Power Control and Active RIS Design for Energy-Efficient Integrated Sensing and Communications

This paper considers the problem of energy efficiency maximization in a reconfigurable intelligent surface (RIS)-aided ISAC wireless system, where a MIMO dual function radar communications base station (DFRC-BS) performs both communication and sensing tasks, and is aided, for the communication tasks, by an active reconfiguration intelligent surface. This work presents an energy-efficient design for the joint allocation of the transmit power and the RIS configuration matrix, subject to power, RIS, and quality-of-service (QoS) requirements for both the users and the radar SNR. An iterative procedure based on alternating optimization for the solution of the considered optimization problem has been developed. Numerical results will show the impact of several system parameters on the attainable energy efficiency, and will highlight that active RISs generally outperform their passive counterparts.