Diagonally weighted orthogonal space-time block codes

This paper shows how the performance of orthogonal space-time block codes can be improved by using a diagonal weighting matrix at the transmitter. The optimal diagonal weighting matrix which minimizes the bit-error-rate is derived: Since the optimal weights depend on the channel, a feedback from the transmitter to the receiver is necessary. However this feedback can be achieved using only log(2)(n(t)) bits where nt is the number of transmit antennas. Simulations show that for a system with two transmit antennas and one receive antenna, an improvement of 1.5 dB can be achieved with a feedback of only one bit. The effect of errors in the feedback is also analyzed, and an error tolerant weighting scheme is introduced to reduce the adverse effects of feedback errors: