Performance Analysis for mm-Wave ISAC Systems with Mutual Benefit

Integrated sensing and communication (ISAC) technique has recently gained significant research interest by supporting dual functions by a unified hardware platform. Traditionally, the ISAC system deemed the sensing and communication functions restricted by each other. In this paper, we demonstrate that a mutual benefit between sensing and communication functions can be achieved for the millimeter-wave ISAC system by efficiently exploiting the common information shared by both functions. Specifically, the sensing estimation can potentially be utilized to improve beamforming accuracy and the communication echo signal can enhance the sensing estimation as well. To demonstrate the mutual performance gain, we evaluate the joint outer bounds of the communication and sensing estimation rates. First, we derive the ergodic communication rate when the communication beamforming is assisted by sensing estimation. The asymptotic characteristic is further explored when the number of antennas approaches to infinity. Then, the closed-form estimation rate is obtained in terms of the Cramer-Rao Bound when the sensing estimation is assisted by communication signals. Numerical results verify the superiority of the mutual benefit when the common information was efficiently exploited by the ISAC BS transceiver. And when the transmission power is equally allocated, there are 10% and 2% gains on the communication rate and the sensing estimation rate simultaneously.