Optimized Precoding Scheme In Massive MIMO Communication Systems

With the development of wireless communication systems,Massive Multiple-Input Multiple-Output(MIMO)technology,as an efficient wireless transmission technology in multi-antenna arrays,can fully utilize spatial multiplexing resources and enable wireless communication systems to achieve higher transmission rates and spectral efficiency.However,as the complexity of wireless systems increases,the size of antenna arrays also grows accordingly.To deploy as many antenna elements as possible in the actual environment has emerged as a significant bottleneck impeding the implementation of massive MIMO technology.Intensive research on large-scale antenna arrays with densely packed elements holds promising solutions to address this issue,On the one hand,a significant factor that constrains the performance of densified arrays is the coupling effect.on the other hand,non-ideal factors such as signal reflections caused by the densification of the arrays can also lead to losses in system performance.Some research work proposes a tunable antenna architecture with reconfigurable coupling to achieve coupling effect regulation,which poses new challenges to traditional digital precoding techniques.Now the joint design of controllable coupling parameters and digital precoding,with the goal of optimizing the performance of wireless communication systems,is a key issue at present.In this thesis,for dense large-scale antenna array communication system,under the architecture of array coupling reconfigurable,the coupling effect is modeled as a function of tunable load impedance in the scenario of downlink multi-user system.To improve the system performance,the tunable impedance and digital precoding schemes are designed jointly.For the above objective,an optimization problem is formulated with the objective of maximizing the spectral efficiency of the downlink system.An alternating iterative framework is implemented to solve this non-convex optimization problem.The Weighted Minimum Mean Square Error(WMMSE)algorithm is used to solve the precoding scheme; for the optimization problem of tunable impedance,multiple subproblems with locally convex structures are constructed for iterative solution in the framework of the Alternating Direction Method of Multipliers(ADMM).Finally,the numerical results on the performance of the proposed algorithms show that the proposed algorithm outperforms than the baseline scheme and the existing algorithms.On this basis,the non-ideal array scenario is taken into account and the non-ideal factor of signal reflection loss is incorporated by expressing it as a function of the tunable impedance.Firstly,the precoding scheme is designed based on WMMSE optimization algorithm.Subsequently,two optimization algorithms for tunable impedance are proposed with coupling effect optimization and reflection loss suppression as the objectives.In the first scheme,the upper bound of the reflected signal energy is constrained and the subproblem is constructed using ADMM to solve; then,a two-stage optimization algorithm is proposed,wherein the first stage involves the construction of the subspace by minimizing the reflection loss,while the second stage transforms the optimization problem of coupling effect into a second-order cone programming problem to slove.The simulation results show that the proposed algorithm achieves the optimization of the spectral efficiency and effectively suppresses the loss caused by the signal reflection,which achieves better performance gain compared with the baseline scheme.