Enhancing Sensing Capabilities in RSMA Downlink Networks through User-Assisted Beamforming

This paper examines the downlink scenario where a transmitting base station (BS) provides communication services to a set of users by utilizing the rate-splitting multiple access (RSMA), while concurrently providing sensing functionalities. Owing to the available transmit power of the cellular users and their capabilities of decoding the RSMA common stream, we propose to leverage the users in the network to assist the sensing process by collectively forming a probing beam towards the target(s). Using this proposed system and to evaluate its potential gains, we formulate an optimization problem to jointly determine the beamforming design at the transmitting BS, the common stream split, and the distributed beamforming design at the users as well as at the receiving BS aiming to maximize the minimum rate of the users. Due to the non-convexity posed by the formulated problem, we perform rigorous mathematical operations and leverage the semi-definite relaxation (SDR) method to solve it using a successive convex approximation (SCA) algorithm. Our numerical results demonstrate the advantage of exploiting users' resources to assist in the sensing process which is reflected in an enhancement in the achieved rate by the users. Moreover, we present the advantage of our model in comparison to Spatial Division Multiple Access (SDMA) scheme.