Blind channel estimation and detection for space–time coded CDMA in ISI channels

In order to accommodate 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 ISI (inter-symbol interference) 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. To assess the performance of the proposed and other potential estimators, we derive an unconditional Cramér–Rao bound (CRB) which, similarly to the proposed blind channel estimator, does not assume the knowledge of the transmitted information symbols. 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.