IRJET- Reduction in Peak to Average Power Ration using Proposed Approach for OFDM Systems

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Reduction in Peak to Average Power Ration Using Proposed Approach
for OFDM Systems
Vishal Garg1, Mandeep Dhami2, Navdeep Singh Randhawa3
1,3Department of Electronics & Communication Engineering, SVIET, BANUR
2Department of Information Technology Engineering, SVIET, BANUR
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Abstract- OFDM is an attractive modulation technique
for transmitting large amounts of digital data in
wireless standards. The multi-carrier phenomena is
considered to be one of the major development in
wireless communication and among them OFDM is
becoming the important standard, because it has
several advantages such as high number of orthogonal
sub-carriers, no inter-symbol interference, high spectral
efficiency, tolerance in multipath delay spread, power
efficiency, frequency selective fading immunity etc. But
one of the challenging issues for Orthogonal Frequency
Division Multiplexing (OFDM) system is its high Peak-to-
Average Power Ratio (PAPR). OFDM consist of large
number of independent sub carriers as a result of which
amplitude of such a signal can have high peak values.
Several methods have been proposed to reduce the
PAPR. In this paper, we proposed a hybrid PAPR
reduction approach for OFDM systems and the
simulation results are carried out in MATLAB.
Keywords—OFDM, PAPR, SLM, ISI, PTS
I. INTRODUCTION1
Wireless data communications are an essential component
of mobile computing. The various available technologies
differ in local availability, coverage range and performance,
and in some circumstances, users must be able to employ
multiple connection types and switch between them. To
simplify the experience for the user, connection can be
used, or a mobile VPN deployed to handle the multiple
connections as a secure, single virtual network. Supporting
technologies include: Wi-Fi is a wireless local area network
that enables portable computing devices to connect easily
to the Internet. The standardized as IEEE 802.11 a, b, g, n,
Wi-Fi approaches speeds of some types of wired Ethernet.
Wi-Fi has become the de facto standard for access in
private homes, within offices, and at public hotspots. Some
businesses charge customers a monthly fee for service,
while others have begun offering it for free in an effort to
increase the sales of their goods. Cellular data service
offers coverage within a range of 10-15 miles from the
nearest cell site. Speeds have increased as technologies
have evolved, from earlier technologies such as GSM,
CDMA and GPRS, to 3G networks such as W-CDMA, EDGE
or CDMA2000 [1].
Mobile Satellite Communications may be used where other
wireless connections are unavailable, such as in largely
rural areas or remote locations. Satellite communications
are especially important for transportation, aviation,
maritime and military use [2]. Wireless Sensor Networks
are responsible for sensing noise, interference, and activity
in data collection networks. This allows us to detect
relevant quantities, monitor and collect data, formulate
meaningful user displays, and to perform decision-making
functions. OFDM is a frequency-division multiplexing
(FDM) arrangement acclimated as an agenda multi-carrier
accentuation method. An ample amount of carefully spaced
erect sub-carrier signals are acclimated to backpack
abstracts on several alongside abstracts streams or
channels [3]. Anniversary sub-carrier is articulate with a
accepted accentuation arrangement (such as quadrature
amplitude accentuation or phase-shift keying) at a low
attribute rate, advancement absolute abstracts ante agnate
to accepted single-carrier accentuation schemes in the
aforementioned bandwidth.
Figure 1: OFDM block diagram.
The primary advantage of OFDM over single-carrier
schemes is its adeptness to cope with astringent approach
altitude (for example, abrasion of top frequencies in a
continued chestnut wire, narrowband arrest and
frequency-selective crumbling due to multipath) after
circuitous equalization filters. Approach equalization is
simplified because OFDM may be beheld as application
abounding boring articulate narrowband signals rather
than one rapidly articulate wideband signal. The low
VOLUME: 05 ISSUE: 08 | AUG 2018 WWW.IRJET.NET P-ISSN: 2395-0072
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attribute amount makes the use of a bouncer breach amid
symbols affordable, authoritative it accessible to annihilate
intersymbol arrest (ISI) and advance echoes and time-
spreading (on alternation TV these are arresting as
ghosting and blurring, respectively) to accomplish an
assortment gain, i.e. a signal-to-noise arrangement
improvement [4]. This apparatus as well facilitates the
architecture of alone abundance networks (SFNs), area
several adjoining transmitters advanced the
aforementioned arresting accompanying at the
aforementioned frequency, as the signals from assorted
abroad transmitters may be accumulated constructively,
rather than interfering as would about action in an
acceptable single-carrier system. The OFDM based
assorted admission technology OFDMA is as well
acclimated in several 4G and pre-4G cellular networks and
adaptable broadband standards.
II. TECHNIQUES USED
The peak-to-average power ratio (PAPR) is the peak
amplitude squared (giving the peak power) divided by the
RMS value squared (giving the average power). It is the
square of the crest factor: The problem with this splendid
technique is that it is power inefficient due to the presence
of hurdle named as PAPR that is peak to average power
ratio which force the non linearity to get emerged into the
transmission. Number of approaches has been developed
to put this problem into a process to have favorable results
that are SLM (selective mapping), clipping and filtering,
PTS (partial transit sequence) etc. Using Selected Mapping
technique (SLM), input data is portioned into sub data
blocks given below of length N, and is [5]:
X= [X0, X1, X2 … XN-1]
Figure 2: Block Diagram of SLM
SLM (Selective Mapping): In selective mapping
arrangement, the sequence of input data is multiplied by
each of the phase sequence to give birth to new input
symbol arrangement. Each of the new born input data
sequence is put in the mode of IFFT operation. When the
data is parallel converted then OFDM data block is
multiplied element by element with Phase sequence given
as [6]:
Pu = [P1, P2, P3… Pu]
After data blocks are phase rotated, the rotated OFDM data
blocks represents similar information which are
unmodified OFDM data blocks, provided with known phase
sequence. A block diagram of the SLM technique is shown
in Fig. 2. Now frequency domain signal is converted into
the time domain X (u), by the help of IFFT.
Clipping and Filteration: This methodology states that
the out of band radiations developed by clipping is
squashed by subsequent filtering operation and in band
hurdle/noise is suppressed by applying coding method or
clipping noise cancellation method [7].
PTS (Partial Transit Sequence): According to PTS
technique an N symbol input block is taken, and is divided
into disjoint sub-blocks. After that the divided sub-bocks
are weighted by the phase vector sequence. The selection
of phase factor such that the PAPR of the resultant signal is
minimum. The divided sub-block is given as:
Xm= [X0, X1, X2 … XV-1]T
Where v = [1, 2, 3…., V], Then, the sub-blocks X are
transformed into time-domain partial transmit sequence x,
by using IFFT which can be represented as:
Xm =∑ IFFT (Xm)
After that, these divided sequences are independently
rotated by the phase factors (P), which is given as:
P = [P1, P2 … Pm]
At the end for manual the applicant with everyman PAPR is
chosen. The assumption anatomy of the C-PTS
arrangement is apparent in the accustomed beneath. The
cold is to optimally amalgamate the “V” sub-blocks to
access the time area OFDM signals with the everyman
PAPR. Without any accident of performance, one can set
P1=1 and beam that there is (V-1) sub blocks to be
optimized. Consequently, to accomplish the optimal
appearance agency for anniversary ascribe abstracts
arrangement (assume that there are (W) appearance
factors in the appearance set), combinations should be
arrested in adjustment to access the minimum PAPR.
Therefore, the seek complication for an optimum set of the
appearance factors increases exponentially with the
amount of sub blocks.
S. No. Technology Used Value of PAPR
1. Clipping and Filtering 5.82 dB
2. Selective Mapping (SLM) 6.5 dB
3. Partial Transit Sequence
(PTS)
Approx. 5.3 dB

Figure 3: Block Diagram of PTS
III. PROBLEM FORMULATION
In wireless communication systems, the orthogonal
frequency division multiplexing (OFDM) method is a
broadly prevalent an attractive plan for high-information
rate transmission because it can cope with frequency
selective fading channel. OFDM is one of the many
multicarrier modulation techniques, which provides high
spectral efficiency, low implementation complexity, less
vulnerability to noise and non – linear distortion. Due to
these advantages of the OFDM system, it is vastly used in
various communication systems. But the major problem
one faces while implementing this system is the high peak
– to – average power ratio (PARP)of this system. 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 multicarrier 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. The input symbol stream of the
IFFT should possess a uniform power spectrum, but the
output of the IFFT may result in a no uniform or spiky
power spectrum. Many Techniques had been proposed
for removing this PAPR from OFDM system, as per
literature recently an clipping algorithm along with
filtration was proposed, the PAPR was reduced up to an
extent but as clipping is not that much efficient as it cut the
signal and also effect the information of the signal so there
is need to update the methodology by using other
techniques.
IV. PROPOSED METHODOLOGY
As PAPR is the the major problem in OFDM ,we need dto
take certain measure to prevennt its effect .The problem
caused by PAPR are:
 Increased complexity in the analog to digital and
digital to analog converter.
 Reduction is efficiency of RF amplifiers
So there is a need to find some technique to reduce the
effect of PAPR .we need to reduce the PARP as low PAPR
makes the RF amplifier works efficiently. PAPR decrease
strategies differ as per the needs of the system and depend
on different elements. PAPR reducing capacity, increment
in power in transmit signal, loss in information rate,
unpredictability of processing and increment in the bit-
error rate at the receiver end are different variables which
are considered before adopting a PAPR decrease strategy
of the system.
A. Effect of PAPR
There are some obstacles in using OFDM in transmission
system in contrast to its advantages:
1. A major obstacle is that the OFDM signal exhibits a
very high Peak to Average Power Ratio (PAPR).
2. 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 intermediation 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. The large peaks cause saturation in power
amplifiers, leading to intermediation products among
the subcarriers and disturbing out of band energy.
Therefore, it is desirable to reduce the PAPR.
4. To reduce the PAPR, several techniques have been
proposed such as clipping, coding , peak windowing,
Tone Reservation and Tone Injection. But, most of
these methods are unable to achieve simultaneously a
large reduction in PAPR with low complexity, with low
coding overhead, without performance degradation and
without transmitter receiver symbol handshake.
5. Complexity is increased in the analog to digital and
digital to analog converter. Criteria For PAPR Reduction
Method Selection The criteria of the PAPR reduction is to
find the approach that it can reduce PAPR largely and at
the same time it can keep the good performance in
terms of the following factors as possible.
V. STEPS OF PROPOSED TECHNIQUE
As it was suggested in earlier section that there is need to
update the clipping based papr reduction methodology so
in this paper a new approach is proposed that having an

advancement over the clipping and the filtering
methodology. The work basically focuses on the
hybridization of the traditional approach and it is found
that the output of the PAPR reduction techniques suchg as
SLM , PTS , Tone reservation methodologies are very much
popular but in the PTS ideas are much considerable. In the
proposed approach, the algorithm firstly work with PTS
technique and then the clipping and the filtration process
occurs that leads to minimum loss of information and the
reduce the PAPR of the transmitted signal. The steps of
proposed approach are deccribed below:
 Generate a random signal for PAPR reduction in
OFDM.
 Apply QPSK modulation on that signal.
 Now perform padding by adding zeros.
 Compute IFFT of padded signal with help of IFFT
equation:
 Now apply PTS technique to reduce the PAPR
value. According to PTS phase shift [1 - 1 j -j],
generate all possible combinations of weighting
factor set in PTS method.
 Then check the values of PAPR of the
corresponding generated signals and the signal
with minimum PAPR value was selected while
others are rejected.
 After PTS now Apply Clipping operation on OFDM
signal. Clipping operation done by threshold level
A.
 Compute the clipping noise D.
 After computing clipping noise D perform FFT on
this.
 Now compute this equation:
Where Xk is OFDM signal And β is noise
Calculation parameter.
 After computing above equation performs IFFT on
Xkc signal and filtering operation is applied on this.
 After clipping and filtering now compute :
Figure 2: PAPR comparison of proposed technique in
contrast with traditional approach.
VI. CONCLUSION
In this, OFDM, peak to average power ratio and its various
reduction techniques are reviewed. Orthogonal frequency
division multiplexing technique is modulation technique
which provides high speed communication in both wired
and wireless systems. PAPR is major drawback of
Orthogonal Frequency Division Multiplexing technique
which degrades the performance of OFDM.As per the
information about all above described techniques to
reduce the PAPR in OFDM system all techniques is
different in their way and using each technique PAPR will
be reduced at some level. Research is going on to further
improve PAPR reduction and improving the performance
of OFDM systems.
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