The Upper Bound of Energy Efficiency for Virtual MIMO System with User Pairing

In this paper, we investigate the user pairing scheme in virtual multiple-input multiple-output (V- MIMO) systems, which can significantly improve system performance and spectral efficiency (SE) using multiuser diversity. Considering the development of green communication, we want to find the upper bound of energy efficiency (EE) under the constraint of SE. Firstly, the optimal transmit power allocation for the optimal EE under the constraint of SE is formulated as a non-convex optimization problem and a novel projective constraint analysis (PCA) is devised for it. Then, we reveal the maximum EE and the corresponding transmit power allocation in the global solution space. According to the location relationship between the maximum EE and the constraint of SE, we propose a spatial approach based on PCA to pursue the upper bound of EE with two different cases. Finally, a novel PCA-based user pairing scheme achieving the upper bound of EE under the constraint of SE is proposed. Numerical results illustrate the impact of different system parameters for the upper bound of EE and prove that the proposed PCA-based iteration algorithm has much lower complexity than the global search approach.