RIS-Enabled Self-Interference Cancellation in Monostatic OFDM-ISAC

Monostatic orthogonal frequency division multiplexing (OFDM) integrated sensing and communication (ISAC) is emerging as an important feature for next-generation wireless systems. The strong self-interference (SI) encountered in monostatic architectures is a major challenge to achieve accurate sensing performance.
In this work, we leverage an active, space-time-coding reconfigurable intelligent surface (STC-RIS) to realize the SI-free monostatic OFDM-ISAC system. By jointly controlling the RIS reflection in spatial and temporal dimensions, the reflected OFDM waveform is modulated into a subspace orthogonal to the SI while its beam is steered toward the target direction. In addition, a complementary base station beamformer is developed to boost the illumination power on the RIS while ensuring the downlink communication requirement. Simulations demonstrate the effectiveness of the proposed approach in SI elimination and superior sensing performance compared with state-of-the-art SI cancellation techniques.