Integrated Cooperative Sensing and Two-Way Communications With Half-Duplex Base Stations

In case the dual-functional base station (BS) is only equipped with half-duplex (HD) transceivers, integrated sensing and communications (ISAC) becomes a challenge task especially when the bidirectional communications for each HD user are involved. To address this situation, under the framework of a wireless network with two adjacent cells and with the aid of BSs cooperation, this paper presents two integrated cooperative sensing and bidirectional communication schemes that involve two and four transmission phases, respectively. Power minimization problems under the constrains of bidirectional communication rates and sensing signal to interference plus noise ratios (SINRs) are formulated for optimizing the downlink transmit beamforming vectors, uplink transmit power, and transmission time of each phase. Due to variables coupling, the problems are shown to be non-linear and non-convex. Relying on the successive convex approximation, iterative algorithms that are guaranteed to be convergent are derived to obtain these design variables. Simulations show that both of the proposed schemes well accomplish the bidirectional communications and cooperative target sensing in the considered situation. By contrast, the scheme with two transmission phases possesses lower implementation complexity while the scheme with four transmission phases owns the performance advantage. When uplink non-orthogonal multiple access is further used, the performance difference between the two schemes is reduced substantially.