Research On Physical Layer Security And Implementation Scheme For 5G Heterogeneous Networks

In the past twenty years,mobile communication has experienced leap-forward development,which brings great convenience to people's production and life.However,with the exponential growth of current mobile data traffic,4G networks are no longer able to meet the ever-growing user experience requirements.5G-oriented heterogeneous networks can effectively improve the spectral efficiency,coverage probability,and other performance of networks by deploying a large number of low power access points to traditional macro cells,while offload from macro cells and save investment costs,which was considered as one of the key techniques to deal with the explosition of network traffic.Meanwhile,with the improvement of computing capability of high performance computing devices such as supercomputers and quantum computers,the traditional encryption algorithm over application level is facing extremely severe challenges.Physical layer security technique can provide “absolute security” because it is independent of computational complexity by effectively utilizing the physical characteristics of the channel,which is an important way to enhance 5G networks security.To this end,this thesis focuses on the implementation of 5G heterogeneous networks and physical layer security.The main research works are as follows:Firstly,a wireless energy harvesting scheme is proposed in D2 D underlay massive MIMO cellular two-tier heterogeneous networks.D2 D user equipment(DUE)can harvest energy from not only the radio frequency(RF)interference signals that near from cellular network user terminal(CUE),but also the RF signals of dedicate power beacons(PBs).In addition,a physical layer security scheme is designed,where the RF signals transmitted by PB are viewed as a kind of artificial noise,and the signals of PBs are known previously at DUE and CUE but are not known at eavesdroppers.Thus,this thesis investigates the energy efficiency and physical layer secrecy performance of system,the lower bound of the probability that DUE harvesting sufficient energy is derived,as well as the ergodic rate and secrecy outage probability of CUE and DUE.The results show that harvesting energy from RF signal near the CUE and PB can significantly improve the energy efficiency of DUE,while viewing RF signals of PB as an artificial noise can improve the physical layer security performance of the networks.Secondly,although the above scheme can enhance secrecy performance of networks,the backhaul transmission in heterogeneous network has not been considered.Therefore,combining with the in-band backhaul and full duplex technology,a physical layer security scheme of heterogeneous network is proposed,which is considering wireless backhaul transmitted signals as interference signals to macrocell downlink and small cell uplink transmission.The small cells underlay the traditional macro cell and share system access bandwidth with macro cell,and all large-scale MIMO macrocell base stations and single antenna small cell base stations work in in-band full-duplex mode.In this regard,the physical layer secrecy performance of marcocell downlink and small cell uplink are discussed,respectively.The results show that when the CUE density is relatively small,the in-band interference can effectively improve the secrecy probability of macrocell and small cellular transmission,and in-band full-duplex mode outpertforms out-band ones.In addition,this thesis also investigates the coverage probability of MBS-CUE and CUE-SBS links,found that due to the impact of backhaul interference,in-band backhaul impaired the coverage performance of the heterogeneous network.Finally,considering the fact that relay can solve the limitation of D2 D network coverage,we design and study a relay-based multi-tier heterogeneous network by replacing D2 D network with relay.In this network,a min-max user pair association(MM-UPA)scheme is proposed.Different from the traditional single hop networks user association,MM-UPA criterion jointly consider the source-relay and relay-destination two hop links gains.In this regard,this thesis investigates the user pair association probability,outage probability,and secrecy probability of MM-UPA scheme.The study shows that the sources' s transmit power and bias factor have different effects on UPA probability in different tier.Compared dual-hoop networks,single-hop ones have lower outage probability and higher system stability.In addition,with the transmit power ratio of relay and source in tie-2 increases,the whole network secrecy probability increases gradually.