2204 IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS, VOL. 13, NO. 4, APRIL 2014
Invertible Subset LDPC Code for PAPR Reduction
in OFDM Systems with Low Complexity
Daiming Qu, Li Li, and Tao Jiang
Abstract—In this paper, we introduce a new family of low-
density parity-check (LDPC) codes, called as invertible subset
LDPC (IS-LDPC) code, for peak-to-average power ratio (PAPR)
reduction in OFDM systems with low complexity. An IS-LDPC
code has a number of disjoint invertible subsets, and each
invertible subset can be independently inverted to generate other
valid codewords of the LDPC code. To construct IS-LDPC codes
with good error-correcting performance, we propose a modified
progressive edge-growth construction algorithm and verify its
effectiveness by analyzing the constructed Tanner graphs. Both
theoretical analysis and numerical results show that the IS-
LDPC codes exhibit good error-correcting performance and the
proposed PAPR reduction scheme based on IS-LDPC codes
significantly reduces the PAPR. Compared with the existing
coding-based candidate generation schemes, the proposed scheme
has a much lower searching complexity when the codeword is
transmitted by multiple OFDM symbols. With all mentioned
advantages, the proposed PAPR reduction scheme based on IS-
LDPC codes could serve as an attractive PAPR reduction solution
for future multicarrier communication systems.
Index Terms—Orthogonal frequency-division multiplexing
(OFDM), peak-to-average power ratio (PAPR), low density
parity-check codes (LDPC), progressive edge-growth (PEG).
I. INTRODUCTION
O
RTHOGONAL frequency-division multiplexing
(OFDM) has been widely adopted in various wireless
communication standards, due to its capability to efficiently
cope with frequency selective channels. However, one
major drawback of OFDM systems is high p eak-to-average
power ratio (PAPR). High PAPR significantly complicates
implementation of the radio frequency front-end, since power
amplifiers with a wide linear range are required. Otherwise,
the nonlinear characteristics o f power amplifiers would distort
the in-band signal and raise the out-of-band radiation. To
reduce PAPR, many schemes have been proposed in the
literature [1], [2], among which coding-based approaches
have attracted considerable attentions due to their inherent
error contro l capability and the simplicity of implementation .
Particularly, coding-based approaches are classified into two
categories in this paper: low PAPR coding and coding-based
candidate generation schemes.
Manuscript received July 17, 2013; revised November 29, 2013; accepted
January 17, 2014. The associate editor coordinating the review of this paper
and approving it for publication was A. Vosoughi.
The authors are with the Department of Electronics and Information En-
gineering, Huazhong University of Science and Technology, Wuhan, 430074,
China (e-mail: Tao.Jiang@ieee.org). T. Jiang is the corresponding author.
This work was supported in part by the National Science Foundation of
China with Grants 61271228, 61172052 and 60872008, and the National and
Major Project under Grant 2013ZX03003016.
Digital Object Identifier 10.1109/TWC.2014.031314.131289
The low PAPR coding: It generates low PAPR codewords
through coding. The low PAPR code was firstly proposed
in [3]. In [4], the existence of asymptotically good codes
with low PAPR was proven. In [5], efficient computation of
the PAPR for any practical code was discussed. The Golay
complementary sequences and Reed-Muller (RM) codes to
achieve excellent PAPR performance were proposed in [6]
and [7]. Later, a complement block-coding (CBC) scheme
was proposed to reduce the PAPR in [8]. However, the error-
correcting performance of these codes are quite far from
the Shannon limit. In [9] and [10], time-frequency turbo
block codes (TBC) were proposed to achieve good error-
correcting performance as well as low PAPR, in which the
frequency domain component code employs codes with low
PAPR, like RM code or dual Bose-Ray-Chaudhuri code, and
the time domain component code uses low density parity-
check (LDPC) code. However, there are still appa rent error-
correcting performance gaps between the TBC codes and the
capacity achieving codes.
The coding-based candidate generation schemes: It g en-
erates candidate codewords for any given codeword and a
candidate with low PAPR is selected for transmission. In
[11], candidates are generated by employing a scrambler
before channel coding, therefore all candidates are also valid
codewords. In [12], candidate codewords are generated with
a number of interleavers before channel coding. Employment
of random-like codes, such as turbo and LDPC code, were
proposed in [13] and [14] to generate candidate codewords,
which d o not require an explicit scrambler/interleaver. More-
over, binary cyclic codes, Reed-Muller codes, Reed Solomon
and simplex codes are considered in [15]–[17]. At first sight,
the coding-based candidate generation schemes share the same
principle of PAPR reduction with the selective mapping (SLM)
[18] or partial transmit sequence (PTS) [19] schemes, which
generate candidate signals and select a candidate of low PAPR
for transmission. However, the m ajor difference is that the
candidates of the coding-based candidate generation schemes
are valid codewords, while those of the SLM and PTS schemes
are not necessarily valid codewords. Unlike the SLM and
PTS schemes, the coding-based candidate generation schemes
refrains from the use of explicit side information in the
receiver, with the help of coding [11].
Compared with low PAPR coding schemes, the coding-
based candidate generation schemes do not suffer significant
degradation of error-correcting performance, by employing
error-correcting codes of proven p erformance [11]. Therefore,
we focus on the coding-based candidate generation schemes
in this paper. However, the existing coding-based candidate
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