Simultaneous Beam Training and Target Sensing for RIS-aided Integrated Sensing and Communication

In this paper, simultaneous beam training and target sensing for reconfigurable intelligent surface (RIS)-aided integrated sensing and communication (ISAC) systems is investigated. The sensing ability of base station (BS) is exploited to acquire the channel state information of the RIS-aided ISAC. Based on our findings that the energy of the echoes from the RIS can be accumulated in the angle-delay domain while the energy of the echoes from the targets can be accumulated in the Doppler-delay domain, we can distinguish the RIS from the targets. Then we propose a simultaneous beam training and target sensing scheme, which enables the BS to perform the beam training with the RIS and to sense the targets simultaneously based on the mixed echoes from the RIS and the targets, and also enables the user equipment (UE) to perform collaborative sensing to figure out their position. Moreover, the beam alignment between the BS and the UE via the RIS can be directly computed without additional beam training overhead. Simulation results verify the effectiveness of the proposed scheme and show that it outperforms the existing schemes with much smaller training overhead, which benefits from the integration of the sensing units.