SLM-PTS BASED PAPR REDUCTION TECHNIQUES IN OFDM SYSTEM

SLM-PTS BASED
PAPR REDUCTION
TECHNIQUES IN
OFDM SYSTEM
PRESENTES BY
CHAGANTI HARINI
B.TECH IN ECE

CONTENTS
• OBJECTIVE
• EXISTING METHODS
• ABSTRACT
• ORTHOGONAL FREQUENCY DIVISION MULTIPLEXING(OFDM)
• PEAK TO AVERAGE POWER RATIO(PAPR)
• BLOCK DIAGRAM OF SLM TECHNIQUE
• FLOW CHART OF SLM TECHNIQUE
• BLOCK DIAGRAM OF PTS TECHNIQUE
• FLOW CHART OF PTS TECHNIQUE
• CODE FOR SPECIFIED INPUT CONDITIONS
• EXPERIMENTAL RESULTS
• ADVANTAGES
• APPLICATIONS
• PROJECT BUDGET
• REFERENCES 2

OBJECTIVE
• The main objective of this project is to analyze and simulate various OFDM based Peak
to Average Power Ratio (PAPR)reduction techniques.
• By using Partial Transmit Sequence(PTS) and Selected mapping reduction techniques,
PAPR in the system can be reduced so that OFDM in the system can be used more
commonly and effectively.
3

EXISTING METHODS
OFDM IMPLEMENTATION WITHOUT PAPR REDUCTION:
 When the OFDM is implemented without PAPR reduction it decreases the signal to quantization
noise ratio of ADC, degrades the efficiency of power amplifier and causes data loss
PAPR REDUCTION USING AMPLITUDE CLIPPING AND FILTERING:
 Amplitude clipping is a technique in which signals having values higher than pre-determined
value are clipped. The problem in this case is that due to amplitude clipping distortion is
observed in this system as a source noise. Also spectral efficiency is hampered by out of band
radiation and over clipping may degrade the performance due to distortion of original signal.
4

ABSTRACT
• Communication is one of the important aspects of life,with advancement in
technology and its growing demands there has been a rapid growth in the field of
communications.
• Signals, which were initially sent in the analog domain, are being sent more in
digital domain .Communication systems with single carrier have shifted to multi
carrier systems
• One of the most used techniques is OFDM.In the OFDM system, orthogonally
placed sub – carriers are used to carry the data from the transmitter end to the
receiver end.
• OFDM offers many advantages like high data rate, better utilization of bandwidth
and no interference. But the large Peak– to –Average Power Ratio of these
signal have some undesirable effects on the system.
• In this project, our aim is to reduce the PAPR in the system by using Selective
mapping (SLM) and partial transmit sequence(PTS) and compare the results for
obtaining efficient technique.
5

ORTHOGONAL FREQUENCY DIVISION MULTIPLEXING(OFDM)
• Orthogonal frequency division multiplexing is a type of digital transmission technique
and a method of encoding digital data on multiple carrier frequencies.
• OFDM uses multiple sub carriers within same single channel and makes use of a large
number of closely spaced orthogonal sub carriers that are transmitted in parallel . The
distinct features of OFDM include:
1. Multiple subcarriers carry the information stream.
2. The subcarriers are orthogonal to each other.
3. The peak of one signal will result in null point of other signals.
6

ADVANTAGES OF OFDM
• Immunity to selective fading.
• Resilience to interference
• High data rate and bandwidth.
• Spectrum efficiency
• Resilient to ISI and narrow band effects.
Applications of OFDM
• Digital television and Audi broadcasting
• DSL internet access
• Wireless networks
• LTE, LTE advanced
• 4G/5G
Disadvantages of OFDM
• High peak to average power ratio 7

PEAK TO AVERAGE POWER RATIO (PAPR)
• 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. Coherent addition of N signals of same phase
produces a peak which is N times the average signal.
• The major disadvantages of a high PAPR are-
1. increased complexity in the analog to digital and digital to analog converter.
2. Reduction is efficiency of amplifiers.
8

• In spite of many advantages and applications , the high PAPR of OFDM has outweighed its potential
features , hence it becomes very important to reduce the peak to average power ratio. Hence, we have
implemented SLM and PTS techniques in our project.

9
BLOCK DIAGRAM OF SELECTIVE MAPPING
(SLM)

SELECTIVE MAPPING
The main aim of this technique is to generate set of data blocks at transmitter representing
original information and select the lowest PAPR for transmission.
DESCRIPTION OF BLOCK DIAGRAM
10
INPUT DATA
In SLM technique, the whole set of information symbol are loaded into the
subcarrier.
Let us consider the input data block with information symbol
X = X[X(0), X(1), … X[N-1]]
SERIAL TO PARALLEL CONVERTOR
A Serial to parallel convertor is basically a digital circuit i.e., shift register made
up of D flip-flops.
S/P is used in SLM to partition the input data into multiple sub-carriers, each
contains the entire original information.

MULTIPLIER:
 The Multiplier contains U different phase sequences represents as PU =[Pu
0, Pu
1...Pu
N-1]T as one
of its input where Pu
V = ejou
v
 Each subcarrier is multiplied with a phase sequence to produce a modified data block given
by Xu = [Xu[1], Xu[2]... Xu[N-1]]T
N POINT IFFT:
 IFFT is basically used to convert the signals from frequency domain to time domain.
 In OFDM symbol is constructed using frequency domain by mapping input bits of QAM
symbols and then ordering them in a sequence according to number of subcarriers.
 But to transmit them, signal must be in time domain.
 So, N-point IFFT blocks converts Xu(v) to xu = [xu(0), xu(1),... xu(N-1)]T
SELECTION OF OFDM SIGNALS:
 This selection is used to calculate the PAPR of all independent xu signals and only the subcarrier
with lowest PAPR is used for transmission.
11

12
ALGORITHM:
Consider input data block X=X[0], X[1]…; X[N-1] divided into sub-
carriers by passing through serial to parallel convertor.
 Multiply with U different phase sequences Pu = [P0
u ,P1
u.. ; P [N-1]
u ]
 This produces a modified data block Xu
IFFT of U independent sequences { XU[V]}are taken to produce Xu.
Among these, X with lowest PAPR is selected for transmission.

FLOW CHART FOR SLM TECHNIQUE
Information data
Serial to parallel convertor
Multiply data with random variable
Taking IFFT of resulting signal
13
Calculating CCDF of resulting signal and compare with threshold
value
Select signal with lowest PAPR

BLOCK DIAGRAM OF PTS TECHNIQUE
14

PARTIAL TRANSMIT SEQUENCE
 In PTS, only a part of data of varying subcarrier covers all information to be
sent in the signal is selected for transmission.
DESCRIPTION OF BLOCK DIAGRAM
15
INPUT DATA:
PTS partitions an input data of N symbols into V disjoints sub-blocks as follows
X = X[X0, X1, X2 ,... XU-1]T
where Xi are the sub-blocks that are consecutively located and also are of equal size.
SERIAL TO PARALLEL CONVERTOR:
A Serial to parallel convertor is basically a digital circuit i.e., shift register made up of D
flip-flops.
S/P is used in SLM to partition the input data into multiple sub-carriers, each contains the
entire original information.
In PTS Serial to Parallel convertor partitions an input data blocks into individual sub-
blocks.

N POINT IFFT:
 IFFT is basically used to convert the signals from frequency domain to time domain.
 In OFDM symbol is constructed using frequency domain by mapping input bits of
QAM symbols and then ordering them in a sequence according to number of
subcarriers.
 For every partitioned unblocks OFDM signal is operated by taking IFFT i.e.,
x = IFFT[∑v
v=1 bv xv] = ∑v
v=1 bv xv
MULTIPLIER:
 In multiplier of PTS each domain unblocks x is multiplied with a corresponding
phase factor bv = ejov where v = 1,2...
SELECTION OF OFDM SIGNALS:
 This section in PTS is used to choose the phase sector so that PAPR is minimized
by using
[b-1,...b-v] = org min(maxn=0,1.. |∑v
v=1 bv xv [n])
 Set of phase factors are searched to find the optimum set of phase sectors for
transmission.
16

17
ALGORITHM:
Initially partition the input data blocks of N symbols into V disjoints.
X=[X0,X1,X2...........XV-1]T .
 Now each sub-block is scrambled.
 Each sub-block is multiplied with a corresponding complex phase factor bv.
 Consequently, take IFFT to obtain
 Set bV=1 for V=1 and set it as PAPR_min
 Set V =2, if PAPR < PAPR_min switch back bV to 1

FLOW CHART FOR PTS TECHNIQUE
START
Partition the input data block into V sub-blocks
Set all the phase factors bv=1 for v=1; V, find PAPR and set it as PAPR minimum with bv=-1
Generate all possible combinations of weighting factor set in PTS method
Applying PTS algorithm with the number of generated OFDM symbols equals to 1000
Calculate and plot complementary cumulative distribution function(CCDF) of different PAPR
If PAPR> PAPR_min, switch bv back to 1. Otherwise, update PAPR_min = PAPR
If v<V, increment v by one and go back, exit its process with the set of optimal phase factor b
END
NO
NO
YES
18

EXPERIMENTAL RESULTS
19
 We have implemented OFDM system by using simulation parameters such as carrier count, bits
per symbol, symbols per carrier and signal to noise ratio.
 We have carried out the following simulations individually:
1. Original signal
2. Amplitude clipping
3. Partial transmit sequence
4. Selective Mapping
 All the simulations are carried out and compared theoretically and graphically in order obtain the
most efficient PAPR reduction technique.
 We have used CCDF,PAPR performances as a measure to verify the effectiveness of the
proposed scheme.

20
SIMULATION PARAMETERS
IFFT bin length 1024
Carrier count 128
Bits per symbol 3,4,6
Symbols per carrier 100
SNR 20

COMPARISION BETWEEN REDUCTION TECHNIQUES VS
ORIGINAL SIGNAL FOR BITS/SYMBOL = 3
21

This table shows percentage of PAPR reduction for these three techniques and it is clear
that PTS gives highest percentage reduction
22
NO. Reduction technique PAPR Reduction
1. Original(without reduction technique) 0
2. Clipping 19.2
3. SLM 27.96
4. PTS 79.4

COMPARISION BETWEEN REDUCTION
TECHNIQUES VS ORIGINAL SIGNAL FOR
BITS/SYMBOL = 4
23

This table shows that percentage of SLM is higher than clipping but PTS is the highest.
24
2. Clipping 20.48
3. SLM 27.39
4. PTS 79.36

COMPARISION BETWEEN REDUCTION RECHNIQUES vs
ORIGINAL SIGNAL FOR BITS/SYMBOL = 6
25

The table shows PAPR result for 64 PSK, it is observed that the
percentage of PTS is highest than clipping and SLM.
26
2. Clipping 20.61
3. SLM 28.08
4. PTS 79.24

CONCLUSION
 This project shows the simulation results of OFDM symbol without PAPR
reduction, clipping, SLM and PTS. The main focus of the project is to
compare PAPR before and after applying these techniques.
 The simulation results indicate that large PAPR reduction is possible also the
results show that PTS is best for reducing PAPR.
27

ADVANTAGES
• OFDM PAPR Reduction techniques are used to increase the signal to noise
ratio of Analog to digital convertor and Digital to analog convertor.
• To improve the efficiency of power amplifier in the transmitter.
• Non – linear effects of the system are reduced.
• The quality of long-distance communication is improved by eliminating inter
symbol interference.
• The complexity of the system is reduced to a great extent by using PAPR
Reduction techniques.
28

APPLICATIONS
• Digital Audio Broadcasting(DAB)
• Digital Video Broadcasting (DVB)
• Wireless LAN network.
• IEEE 802.16 Broadband wireless access system (WiMAX)
• 4G/5G mobile communications
29

PROJECT BUDGET
• MATLAB version R2013 installation : 2500/-
• Documentation charges : 500/-
• Total budget of our project : 3000/-
30

REFERENCES
• Yasir Rahmatallah and Seshadri Mohan, "Peak-to-Average Power Ratio
Reduction in OFDM Schemes: A Survey And Taxonomy", IEEE
Communications Surveys and Tutorials, vol. 15
• R. Buml, R. Fischer and J. Huber, "Reducing the peak-to-average power ratio
of multicarrier modulation by selected mapping", Electron. Lett., vol. 32.
• S.H. Muller and J.B. Huber, "OFDM with reduced peak-to-average power ratio
by optimum combination of partial transmit sequences", IEE Electronic
Letters., vol. 33, no. 5, pp. 368-369.
31

SLM-PTS BASED PAPR REDUCTION TECHNIQUES IN OFDM SYSTEM

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