A Research On Performance Theory And Scheduling Technique Of Network-assisted Full-duplex For Cell-free Massive MIMO

The rapid growth of mobile data service,the increasing shortage of spectrum resources and the sharp increase of energy consumption have put forward higher requirements for the communication systems after the 5th Generation(5G)mobile communication system.In the Beyond 5th Generation(B5G)or the 6th Generation(6G)mobile communication system,enhanced broadband mobile communications as well as a wide variety of Internet-of-Things(Io T)applications should be supported and the uplink and downlink traffic will change dynamically and significantly.Therefore,flexible schemes which support dynamically configuring wireless resources should be proposed and the cross link interference(CLI)problem should be solved from both network architecture and wireless transmission.From the point of view of network architecture,instead of traditional cell architecture,a novel concept named as cell-free massive multiple-input multiple-output(MIMO)has been proposed in academia to overcome the interference problem between cells.Since more flexible duplex methods can be supported based on the cell-free massive distributed MIMO network,a novel full-duplex method named as network-assisted full duplex(NAFD)is proposed in this paper,which can unify flexible duplex,hybrid duplex,full-duplex and other duplex methods as well as solve the CLI problem.Thus,the true flexible duplex can be achieved,which is crucial to the dynamic configuration of resources in the 5G New Radio(NR)and 6G mobile communication systems.In this paper,cell-free massive MIMO with NAFD is studied in detail and the main contributions are as follows.First,the overview of large-scale distributed antenna systems is introduced,including large-scale distributed MIMO,cell-free massive MIMO and cloud radio access network(C-RAN).The comparison of the three system architecture is made.In addition,the overview of novel duplex technologies is introduced,including flexible duplex,co-frequency co-time full duplex(CCFD)and coordinated multi-point transmissions for in-band wireless full-duplex(Co MPflex).Then,under the cell-free massive MIMO network architecture,a novel full-duplex method NAFD is proposed,which unifies flexible duplex,hybrid duplex,full duplex and other duplex methods.The proposed NAFD is quite general and the derived results can be applied to its special cases such as CCFD massive MIMO,Co MPflex,hybrid full-duplex and half-duplex,and full-duplex C-RAN.Besides,the performance comparisons are given for NAFD with half-duplex,CCFD-CRAN and CCFD massive MIMO.After that,in order to give a generalized system model of NAFD,large system analysis is given for the spectral efficiency of NAFD with the consideration of imperfect channel state information(CSI)and the impact of spatial correlations.With zero-forcing(ZF)or regularized zero-forcing(RZF)precoders for downlink transmission as well as minimum-mean-square-error(MMSE)receiver for uplink transmission,the deterministic equivalents of uplink sum-rate and downlink sum-rate for the cell-free massive MIMO with NAFD are provided based on large dimensional random matrix theory.Given statistical channel knowledge,the spectral efficiency of the system can be approximated without knowing the actual channel realization.Furthermore,the imperfect cancellation of downlink-to-uplink interference is considered and a deterministic equivalent of the covariance matrix for the residual interference plus noise is given,which can simplify the computation in the uplink receiver.Finally,in order to alleviate the uplink-to-downlink interference in the cell-free massive MIMO with NAFD,a novel genetic algorithm based user scheduling strategy(GAS)is proposed in this paper,which provides a low complexity scheme to minimize the uplink-to-downlink interference and further improve the spectral efficiency of NAFD system.