Spatial Multiplexing Enabled 5G Heterogeneous Networks In Unlicensed Band

With the rapid development of wireless communication technologies,the number of mobile devices have increased dramatically.Varieties of requirements on higher data rate,lower latency,and larger connectivity have brought huge challenges to 5G communication system.Besides,5G wireless networks would confront with much more severe spectrum scarcity problems,which makes the utilization of unlicensed band for auxiliary communications ever more necessary.For the purpose of supporting multiple frequency bands,deployment schemes,and different access technologies of 5G heterogeneous networks,NR-U technology has emerged.However,NR-U still faces a series of problems,including the compatibility of different access mechanisms,the suppression of severe co-channel interference,and the joint optimization of multidimensional variables in heterogeneous networks.Though there have been lots of researches on the fusion mechnisms of NR-U heterogeneous networks,coexistence mechanisms are always based on time-division multiplexing and only support discontinuous data transmission,which fail to cope with the ever-increasing communication demands.To handle these problems,we focus on the spatial multiplexing enabled fusion and optimization of 5G NR-U heterogeneous networks in this paper.We attempt to make full use of space resources to achieve harmonious coexistence of heterogeneous networks,and further improve spectrum efficiency.The main research contents of this paper are summarized as follows:(1)This paper proposes a Co MP based coordinated transmission scheme for NRU heterogeneous networks.We first introduce a spatial multiplexing based enhancedLBT scheme to control the cellular base stations to coexist with the incumbent Wi Fi devices orthogonally.To further suppress the strong co-channel interference among multiple cellular networks,we investigate a joint beamforming and user selection problem,and introduce a semi-distributed ADMM algorithm to solve the NP-hard problem with significantly reduced signaling overheads.Simulation results not only prove the applicability of the Co MP mechanism in realizing the coordinated transmission of NR-U heterogeneous networks and improving spectrum efficiency,but also demonstrate the feasibility of applying the semi-distributed algorithm in largescale networks.(2)This paper proposes a RIS based fair coexistence scheme in unlicensed band.We utilize the cheap and easy-deployed RIS to improve spatial multiplexing gain,and to achieve the interference cancellation and signal enhancement by controlling its reflective beamforming.To guarantee the fairness of multiple heterogeneous networks,we propose a joint optimization problem of BS power allocation,RIS reflective beamforming and Wi Fi user selection scheme.And we introduce an AO-SCA based two-layer algorithm to maximize the minimum rate of heterogeneous networks,and finally achieve the performance compromise between Wi Fi system and heterogeneous cellular networks.Experimental results prove that reasonable deployment of RIS through the proposed AO-SCA algorithm can help effectively improve the coexistence performance on unlicensed band.Compared with the traditional time division multiplexing coexistence schemes,these two spatial multiplexing enabled 5G NR-U heterogeneous network fusion schemes proposed in this paper can significantly improve system performance.These schemes have some reference significance for the researches on the coexistence of multiple heterogeneous networks with higher efficiency,lower signaling overheads and lower cost in future communication systems.