Optimal Design Of Green Communication Network Based On Reconfigurable Intelligent Surface

With the rapid development of wireless communication technologies,the application scenarios of communication networks are increasing daily.The service volume and the scale of access devices of future communication networks will have a blowout growth.With this comes the huge energy consumption of wireless communication.Therefore,in future research of wireless communication technology,it is necessary to develop green communication with energy efficiency as the core evaluation index to reduce the energy consumption in communication networks.Reconfigurable Intelligent Surface(RIS)can consist of many passive reflective elements,and passive reflective elements’ energy consumption and cost are low.In addition,the RIS has the advantages of extending the coverage range and improving the received signal strength.Thus,the RIS can be considered a technology for achieving green communication.Firstly,the emerging User-specific Reconfigurable Intelligent Surfaces(US-RIS)deployed on the user side are considered in this paper.A multi-objective optimization problem is constructed to maximize energy efficiency of a US-RIS-assisted uplink communication network.Since the formulated energy efficiency maximization problem is nonconvex,the problem is decomposed into three subproblems using the Block Coordinate Descent(BCD)algorithm.The subproblems are solved separately by transformation.For the base station receive beam assignment vector and RIS phase shift matrix,the original optimization problem is transformed into a signal-to-noise ratio maximization problem,and a closed-form solution is derived.The uplink beam assignment vector of user is solved using the Semidefinite Relaxation(SDR)algorithm to obtain a suboptimal solution.The results of these three subproblems are updated alternatively to obtain the suboptimal solution of the original problem.Further,the relationship between the number of components of the RIS and the energy efficiency of the communication network is explored,and the convergence of the solution algorithm is also analyzed.The results show that the proposed BCD algorithm-based optimal design for energy efficiency of the communication network has been significantly improved in the energy efficiency.Secondly,to further improve the coverage and resource utilization efficiency of the communication network and take advantage of the non-Orthogonal Multiple Access(NOMA)technologies in terms of spectral efficiency,this paper studies the RIS-assisted uplink NOMA communication network.Under the constraints of passive beam assignment and user power control,a multi-objective nonconvex optimization problem is constructed with maximizing the energy efficiency in the communication network as the optimization objective.The energy-efficiency optimization precoding design is proposed,and the optimization problem is divided into three subproblems solved separately according to the idea of alternating optimization.In particular,the uplink precoding vector in the communication network is solved using the Dinkelbach and SDR algorithms.In the optimization of the passive beam assignment matrix and the received combination vector of the RIS,the energy efficiency of the optimization problem is converted to the total power of the user signal for the solution,and the suboptimal solution of the original problem is obtained.The simulation results show that the proposed energy-efficient optimized design has better energy efficiency than the Orthogonal Multiple Access(OMA)schemes and the RIS random phase shift scheme.Finally,Ambient Backscatter Communication(Am BC)technology has the advantage of low cost and low energy consumption,which can also be considered a technology to achieve green communication.Considering the importance of energy efficiency optimization for downlink communication networks,the RIS-assisted downlink Am BC-NOMA communication network is proposed.Moreover,a multi-objective nonconvex optimization problem is constructed,and an energy-efficiency-based resource allocation design is proposed to maximize the energy efficiency of the communication network.The nonconvex problem is decomposed into three subproblems for solving.In the optimizing downlink beam assignment variables,the Dinkelbach algorithm is used to handle the objective function.And the maximization problem is solved using a derivative and SDR algorithm that can change the concavity of the function.When optimizing the RIS phase shift and backscatter coefficients,the optimization objective is transformed to the sum rate,which is solved using the same Lemma and SDR algorithms.The final suboptimal solution of the original optimization problem is obtained.In the simulation results,the proposed NOMA scheme has better energy efficiency than the OMA scheme and the RIS random phase shift scheme,and the impact of the change in the location of the backscattering device on the energy efficiency of the communication network is analyzed.