SOS-based blind channel estimation in multiuser space-time block coded systems

In this paper the problem of blind channel estimation in multiuser space-time block coded (STBC) systems is considered. Specifically, a new blind channel estimation technique is proposed. The method is solely based on second-order statistics (SOS) and it generalizes previously proposed techniques, which are specific to orthogonal codes, to a wide class of STBCs and multiuser settings. Additionally, the STBC identifiability conditions are analyzed, and a new transmission technique is proposed. This technique is able to resolve many of the indeterminacy problems associated to the blind channel estimation process, and it is based on the use of different codes for transmitting different data blocks (a technique that we refer to as code diversity). In the simplest case, the proposed transmission technique reduces to a set of rotations or permutations of the transmit matrices of each user (non-redundant precoding). Finally, the performance of the proposed method is demonstrated by means of some simulation examples.