Open Access

Robust Adaptive OFDM with Diversity for Time-Varying Channels

EURASIP Journal on Wireless Communications and Networking20072007:078156

https://doi.org/10.1155/2007/78156

Received: 23 November 2006

Accepted: 17 April 2007

Published: 14 June 2007

Abstract

The performance of an orthogonal frequency-division multiplexing (OFDM) system can be significantly increased by using adaptive modulation and transmit diversity. An accurate estimate of the channel, however, is required at the transmitter to realize this benefit. Due to the time-varying nature of the channel, this estimate may be outdated by the time it is used for detection. This results in a mismatch between the actual channel and its estimate as seen by the transmitter. In this paper, we investigate adaptive OFDM with transmit and receive diversities, and evaluate the detrimental effects of this channel mismatch. We also describe a robust scheme based on using past estimates of the channel. We show that the effects of the mismatch can be significantly reduced with a combination of diversity and multiple channel estimates. In addition, to reduce the amount of feedback, the subband approach is introduced where a common channel estimate for a number of subcarriers is fedback to the transmitter, and the effect of this method on the achievable rate is analyzed.

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Authors’ Affiliations

(1)
Department of Electrical and Computer Engineering, University of Delaware

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Copyright

© E. Bala and L. J. Cimini, Jr. 2007

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.