Improving a Power Line Communications Standard with LDPC Codes
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Research Article Improving a Power Line Communications Standard with LDPC Codes Christine Hsu,1 Neng Wang,1, 2 Wai-Yip Chan,1 and Praveen Jain1 1 Department 2 Nortel
of Electrical and Computer Engineering, Queen’s University, Kingston, ON, Canada K7L 3N6 Networks, Richardson, TX 75082-4399, USA
Received 31 October 2006; Revised 7 March 2007; Accepted 4 May 2007 Recommended by Lutz Lampe We investigate a power line communications (PLC) scheme that could be used to enhance the HomePlug 1.0 standard, specifically its ROBO mode which provides modest throughput for the worst case PLC channel. The scheme is based on using a low-density parity-check (LDPC) code, in lieu of the concatenated Reed-Solomon and convolutional codes in ROBO mode. The PLC channel is modeled with multipath fading and Middleton’s class A noise. Clipping is introduced to mitigate the effect of impulsive noise. A simple and effective method is devised to estimate the variance of the clipped noise for LDPC decoding. Simulation results show that the proposed scheme outperforms the HomePlug 1.0 ROBO mode and has lower computational complexity. The proposed scheme also dispenses with the repetition of information bits in ROBO mode to gain time diversity, resulting in 4-fold increase in physical layer throughput. Copyright © 2007 Christine Hsu et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
1.
INTRODUCTION
Power line communications (PLC) have received increasing attention due to the wide availability of power lines, even though PLC face the challenge of harsh and noisy transmission channels. HomePlug 1.0 is a current industry standard for PLC in North America [1]. It uses concatenated Reed-Solomon (RS) and convolutional forward error correction (FEC) with interleaving for coding payload data and orthogonal frequency division multiplexing (OFDM) for modulation. HomePlug guarantees rates from 1–14 Mbps for the physical layer (PHY) throughput. The low-end 1 Mbps throughput is obtained when operating the robust-OFDM (ROBO) mode over severely degraded channels. The goal of this paper is to improve the low-end throughput. As we describe below, the throughput can be increased considerably with no increase in complexity. The convolutional decoder in ROBO mode performs hard decision decoding. Recently, various studies have been carried out to investigate the application of various powerful FEC techniques with soft decision decoding, such as turbo codes and low-density parity-check (LDPC) codes, to PLC and reported promising results [2–4]. Ardakani et al. [2] model the PLC channel by the concatenation of an additive white Gaussian noise (AWGN) channel with an erasure
channel. Umehara et al. [3] and Nakagawa et al. [4] use the Middleton class A noise (AWCN) model [5] to simulate the impulsive noise for the PLC channel. The Middleton class A noise model has been shown in the literature to be
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