A Sufficient Condition for Blind Identifiability of MIMO-OSTBC Channels Based on Second Order Statistics

In this paper the conditions for blind identifiability of multiple-input multiple-output (MIMO) channels under orthogonal space-time block coded (OSTBC) transmissions are studied. Specifically we prove that, regardless of the number of receive antennas, any real or complex OSTBC transmitting an odd number of real symbols permits the blind identification of the MIMO channel by only exploiting the second order statistics (SOS) of the received signal. This result extends to complex OSTBCs and provides an alternative proof of an identifiability theorem previously proved only for real OSTBCs in N. Ammar and Zhi Ding (2002). Furthermore, this sufficient condition suggests that any non-identifiable OSTBC can be made identifiable simply by not transmitting one real symbol of each block (either the real or imaginary part of a symbol in the case of complex OSTBCs). In order to minimize the reduction in the transmission rate, several OSTBC blocks are grouped before erasing one real symbol. It is shown in the paper that the proposed rate-reduction technique outperforms the differential OSTBC scheme in terms of capacity for a wide range of SNRs