Energy efficiency maximization in downlink multiuser MIMO systems: An asymptotic analysis approach

With tremendous power shortage and raising voice of greener energy usage, energy efficiency (EE) maximization in MIMO systems has received much attention in next generation wireless communications. Within recent years, there has been a lot of great work on power allocation and antenna selection in order to maximize EE under holistic power models. However, it is not a trivial work to derive a closed-form solution for energy efficiency optimization. In this paper, an asymptotic approach is adopted to obtain the analytical solutions of the EE optimal transmission schemes, as well as its performance limits. More specifically, we are interested in the capacity achieving dirty paper coding (DPC) and practical low-complexity zeroforcing beamforming (ZFBF), where EE is optimized with and without total power constraint. Closed-form formulas are given to determine the EE optimal number of antennas and transmit power. The proposed asymptotic analysis matches well with the numerical results when the number of users is moderately large, i.e., over 30.