| By employing very large scale antenna arrays at the base station, Massive MIMO systems can provide more users with wireless communication services, and take the advantages of the spatial degrees of freedom simultaneously, which is expected to improve the system spectrum efficiency and energy efficiency significantly without additional system bandwidth and transmit power. Therefore, Massive MIMO systems have attracted significant attention from wireless communication academic research filed as the most competitive one of mainstream alternatives in the future 5G mobile communication systems. Massive MIMO systems need to install the same number radio frequency chains as the number of the base station antennas when using all antennas for wireless data transmission, resulting in the higher system implementation complexity and hardware cost. By selecting the appropriate subset of transmit and/or receive antennas for data transmission, antenna selection technology can reduce system cost and implementation complexity while obtain higher spectrum efficiency and energy efficiency, thus achieving the requirement of green broadband mobile communications. Therefore, Massive MIMO systems based on antenna selection become the current research focus. In the paper, the energy efficiency optimization problem of Massive MIMO systems based on antenna selection scheme is investigated, and the main contents are as follows:1) Energy efficiency optimization problems in different Massive MIMO systems with transmit antenna selection are studied. The existence and uniqueness of the optimal number of selected antennas to maximize the energy efficiency are proved through the mathematical derivation.2) The energy efficiency optimization problem in single-user Massive MIMO downlink system with transmit antenna selection is investigated. And a new simple but efficient antenna selection algorithm based on the Binary Search Algorithm is proposed, which makes the system improve the system capacity, taking into account its own power consumption. The existence of the optimal number of selected antennas to maximize the energy efficiency in the downlink system is proved through the mathematical derivation. The simulation results indicate that the proposed transmit antenna selection scheme in single-user Massive MIMO system can improve the energy efficiency significantly.3) The energy efficiency optimization problem in multiuser Massive MIMO system with transmit antenna selection is discussed. Under such a scenario, the linear multiuser precoding scheme is considered to reduce the inter-user interference problem. In the paper, a new power consumption model is established, and the effects of the number of transmit antennas at the base station and the number of users at the receiver on the total power consumption as well as the energy efficiency are discussed respectively. The existence and uniqueness of the optimal number of selected antennas to maximize the energy efficiency under such a scenario are proved through the mathematical derivation, and its approximate closed-form solution is also derived. Numerical simulation results demonstrate the effectiveness of the transmit antenna selection techniques in improving the energy efficiency of the multiuser Massive MIMO systems. |
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