Full-Duplex ISAC

In-band full-duplex (IBFD), i.e., simultaneous transmit-and-receive (STAR), operation is inherent to both sensing-centric and communication-centric integrated sensing and communications (ISAC). In both cases, the monostatic transceiver and antenna implementations need to overcome the technical challenge of self-interference (SI). The specific transceiver architecture of frequency-modulated continuous-wave (FMCW) radars offers a promising STAR solution for sensing-centric ISAC systems because it allows analog SI cancellation with a simple fixed high-pass filter instead of adaptive radio frequency filters that are typical for IBFD communication systems. Despite the limitation to constant-envelope waveforms, FMCW radars' frequency sweeps can still carry communication data quite efficiently with phase- and frequency-shift keying. In communication-centric ISAC, where typical communication waveforms are used for radar sensing, the IBFD capability and more complicated SI cancellation are required, because the data symbols or frames of standard wireless systems are too long to be employed as radar pulses unless their blind range becomes unreasonably long. This chapter discusses the implementation and performance of ISAC transceivers and SI cancellation for both radar-centric FMCW and communication-centric direct-conversion system architectures, including monostatic antenna and array solutions. Furthermore, the chapter overviews the monostatic ISAC applications that require and/or benefit from IBFD, i.e., STAR, operation.