A Nonorthogonal Uplink/Downlink IoT Solution for Next-Generation ISAC Systems

An integrated sensing and communication (ISAC) system is investigated, where the base station (BS) provides both uplink and downlink Internet of Things (IoT) services as well as target sensing services. Furthermore, nonorthogonal transmission (NO-T) is introduced for improving the spectrum efficiency. The deleterious effects of hardware impairments, channel estimation errors, and imperfect successive interference cancellation are taken into account. Both the exact and asymptotic outage probabilities ( OPs) of the IoT devices as well as the Probability of successful Detection (PoD) are derived for characterizing the communication and sensing (C&S) performances. As a further development, in the presence of the sensing requirements, a communication-centric power allocation (PA) problem is formulated for maximizing the sum rate of the IoT devices. Given the nonconvexity of the problem, an alternating optimization algorithm is developed for finding a near-optimal PA. The simulation results confirm the accuracy of the analysis and demonstrate that: 1) the above nonideal factors degrade the C&S performances; 2) the NO-T ISAC system considered outperforms pure ISAC in terms of both its OP and PoD; and 3) compared to other baseline PA schemes, the proposed algorithm maximizes the sum rates while meeting the sensing requirements.