Joint Beam Alignment and Resource Allocation for Multi-User mmWave Integrated Sensing and Communication Systems

Integrated sensing and communication has been considered as one of the key technologies for the 6th generation mobile networks. To achieve higher beamforming gains, arrays with massive antennas are employed in millimeter wave band. However, the narrowing of the beam will also lead to increasing difficulty in beam alignment while increasing the error and overhead of conventional codebook-based beam sweeping schemes. In this article, a sensing-aided beam alignment scheme and corresponding resource allocation algorithm for the multi-user system is proposed. Specifically, the base station senses the angle of departure (AoD) of each user and performs beam alignment based on obtained AoDs in a time-divisional manner. Then, to reduce the effect of beam misalignment caused by sensing errors, a projected gradient descent algorithm based on Monte Carlo estimation is proposed to solve the non-convex and non-closed optimization problem for power allocation among users. Moreover, aiming to obtain the optimal trade-off between communication and sensing, a method for time interval allocation is developed. The proposed scheme can match the communication power allocated to each user with the estimation accuracy of its AoD, which can improve the achievable sum communication rate in the case of imperfect beam alignment. Simulation results are provided to verify the effectiveness of the proposed algorithm.