This letter investigates a distinct set of complex unitary matrices for differential space time coding by using QPSK modulation. The numerical results show that the properly selection of the initial transmission matrix and the set of unitary matrices can efficiently improve the bit error rate (BER) performance, especially for the antennas correlated fading channel. The computer simulations are evaluated over slow and fast Rayleigh fading channels.

Diagonal algebraic space time (DAST) block codes was proved to achieve the full transmit diversity over a quasi-static fading channel and to maintain 1 symbol/s/Hz. When the number of transmit antennas employed is larger than 2, DAST codes outperform the codes from orthogonal design with the equivalent spectral efficiency. However, due to the limitation on the signal constellation with complex integer points, no good 3bits/symbol DAST block code was given previously. In this paper, we propose a general form of 8-star-PSK constellations with integer points and present some theoretical results on the performance of the equivalent 8-star-PSK modulations. By using our proposed 8-star-PSKs, we present a searching algorithm to construct DAST codes with 3 bits per symbol under some criteria and investigate their performances over flat Rayleigh fading channels. It is shown that (5,2) 8-star-PSK scheme has a comparable performance to conventional 8PSK over additive white Gaussian noise (AWGN) channel and the corresponding DSAT codes constructed can achieve significant performance gain over flat Rayleigh fading channel.

Beam-space time coding methods are being extensively investigated, since they provide levels of performance appropriate for the next and future generations of wireless communication systems. In this paper, we focus on beam-domain space-time coding, especially considering the case when transmit beams have inter-beam interference (IBI). A new beam-space time coding scheme that takes into account the overlap amount among beams is proposed. We observe that the overlap of beams introduces an amount of correlation to the channels in a similar way to the well-known Partial Response (PR) channel in magnetic recording. Based on that observation, the proposed system can make use of IBI to encode and decode the signals. We evaluate the proposed system both via theoretical upper bound and via computer simulations. The Bit Error Rate (BER) performance of the proposed system using IBI is better than that of the system with no-IBI because the proposed system delivers more coding gain. However, the overlap of beams decreases the diversity gain. The tradeoff relationship between diversity gain and coding gain is investigated.