Investigations on transmitter beamforming control based on firefly algorithm in massive MIMO systems with per-antenna power constraint for system throughput maximization

Abstract

In this paper, we investigate transmitter beamforming (BF) control based on the firefly algorithm (FA) in the massive multiple-input multiple-output (MIMO) downlink with a per-antenna power constraint with the aim of maximizing the variously defined system throughput. In the massive MIMO downlink, transmitter BF is essential to achieve a beamforming (power) gain and/or a reduction in the inter-user interference in a multiuser MIMO case based on the channel state information (CSI). Massive MIMO requires a large number of transmitter power amplifiers dedicated to each transmitter antenna and the allowable transmission power per power amplifier (thus per transmitter antenna) is severely limited. Therefore, it is necessary to perform transmission BF considering the limitation on the transmission power per antenna, which is in general a difficult problem to resolve. In this paper, we apply our recently reported BF control method using the FA under various definitions of the system throughput considering the tradeoff between the frequency efficiency and user fairness. By setting the BF matrix as the position for the firefly and the obtainable metric for the system throughput maximization as the brightness of the firefly, we apply the FA to the BF control. We evaluate the performance of the BF control using the FA when the system throughput is the arithmetic mean, geometric mean, harmonic mean, and minimum user throughput based on computer simulations and compare the results to those for the case using conventional zero forcing (ZF)-based BF.