International Journal of Engineering Trends and Technology (IJETT) – Volume 16 Number 2 – Oct 2014
Efficient BER and PAPR Reduction using PTS
with Median Filtering in OFDM system using
64 FFT
Sandeep kumar Patel1, Prof. K. Suresh,2 Prof. Navin Chourasia3
1
M-Tech Research Scholar, 2Research Guide, 3HOD of EC Department, Swami Vivekananda College of Technology,
Bhopal
Abstract - The signal having sufficient power is the primary
requirement to make the communication properly. To keep the
power of signal throughout communication and it can be achieved
by maintaining the average power of the signal and it is in terms
of peak to average power ratio (PAPR). Means if PAPR is reduced
the performance of the system will improve. In this paper we are
adopting a methodology which using PTS algorithm with 32 and
64 FFT size and median filtering to reduce the PAPR. All the
analysis done for variable data sizes to check out the performance
of the proposed approach. Simultaneous analyzing the
performance of the system in terms of BER for the same
specifications to reduce PAPR.
Keywords - PAPR, BER, SNR, PTS and CCDF etc.
I.
INTRODUCTION
Digital communications experienced a fast growth with the
success of Internet in the 90’s, mostly using wired
infrastructures; in this same period mobile communications
became very popular and they together evolved in the
necessity of wireless Internet. The application of wireless
telegraphy to mobile communication systems started in the
1920’s.
In the last years wireless communications have experienced a
fast growth due to the high mobility that they allow.
However, wireless channels have some disadvantages, like
multipath fading, that make them difficult to deal with. A
modulation that efficiently deals with selective fading
channels is orthogonal frequency division multiplexing
(OFDM), which consists on N orthogonal subcarriers
generated and modulated in frequency domain. The fact that
the subcarriers are orthogonal allows the usage of the Fourier
transform without introducing inter-carrier interference (ICI).
The advancements in digital signal processing and very large
scale integrated circuits allow efficient and cost-effective
implementation of the fast Fourier transform (FFT)
operations making OFDM an attractive solution for wireless
channels.
An important disadvantage of OFDM systems is their high
peak-to-average power ratio (PAPR). When the OFDM
ISSN: 2231-5381
signal is transformed to time domain, the resulting signal is
the sum of all the subcarriers, and when all the subcarriers
add up in phase the result is a peak N times higher than the
average power. High PAPR degrades performance of OFDM
signals by forcing the analog amplifier to work in the
nonlinear region, distorting this way the signal and making
the amplifier to consume more power.
A simple technique used to reduce the PAPR of OFDM
signals is to clip the signal to a maximum allowed value, at
the cost of BER degradation and out-of-band radiation.
Clipping does not add extra information to the signal and
high peaks occur with low probability so the signal is seldom
distorted. Out-of-band radiation can be reduced by filtering at
the transmitter, the filter used in this project consists on a
FFT-IFFT pair which is easier to implement than traditional
FIR filters and allows the implementation of the clip & filter
set several times in order to reduce the peak regrowth that
filtering introduces. The BER degradation can be mitigated
by reconstructing the signal at the receiver.
II. PEAK TO AVERAGE POWER RATIO
When in time domain all the N subcarriers are added up
constructively, they produce a peak power that is N times
greater than the average power of the signal. The PAPR is
calculated by the following equation
=
max(x (t))
mean(x (t))
Where x(t) is the amplitude of the signal.
The peak power of the OFDM signal, regarding the worst
case when all the subcarriers are added-up constructively, is
the sum of all the N subcarriers: 1 ・N = N. The mean power
of the OFDM signal is the sum of all the values of the signal,
which is actually N, divided by the total number of
subcarriers, which is also N. Therefore the maximum PAPR
is:
http://www.ijettjournal.org
Page 83
International Journal of Engineering Trends and Technology (IJETT) – Volume 16 Number 2 – Oct 2014
=
=
lim(1 −
͢
This maximum PAPR increases whenever the number of
subcarriers increases. Thus, if N →¥⇒xk becomes Gaussian
distributed, for k = 1, ..,N, which means that
(
<
)<1
When the number of subcarriers tends to ¥ this probability
gives
(
<
)) = 0
The above statement can be better understood shows the
complementary cumulative distribution function (CCDF) of
an OFDM signal. The CCDF denotes the probability of a
signal to have a higher PAPR than a threshold PAPRm, so in
the figure, horizontal and vertical axes represent the threshold
values of PAPR and the CCDF respectively.
III. PROPOSED METHODOLOGY
lim
͢
(
<
)=0
If the above statement represents the probability of a signal
xk to have a smaller PAPR than the given one PAPRm, the
probability of the signal to have a PAPR greater than PAPRm
is
The wireless system need to be efficient in terms of signal
power. The overall power of signal should be more than the
maximum power which is called as peak power. So here is
the need to maintain the average power of the signal and the
figure of merit to check out this is peak to average power
ratio (PAPR).
Fig. 3.1 Block Diagram of OFDM Wireless Communication System to Reduce PAPR
In this section the PAPR of the OFDM based wireless
communication system is trying to reduce to achieve better
performance of the system. The proposed methodology is
shown in the figure below. The major sections (blocks) of the
OFDM based wireless communication system considering
AWGN channel displayed in the Fig. 3.1.
The flowchart of the proposed system is explained in the Fig.
3.2 where execution of the simulation model to reduce PAPR
is shown. The steps are as follows:
The first block modulates the data using QAM-modulation.
The modulated signal pass through OFDM system in which
IFFT operation is performed and cyclic prefix is added to the
signal which can be source and destination address or error
detection or correction information or any kind of
redundancy bits.
Step 2: Generate random data to transmit through system
Now the signal is transmitted through AWGN channel where
signal encountered with random noises and noisy signal
received at receiver. Now at receiver first cyclic prefix is
removed and OFDM demodulation (FFT) is performed than
QAM demodulation is applied and we get the final data at the
output of the system.
ISSN: 2231-5381
Step 1: Variables need to be initialized to create simulation
environment
Step 3: QAM modulation is applied on data
Step 4: Than IFFT operation is performed i.e. OFDM System
Step 5: Applying partial transmit sequence (PTS) algorithm
Step 6: Now Median Filtering is introduced to compensate
the error
Step 7: Now calculate the powers which are peak power,
average power to estimate PAPR
Step 8: Compare and display results
http://www.ijettjournal.org
Page 84
International Journal of Engineering Trends and Technology (IJETT) – Volume 16 Number 2 – Oct 2014
Fig. 3.2 Flow chart of proposed methodology to reduce
PAPR
The flowchart of the proposed system is explained in the Fig.
3.3 where execution of the simulation model to check
performance of the proposed system is shown. The steps are
as follows:
Step 1: Variables need to be initialized to create simulation
Fig. 3.3 Flow chart of proposed methodology to check BER
performance
environment
Step 2: Generate random data to transmit through system
IV. SIMULATION RESULTS
Step 3: QAM modulation is applied on data
Step 4: Than IFFT operation is performed i.e. OFDM System
Step 5: Add cyclic prefix
Step 6: Transmit the signal through AWGN channel
Step 7: Remove Cyclic Prefix at the receiver
Step 8: Than FFT operation is performed i.e. OFDM System
Step 9: QAM demodulation is performed
Step 10: Calculate BER
Step 11: Compare and display results
The outcomes of the above simulation algorithms are
explained in the next section of the paper.
ISSN: 2231-5381
The proposed system is explained in the previous section of
the paper with the methodology adopted to get the reduced
PAPR. The simulation results contains the two figure of
merits which are bit error rate (BER) and peak to average
power ratio (PAPR).
BER shows the end to end performance of the system it can
be considered the overall performance of the system. PAPR
of the system is shows the ratio of powers i.e. reduced PAPR
means average power of the system is more than the peak
power.
The BER vs SNR curves for the proposed system are shown
in Fig. 4.1 to 4.4. The BER is calculated using 5 iterations
and with 32 FFT sizes of OFDM system and performed over
1000, 5000 and 10000 OFDM symbols. From the result it is
clear that 5000 symbols are good for the proposed system.
http://www.ijettjournal.org
Page 85
International Journal of Engineering Trends and Technology (IJETT) – Volume 16 Number 2 – Oct 2014
10
BER of OFDM System using 5 Iterations and 32 FFT
-1
10
1000 Symbols
5000 Symbols
10000 Symbols
10
10
BER
-3
10
BER
10
10
-4
10
10
-6
0
2
4
6
8
SNR(dB)
10
12
14
Fig. 4.1 Performance of the proposed system using 5
iterations and 32 FFT
BER of OFDM System using 5 Iterations and 64 FFT
-1
10
1000 Symbols
5000 Symbols
10000 Symbols
-2
10
-3
10
BER
-3
-4
-5
-6
-5
10
10
1000 Symbols
5000 Symbols
10000 Symbols
-2
-2
10
10
BER of OFDM System using 10 Iterations and 64 FFT
-1
-4
10
-5
10
-7
0
2
4
6
8
SNR(dB)
10
12
14
Fig. 4.4 Performance of the proposed system using 10
iterations and 64 FFT
The BER is calculate using 5 iterations and with 64 FFT sizes
of OFDM system and performed over 1000, 5000 and 10000
OFDM symbols. From the result it is clear that 10000
symbols are good for the proposed system. The BER is
calculate using 10 iterations and with 32 FFT sizes of OFDM
system and performed over 1000, 5000 and 10000 OFDM
symbols. From the result it is clear that 1000 symbols are
good for the proposed system. The BER is calculate using 5
iterations and with 64 FFT sizes of OFDM system and
performed over 1000, 5000 and 10000 OFDM symbols.
From the result it is clear that 10000 symbols are good for the
proposed system.
-6
10
-7
10
0
2
4
6
8
SNR(dB)
10
12
14
Fig. 4.2 Performance of the proposed system using 5
iterations and 64 FFT
10
BER of OFDM System using 10 Iterations and 32 FFT
-1
CCDF computes the power complementary cumulative
distribution (CCDF) function from a time domain signal. The
CCDF curve shows the amount of time a signal spends above
the average power level of the measured signal, or
equivalently, the probability that the signal power will be
above the average power level.
1000 Symbols
5000 Symbols
10000 Symbols
10
-2
PAPR Reduction using PTS with 64 FFT 1000 Symbols
0
10
Orignal
PTS with Median Filter
-3
BER
10
-1
10
-4
CCDF
10
10
-5
-2
10
10
-6
0
2
4
6
8
10
12
14
SNR(dB)
Fig. 4.3 Performance of the proposed system using 10
iterations and 32 FFT
-3
10
0
2
4
6
PAPR(dB)
8
10
12
Fig. 4.5 Performance of the proposed system using 64 FFT
and 1000 symbols
ISSN: 2231-5381
http://www.ijettjournal.org
Page 86
International Journal of Engineering Trends and Technology (IJETT) – Volume 16 Number 2 – Oct 2014
10
PAPR Reduction using PTS with 64 FFT 5000 Symbols
0
SLM and filters make additional efforts to reduce PAPR with
higher configurations.
Orignal
PTS with Median Filter
CCDF
10
10
10
10
REFERENCES
-1
-2
-3
-4
0
2
4
6
PAPR(dB)
8
10
12
Fig. 4.6 Performance of the proposed system using 64 FFT
and 5000 symbols
10
PAPR Reduction using PTS with 64 FFT 10000 Symbols
0
Orignal
PTS with Median Filter
CCDF
10
10
10
10
-1
-2
-3
-4
0
2
4
6
PAPR(dB)
8
10
12
Fig. 4.7 Performance of the proposed system using 64 FFT
and 10,000 symbols
The performance of the proposed methodology to reduce
PAPR is shown in the figures from 4.5 to 4.7. The PAPR is
calculated for 64 FFT sizes and 1000, 5000 and 10000
OFDM symbols. The system is evaluated under original
condition and PTS with Median Filtering. From the results it
can be say that the system perform better with PTS and
Median Filtering if the OFDM system having 64 FFT points
and 10000 symbols.
V. CONCLUSION AND FUTURE WORK
The simulations of the OFDM based wireless system and its
performance analysis has been done in the previous section.
From the results the performance of the system is better with
the proposed methodology, and the power requirements to
outperform during transmission will be good if the system is
operated under given factors.
The future advancement of the system to reduce PAPR will
highly depend on the advancement of algorithms like PTS or
ISSN: 2231-5381
[I]
Taewon Hwang, Chenyang Yang, Gang Wu, Shaoqian Li and
Geoffrey Ye Li, "OFDM and its Wireless Applications: A Survey", IEEE
Transaction on Vehicular Technology, vol. 58, no. 4, pp. 1673-1694, May
2009.
[2]
V. Vijayarangan, DR. (MRS) R. Sukanesh “An overview of
techniques for reducing peak to average power ratio and its selection criteria
for orthogonal frequency division multiplexing radio systems”, Journal of
Theoretical and Applied Information Technology, 2009.
[3]
Kangwoo Park and In-Cheol Park “Low-Complexity Tone
Reservation Method for PAPR Reduction of OFDM Systems ” IEEE 2010.
[4]
TELLADO, J. Multicarrier Modulation with Low PAR, Kluwer
Academic Publishers, 2000
[5]
B. Hirosaki, “An Analysis of Automatic Equalizers for
Orthogonally
Multiplexed
QAM
Systems,”
IEEE
Transaction
Communication, Vol.28, pp.73-83, Jan.1980.
[6]
B. Hirosaki, S.Hasegawa, and A. Sabato, “Advanced Group-band
Data Modem Using Orthogonally Multiplexed QAM Technique,” IEEE
Trans. Commun. Vol. 34, no. 6, pp. 587-592, Jun. 1986.
[7]
Josef Urban and Roman Marsalek, “OFDM PAPR Reduction by
Combination of Interleaving with Clipping and Filtering,” IEEE
Communication Letter, pp. 249– 252, June 2007.
[8]
S.H Muller and J.B Huber, “OFDM with Reduced Peak-toAverage power Ratio by Optimum Combination of Partial Transmit
Sequences,” IEEE Electronics Letters on Communication & Signal
Processing, Vol. 33, Issue. 5, pp. 368-369, 27 Feb. 1997.
[9]
L. J. Cimini Jr. and N. R. Sollenberger, "Peak- to-Average Power
Ratio Reduction of an OFDM Signal using Partial Transmit Sequences,"
IEEE Communications Letters, Vol. 4, no. 3, pp. 86-88, 2000.
[10]
Bauml, R.W.; Fischer, R.F.H.; Huber, J.B, “Reducing the Peakto-Average Power Ratio of Multicarrier Modulation by Selected Mapping,”
IEEE Electronics Letters, Vol.32, pp. 2056-2057, 24 Oct. 1996.
[11]
R.F.H. Fischer, “Widely-Linear Selected Mapping for Peak-toAverage Power Ratio Reduction in OFDM,” IEEE Electronics Letters, pp.
766–767, July 2007.
[12]
Seung Hee Han and Jae Hong Lee. An overview of peak-toaverage power ratio reduction techniques for multicarrier transmission. IEEE
Wireless Communications, 12(2):56 – 65, 2005.
Author’s Profile
Sandeep Kumar Patel (skp1600@gmail.
com) is research scholor at Swami
Vivekanand College of Science &
Technology Bhopal under Rajiv Gandhi
Proudyogiki Vishwavidyalaya Bhopal he is
Pursuing
M.
Tech
in
Digital
communication. He has keen to work on for technique
of Efficient BER and PAPR Reduction using PTS with Medi
an Filtering in OFDM Transmission system using 64 FFT.
Prof. K. Suresh (ksureshsvcst@gmail.com) is a college
guide at Swami Vivekanand College of Science &
Technology Bhopal.
Prof. Navin Chourasia (navin_chourasia@yahoo.com) is a
HOD OF Electronics and communication department at
Swami Vivekanand College of Science & Technology
Bhopal.
http://www.ijettjournal.org
Page 87