Full-Duplex ISAC: Self-Interference Separation and Cancellation With Superimposed Waveform

Abstract

In-band Full-Duplex (IBFD) Integrated Sensing and Communication (ISAC) framework surpasses the conventional Time Division Duplex (TDD) scheme by enhancing communication capacity, eliminating sensing coverage gaps, and enabling seamless communication-sensing coordination. However, IBFD operation introduces severe self-interference (SI), which substantially erodes the sensing receiver. Unlike traditional IBFD communication systems, IBFD-ISAC systems face an additional complication: the SI and the desired target echoes are homogeneous. Therefore, a critical challenge lies in effective separation of weak sensing echoes from SI, along with sufficient cancellation of the latter. In this paper, we propose a spectrally efficient superimposed waveform for IBFD-ISAC systems that facilitates the efficient separation of these two signals. Building on this waveform, a novel, low-complexity SI separation and cancellation (SISC) algorithm is developed. Moreover, the cancellation performance, sensing performance and downlink maximum achievable rate of the proposed method are analytically evaluated. Finally, numerical results demonstrate that the proposed scheme achieves cancellation and sensing performance comparable to the frequency-domain differential interference cancellation (F-DIC) method for high-speed targets, while exhibiting significant superiority in low-velocity scenarios.