Space-time suppression of self-interference and inter-symbol interference for target detection in ISAC systems

Utilizing existing communication infrastructures and signals for target detection encounters many challenges. Among them, the inherent self-interference in monostatic multiple-input multiple-output (MIMO) systems, along with the inter-symbol interference resulting from continuous signal transmission, severely degrades the detection performance. To suppress the self-interference and inter-symbol interference at receiver, we propose a space-time processing method in this paper. Our approach involves the design of beamforming vectors to mitigate self-interference in the spatial domain, and the design of a filter in the time domain for suppressing inter-symbol interference. An optimization problem for beamforming vector is formulated to maximize the signal to interference plus noise ratio (SINR) at receiver. Successive convex approximation (SCA) is deployed to obtain optimal beamforming vectors. Additionally, a filter in time domain is designed to lower the sidelobe and retain the peak value of the filtering output at receiver. Meanwhile, the inter-symbol interference brought by continuous transmission is also constrained by designing the filter. Numerical simulation demonstrates the effectiveness of our space-time processing method in suppressing both self-interference and inter-symbol interference, thereby enhancing overall detection performance.