Spectral Efficiency Maximization for Massive Multiuser MIMO Downlink TDD Systems via Data Power Allocation with MRT Precoding

This paper studies the problem of maximizing the spectral efficiency in a massive multi-user MIMO downlink (DL) system where the base station employs a large number of antennas and serves single-antenna users in one cell, assuming time- division duplex transmission. In order to maximize the spectral efficiency in a DL transmission, a new method for power allocation among users is proposed based on the water-filling approach. To this end, a lower bound on the achievable rate is derived for each user in the presence of maximum- ratio transmission precoding and employed in defining the spectral efficiency. Since maximizing the spectral efficiency is an NP-hard problem, an effective algorithm is also proposed to find Karush-Kuhn-Tucker (local maximum) points. The performance of the proposed power allocation method is verified by conducting simulations and shown to be superior to other existing methods in terms of higher spectral efficiency.