On the Characterization of Pareto Boundary for Joint Communication and Sensing in MIMO Wireless Systems

A joint communication and sensing (JCAS) system is considered with a user for downlink communication and a sensing target of interest using a multi-input multi-output (MIMO) terrestrial base station (BS). We provide a MIMO joint beamforming design for joint communication and sensing functionalities. As performance metrics, we use the mutual information (MI) and the Fisher information (FI) for the communication user and the sensing object, respectively. Our main objective is to characterize the MI/FI Pareto boundary of a JCAS system. To this end, we propose an optimization problem to maximize the weighted sum of the FI and the MI while satisfying the transmit power budget at the BS. We develop a closed-form solution up to one scalar (to be found numerically) for the single-user, single-sensing object scenario while achieving a trade-off between communication and sensing. Analytical and numerical results show that, for JCAS, joint beamforming is better than separate independent beamforming. The trade-off reveals differences in the performance of JCAS with the user's and the target object's angles of departure (AoD), as well as the number of transmitting and receiving antennas at the BS.