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Abstract
We propose an iterative multiuser detector for turbo-coded synchronous and asynchronous direct-sequence CDMA (DS-CDMA) systems. The receiver is derived from the maximum a posteriori (MAP) estimation of the single user's transmitted data, conditioned on information about the estimate of the multiple-access interference (MAI) and the received signal from the channel. This multiple-access interference is reconstructed by making hard decisions on the users' detected bits at the preceding iteration. The complexity of the proposed receiver increases linearly with the number of users. The proposed detection scheme is compared with a previously developed one. The multiuser detector proposed in this paper has a better performance when the transmitted powers of all active users are equal in the additive white Gaussian noise (AWGN) channel. Also, the detector is found to be resilient against the near-far effect.
Highlights
A significant amount of work has been done on the development of multiuser detectors (MUD) for CDMA since the publication of the novel work of Verdu [1]
Realizing that error correction coding alone cannot remove the effects of the multiple-access interference effectively, a lot of emphasis is being placed on designing multiuser detectors for channel-coded CDMA systems
Work done on reducing the complexity of iterative detectors to levels that can be practically implemented has mainly focused on combining various suboptimal multiuser detectors with iterative channel decoding in an integrated manner
Summary
A significant amount of work has been done on the development of multiuser detectors (MUD) for CDMA since the publication of the novel work of Verdu [1]. The main focus of work on MUD development has been the search for suboptimal detectors because the optimum receiver of [1] has an implementation complexity that increases exponentially with the number of users. Nonlinear multiuser detection involves the subtraction of the estimate of the multiple-access interference from the received signal [2, 3]. Work done on reducing the complexity of iterative detectors to levels that can be practically implemented has mainly focused on combining various suboptimal multiuser detectors with iterative channel decoding in an integrated manner. In [9], an iterative interference canceller was proposed for convolutional-coded CDMA. This scheme integrates the subtraction of the estimated multiple-access interference and channel decoding.
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