Research On Physical Layer Security For Heterogeneous Cellular Networks Using Stochastic Geometry

Due to the dramatic development of intelligent equipment and digital life,the traditional homogeneous cellular networks,which intend to cover a large area by each single cell,are unable to meet the exploding demand for diversified wireless communications.In order to further improve the system capacity and spectrum efficiency,the existing cellular networks are converging toward multi-tier heterogeneous cellular networks(HetNets),where macro-cells are overlaid by diversified small-cells.However,with the progress of computing technology and the growth of wireless data value,if HetNets secure communications solely rely on the upper layer cryptographic techniques,it will be difficult to cope with the diversified security threats.In recent years,physical-layer security(PLS)has drawn ever-increasing attention as it can be a complement to the traditional cryptographic techniques for secure transmission.Motivated by the above reasons,this paper aims to promote the emerging research on PLS for HetNets.According to the features of HetNets,such as the diversification of node types,hugeness of node number,complexity of interference,and randomization of network topology,considering the requirements of future mobile communications for high-rate,security,and economic sustainability,this paper studies how to make use of the PLS technologies(including beamforming,artificial noise,cooperative transmission and so on)to improve the HetNet secrecy transmission performance,and provides mathematical analysis framework as well as theoretical guidance for the design and operation of HetNets.The main contributions are summarized as follows:1.Aiming at the difficulty of analysis for PLS in HetNets caused by the complex system architecture,a fundamental system model of PLS performance for HetNets is proposed based on stochastic geometry.With the fundamental system model,an analysis framework to evaluate PLS performance in Het Nets based on Poisson point process,an analysis framework to evaluate PLS performance in orthogonal spectrum allocation HetNets based on long-term average received-signal power,and an analysis framework to evaluate PLS performance in dense HetNets based on Poisson cluster process are proposed,respectively.Based on the above frameworks,the impacts of access strategy,secrecy rate threshold,eavesdropper density,and base station(BS)deployment relative density on PLS performance in HetNets are examined.Based on the theoretical analyses and simulation results,a secrecy and economic efficiency oriented strategy for HetNets dense deployment is proposed.2.Aiming at the problems of the limited of security assurance ability for a single node and the unexcavated security potentiality for the whole HetNet,the cooperative secrecy transmission based on secure beamforming and artificial noise is analyzed in HetNets.The influences of cooperative BSs types,cooperative BSs know/unknow perfect channel state information,the cooperative power allocation between cooperative transmission and cooperative jamming,and the power allocation for artificial noise(AN)on PLS secrecy transmission performance in HetNets are examined.Based on the results of above analyses,secrecy transmission guiding strategies for different scenarios in HetNets are proposed.3.Aiming at the contradiction between secrecy capacity maximization and ecological sustainability,secrecy spectrum efficiency(SSE)and secrecy energy efficiency(SEE)are analyzed in HetNets.Considering massive multiple-input multiple-output(MIMO)technology and colluding eavesdropping,a tractable approach to evaluate the SSE and SEE performance in massive MIMO enabled HetNets is proposed.The impacts of transmit antenna number,number of users served by each macro-cell BS,and power allocation for AN on SSE as well as SEE are examined.Further,the SSE-SEE tradeoff is studied in massive MIMO enabled HetNets.