SOS-based blind channel estimation under space-time block coded transmissions

In this paper, a new blind channel estimation technique for multiple- input multiple-output (MIMO) space-time block coded (STBC) systems is proposed. The technique is solely based on second-order statistics (SOS), and it consists on the extraction of the main eigenvector of a modified correlation matrix. Furthermore, it can be interpreted as a deterministic technique, i.e., in the absence of noise it is able to exactly recover the channel, up to a real scalar, within a finite number of observations. Unfortunately, in many practical cases there exist ambiguities associated to the problem of blind channel estimation from SOS. In order to resolve these problems we propose a new transmission technique, which is based on the combination of different STBCs (code diversity). In the simplest case, this technique reduces to a rotation or permutation of the transmit antennas (non-redundant precoding). Finally, the performance of the proposed method is demonstrated by means of some simulation examples.