Spectrally-efficient differential-space-time coding using non-full-diverse constellations

A method to construct spectrally-efficient unitary space-time codes is proposed for high-rate differential communications over multiple-antenna channels. Unlike most of the known methods which are designed to maximize the diversity product (minimum determinant distance), we aim at increasing the spectral efficiency. Simulation results indicate that for high spectral efficiency and for more than one receive antenna, the new method significantly outperforms the known alternatives. In the special case of two transmit antennas, which is the main focus of the paper, the relation between the proposed code and the Alamouti scheme helps us to provide an efficient maximum likelihood decoding algorithm. We also show that similar ideas can be applied to more than two transmit antennas. As an example, we present a construction for 4 by 4 unitary constellations which has good performance as compared to the other known codes.