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International Journal of Digital Multimedia Broadcasting
Volume 2008, Article ID 897069, 7 pages
http://dx.doi.org/10.1155/2008/897069
Research Article

Turbo Decoder for Low-Power Ultrawideband Communication Systems

Department of Electrical Engineering, University of Mississippi, Oxford, MS 38677, USA

Received 1 April 2008; Revised 11 July 2008; Accepted 8 October 2008

Academic Editor: Marina Mondin

Copyright © 2008 Esam A. Obiedat and Lei Cao. 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.

Abstract

A new method to reduce the computational complexity of the turbo decoding in ultrawideband (UWB) orthogonal frequency division multiplexing (OFDM) system is proposed. Existing stopping techniques for turbo decoding process using constrained decoding assume fixed signal-to-noise ratio (SNR) for all the OFDM symbol bits so they fail to yield an acceptable bit-error rate (BER) performance in multicarrier systems. In this paper, we propose a bit-level stopping technique for turbo decoding process based on the constrained decoding method. In this technique, we combine the cyclic redundancy check (CRC) with an adaptive threshold on the log likelihood ratio (LLR) on each subcarrier to detect for convergence. The threshold is adaptive in the sense that the threshold on the LLR of a bit is determined by the average SNR of the OFDM symbol and the channel gain of the transmission subcarrier. Results show that when the channel state information (CSI) is used to determine the threshold on LLR, the stopping technique can reduce the computational complexity by about 0.5–2.5 equivalent iterations compared to GENIE turbo without degradation in the BER performance.