Abstract
The Cayley differential (CD) codes constitute a systematic way to construct differential unitary space-time codes for noncoherent MIMO communications. The present authors propose designing CD codes by minimising the union bound based on the exact pairwise error probability (PEP). The gradient descent method is employed to numerically search the optimum dispersion matrices. They search the optimum CD codes for a particular scenario taking into account the number of transmit and receive antennas and the operating SNR. Simulation results show that codes optimised by the new criterion generally outperform the CD codes designed by maximising the expected distance between codeword pairs and the Cayley TAST codes that satisfy the full rank criterion. The new CD codes also enjoy better or comparable performance over other group-based or non-group codes.
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