In this paper, a blind RAKE receiver with robust multiuser access interference cancellation is presented for frequency-selective Rayleigh fading channels. In contrast to a conventional receiver, here, only knowledge of the spreading code and rough timing of the desired user is required. By investigating the code space of the multipath signals and the data vector space, a RAKE filtering vector is developed to extract the desired data from all the paths of the desired user. Our proposed technique not only exploits the characteristics of multipath propagation but also the characteristics of timing offsets that may occur in the receiver, to facilitate the application of a blind linear filter-optimization technique for robust interference suppression. Based on the RAKE filtering vector, interference rejection is implemented by using the auxiliary-vector (AV) technique. Our approach, however, effectively overcomes the sensitivity of the original AV method to multipath propagation and timing offsets. To mitigate the signal cancellation at relatively high signal-to-interference and noise ratios (SINR) resulting from the estimation errors of the RAKE filtering vector, robust strategies are introduced in addition to the linear filter optimization. Simulation results are presented to show the effectiveness of the proposed techniques.

In this paper, we consider the maximum-likelihood multi-block decoding in differential space-time block coding systems. Since the computational complexity of the maximum-likelihood multi-block detector increases exponentially as a function of the number of signal blocks used in the decoding, a trellis-based Viterbi algorithm is proposed to implement multi-block space-time decoding without an increase in the computational complexity in each new branch-metric evaluation stage. It is demonstrated that by increasing the number of blocks, one can more efficiently utilize the differential coding relationship in the decoding process. A forgetting factor is further introduced into the maximum-likelihood decoding and the corresponding branch-metric is derived. Numerical results are presented to demonstrate the effects of fading rate, the value of the forgetting factor, and the number of comparative paths on the performance of the proposed approaches.

In this paper, we consider blind signal detection in a multicarrier direct-sequence code-division multiple- access system using an antenna array. A space-frequency filtering approach is proposed to coherently combine the desired signal contribution from all the space-frequency branches. Under the assumption of ideal knowledge of the channel and direction of arrival parameters, it is shown that the proposed space-frequency matched filtering approach provides the same performance as that of beamforming with maximum ratio combining. When blind detection is considered, however, the proposed approach exhibits superior performance to the latter. Numerical results are presented to demonstrate the effectiveness of the proposed blind detection approach.