Non-Diagonal Phase Shifts in IRS Assisted OTFS System

Intelligent reflecting surfaces (IRS) have gained the interest of researchers in the field of wireless communication. The ease of configurability of the IRS and ability to modify the signal propagation environment make them primary candidates for future wireless communication systems beyond fifth-generation (B5G) technologies. Orthogonal time frequency space (OTFS) modulation has proved to be a viable option for high-mobility wireless channels. IRS-assisted OTFS (IRS-OTFS) system can improve the coverage and combat inter-carrier interference (ICI) caused due to Doppler shifts at high velocity. In this paper, we apply the non-diagonal (ND) phase shifts in IRS-assisted OTFS (ND-IRS-OTFS) systems. We formulate the system model for NDIRS-OTFS system and also present the design of phase shift matrix to improve the channel gain and the error performance. We compare the bit error rate (BER) performance of ND-IRSOTFS system and the conventional IRS-assisted OTFS system in synthetic and extended vehicular A (EVA) channel scenarios. For an IRS system consisting of 16 reflecting elements under synthetic channel scenario, simulations show that ND-IRS-OTFS system achieves a 9 dB performance improvement at a certain BER compared to conventional IRS-OTFS system.