A Broadcast Channel Framework for Joint Communications and SensingPart II: Superposition Coding

The technology of joint communications and sensing (JCS) integrates both functions in the same waveform and thus the same frequency band. It is expected to be a distinguishing feature in 6G wireless networks. A major challenge to JCS is how to seamlessly integrate the two historically distinct functions of communications and radar sensing. In the second part of this paper, a framework of superposition coding, motivated by the similarity to broadcast channels, is proposed for the functional multiplexing in JCS, which is motivated by the studies on broadcast channels in data communications. In this framework, communications and sensing are considered as genuine and virtual users, respectively. Sensing is considered as the bottom user in the layered structure of superposition coding; thus a sensing waveform is generated according to a certain criterion of sensing, which plays the role of cloud in superposition coding. Then, the communication message is superimposed on top of the cloud. Different superposition schemes are proposed, each corresponding to one type of mathematical operation on vectors in linear spaces. Moreover, the waveform diversity recently proposed in the radar community, which prepares a set of waveforms for handling the variance of environment, is taken into account. The cases of sensing waveform known/unknown to the communication receiver are discussed. The performance of the proposed JCS schemes is demonstrated using numerical simulations.