“…The studies in [15], [16], [17], [18] minimize the total relay transmit power under an overall quality of service (QoS) constraint, using either a convex semi-definite programme (SDP) relaxation method or a convex second-order cone programme (SOCP). The works in [15], [16] consider the channel errors as Gaussian random vectors with known statistical distributions between the source to the relay nodes and the relay nodes to the destination, whereas [17] models the channel errors on their covariance matrices as a type of matrix perturbation. The work in [17], [19], [20] presents a robust design, which ensures that the SNR constraint is satisfied in the presence of imperfect CSI by adopting a worst-case design and formulates the problem as a convex optimization problem that can be solved efficiently.…”