In-Band-Full-Duplex Integrated Sensing and Communications for IAB Networks

In this paper, we develop an in-band-full-duplex (IBFD)-integrated sensing and communications (ISAC)-integrated access and backhaul (IAB) network operating at frequency range 2 (FR2) for vehicle-to-everything (V2X) com-munications, where the IAB-node acts as a roadside unit (RSU) performing sensing and communication simultaneously (i.e., at the same time and frequency band). Self-interference (SI) due to the IBFD operation can be canceled in the propagation, analog, and digital domains; only the residual SI (RSI) is reserved for performance analysis. Unscented Kalman filter (UKF) is used for tracking multiple vehicles in the studied scenario. Considering the subarray-based hybrid beamforming structure, including hard-ware impairments (HWI) and RF effective SI channel estimation error, with sufficient SI cancellation, simulations show that the UKF can give satisfactory radar tracking accuracy. The resulting tracking mean-squared errors averaged across all vehicles of each state parameter are close to their posterior Cram´er-Rao lower bounds. Compared with half-duplex-ISAC-IAB networks, IBFD-ISAC-IAB networks nearly double the spectral efficiency for both the backhaul and access links. Moreover, the less the RF effective SI channel estimation error is, the higher the backhaul link spectral efficiency is.