Subspace-based channel identification and multiuser detection for space-time coded DS-CDMA systems

In order to accomodate high data-rate applications, there is a significant interest in extending space-time (ST) coding, originally proposed for frequency-nonselective channels assumed known to the receiver, to unknown multipath channels. In this paper, we consider the problem of blind channel identification and linear multiuser receiver design for ST-coded CDMA (code-division multiple-access) systems operating in frequency-selective fading channels. We investigate the identifiability conditions and present a subspace-based blind channel estimator for such systems. We discuss various linear multiuser detection schemes that can be used in conjunction with the proposed channel estimator for symbol demodulation in ST-coded CDMA systems. Numerical examples are presented to illustrate the performance of the proposed channel estimator and linear detectors in multipath Rayleigh fading channels.