RIS-based Passive Transmitter Reflection Optimization with Performance Complexity Trade-Offs

This study considers a multiuser multiple-input multiple-output system realized via the reconfigurable intelligent surface-based passive transmitter setup, also known as modulating intelligent surface transmitter. The realistic assumption of discrete phase shifts of the reconfigurable intelligent surface’s elements is considered. Under this framework, the study formulates a symbol-level power minimization problem under the condition that the symbol-error probability is below a given requirement. Based on the proposed formulation a branch-and-bound algorithm is devised that improves on standard Full branch-and-bound approaches by accepting any solution that either attains the given target power budget of the system or is sufficiently close to the optimal such that it is considered unnecessary to continue the search process. Numerical results demonstrate the effectiveness of the proposed approach in minimizing the transmit power for different symbol-error probability requirements. Moreover, numerical results show that applying the proposed branch-and-bound approach instead of Full branch-and-bound techniques yields a negligible increase in transmit power for a significant reduction in computational complexity.