ISAC STAR-RIS Transceivers With Space-Time Coded Pulsed Signals

This work investigates a radar-centric integrated sensing and communication (ISAC) transceiver that incorporates a simultaneous transmitting and reflecting reconfigurable intelligent surface (STAR-RIS) and a radar receiver equipped with a passive electronically scanned array (PESA) and a single digital channel. A periodic pulsed waveform, emitted by a feeder, illuminates the STAR-RIS, which applies space-time modulation to the redirected pulses. The spatial response of the STAR-RIS and the spatial beamformer of the radar receiver are jointly designed to illuminate desired directions on each side of the STAR-RIS, i.e., those monitored by the radar and those corresponding to communication users, while mitigating clutter returns. Time modulation enables both the embedding of communication data and the assignment of unique signatures to echoes from each side of the STAR-RIS. Two encoding schemes are proposed, enabling either simultaneous or sequential illumination of the two sides, while the corresponding radar and communication receivers are designed using a generalized information criterion. Several trade-offs between radar and communication functionalities can be achieved by adjusting the STAR-RIS and PESA array power patterns; in addition, the proposed data encoding schemes allow different data transmission and error rates, while having minimal impact on the radar performance.