Slide Tssa 2015

PTS-Based PAPR Reduction in Fixed WiMAX System With Grouping

Phase Weighting (GPW)

Chaeriah B.A. Wael, Nasrullah Armi, Budiman P.A.R

The International Conference on Telecommunication Systems Services and

Applications (TSSA) 2015November, 25-26 2015Bandung - Indonesia

Outline

PAPR Problem in OFDM Based System

IEEE 802.16-2004 Physical Layer

Introduction

Simulation Result and Analysis

Conclusions

Introduction : Motivation

High demand on broadband

connectivity

BWA has advantages compared to wired

media

WiMAX is a promising broadband wireless technology

• Wired : xDSL• Wireless : Broadband

Wireless Access (BWA)

• Solving distance limitations of DSL and high costs of cable

• high scalability and lower maintainance and upgrade costs.WiMAX can offer high speed

data, voice and video service to the end customer in a large geographical

WiMAX prefaces high Peak to Average

Power Ratio (PAPR) problem

WiMAX system needs to reduce its PAPR

IEEE 802.16-2004 Physical Layer

Randomizing

FEC Encodi

ng

Interleaving

Mapping

OFDM Mod

Channe

l

Derandomizing

FEC Decodi

ng

Deinterleaving

Demapping

OFDM Demo

d

Block diagram of WiMAX transceiver physical layer


□ An OFDM signal consists of N independently modulated subcarriers. When N signals are added with the same phase, they produce a peak power that is N times the average power.

□ Problems due to high PAPR : High peak signals will saturate power amplifier

(PA) PA operates at its nonlinear region. Such condition leads to high out of band

radiation and inter-modulation distortion. High PAPR signal requires highly linear PA (PA with

large dynamic range) quite expensive and increase overall cost of the system.

□ Solution : modifying the signal by reducing its PAPR.


□ The PAPR of the discrete time baseband OFDM signal is defined as the ratio of the maximum peak power divided by the average power of the OFDM signal.

2

2

1010)()(

)(maxlog10log10

nxE

nx

P

PPAPR n

average

peakdB

10;1

)(21

0

NneXN

nxn

N

kjN

kk

Where :N : number of

subcarriersXk : modulated

input symbols


□ Complementary Cumulative Distribution Function (CCDF) is used to evaluate the performance of any PAPR reduction scheme.

□ A CCDF curve shows how much time the signal spends at or above a given power level.

□ A CCDF curve is a plot of relative power levels versus probability.

Construction of a CCDF curve


PAPR Reduction Methods

Distortion :

• Clipping• Windowing • Envelope

scaling• Companding

Distortionless (Scrambling) :

• Selected Mapping (SLM)• Partial Transmit Sequence (PTS)• Tone Reservation (TR)• Tone Injection (TI)• Dummy Signal Insertion (DSI)• Active Constellation Extension

(ACE) • Interleaving • Block Coding techniques

Partial Transmit Sequence (PTS)

MapperS/P

LN-IFFTΣ and find

lowest

PAPR

LN-IFFT

LN-IFFT

...

Optimize phase factor

X

X0

X1

XV-1

x0

x1

xV-1

PAPR reduction using PTS :1.X is partitioned into V disjoint subblocks.2.Apply IFFT to each subblock Xv.3.xv is multiplied by a corresponding complex weighting factors wv.4.Choose one suitable rotation factor which gives minimum PAPR.5.Transmitted signal is the sum of each subblock with minimum PAPR.

PTS Using Group Phase Weighting (GPW)

□ In GPW-PTS, all subblocks from step (1) in conventional PTS are separated into several groups.

□ Phase weighting process is applied to every subblock in each group by using the same set of phase weighting factors and bring out subcandidate sequences.

V

riii

r

riii

r

iii

R

V

iii

R

xwxwxw

GGGxwx

1

2

1

1

...

...

11

211

Partial Transmit Sequence (PTS)

□ Advantage vs. drawback :Advantage : no distortion, PTS gives better PAPR

reduction. Drawback : high computational complexity.

□ Computational complexity of conventional PTS : Weighting factor for the first block b1 = 1 To optimize rest of V-1 subblocks, WV-1 combinations

are analyzed to select candidate with minimum PAPR. Each candidate requires (V-1) complex addition and

multiplication. So total number of complex multiplication and

additions are WV-1 x (V - 1) each.


Example : WiMAX system N = 256 subcarriers ; V = 4 ; W = 2 ; subblock partition : adjacent ; R = 2

PTS using GPW : • An OFDM signal with 256 subcarriers are splitted into 4

subblock.Ex :

• These subblocks and phase factor are grouped into 2 group :

G1 : x1, x2

1

X = (1, -1, 1, 1, 1, -1, 1, -1)T

X1 : 1 -1 0 0 0 0 0 0X2 : 0 0 1 1 0 0 0 0X3 : 0 0 0 0 1 -1 0 0X4 : 0 0 0 0 0 0 1 -1

G2 : x1, x2

Phase factor G1 : [1 1]T, [1 -1]T

G2 : [1 1]T, [1 -1]T, [-1 1]T, [-1 -1]T


• The OFDM candidate sequences, x’, are obtained by combining candidate sequences from both groups.

• Transmitted signal is chosen from these candidate sequences with minimum PAPR.

• From this example, we only need 8 complex multiplication and additions. By using C-PTS, we need (2(4-1) x (4-1)) = 24 multiplication and additions.

Simulation Parameters

Parameters Value

Number of OFDM symbols 1000

Number of subcarriers (N) 256

Modulation schemeQPSK, 16-

QAM, 64-QAM

Number of subblocks used in PTS

method (V)4

Oversampling factor 4

PTS partition method adjacent

Simulation Result and Analysis (1)

3 4 5 6 7 8 9 10 11 1210

-3

10-2

10-1

100

PAPR0 (dB)

CC

DF

CCDF of OFDM signal with various modulation type

OFDM-QPSK

PTS OFDM-QPSK

OFDM-16-QAM

PTS OFDM-16-QAM

OFDM-64-QAM

PTS OFDM-64-QAM


NoModulation

Type

PAPR of original OFDM (dB)

PAPR of PTS-OFDM

(dB)

PAPR Reduction

(dB)

1 QPSK 10,9414 5,9728 4,9686

2 16-QAM 11,4176 6,4974 4,9202

3 64-QAM 11,0673 6,5593 4,508

Comparison of GPW-PTS Performance of OFDM signal with Various Modulation Types


2 3 4 5 6 7 8 9 10 11 1210

-3

10-2

10-1

100

PAPR0 (dB)

CC

DF

CCDF of QPSK with vary channel coding rate

OFDM-QPSK 1/2

PTS OFDM-QPSK 1/2

OFDM-QPSK 3/4

PTS OFDM-QPSK 3/4

3 4 5 6 7 8 9 10 11 1210

-3

10-2

10-1

100

PAPR0 (dB)

CC

DF

CCDF of 16-QAM with vary channel coding rate

OFDM-16-QAM 1/2

PTS OFDM-16-QAM 1/2

OFDM-16-QAM 3/4

PTS OFDM-16-QAM 3/4


Comparison of GPW-PTS Performance of OFDM signal with Various channel coding rate

NoModulation Type

Channel Coding Rate

PAPR of original

OFDM (dB)

PAPR of PTS-OFDM

(dB)

PAPR Reduction

(dB)c = a - b

(a) (b) (c)

1 QPSK1/2 11,4643 6,6327 4,8316

3/4 10,9414 5,9728 4,9686

2 16-QAM1/2 11,8504 7,3148 4,5356

3/4 11,4176 6,4974 4,9202

Conclusions

□ GPW-PTS has less computational complexity then C-PTS.

□ The choice of modulation type does not give significant effect on the PAPR value.

□ Even though, for QAM modulation, the higher order of modulation type gives less PAPR reduction.

□ The use of GPW-PTS in 802.16d system with various channel coding rate shows that higher channel coding rate gives higher PAPR reduction.

References

1. A.N Naqvi, A.M Abbas, T.A Chouhan, “Performance Evaluation of Fixed and Mobile WiMAX Networks for UDP Traffic,” International Journal of Advanced Research in Computer and Communication Engineering (IJARCCE), vol. 1, Issue 8, pp. 563-569, Oct. 2012.

2. B.S.K Reddy and B. Lakshmi, “Channel Coding and Clipping in OFDM for WiMAX using SDR,” International Journal on Recent Trends in Engineering and Technology (IJRTET), vol. 9, no. 1, pp. 66-74, July 2013.

3. S.H. Han, J.H. Lee, “An Overview of Peak-to-Average Power Ratio Reduction Techniques for Multicarrier Transmission,” IEEE Wireless Communications, vol. 12, no. 2, pp. 56–65, April 2005.

4. T. Jiang and Y. Wu, “An Overview : Peak-to-Average Power Ratio Reduction Techniques for OFDM Signals,” IEEE Transactions on Broadcasting, vol 54, no. 2, pp. 257-268, June 2008.

5. D.W. Lim, S.J. Hoe, J.S No, “An Overview of Peak-to-Average Power Ratio Reduction Schemes for OFDM Signals,” IEEE Journal of Communications and Networks, vol. 11, no. 3, pp. 229-239, June 2009.

6. P. Manhas and M.K. Soni, “A Review of PAPR Reduction Techniques for OFDM System,” MR International Journal of Engineering and Technology, vol. 6, no. 2, pp. 49-53, Dec. 2014.

7. S. H. Muller and J. B. Huber, “OFDM with Reduced Peak-to-Average Power Ratio by Optimum Combination of Partial Transmit Sequences,” IEEE Electronics Letters, vol. 33, no. 5, pp. 368-369, Feb. 1997.

8. L.J. Cimini 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, March 2000.

9. L. Wang and J. Liu, “PAPR Reduction of OFDM Signals by PTS With Grouping and Recursive Phase Weighting Methods,” IEEE Transactions on Broadcasting, vol. 57, no. 2, pp. 299-306, March 2011.

10.P. Pandey and R. Tripathi, “Computational Complexity Reduction of OFDM Signals by PTS with Alternate Optimised Grouping Phase Weighting Method,” International Journal of Computer Applications, vol. 78, no. 1, pp. 1-7, Sept. 2013.

11.P. Pandey and R. Tripathi, “Computational Complexity and Peak-to-Average Power Reduction of OFDM signals by PTS with Sub-optimum Grouping Phase Weighting Method,” International Journal of Computer Applications, vol. 79, no. 11, pp. 6-11, Oct. 2013.

12.A.B. Narasimhamurthy, M.K. Banavar, C. Tepedelenlioglu, OFDM System for Wireless Communications, Morgan Claypool Publishers, 2010, pp. 31-32.

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