Joint Time Index Modulation and Receive Antenna Selection for RIS-Aided Communications

In this paper, a novel design, named after time index modulation (TIM) with reconfigurable intelligent surface (RIS)-aided receive antenna selection (RAS), is proposed to improve the spectral efficiency (SE) and the bit error rate (BER) performance. By exploiting both the time and space domains, the TIM-RIS-RAS is able to convey the extra index information by using the indexes of both time index (TI) vectors and receive antennas (RA). Specifically, at the transmitter with only single transmit antenna, a TI vector is selected from a TI vector set according to the TI information to modulate the quadrature amplitude modulation/phase-shift keying (QAM/PSK) symbol(s), resulting in the TI vector symbol. Then, based on the TI vector symbol with zero and non-zero elements, the TIM is amalgamated with the RAS to support the RIS-spatial modulation/spatial shift keying (RIS-SM/SSK). Finally, the comparison of detection complexity and the bit error probability are analyzed. Simulation results show that the proposed TIM-RIS-RAS can significantly enhance the BER performance compared with the traditional RIS-aided communication systems such as RIS-SM and RIS-GSM, and with the spatial time (ST)-aided communication systems such as ST-aided quadrature SM.