IS-LDPC码优化OFDM-WLAN系统的PAPR与频谱多样性

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本文探讨了在OFDM-WLAN系统中降低峰值信噪比(Peak-to-Average Power Ratio, PAPR)的一种新型低密度奇偶校验码（Low Density Parity Check, LDPC）技术——可逆子集LDPC (IS-LDPC) 码。IS-LDPC码是一种最近提出的新编码方法，它以较低的复杂度实现了高效的PAPR降低效果。PAPR是OFDM系统中的一个重要挑战，尤其是在无线局域网络(WLAN)如IEEE 802.11标准的OFDM-WLAN系统中，高PAPR可能导致信号失真和功率效率下降。本文首先介绍了IS-LDPC码的基本原理，这种编码方式利用子集的特性来设计，其编码过程不仅保持了信息的有效传递，还能够在编码过程中实现某种程度的反转性，有助于平滑OFDM信号的幅度波动，从而减少PAPR。作者关注的是将其应用到实际的OFDM-WLAN系统中，以满足IEEE 802.11标准对系统性能的要求。为了进一步提升系统的性能，文中提出了一种交错子集映射方案。这种方案旨在通过频域上的多样化映射，增强信号的空间多样性，从而提高系统的抗干扰能力和数据传输的可靠性。这样做的目的是在降低PAPR的同时，不牺牲系统的其他关键指标。通过仿真结果，作者证明了IS-LDPC码对于IEEE 802.11 OFDM-WLAN系统具有出色的纠错能力，并显著降低了PAPR。IS-LDPC编码方案的优势明显，包括高效的PAPR降低、良好的错误纠正性能以及对系统整体性能的积极影响。因此，基于IS-LDPC码的PAPR降低方案对于OFDM-WLAN系统来说是一个有前景的技术解决方案，值得在实际应用中进一步研究和优化。

Invertible Subset LDPC Codes for PAPR Reduction

in OFDM-WLAN Systems

Si Shu and Daiming Qu

School of Electronic Information and Communications

Huazhong University of Science and Technology

Wuhan 430074, China

shusihoon@gmail.com

qudaiming@hust.edu.cn

Xuebing Pei

China Ship Development and Design Center

Wuhan 430064, China

peixbhust@163.com

Abstract—A new type of low density parity-check (LDPC)

codes, called as invertible subset LDPC (IS-LDPC) codes, was

proposed to reduce the peak-to-average power ratio (PAPR)

for orthogonal frequency-division multiplexing (OFDM) systems

with low complexity recently. In this paper, we apply IS-

LDPC codes to OFDM-wireless local area networks (OFDM-

WLAN) systems and design parameters of IS-LDPC codes to

satisfy requirements of the IEEE 802.11 OFDM-WLAN system.

Moreover, we propose interleaved subset mapping scheme to

guarantee the frequency diversity gain. The simulation results

show that the IS-LDPC codes for the IEEE 802.11 OFDM-

WLAN system exhibit good error-correcting performance and

signiﬁcantly reduce the PAPR. With all mentioned advantages,

the PAPR reduction scheme based on IS-LDPC codes could serve

as an attractive PAPR reduction solution for the IEEE 802.11

OFDM-WLAN systems.

Keywords—orthogonal frequency-division multiplexing (OFD-

M); wireless local area networks (WLAN); peak-to-average

power ratio (PAPR); invertible subset low density parity-check

codes (IS-LDPC); IEEE 802.11

I. INTRODUCTION

The IEEE 802.11 Wireless Local-Area Networks (WLAN)

[1] is the dominant technology adopted in many local broad-

band wireless communication scenarios. The IEEE 802.11

adopts orthogonal frequency-division multiplexing (OFDM)

as its physical layer speciﬁcations due to its immunity to

frequency selective channels. However, one major drawback

of OFDM-WLAN systems is high peak-to-average power ratio

(PAPR). High PAPR results in the in-band distortion and

out-of-band radiation when the OFDM signal is fed into a

nonlinear power ampliﬁer [2].

Recently, a new kind of low density parity-check (LDPC)

codes, called as invertible subset LDPC (IS-LDPC) codes,

was proposed in [3], of which each invertible subset can be

independently inverted to generate other valid codewords of

the LDPC code. The main idea of PAPR reduction scheme

with IS-LDPC codes is to generate candidate codewords and

select the candidate with low PAPR for transmission. It is ob-

vious that IS-LDPC codes belong to the type of coding-based

candidate generation schemes [3], [4]. It has been concluded

This work was supported in part by the National Science Foundation of

China with Grants 61271228.

that the PAPR reduction scheme with IS-LDPC codes has good

error-correcting and signiﬁcant PAPR reduction performance.

Moreover, it supports multiple-OFDM-symbol frames very

well, by dramatically reducing the searching complexity [3].

In this paper, we apply IS-LDPC codes to the IEEE 802.11

OFDM-WLAN system. We design parameters of IS-LDPC

codes to satisfy requirements of the IEEE 802.11 OFDM-

WLAN systems and propose a novel subset mapping scheme

that distributes symbols of invertible subsets over the sub-

carriers in an interleaved manner. Moreover, we verify their

error-correcting and PAPR reduction performance by simula-

tions.

II. B

RIEF REVIEW OF IS-LDPC CODES

A. Deﬁnitions of IS-LDPC Codes

Deﬁnition 1 (Invertible Subset): Let vector A =

, ··· ,a

] denote a codeword of binary linear

block code A, and subset S = {i

, ··· ,i

} denote

a subset of indexes of the coded bits, i.e., {i

, ··· ,i

}

⊆{1, 2, ··· ,n}. Subset S is an invertible subset if, for any

valid codeword A of A, codeword



A =[a

, a

, ··· , a

] is a

valid codeword of A, where

a



,i∈S

, otherwise

. (1)

Deﬁnition 2 (IS-LDPC codes of inversion freedom U): An

invertible subset LDPC (IS-LDPC) code of inversion freedom

U is an LDPC code with U invertible subset, and there is no

intersection among different invertible subsets.

According to the above deﬁnitions, if an IS-LDPC code

has multiple disjoint invertible subsets, these subsets can be

inverted independently, and all generated codewords are valid

codewords.

B. PAPR Reduction Based on IS-LDPC Codes

Fig. 1 illustrates the transmitter of the OFDM system

with an IS-LDPC code for PAPR reduction. After the IS-

LDPC encoding, the coded bits can be represented as A =

, A

, ··· , A

], where A

(1 ≤ u ≤ U ) represents the

coded bits of the uth invertible subset S

, and A

represents

____________________________________



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