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 have well known rate limitations (Tarokh et al. 1999, Tirkkonen and Hottinen 2000). If the symbol rate is increased beyond those limits either code orthogonality (Tirkkonen et al. 2000) 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-orthogonality is randomized with a sequence of pseudo-random unitary transformations.