High-Rate 3-D Reflection Space-Time Shift Keying With Indexed Additional Phases

Space-time shift keying (STSK) systems can transmit information in the form of indices activated by dispersion matrices, which allows a high degree of freedom in system design to balance the tradeoff between diversity gain and multiplexing gain. This paper proposes a high-rate reflection STSK system based on a 3-D constellation and a reconfigurable intelligent surface (RIS). To implement reflection phase shifting, a set of reflection dispersion matrices (RDMs) are constructed without power limit. To improve bandwidth efficiency, an additional phase is introduced to the selected 3-D constellation point and carries up to three bits. An upper bound for bit error rate (BER) is derived under maximum-likelihood (ML) detection. It is shown that both diversity gain and coding gain rely on the construction of the RDMs for the system. Accordingly, a genetic algorithm is proposed for randomly generating an optimal family of the RDMs and the additional phase parameter. Simulation results show that the proposed system can improve both bandwidth efficiency and power efficiency, when compared with the traditional 3-D STSK and RIS-based SSK-assisted Alamouti space-time block coding systems.