A Hybrid Receiver Scheme for Multiuser Multicode CDMA Systems in Multipath Fading Channels

• Published in: IEEE transactions on vehicular technology 2007-09, Vol.56 (5), p.3014-3023
• Main Authors: Thian, Boon Sim, Wang, Yuhong, Tjhung, Tjeng Thiang, Wong, Lawrence Wai-Choong
• Format: Article
• Language: English
• Subjects: Applied sciences; Bit error rate; Channels; Code division multiple access; Coding, codes; Computer errors; Computer simulation; Degradation; Detection, estimation, filtering, equalization, prediction; Equalization; Equalizers; Errors; Estimates; Exact sciences and technology; Fading; Information, signal and communications theory; Interference cancellation; iterative interference cancellation (IC); Miscellaneous; Multiaccess communication; multicode code-division multiple access (M-CDMA); Multipath channels; RAKE receivers; Rakes; Receivers; Signal and communications theory; Signal processing; Signal, noise; Studies; Systems, networks and services of telecommunications; Telecommunications; Telecommunications and information theory; Transmission and modulation (techniques and equipments)
• ISSN: 0018-9545; 1939-9359
• DOI: 10.1109/TVT.2007.900387

In this paper, we present a system model for multiuser multicode code-division multiple access (CDMA) in a multipath fading channel and propose a hybrid receiver scheme for the system. Conventional receivers for CDMA systems utilized interference cancellation (IC) schemes, with the RAKE receiver as an initial data estimator. However, the RAKE receiver generates inaccurate data estimates due the interference that is caused by the cross correlation between the spreading codes. This inaccurate data estimate leads to significant error propagation to the subsequent stages and thus degrades the bit error rate (BER) performance. Our proposed scheme overcomes the problem by using a more accurate initial data estimator. It consists of an equalizer for obtaining initial data estimation, followed by several stages of parallel IC (PIC). Computer simulation results show that the BER curves of our proposed scheme do not encounter an error floor under all channel conditions; in contrast, the BER curves of the conventional RAKE-PIC receiver are constrained by an irreducible error floor. In addition, in an uplink four-path channel and at a BER of 10 -3 , our simulation results show that a one-stage PIC achieves a 2.5-dB gain over the first stage equalization receiver.