EURASIP Journal on Wireless Communications and Networking 
Volume 2005 (2005), Issue 2, Pages 206-215
doi:10.1155/WCN.2005.206

Blind Multiuser Detection for Long-Code CDMA Systems with Transmission-Induced Cyclostationarity

Tongtong Li,1 Weiguo Liang,1 Zhi Ding,2 and Jitendra K. Tugnait3

 1Department of Electrical and Computer Engineering, Michigan State University, East Lansing 48824, MI, USA
2Department of Electrical and Computer Engineering, University of California, Davis 95616, CA, USA
3Department of Electrical and Computer Engineering, Auburn University, Auburn, AL 36849, USA
Received 30 April 2004; Revised 5 August 2004

Abstract

We consider blind channel identification and signal separation in long-code CDMA systems. First, by modeling the received signals as cyclostationary processes with modulation-induced cyclostationarity, long-code CDMA system is characterized using a time-invariant system model. Secondly, based on the time-invariant model, multistep linear prediction method is used to reduce the intersymbol interference introduced by multipath propagation, and channel estimation then follows by utilizing the nonconstant modulus precoding technique with or without the matrix-pencil approach. The channel estimation algorithm without the matrix-pencil approach relies on the Fourier transform, and requires additional constraint on the code sequences other than being nonconstant modulus. It is found that by introducing a random linear transform, the matrix-pencil approach can remove (with probability one) the extra constraint on the code sequences. Thirdly, after channel estimation, equalization is carried out using a cyclic Wiener filter. Finally, since chip-level equalization is performed, the proposed approach can readily be extended to multirate cases, either with multicode or variable spreading factor. Simulation results show that compared with the approach using the Fourier transform, the matrix-pencil-based approach can significantly improve the accuracy of channel estimation, therefore the overall system performance.