A New Co-Channel Interference Cancellation Scheme for Full-Duplex ISAC Systems

Integrated sensing and communication (ISAC) has been widely recognized as one of the cornerstone technologies to reduce hardware complexity and power consumption in the future sixth generation (6G) cellular networks through multiplexing waveform, hardware and spectral resources. By incorporating full-duplex (FD) technology into ISAC systems, known as FD-ISAC, spectral efficiency (SE) can be further improved and sensing coverage gaps can be effectively eliminated compared to conventional half-duplex (HD)-ISAC systems. However, the inherent self-interference (SI) and co-channel interference (CCI) pose serious obstacles, severely degrading the signal-to-interference-plus-noise ratio (SINR) in FD-ISAC systems. To mitigate SI, multi-domain (antenna-domain, radio frequency (RF)-domain and digital-domain) SI cancellation (SIC) techniques have been developed, effectively suppressing SI to a level close to the noise floor. Despite these advancements in SIC, CCI cancellation (CCIC) remains a far greater challenge due to the absence of prior information and the combined impacts of carrier frequency offset (CFO), IQ imbalance (IQI) and multipath effects. In this paper, we propose a new superimposed pilot (SP) transmission scheme based on a pseudo-noise (PN) sequence for CCIC. Moreover, a new SP-based CCIC algorithm that accounts for CFO, IQI and multipath effect is developed. Finally, numerical and experimental results are presented to validate the effectiveness of our proposed SP-based CCIC scheme.