Research On Spectral Efficiency And Energy Efficiency Optimization Of Massive MIMO System

Massive multiple-input multiple-output(MIMO)technology is widely used in the field of wireless communication because of its obvious advantages in spectral efficiency,energy efficiency,and robustness.In an actual communication system,if massive MIMO want to achieve these performance advantages,the first step is to obtain accurate channel state information(CSI).At present,orthogonal pilot sequences are mainly used to estimate channel.However,since the coherence time is limited,it is inevitable to use pilot reuse.The use of non-orthogonal pilots will interfere with each other,and cause errors in estimation information.And it will hinder the improvement of system performance.Spectral efficiency and energy efficiency are two important indicators to measure the performance of massive MIMO system.Based on the above,this paper will study and analyze how to improve the spectral efficiency and energy efficiency of the system.The spectral efficiency and energy efficiency are optimized for the uplink of a massive MIMO multi-cell system that uses maximum ratio combine(MRC)receiver technology and zero-forcing(ZF)receiver technology.The optimization models are established to maximize the sum spectral efficiency,to maximize the minimum spectral efficiency,and to maximize the energy efficiency.Given the total power limitation for a coherence time,the optimization of pilot length and power assignment is carried on to maximize energy efficiency.The joint power and pilot assignment to maximize spectral efficiency and minimum spectral efficiency is performed at the same time.Simulation results show that the combination of pilot and power assignment can bring significant gains in spectral efficiency.At high SINR,ZF receiver can bring greater spectral efficiency and energy efficiency gain than MRC receiver.The energy efficiency is optimized for the downlink of a massive MIMO system that uses ZF precoder technology.For a single cell system under perfect CSI,an energy efficiency optimization model that meets the user's spectral efficiency limit is established,and the energy efficiency is maximized by combining the data transmission power and the number of antennas of the base station.The fractional optimization problem is transformed into a subtractive form,and the objective function is expressed as a Lagrange function.The closed-form solution of the transmit power and the range of the number of antennas are derived.And a binary search algorithm is proposed to solve the optimal number of antennas,finally an iterative method is used to find the optimal energy efficiency value.For a single cell system under imperfect CSI,an energy efficiency lower bound optimization model under the condition that the total transmit power limit of the base station is relatively small is established.A binary search algorithm is proposed to solve the Lagrange multiplier and an iterative method is used to find the lower bound of the optimal energy efficiency value.The simulations confirm the validity of the proposed algorithm and analyze the influence of the transmit power,the number of users and the number of antennas on the energy efficiency.For a multi-cell system with imperfect CSI,a compromise method of energy efficiency optimization is analyzed.Under the condition of satisfying the SINR limit,the consumed total power of the system is minimized to improve the energy efficiency.Simulations verify that with the increase of limited power,this compromise method not only guarantees the system's spectral efficiency and energy efficiency,but also has the high power saving capability.