Structured space-time block codes with optimal diversity-multiplexing tradeoff and minimum delay

It is well-known that using multiple antennas can substantially increase the data rate and robustness of communication systems in a fading environment. It was recently established that there is a tradeoff between these two types of gains, termed diversity-multiplexing tradeoff. We develop a family of short structured space-time block codes that achieves the optimal tradeoff for the two-transmit two-receive antenna system with the minimum delay of two necessary for optimality. It uses the idea of rotation of cross-diagonal entries of an uncoded system to achieve spreading of information across space and time to obtain the maximum diversity while preserving multiplexing gain. Rotation angles that are optimal in terms of a determinant criterion and universal for all rates are identified. Performance analysis and simulation results are presented to demonstrate the achieved tradeoff.