Study On Energy Efficiency For Multi-User Massive MIMO Systems

As a key technology in the 5G,massive MIMO equipped with dozens or even hundreds of antennas in the BS,can take a good advantage of the radio resources of spatial dimension and improve the performance of wireless communication system.However,these performance improvements increase system hardware costs and energy consumption.As an important measurement index of 5G,energy efficiency is defined as the number of bits per joule of energy transmitting,which can reflect the relationship between the spectrum efficiency and consumed power.In this thesis,it researches on the spectral efficiency and energy efficiency of massive MIMO systems.Firstly,the thesis stduies the spectral efficiency and energy efficiency of the multi-user massive MIMO downlink system.Analyzes the closed form of the DL achievable rate,establishes the model of energy efficiency,analyzes how the number of antennas,users and transmitting power will affect the spectrum efficiency and energy efficiency of the system.The results show that the spectrum efficiency of the single cell system is increasing with the quantity increment of antennas,the spectrum efficiency of multi-cell system increases with the number of antennas,then tends to a certain value;Performance of multi-cell cell is poorer than single cell,because of pilot pollution and inter cell interference;The energy efficiency is shown to be a concave function of the number of antennas,users and transmitting power respectively;Increasing the transmitting power can improve the system spectrum and energy efficiency temporarily,when sending power exceeds a certain value,the system spectrum efficiency tends to be a constant value,the energy efficiency starts to decrease;Secondly,we consider jointly the uplink and downlink of a single-cell multi-user MIMO system and a new realistic power consumption model,research the maximal energy efficiency of multiple user MIMO system.The new power consumption model not only contains linear consumed power of antennas in the transmitting and receiving terminal,but also includes consumed power of the linear processing of signal,coder and decoder,backhaul,channel estimation.Analyzes how to select the number of antennas,the number of users and transmitting power to achieve the optimal energy efficiency in theory.Derived the closed form between energy efficiency and achieve user rate.The simulation results show that the energy efficiency and spectral efficiency of ZF processing is higher than MRT/MRC processing.There is a 3-fold improvement in optimal EE for ZF processing as compared to MRT/MRC,the relative achievable rate is an 8-fold improvement.The total transmitting power should be increased with the number of antennas to compensate the loss of energy efficiency due to circuit power.The tendency of energy efficiency and user rate is not always constant.This is because when user rate is low,circuit power dominates the power model,and transmitting power dominates the power model when user rate is relatively high.