can be very high as
compared to the average of the whole system. This ratio of
the peak to average power value is termed as Peak-to-
Average Power Ratio. An OFDM signal consists of a
number of independently modulated sub-carriers which
can give a large PAPR when added up coherently. When
N signals are added with the same phase they produce a
peak power that is N times the average power of the
signal. So OFDM signal has a very large PAPR, which is very
sensitive to non-linearity of the high power amplifier. In
OFDM, a block of N symbols{X , k = 0,1,....,N -1} k , is
formed with each symbol modulating one of a set of
subcarriers, {f , k = 0,1,.....,N -1} k . The N subcarriers are
chosen to be orthogonal, that is, f k f k = D , where Df =1 NT
and T is the original time period. The resulting signal is
given as:
PAPR is defined as:
where E[.] denotes the expectation operator.
2.1 Effect of PAPR
There are some obstacles in using OFDM in
transmission system in contrast to its advantages:
A. A major obstacle is that the OFDM signal exhibits a
very high Peak to Average Power Ratio (PAPR).
B. Therefore, RF power amplifiers should be operated
in a very large linear region. Otherwise, the signal
peaks get into non-linear region of the power
amplifier causing signal distortion. This signal
distortion introduces inter-modulation among the
subcarriers and out of band radiation. Thus, the power
amplifiers should be operated with large power
back-offs. On the other hand, this leads to very
inefficient amplification and expensive transmitters.
Thus, it is highly desirable to reduce the PAPR
3. PAPR REDUCTION TECHNIQUES
3.1 Signal Distortion
A. Clipping & Filtering:
A threshold value of the amplitude is set in this process and
any sub-carrier having amplitude more than that value is
clipped or that sub-carrier is filtered to bring out a lower
PAPR value.
B. Peak Windowing:
Peak windowing reduces PAPRs at the cost of increasing the
BER and out-of-band radiation. In peak windowing method
we multiply large signal peak with a specific window, for
example; Gaussian shaped window, cosine, Kaiser and
Hamming window.
A. 3.2 Signal Scrambling Techniques
B. 3.2 Signal Scrambling Techniques
3.2 Signal Scrambling Techniques
I. Selected Mapping
In this a set of different data blocks representing the
information same as the original data blocks are selected.
Selection of data blocks with low PAPR value makes it
suitable for transmission.
II. Partial Transmit Sequence
Transmitting only part of data of varying sub-carrier which
covers all the information to be sent in the signal as a whole
is called Partial Transmit Sequence Technique.
III. Interleaving
The notion that highly correlated data structures have large
PAPR can be reduced, if long correlation broken down. The
basic idea in adaptive interleaving is to set up an initial
terminating threshold. PAPR value goes belowthethreshold
rather than seeking each interleaved sequences.
IV. Tone Reservation (TR)
The main idea of this method is to keep a small set of tones
for PAPR reduction. This can be originated as a convex
problem and this problem can be solved accurately.. Tone
reservation method is based on adding a data blockand time
domain signal. A data block is dependent timedomainsignal
to the original multicarrier signal to minimize the highpeak.
V. Tone Injection (TI)
It is based on additive method for PAPR reduction. Using an
additive method achieves PAPR reduction of multicarrier
signal without any data rate loss. It uses a set of equivalent
constellation points for an original
3.3 Coding
A. Block Coding
The fundamental idea is that of all probable message
symbols, only those which have law peak power will be
chosen by coding as valid code words for transmission.
B. Pre-coding
In pre-coding method, modulated data is multiplied with
shaping matrix before the formation of OFDM symbol. This
type of technique utilizes the positive feature of the

frequency selective multipath channel of OFDM system. In
this first the input data is modulated in baseband using
modulation scheme like M-PSK, M-QAM etc. The baseband-
modulated data stream is transformed bypre-codingmatrix.
Different methods like pulse shaping function, discrete
cosine transformation (DCT) matrix, Hadamard matrix,
zadoff-chu sequence, generalized chrip-like (GCL) sequence
etc. are used to generate pre-coding matrix. After that these
pre-coded data are transmitted through IFFT and generate
OFDM symbols. Each elementofpre-codingmatrixshould be
carefully designed, so that it can reduce the PAPR. Since, we
are multiplying modulated data with predefined pre-coding
matrix, there is no need of handshake between transmitter
and receiver.
4. PROPOSED WORK
In this pre-coder will be combined with scrambling
technique and the system performance will be compared.
SLM, PTS, DCT can provide good performance for PAPR
reduction, and this improvement requires a high
computational complexity. Several techniques have been
proposed based on low-complexity SLM techniques. SLM
requires the transmission of several sideinformationbits for
each data block. These bits must generally be channel-
encoded because they are particularly sensitive to the error
performance of the system. This increases the system
complexity and transmission delay, and decreases the data
rate. In this work, a VLM pre-coded SLM and combination of
DCT with SLM and HADAMARD with SLM techniques has
been proposed to reduce the PAPR in OFDM signals.
Combination of pre-coding and scrambling techniques
reduce PAPR much more as compare to other techniques.
5. DCT SLM TECHNIQUE
The main idea of the proposed scheme is to use a com-
bination of two appropriate methods. One is the DCT matrix
transform technique and the other is theSLMtechnique.The
transmitter block is showed in Figure 3. We call this scheme
is scheme 1. In the transmit end, the data stream is firstly
transformed by DCT matrix, then the transformed data is
processed by the SLM unit. If data block passed by DCT
matrix before IFFT, the autocorrelation coefficients of IFFT
input is reduced, then the PAPR of OFDM signal could be
reduced.
In this we use DCT matrix after SLM to further reduce the
PAPR of signal. We call this scheme as scheme 2. In his
fashion, the autocorrelation of the signal, which has been
processed by SLM, is reduced by DCT matrix transform. The
PAPR of fine output signal is further reduced. The block of
transmitter is showed in Figure 4.
Fig.3 Diagram of proposed SLM scheme1
Fig. 4 Diagram of proposed SLM scheme2
6. HADAMARD SLM TECHNIQUE
In this technique to reduce the occurrence of the high peaks
compared to the Simplified SLM. The idea to use the
Hadamard Transform is to reduce the autocorrelation ofthe
input sequence to reduce the peak to average power
problem and it requires no side information to be
transmitted to the receiver. In the section, we briefly review
Hadamard Transform. We assume H is the Hadamard
Transform matrix of N orders, and Hadamard matrix is
standard orthogonal matrix. Every element of Hadamard
matrix only is 1 or -1. The Hadamard matrix of 2 orders is
stated by
Y=HX
The coming input data stream is firstly transform by the
Hadamard Transform then the transformed data stream is
applied as input to IFFT signal processing unit.
The signal processing step is below:
1. The sequence X is transformed by Hadamard matrix, i.e.
Y=HX
2. Apply inverse IFFT i.e y=IFFT (Y)
3. The equivalent SFBC encoding operations in the time
domain for generating candidate signal sets is performed,
where one with the lowest maximum PAPR is selected for
transmission.
The block diagram of Hadamard SLM is shown below.
Fig. 5 Block diagram of Hadamard SLM

7. CCDF OF PAPR
The cumulative distribution function (CDF) is one of the
most regularly used parameters, which is used to measure
the efficiency of any PAPR Technique. The cumulative
distributed function (CDF) of the signal is
F (z) = 1 − exp (z)
The complementary cumulative distributed function(CCDF)
is used instead of CDF which helps us to measure the
probability that the PAPR of a certain data block exceeds the
given threshold.
P (PAPR > z) = 1 − P (PAPR ≤ z)
= 1 − F (z) N
= 1 − (1 − exp (−z)) N
8. RESULT & DISCUSSION
From the above graph, it can be seen that the value of
PAPR in original OFDM signal is 10.85dB.
The above graphs gives the value of PAPR in
Hadamard Transform OFDM signal is 7.5dB.
The above graph shows that the value of PAPR in
Discrete Cosine Transform OFDM is 5.69dB.
The above graph shows that the value of PAPR in VLM
Precoded SLM scheme is 5dB
Table No. 5.1 shows comparison between ofdm,
hadamard ofdm, dct-ofdm, vlm precode slm ofdm on
the basis of PAPR
In this paper a survey on PAPR reduction techniques has
been discussed. This is concluded that scrambling
techniques give good performance but it needs side
information for receiver torecoveroriginal data block,alsoit
increases complexity. Pre-coding based techniques result
good with no need of side information and works with less
complexity. Hybrid technique pre-coding plus scrambling
give best result for PAPR reduction.

References
[1] Agarwal, A., Behera, C. and Agarwal,K.(2013) “Effectof
Guard Time on BER Performance of OFDM based
WiMAX (IEEE 802.16d) System,” International Journal
of Electronics and Communication Engineering,
Volume 6, Number 1, 2013.
[2] Ahmed, H. A., Sulyman, A. I. and Hassanin, H. S. (2009)
“BER Performance of OFDM system with channel
Impairments,” The 9th IEEE InternationalWorkshopon
Wireless Local Networks (WLN 2009), October 2009
20-23.
[3] Arundash, A. and Gagri, V. (2006-2010) “OFDM system
and PAPR reduction techniques in OFDM systems”,
Department of Electronics and Communication
Engineering NationalInstituteofTechnology,Rourkela.
[4] Aulakh, S. K. and Sheetal, A. (2012) “ Bit Error Rate
analysis of Wimax based OFDM system using different
constraint lengths of convolution encoder,”
International journal of research & Innovation in
Computer Engineering, Vol 2, issue 2, April 2012.
[5] Awon, N. T., Rahman, Md. M., Islam, Md. A. and Islam,A.
Z. M. T. (2012) “Effect of AWGN and Fading(Rayleigh &
Rician) channels on BER performance of a Wimax
communication system,” International Journal of
Computer Science and Information Security, Vol. 10,
No. 8, August 2012.
[6] Bakshi, H. and Shirvani, M. (2009) “Peak To Average
Power ratio reduc tion by combining SelectiveMapping
and Golay complementary sequences,” IEEE, 2009.
[7] Bhardwaj, M., Gnagwar, A. and Soni, D. (2012) “A
review on OFDM: Concept, Scope and its Applications,”
IOSR Journal of Mechanical and Civil Engineering
(IOSRJMCE), Volume 1, Issue 1, May-June 2012.
[8] Park, M., Heeyong, J., Cho, J., Cho, N., Hong, D.,&Kang,C.
(2000). PAPR Reduction in OFDM Using Hadamard
Transform. In IEEE international conference on
communications (Vol. 1, pp. 430–433).
[9] Baig, I., & Jeoti, V. (2011). A new DHT precoding based
Interleaved-OFDMA uplink system with improved
PAPR for 4G cellular networks. Journal of Engineering
Science and Technology (JESTEC), 6(6), 685–694.
[10] Baig, I., & Jeoti, V. (2013). A ZCMT precoding based
multicarrier OFDM system to minimize the high PAPR.
Wireless PersonalCommunications,68(3),1135–1145.
[11] Sun, E., Yi, K., Tian, B., & Wang, X. (2006). A method for
PAPR reduction in MSE-OFDM systems. In Advanced
information networking and applications, 2006. AINA
2006. 20th international conference on (Vol. 2, p. 4).
[12] Baig, I., & Jeoti, V., (2010) DCT precodedSLMtechnique
for PAPR reduction in OFDM systems. In 2010
international conference on intelligent and advanced
systems (ICIAS) (pp. 1–6).
[13] Yuan-Pei, L., & See-May, P. (2003).BER minimized
OFDM systems with channel independent precoders.
IEEE Transactions on Signal Processing, 51(9), 2369–
2380.
[14] Ciochina, C., Buda, F. and Sari, H. (2006) “An analysis of
Peak Power Reduction techniques forWimaxsystems,”
IEEE, 2006.
[15] Dey, M. R. and Islam, M. S. (2012) “Performance
Analysis of PAPR reduction for OFDM- BPSK, -QPSK
and – QAM using forward error correcting code,” 7th
International Conference on Electrical and Computer
Engineering, 20-22 December, 2012.

PAPR Reduction in OFDM using New Hybrid Techniques

More Related Content

What's hot (19)

Similar to PAPR Reduction in OFDM using New Hybrid Techniques (20)

More from ijtsrd (20)

Recently uploaded (20)

PAPR Reduction in OFDM using New Hybrid Techniques