Joint Transmit Antenna Selection and Passive Beamforming in IRS-Aided OTFS Systems

We develop a comprehensive and a practically relevant model for an intelligent reflecting surface (IRS)-assisted orthogonal time frequency space (OTFS) system in which the transmitter performs low complexity antenna selection (AS) and multiplexes data in the delay Doppler domain. We propose two new algorithms to jointly select antennas at the transmitter and program phase shifts at the IRS and also analyze their computational complexities. We show that the proposed algorithms cover a wide range of performance-complexity tradeoff. Our work also suggests a trade-off between power-hungry radio frequency (RF) chains at the transmitter and power-efficient passive elements at the IRS while obtaining improved bit error rate (BER) performance. We also elucidate that 3-bit discrete phase shifts at the IRS can provide the same BER performance as an IRS with continuous phase shifts in an OTFS system.