Improved MIMO performance with non-orthogonal space-time block codes

Transmission over multiple input multiple output (MIMO) radio channels is considered. When multiple Rx antennas are present, one may simultaneously increase the rate and improve performance by optimizing transmit diversity, using nonorthogonal space-time block codes. This improves the performance of MIMO systems considerably, especially when the number of Tx and Rx antennas is small. As an example, we consider a 2 Tx, 2 Rx system, and construct a 2×2 nonorthogonal space-time block code with symbol rate 2, which performs 2.5 dB better than the corresponding BLAST system at BER 10^-3.