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H.-G. Ryu et al.: Dummy Sequence Insertion (DSI) for PAPR Reduction in the OFDM Communication System

Contributed Paper Manuscript received November 11, 2003 0098 3063/04/$20.00 © 2004 IEEE

89

Dummy Sequence Insertion (DSI) for PAPR Reduction

in the OFDM Communication System

Heung-Gyoon Ryu, Member, IEEE, Jae-Eun Lee and Jin-Soo Park, Member, IEEE

Abstract — OFDM communications system is very

useful for the high data rate transmission. However, power

efficiency of HPA (high power amplifier) is very poor, since

there should be a large back-off because of the high PAPR

(peak-to-average power ratio) of the OFDM signal.

Otherwise, OFDM signal may be distorted by the nonlinear

HPA. In this paper, we propose a DSI (dummy sequence

insertion) method for PAPR reduction. The complementary

sequence and the combination of the correlation sequence

belong to the dummy sequence. Flipping technique can be

combined into DSI method to effectively lower the PAPR

reduction. Also, PAPR threshold technique escalates the

processing speed. Unlike the conventional PTS (partial

transmit sequence) and SLM (selected mapping) methods,the specified dummy sequence is inserted only for PAPR

reduction and any kind of side information is not necessary.

So, BER of the DSI method is independent of the error in

the dummy data sequence. Although the DSI method is not

better than the conventional PTS and block coding methods

with respect to the PAPR reduction performance, the DSI

method improves the BER performance than the

conventional PTS and is even more spectrally efficient than

the conventional block coding for PAPR reduction.

Index Terms: OFDM, HPA, PAPR reduction and

DSI (dummy sequence insertion )

ⅠⅠⅠⅠ. INTRODUCTION

OFDM (orthogonal frequency division modulation)

system has been adopted as standard for the DAB/DVB

(digital audio/video broadcasting) system, wireless LAN

(IEEE802.11x and HyperLAN II), xDSL, due to the

robustness to the ISI (inter symbol interference) and

multipath fading. However, OFDM signal has high PAPR

(peak-to-average power ratio) to make the power efficiency

and system performance poor. So, LPA (linear power

amplifier) or large back-off should be necessary to protect

the nonlinear distortion from the nonlinear HPA(high power amplifier). However, these methods are not effective with

respect to the cost and power efficiency.

1 Heung-Gyoon Ryu and Jae-Eun Lee are with the Department of Electronic Engineering, Chungbuk National University, San 48 Kaesin-dong, Cheongju, Chungbuk, 361-763, Republic of KOREA (e-mail:[email protected], [email protected] ).Jin-Soo Park is with Dept. of Information & Communication Engineering, Chongju University, 36 Naedok-Dong , Cheongju, Chungbuk, 360-764,Republic of Korea (e-mail: [email protected]).

So, many methods have been proposed to solve this high

PAPR problem: clipping method [1], block coding method

[2-3], SLM (selected mapping) method [4] and PTS (partial

transmit sequence) method [5-7]. At first, clipping is a very

simple method to reduce PAPR [1]. This can lower the

PAPR easily by cutting away the signal above the assigned

clip level. Out-of-band radiation and in-band distortion

appear so that the signal quality becomes poor. The second

one is a block coding method to keep the PAPR below 3dB

by orthogonal sequence [2]. It has been used in Magic

WAND (wireless ATM network demonstrator) system

because it does not degrade the OFDM signal and shows an

additional coding effect. However, the code rate and

bandwidth efficiency are very low. Also, computation isexponentially increased with the number of subcarriers.

Thirdly, SLM and PTS are the phase control method to

reduce PAPR [3,4]. SLM multiplies an OFDM data by

several phase sequences in parallel and selects the data

sequence of the lowest PAPR among them. PTS divides the

input OFDM data into several clusters and phase rotation

factors (or combining sequences) are multiplied to get the

low PAPR signal. Although these two methods can reduce

PAPR effectively without any signal distortion, the side

information about the phase rotation should be transmitted

to the receiver. Overall BER performance may be degraded

if there may be error in the side information. Furthermore,

system complexity considerably goes up because of many IFFT (inverse fast Fourier transform) stages and the

long phase optimization processes.

We present a DSI(dummy sequence insertion) method. It

is more spectrally efficient than the block coding method

and is very simple than PTS and SLM method. In this DSI

method, dummy sequence is added into the input data for

the PAPR reduction before the IFFT stage. Complimentary

sequence, correlation sequence and other specific sequence

may be used as the dummy sequence that does not work as

the side information unlike the PTS and SLM methods. So,

DSI has better BER performance than the PTS and SLM

since there is no degradation from the side information

error. PAPR threshold technique is combined into this DSI

method. If the PAPR of IFFT output is lower than a certain

prescribed PAPR threshold level, the IFFT output data is

transmitted. Otherwise, dummy sequence is inserted to

lower the PAPR. This technique escalates the processing

speed. We introduce the 4 kinds of DSI method according

to the dummy sequences. CCDF(complimentary cumulative

distribution function) property for PAPR reduction and the

BER performance are studied in the nonlinear HPA.



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