A randomization technique for non-orthogonal space-time block codes

In this paper we propose a transmission concept that improves the performance of high rate non-orthogonal space-time block codes. Orthogonal space-time codes hare well known rate limitations [9], [7]. If the symbol rate is increased beyond those limits either code orthogonality [5] or the effective diversity gain is necessarily compromised. In the presence of channel coding the performance of non-orthogonal space-time codes is further degraded by "block-interference" inherent in the code construction. In this paper we present a general approach in which the non-orthogonaliiy is randomized with a sequence of pseudo-random unitary transformations.