Multiple target detection in OTFS-ISAC

In this paper, we propose a hybrid beamforming design for multiple target detection in an orthogonal time frequency space (OTFS)-based integrated sensing and communication (ISAC) multiple-input multiple-output (MIMO) system. The proposed hybrid beamformer allows spatial separation of the beams for communication and sensing, thereby eliminating inter-beam interference (IBI), while reducing the number of required radio frequency (RF) chains. More specifically, in addition to the beams allocated for communication users, multiple beams are assigned for target scanning and detection. By applying a combiner to the received echo signals, information about the target's existence, along with its angular, range, and Doppler characteristics, can be directly obtained across different RF chains. To shed light on the system performance, we analyze the signal-to-interference-plusnoise ratio (SINR) and discuss the effect of the beamformer in the on-grid and off-grid cases, respectively. Our simulation results indicate that accurate sensing can be achieved with integer delay and Doppler indices; however, in the cases of fractional delay and Doppler, the sensing accuracy depends on the resolution of these parameters.