For a user cooperation system with multiple antennas, we consider trust degree-based cooperation techniques to explore the influence of the trustworthiness between users on the communication systems. For the system with two communication pairs, when one communication pair achieves its quality of service (QoS) requirement, they can help the transmission of the other communication pair according to the trust degree, which quantifies the trustworthiness between users in the cooperation. For given trust degree, we investigate the user cooperation strategies, which include the power allocation and precoder design for various antenna configurations. For single-input-single-output and multiple-input-single-output (MISO) cases, we provide the optimal power allocation and beamformer design that maximize the expected achievable rates while guaranteeing the QoS requirement. For a single-input-multiple-output (SIMO) case, we resort to semidefinite relaxation technique and block coordinate update method to solve the corresponding problem, and guarantee the rank-one solutions at each step. For a multiple-input-multiple-output (MIMO) case, as MIMO is the generalization of MISO and SIMO, the similarities among their problem structures inspire us to combine the methods from MISO and SIMO together to efficiently tackle MIMO case. Simulation results show that the trust degree information has a great effect on the performance of the user cooperation in terms of the expected achievable rate, and the proposed user cooperation strategies achieve high achievable rates for give trust degree.
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