Channel Estimation and Detection for Intelligent Reflecting Surface-Assisted Orthogonal Time Frequency Space Systems

Orthogonal time frequency space (OTFS) modulation is a promising technique for the next-generation communications in high-mobility scenarios. However, in the delay-Doppler (DD) domain, the received signals suffer from a decrease in power due to the non-coherent superposition of all symbols transmitted through wireless channels. To address this issue, this paper proposes the incorporation of an intelligent reflecting surface (IRS) to assist the transmission for the OTFS systems, and jointly designs the OTFS frame structure and IRS phase shifts to achieve a coherent combination of the received signals. To address the problem of outdated channel state information in high-mobility systems, we propose a location-aided channel estimation strategy at the IRS. Additionally, to mitigate the adverse effects of the fractional Doppler shifts, a delay and shifted-Doppler domain-based channel estimation method is designed at the base station. By utilizing the well-designed OTFS frame structure and IRS phase shifts, we propose a low-complexity iterative interference cancellation (IIC) detector, and analyze the lower bound for its symbol error probability. To provide a clear understanding for the process of the considered systems, we describe a two-stage transmission protocol. Finally, the numerical results are provided to evaluate the effectiveness and superiority of the proposed estimation methods and IIC detector.