Robust Cooperative Beamforming and its Feasibility Analysis in Multi-user Multi-relay Networks

In this paper, we study the optimal cooperative beamforming problem in amplify-and-forward (AF) multi-user and multi-relay networks, which face challenges of rapid node number variations per-node power limits. To achieve extra diversity gain, direct-link (source-to-destination) distributed relay-link signals are jointly exploited. The is formulated as maximum relay transmit minimization problem, subject to per-relay minimum destination signal-to-noise ratio (SNR) constraints. Since non-convex, present a phase-regulation (PR) method transform non-convex into tractable second-order cone programming (SOCP) problem. It demonstrated that proposed can provide much more robustness against terms worst-case convergence rates than Lagrange dual successive convex approximation (SCA) methods. Furthermore, closed-form expressions two necessary feasibility conditions derived, by infeasible channels be identified excluded. Consequently, computational costs reduced. equivalence Necessary Condition I (NC1) signal-to-interference (SIR) condition proved theoretically numerically. II (NC2) has lower upper-bound SIR condition, thus reducing costs. This applicable both non-direct-link scenarios.