Based on the Khatri-Rao matrix product, we propose a novel unitary space-time modulation design called KR-USTM in this paper. Different from existing USTM schemes, such as the systematic approach and space-time frequency-shift keying (ST-FSK), KR-USTM does not require any computer search and can be applied to any number of transmit antennas. Moreover, the special structure of KR-USTM also makes it a high-rate scheme and achieve full antenna diversity as well as lower decoding complexity. Simulation results show that the proposed KR-USTM constellation achieves error performance comparable to existing USTM designs at low rates, while it outperforms them at high rates.

The complexity of maximum-likelihood (ML) decoding for unitary space-time modulation (USTM) is exponential in the code rate times symbol periods. In this letter, we propose a new USTM scheme which consists of USTMs with noncoherent multistage decoding. The decoding of the proposed scheme is less complex than ML decoding. We also find some good codes of the proposed scheme according to the design criterion. Simulation results indicate that our codes perform better than seamless USTMs over the quasistatic fading channels.

Unitary space-time modulation (USTM) is well-tailored for flat fading channels where neither the transmitter nor the receiver knows the fading coefficients. A systematic approach to designing USTM is proposed by Hochwald et al., which is not guaranteed full diversity and difficult to put into practice due to the large number of signal points in the two-dimensional constellation. Consequently, we modify the systematic method to search new unitary space-time coded 8PSK with full diversity. Simulation results indicate that the error performances of the searched codes are better than or at least the same as those of the USTM in [2].