Research On Key Technologies Of Physical Layer Security For Heterogeneous Cellular Wireless Networks

In order to solve the explosive growth of data traffic generated by various wireless devices,heterogeneous network(HetNet)is becoming an effective mean to enhance system capacity and coverage as well as ensure quality-of-service of users.HetNets are usually composed of various macro cells,small cells,relay stations and distributed antennas.Typically,macro cell base stations and above heterogeneous devices are permitted to simultaneously transmit their respective confidential messages over the same spectrum bands.As a result,with the increase of network capacity,spectrum efficiency can be significantly improved.However,on the one hand,due to simultaneous access to the same frequency band,there may be interference between heterogeneous devices.On the other hand,due to the broadcast nature of wireless communication and the open system architecture of HetNet,confidential messages are more vulnerable to eavesdropping attacks.Therefore,it is important to investigate the secrecy and reliable transmission of HetNet.This paper studies the key technologies of physical layer security,and improves the security and reliability of heterogeneous cellular wireless networks.The main research contents and achievements of this paper are summarized as follows:Firstly,we study a heterogeneous wireless communication scenario,which is comprised of a source(S)and a destination(D)in the presence of an eavesdropper(E),each equipped with multiple heterogeneous radio access interfaces.In order to enhance the transmission security against eavesdropping,a multi-radio cooperation(MRC)scheme is proposed,where the multiple radio interfaces at S are simultaneously utilized to transmit a source signal to D along with a weight design.For the convenience of performance comparisons,the conventional multiradio switch(MRS)scheme is also considered as a benchmark scheme,in which only the single “best” radio interface is selected at S to transmit the source signal.We evaluate the secrecy capacity and intercept probability(IP)of conventional MRS and proposed MRC schemes over Rayleigh fading channels.It is proved that the proposed MRC scheme can achieve zero IP.Numerical results show that the proposed MRC scheme performs better than conventional MRS scheme in terms of their secrecy capacity and IP.Secondly,the physical layer security of a heterogeneous cellular network consisting of a macro cell and a small cell is investigated,where a passive eavesdropper intends to tap legitimate transmissions.Both the orthogonal multiple access(OMA)and non-orthogonal multiple access(NOMA)are considered for the heterogeneous cellular network.As a consequence,two NOMA schemes,namely the interference-limited NOMA(IL-NOMA)and interference-canceled NOMA(ICNOMA),are present,where the mutual interference is constrained below a tolerable level in the ILNOMA through power control and the IC-NOMA scheme exploits a sophisticatedly-designed signal for canceling out the interference while interfering with the passive eavesdropper.The closed-form expressions of an overall intercept probability for the IL-NOMA,IC-NOMA and OMA schemes are derived.We further characterize the secrecy diversity of IL-NOMA,IC-NOMA and OMA schemes through an asymptotic secrecy outage analysis in the high signal-to-noise ratio(SNR)region.It is shown that the OMA and IL-NOMA methods obtain the same secrecy diversity gain of zero only,and a higher secrecy diversity gain is achieved by the IC-NOMA scheme.Finally,we investigate physical-layer security for a spectrum-sharing heterogeneous cellular network comprised of a macro cell and a small cell in the presence of an eavesdropper.In the macro cell,a macro base station(MBS)equipped with multiple distributed antennas sends its confidential information to a macro user(MU)through an opportunistic transmit antenna.Meanwhile,in the small cell,a small base station(SBS)transmits to a small user(SU)over the same spectrum used by MBS.We propose an interference-canceled opportunistic antenna selection(IC-OAS)scheme to enhance physical-layer security for the heterogeneous network.For comparison,the conventional interference-limited opportunistic antenna selection(IL-OAS)is considered as a benchmark.We characterize the security-reliability tradeoff(SRT)for the proposed IC-OAS and conventional ILOAS schemes in terms of deriving their closedform expressions of intercept probability and outage probability.Numerical results show that compared with the conventional IL-OAS,the proposed ICOAS scheme not only brings SRT benefits to the macro cell,but also has the potential of improving the SRT of small cell by increasing the number of distributed antennas.