A two-stage vector perturbation scheme for adaptive modulation in downlink MU-MIMO

Conventional vector perturbation (VP) is not directly applicable to adaptive modulation, whereas other existing algorithms are suboptimal due to the reduced search dimension of perturbation vectors. In this paper, by applying a simple transformation to the conventional VP operation, the search dimension for the proposed joint VP is made equal to that of conventional VP, and therefore, the performance advantages of VP still hold in this scenario. Furthermore, to reduce the computational complexity, a joint constructive VP scheme is introduced by exploiting constructive interference to simplify the VP operation. By doing so, the sophisticated search for perturbation vectors is partially replaced by a quadratic programming problem, therefore saving significant computational complexity. Our analysis and results show that the proposed scheme offers an improved performance-complexity tradeoff compared with conventional VP approaches by means of the measurement in energy efficiency.