Improved Iterative Parallel Interference Cancellation Receiver for Future Wireless DS-CDMA Systems
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Improved Iterative Parallel Interference Cancellation Receiver for Future Wireless DS-CDMA Systems Simone Morosi Electronics and Telecommunication Department, University of Florence, Via di S. Marta 3, Firenze 50139, Italy Email: [email protected]
Romano Fantacci Electronics and Telecommunication Department, University of Florence, Via di S. Marta 3, Firenze 50139, Italy Email: [email protected]
Andrea Bernacchioni Electronics and Telecommunication Department, University of Florence, Via di S. Marta 3, Firenze 50139, Italy Email: [email protected] Received 1 August 2003 We present a new turbo multiuser detector for turbo-coded direct sequence code division multiple access (DS-CDMA) systems. The proposed detector is based on the utilization of a parallel interference cancellation (PIC) and a bank of turbo decoders. The PIC is broken up in order to perform interference cancellation after each constituent decoder of the turbo decoding scheme. Moreover, in the paper we propose a new enhanced algorithm that provides a more accurate estimation of the signal-to-noiseplus-interference-ratio used in the tentative decision device and in the MAP decoding algorithm. The performance of the proposed receiver is evaluated by means of computer simulations for medium to very high system loads, in AWGN and multipath fading channel, and compared to recently proposed interference-cancellation-based iterative MUD, by taking into account the number of iterations and the complexity involved. We will see that the proposed receiver outperforms the others especially for highly loaded systems. Keywords and phrases: code division multiple access, parallel interference cancellation, turbo multiuser detection, iterative detection and decoding, nonlinear MMSE soft decision.
1.
INTRODUCTION
One of the main shortages of the code division multiple access (CDMA) communication systems can be identified in their vulnerability to multiple access interference (MAI): hence, during the 90s, great attention has been devoted to multiuser detection strategies that constitute the natural answer to this problem; the receivers based on this technique aim to exploit the interference as an additional information source but, generally, are characterized by a very high complexity. Firstly, multiuser detection researches have been focused on uncoded systems; however, practical CDMA communications rely on the utilization of error control coding and interleaving so that, recently, more and more attention has been addressed to coded systems. Optimal joint decoding/detection is an excellent solution to this problem, as shown in [1]. However, this scheme results in a prohibitive computational complexity for actual implementa-
tion. In contrast, suboptimal solutions, which separate the operations of symbol detection and channel decoding, appear more attractive for practical applications. Particularly, the successful proposal of turbo codes [2] naturally leads to investigate the feasibility of iterative (turbo) processing techniques in t
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