PAPR Reduction of OFDM Signal Using Error Correcting Code and Selective Mapping

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International Journal of Computer Information Systems,

PAPR REDUCTION OF OFDM SIGNAL USING
ERROR CORRECTING CODE AND SELECTIVE
MAPPING
Anshu Er. Himanshu Sharma
ECE Deptartment Lecturer, ECE Department
Mahrishi Markendeshwar University Maharishi Markendeshwar University
Mullana, India Mullana, India
guddal88@gmail.com himanshu.zte@gmail.com

of selective mapping (SLM) [1], in which a set of independent
I. ABSTRACT sequences are generated by some means from the original
Orthogonal frequency division multiplexing (OFDM) signal, and then the sequence with the lowest PAPR is
technique is a promising technique to offer high data rate and transmitted. To generate these sequences we use code en
reliable communications over fading channels. The main encoder. Using error correcting coding will offer two
implementation disadvantage of OFDM is the possibility of advantages,significant PAPR reduction and astonishing bit
high peak to average power ratio (PAPR). This paper presents error rate (BER) performance.
a novel technique to reduce the PAPR using errorcorrecting
coding and selective mapping (SLM).We show that the The rest of the paper is organized as follows: The problem
probability of the PAPR of OFDM signal with 100 subcarriers. of high PAPR of OFDM signal is briefly defined in section 2.
Section 3 introduces the proposed technique. Some simulation
Keywords-OFDM,SLM,CCDF, PAPR, PAR. results are shown in section 4. Finally, the conclusions are
drawn in section 5.
II. INTRODUCTION
III. PROBLEM DEFINITION
OFDM, orthogonal frequency division multiplexing, is a
multicarrier communication technique, where a single data We suppose an OFDM transmission scheme, where a block
stream is transmitted over a number of lower rate subcarriers. of N complex symbols is first over-sampled using over
OFDM has become tangible reality, it has been employed for sampling factor J and then transformed into time domain using
wire-line communications and also has been employed in the inverse fast Fourier transform (IFFT). This results in the
wireless local area network (WLAN) e.g. IEEE 802.11. Other following signal:
applications of OFDM are digital audio broadcasting (DAB)
and digital video broadcasting (DVB).
(1)
Unfortunately, OFDM has the drawback of a potentially
high peak to average power ratio (PAPR). Since a multicarrier Where sk is the data to be transmitted and 1 < t < NJ.
signal consists of a number of independent modulated
subcarriers that can cause a large PAPR when the subcarriers The PAPR is defined as the ratio between the
are added up coherently. maximum powers occurring in OFDM symbol to the average
power of the same OFDM symbol:
To reduce the PAPR different techniques were proposed.
These techniques can be categorized into the following,
clipping and filtering [1], coding [2], phasing [3], scrambling (2)
[4], interleaving [5], and companding [6].

In this paper we propose and examine a technique for WhereE [.] denotes expectation.
reducing the probability of a high PAPR, based on part on a When the OFDM signal with high PAPR passes through a
method proposed in [1] and [8]. This technique is a variation non-linear device, (power amplifier working in the saturation

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International Journal of Computer Information Systems,
region), the signal will suffer significant non-linear distortion same information. In order to achieve a PAPR reduction, the
[9]. This non-linear distortion will result in in-band distortion symbol with the lowest PAPR is transmitted. We define
and out-of-band radiation. The in-band distortion causes
system performance degradation and the out-of-band radiation (6)
causes adjacent channel interference (ACI) that affects
systems working in the neighbour bands. To lessen the signal
distortion, it requires a linear power amplifier with large
dynamicrange. However, this linear power amplifier has poor In SLM, we use log2 D bits side information to indicate the
efficiency and is so expensive. phase weighting. As this side information is of highest
importance to recover the data, it should be carefully protected
by channel coding.

x With , the transmitted signal is . In the receiver, X can
Label
be recovered with
b1…..b
v x
(7)
Label Select
encod Mapp IFFT
Invert
or
x
Binar
y
To recover X it is necessary for the receiver to have a table of
all .

Figure: 1 System model The phase sequence combination that results in the lowest
PAR of the time-domain signal is used for transmission. Here
we encode the information fist with forward error correcting
IV. SELECTIVE MAPPING USING ERROR code and then do SLM. The technology combines SLM, which
CORRECTING CODING aims at PAPR reduction, and coding(basically we use
hamming code, rsc code, and convolution code), which are
Selected mapping (SLM) is a specific scheme for excellent in error control and are play excellent role in further
PAPRreduction that was introduced in [13].SLM takes reduction in PAPR. In this paper we show comparison of all
advantage of the fact that the PAR of an OFDM signal is very the three coding with SLM.
sensitiveto phase shifts in the frequency-domain data. PAR
reduction is achieved by multiplying independent phase After coding the process is done just like what is applied on
sequences to the original data and determining the PAR of the carriers in the usual SLM algorithm. The process is given
each phasesequence /data combination. The combination with in figure1. Finally all of the different sequences, after serial to
the lowest PAR is transmitted. In other words, the data parallel conversion, pass through the IFFT block to produce D
sequence X is element-wise phased by D N-length phase block of time domain signal. The block with the lowest PAPR
sequences, is to be sent to the receiver through the channel.

(3) V. SIMULATION RESULTS
In this section the results obtain through the simulations using
Where d is an integer such that After MATLAB are examined. Quarter phase shift keying (QPSK)
phasing, the D possible frequency-domain OFDM is used. The results are given here in terms of PAPR-CCDF.
First we show comparison of PAPR with SLM and the original
symbols where is the element-wise OFDM signal. Secondly the comparison with SLM and coded
multiplication. SLM.

We assume that In the following the performance of the system for both
conventional SLM and coded are examined.
(4) A. CCDF-PAPR
Figure 1 shows the difference between the results of SLM and
Original OFDM signal in terms of CCDF-PAPR. In this we
So that (5) consider the OFDM signal with number of subcarriers N=64.
The hamming encoder has constraint length K=16 is used.
Define the D candidate time-domain OFDM symbols x(d) = B. CCDF-PAPR
IFFT{X(d)}. Note that all of the candidate symbols carry the

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International Journal of Computer Information Systems,
Figure 2 in this section, the performance of the system for reduces the hardware complexity of the system. An excellent
each coded SLM i.e. SLM using hamming code,SLM using style manual for science writers is [7].
rsc code and SLM using convolution code. In this the OFDM
signal with number of subcarriers N=100 and hamming VII. ACKNOWLEDGEMENT
encoder has constraint lengthK=16 is used. I would like to express my gratitude toward those who have
supported me through the work. First, I would like give my
sincerest thanks to my guide, Er. Himanshu Sharma, for his
unreserved guidance, support and encouragement. He has
looked out for me at every time and has given me every
opportunity to succeed; for that, I am truly grateful. I consider
myself lucky to be one of her students. I want to thank my
thesis committee, Dr.AmitGarg and Dr. H.P Sinha, for taking
the time to review and critique my work. Additionally, I would
like to thank my fellow research group members for their
friendship and insightful comments. Finally, I want to thank
my family, who have supported me through every step of my
life.

VIII. REFERENCES
[1] X. Li and L. J. Cimini Jr., ”Effects of clipping and filtering
on the performance of OFDM,” IEEE Communication Letters,
pp. 131-133, May 1998.

[2] A. E. Jones, T. A. Wilkinson and S. K. Barton, ”Block
coding scheme for reduction of peak to mean envelope power
Figure2: Comparison between the original OFDM &SLM ratio of multicarrier transmission schemes,” Electronic Letters,
pp. 2098-2099, Dec. 1994.

[3] V. Tarokh and H. Jafakhani, ”On the computation and
reduction of peak to average power ratio in multicarrier
communications,” Proc. IEEE 53rd Vehicular Technology
Conference, vol.2, pp. 37-44, Jan 2000.

[4] P. Van Eetvelt, G. Wade and M. Tomlinson, ”Peak to
average power reduction for OFDM schemes by selective
scrambling,” Electronic letters, vol. 32, pp. 1963-1994, Jan
2000.

[5] A. D. S. Jayalath and C. Tellambura ” The use of
interleaving to reduce the peak to average power ratio of an
OFDM signal,” Global Telecommunication

Conference, 2000, GLOBECOM ’00. IEEE, vol. 1, pp. 82-86,
Nov.-1 Dec. 2000.

Figure3: Comparison among the various coding with SLM [6] Xiao Huang, Jianhua Lu, Justin Chuang, and JunliZheng,
”Companding transform for the reduction of peak to average
VI. CONCLUSIONS power ratio of OFDM signal,” IEEE Trans. On Common. vol.
48, pp. 835-839, May 2001.
We have shown that, coding and SLM can be combined to
reduce the PAPR of OFDM signal with quite moderate
[7] R. B¨auml, R. Fischer and J. Huber, ”Reducing the peak to
additional complexity. The advantage of the proposed scheme
average power ratio of multicarrier modulation by selected
is that, the coding is used for two purposes, error correction
mapping,” Elect. Letts., vol. 32, pp. 2056-2057, Oct. 1996.
and PAPR reduction. Here we see that combination of RS
code and SLM gives the better results instead of hamming
with SLM and convolution with SLM as shown in fig 2.This

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International Journal of Computer Information Systems,
[8] N. Carson, T. A. Gulliver, ”PAPR reduction of OFDM
using selected mapping, modified RA codes and clipping”, in
Proc. IEEE VTC, vol.2, pp. 1070-1073, Sep. 2002.

[9] S. Merchan, A. Garcia Armada and J. L. Garcia,” OFDM
performance in ampli- er nonlinearity,” IEEE Trans. On
Broadcasting, vol. 44 Issue:1, pp.106-114, Mar. 1998.

[10] M. Breiling, S. M¨uller-Weinfurtner and J. Huber, ”Peak-
power reduction in OFDM without explicit side information,”
Proc. 5th Int. OFDM Workshop, Germany, pp- 28.1-
28.4,2000.

[11] C. Berrou, A. Glavieux and P. Thitimajshima, ”Near
Shannon limit error correcting coding and decoding: Turbo
Codes.” in Proc. of ICC’93, (Geneva, Switzerland), pp. 1064-
1070, May 1993.

[12] S. Benedetto, G. Montorsi, D. Divsalar, and F. Pollara,
”A soft-input soft-output maximum a posterior (MAP) module
to decode parallel and serial concatenated codes”, TDA
progress report 42-127, Jet Propulsion Lab., Pasadena, CA,
Nov. 15 1996.

[13] K.Kasiri&M.j.Dehghani, “A Blind SLM Scheme for
Reduction of PAPR in OFDM System.”

Author Profile:

Anshu
M.Sc., Kurukshetra University
Pursuing M.Tech at Mahrishi Markendeshwar University,
MULLANA

Er. Himanshu Sharma
M.E.(ECE)from THAPER UNIVERSITY, PATIALA
Currently he is a Lecturer, ECE Department
Mahrishi Markendeshwar University, MULLANA
Experience in Wireless Communication.

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