MAC Scheduling in Joint Communications and Sensing Networks Based on Virtual Queues

In joint communications and sensing (JCS), which is expected to be among the major features of 6G wireless networks, the functions of communications and sensing are accomplished by the same JCS transmitter, possibly sharing the same waveform and thus the same frequency band and transmit power. In JCS networks, scheduling in the MAC layer is needed to balance the tasks of delivering data packets (particularly when there are multiple hops) and the radar target sensing, given limited wireless resources. In this paper, a unified framework is proposed, by considering virtual queues, in which virtual information bits for sensing that characterize the uncertainties of the mobile radar targets are backlogged if sensing is not carried out, or are cleared if significant resource is dedicated to sensing. The entropy reduction by sensing and entropy accumulation due to random perturbations to the radar target motions are quantified using the framework of Kalman filtering. Then the back pressure scheduling is employed for both the real communication queues and virtual sensing queues. Both JCS schemes of simple time-division multiplexing (TDM) and more flexible coding-spreading multiplexing (CSM) are taken into account. Numerical simulations are carried out to demonstrate the performance of the proposed algorithms, with the baseline of round-robin scheduling.