Skip to content


  • Research Article
  • Open Access

Adaptive Iterative Soft-Input Soft-Output Parallel Decision-Feedback Detectors for Asynchronous Coded DS-CDMA Systems

EURASIP Journal on Wireless Communications and Networking20052005:721714

  • Received: 29 April 2004
  • Published:


The optimum and many suboptimum iterative soft-input soft-output (SISO) multiuser detectors require a priori information about the multiuser system, such as the users' transmitted signature waveforms, relative delays, as well as the channel impulse response. In this paper, we employ adaptive algorithms in the SISO multiuser detector in order to avoid the need for this a priori information. First, we derive the optimum SISO parallel decision-feedback detector for asynchronous coded DS-CDMA systems. Then, we propose two adaptive versions of this SISO detector, which are based on the normalized least mean square (NLMS) and recursive least squares (RLS) algorithms. Our SISO adaptive detectors effectively exploit the a priori information of coded symbols, whose soft inputs are obtained from a bank of single-user decoders. Furthermore, we consider how to select practical finite feedforward and feedback filter lengths to obtain a good tradeoff between the performance and computational complexity of the receiver.


  • soft-input soft-output multiuser detection
  • adaptive multiuser detection
  • parallel decision-feedback detection
  • adaptive soft-input soft-output parallel decision-feedback detection
  • asynchronous coded CDMA systems

Authors’ Affiliations

School of Information Technology and Engineering (SITE), University of Ottawa, 800 King Edward Avenue, Ottawa, ON, K1N 6N5, Canada


© Zhang et al. 2005

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.