  One of the most important challenges in the fifth generation (5G) of
telecommunication systems is the efficiency of energy and spectrum. Massive
multiple-input multiple-output (MIMO) systems have been proposed by researchers
to resolve existing challenges. In the proposed system model of this paper,
there is a base station (BS) around which several users and an eavesdropper
(EVA) are evenly distributed. The information transmitted between BS and users
is disrupted by an EVA, which highlights the importance of secure transfer.
This paper analyzes secure energy efficiency (EE) of a massive MIMO system, and
its purpose is to maximize the secure EE of the system. Several scenarios are
considered to evaluate achieving the desired goal. To maximize the secure EE,
selecting optimal number of antennas and cell division methods are employed.
Each of these two methods is applied in a system with the maximum ratio
transmission (MRT) and the zero forcing (ZF) precodings, and then the problem
is solved. Maximum transmission power and minimum secure rate for users insert
limitations to the optimization problem. Channel state information (CSI) is
generally imperfect for users in any method, while CSI of the EVA is considered
perfect as the worst case. Four iterative algorithms are designed to provide
numerical assessments. The first algorithm calculates the optimal power of
users without utilizing existing methods, the second one is related to the cell
division method, the third one is based on the strategy of selecting optimal
number of antennas, and forth one is based on a hybrid strategy.
