A Broadcast Channel Framework for Joint Communications and Sensing-Part I: Feasible Region

In various cyber physical systems (CPSs), communications and sensing are conducted simultaneously. Therefore, the mechanism of joint communications and sensing (JCS) is envisioned to integrate both functions in the same waveform, frequency band and hardware. It is expected to be one of the major features of 6G wireless communication networks. A major challenge to the design and analysis of JCS is a unified framework that incorporates the distinct functions of communications and sensing. In the first par of this paper, the framework of broadcast channel that has been intensively studied in data communications and information theory is adopted for JCS, in which communication and sensing signals are broadcast to the concrete communication users and virtual sensing users. Such a broadcast channel framework benefits the applications of existing multiplexing schemes, such as dirty paper coding (DPC) or frequency division multiplexing (FDM). Based on the framework, the feasible performance region bound is derived, based on the broadcast-multiaccess duality. The design of dedicated sensing signal is studied for the scenarios of communication-first (or sensing-first) priority, based on the ambiguity function (AF) of radar sensing. The proposed scheme is numerically demonstrated using typical short-range communication and sensing setups. The scheme based on superposition coding will be discussed in the second part of this paper.