Energy-efficiency Maximization Scheme For The MU-MIMO Wireless Information And Power Transfer System

The past decades has witnessed the rapid development in wireless communications,a broad and dynamic field.Among different technologies,the development of MIMO is particularly fast.MIMO systems can increase channel capacity without occupying additional spectral bandwidth.Therefore,the spectral efficiency of the system is improved.According to different usage of situations of time-frequency resource,there are two types of MIMO systems: SU-MIMO and MU-MIMO.In SU-MIMO,different users occupy different time-frequency resources.While MU-MIMO allows multiple users share the same time-frequency resources by spatial division multiplexing,which further increases the spectral efficiency.Thus MU-MIMO has higher spectral efficiency and has been widely used in wireless communications nowadays.Meanwhile,with the development of the Internet of Things,the wireless information and power systems have drawn considerable research attentions.In these systems,terminals usually do not have fixed power facilities,or their sole power facilities can only support their activation states.Therefore,terminals should harvest wireless transferred energy from the base station and transfer it into the power that can support their wireless information transmission on the uplink.This paper considers the design of the wireless information and power transfer system,with MIMO as its uplink access mode.The system supports multiple terminals with different QoS requirements,i.e.,MU-MIMO.Time is divided into time slots and the system works in time slots.At the beginning of each time slot,the energy transmitter of the base station broadcasts energy to the energy receiver of terminals.With the harvested energy,in the rest of the time slot,terminals transmit information to the base station.Taking the concept of green energy usage,in this paper we choose energy efficiency as the performance metric of the system and we propose a scheme that jointly optimize the switching point of downlink and uplink and the transmit power of the base station in the downlink,in order to reach the best energy efficiency.Simulation results show that comparing to MISO multiple access mode and single parameter optimization,joint parameters optimization with MU-MIMO mode can reach higher energy efficiency.