Joint Iterative Multiuser and Narrowband Interference Suppression inCoded Asynchronous DS-CDMA Channels

  • Authors:

  • Joseph Thomas;Evaggelos Geraniotis

  • Affiliations:

  • Department of Electrical and Computer Engineering and Institute for Systems Research, University of Maryland, College Park, MD, U.S.A.;Department of Electrical and Computer Engineering and Institute for Systems Research, University of Maryland, College Park, MD, U.S.A.

  • Venue:
  • Wireless Personal Communications: An International Journal
  • Year:
  • 2001

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Abstract

Multiuser interference suppression in coded direct sequence code division multiple access (DS-CDMA) uplink channels is significantly impacted by the application of the turbo processing concept. This paradigm essentiallyinvolvesthe iterative exchange of soft information between a multiuser demodulator andabank of single-user decoders, to their mutual benefit. The present workproposesa joint iterative minimum mean square error (MMSE) multiuser and narrowbandinterference suppressor for coded asynchronous DS-CDMA channels. Since theparameters of the narrowband interference are unknown a priori, the first iteration in this scheme is effectively just MMSE multiuser interferencesuppression. The outputs of all users' soft decoders (available at the end of each iteration) are fed back to subtract their (estimated) cumulativecontribution from the received signal vector. The residue comprisesthe narrowband interference embedded in wideband noise, so that the former can be piecewise interpolated over chipintervals of appropriate duration, and then subtracted from the receivedsignal, to provide a narrowband-interference-free input signal for the next iteration. The soft-decoded feedback estimates of theinterferers' signals are used in each iteration also to perform soft MMSEmultiuser interference suppression, in conjunction with subtractiveinterferencecancellation. This scheme performs well at both low and high received signal powers,and displays the successive cancellation property across iterations,exhibiting good near-far resistance. Introducing multisensor arraysat the receiver relaxes the limitations imposed by the inherent suboptimalityof MMSE multiuser demodulation, insofar as it enhances interuser separation,nowin the spatial sense. Simulations indicate that the performance of theproposedtechnique surpasses that of all existing suboptimal algorithms in thiscontext.