Iterative (Turbo) soft interference cancellation and decoding for coded CDMA

doi:10.1109/26.774855

1999-07-01

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Xiaodong Wang *

H. Vincent Poor

DOI：10.1109/26.774855

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摘要

En 中文

The presence of both multiple-access interference (MAI) and intersymbol interference (ISI) constitutes a major impediment to reliable communications in multipath code-division multiple-access (CDMA) channels. In this paper, an iterative receiver structure is proposed for decoding multiuser information data in a convolutionally coded asynchronous multipath DS-CDMA system. The receiver performs two successive soft-output decisions, achieved by a soft-input soft-output (SISO) multiuser detector and a bank of single-user SISO channel decoders, through an iterative process, At each iteration, extrinsic information is extracted from detection and decoding stages and is then used as a priori information in the next iteration, just as in Turbo decoding, Given the multipath CDMA channel model, a direct implementation of a sliding-window SISO multiuser detector has a prohibitive computational complexity, A low-complexity SISO multiuser detector is developed based on a novel nonlinear interference suppression technique, which makes use of both soft interference cancellation and instantaneous linear minimum mean-square error filtering. The properties of such a nonlinear interference suppressor are examined, and an efficient recursive implementation is derived. Simulation results demonstrate that the proposed low-complexity iterative receiver structure for interference suppression and decoding Offers significant performance gain over the traditional noniterative receiver structure. Moreover, at high signal-to-noise ratio, the detrimental effects of MAI and ISI in the channel can almost be completely overcome by iterative processing, and single-user performance can be approached.

Keyword:

coded CDMA

instantaneous MMSE filtering

multiuser detection

soft interference cancellation

Turbo processing