Open Access

An Opportunistic Error Correction Layer for OFDM Systems

EURASIP Journal on Wireless Communications and Networking20092009:750735

https://doi.org/10.1155/2009/750735

Received: 29 July 2008

Accepted: 14 January 2009

Published: 18 February 2009

Abstract

We propose a novel cross layer scheme to reduce the power consumption of ADCs in OFDM systems. The ADCs in a receiver can consume up to 50% of the total baseband energy. Our scheme is based on resolution-adaptive ADCs and Fountain codes. In a wireless frequency-selective channel some subcarriers have good channel conditions and others are attenuated. The key part of the proposed system is that the dynamic range of ADCs can be reduced by discarding subcarriers that are attenuated by the channel. Correspondingly, the power consumption in ADCs can be decreased. In our approach, each subcarrier carries a Fountain-encoded packet. To protect Fountain-encoded packets against bit errors, an LDPC code has been used. The receiver only decodes subcarriers (i.e., Fountain-encoded packets) with the highest SNR. Others are discarded. For that reason a LDPC code with a relatively high code rate can be used. The new error correction layer does not require perfect channel knowledge, so it can be used in a realistic system where the channel is estimated. With our approach, more than 70% of the energy consumption in the ADCs can be saved compared with the conventional IEEE 802.11a WLAN system under the same channel conditions and throughput. In addition, it requires 7.5 dB less SNR than the 802.11a system. To reduce the overhead of Fountain codes, we apply message passing and Gaussian elimination in the decoder. In this way, the overhead is 3% for a small block size (i.e., 500 packets). Using both methods results in an efficient system with low delay.

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Authors’ Affiliations

(1)
The Signals and Systems Group, Department of Electrical Engineering Mathematics and Computer Science (EEMCS), University of Twente

Copyright

© Xiaoying Shao et al. 2009

This article is published under license to BioMed Central Ltd. 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.