Research On Key Technologies Of Physical Layer Security For D2D-Enabled Cellular Networks

D2D(Device-to-Device)communication allows proximity user equipments to deliver their own messages over the direct link established between them without the base station relaying messages,which has the promise of many types of advantages: superior spectrum efficiency,increasing network capacity,and son on.D2 D communication underlaying cellular networks has been regarded as an ideal candidate technology for the next generation mobile communication.To overcome security threats in wireless communication systems,physical layer security,as a remedy of traditional encryption techniques,has been recognized as a prominent component to achieve secure communication by exploiting the characteristics of wireless channels.As well as other wireless systems,since the inherent openness of the transmission medium makes wireless information more vulnerable to being eavesdropped,secure communication is identified as a critical challenge in D2D-enabled cellular network.Hence,how to make full use of physical layer security technologies to achieve the secure communication in D2D-enabled cellular network has attracted remarkable attentions in recent years.D2D communication has many advantages including better wireless channel quality,higher channel capacity,apparently resulting in a much higher secrecy performance.Hence,it is easier to meet the security requirements of D2 D users when lower-security traffics are transmitted over direct D2 D links.In this case,we mainly consider the security requirements of cellular users,but not consider the security requirements of D2 D users when designing the resource allocation mechanism.However,when more private traffics are transmitted over direct D2 D links,the security requirements of both cellular users and D2 D users should be simultaneously considered.For simplicity,the two different scenarios above are respectively distinguished by: I)the case in which only security requirements of cellular users are considered;II)the case in which security requirements of both cellular users and D2 D users are simultaneously considered.The research on the physical layer security in D2D-enabled cellular networks has yielded heartening fruits in different scenarios.However,there still exist some problems which are urgent to be solved.In the case where security requirements of both cellular users and D2 D users are simultaneously considered,the unsolved problems are presented as follows: 1)the difference of their priorities for both cellular users and D2 D users is not considered in the proposed resource allocation mechanism;2)there is no the reasonable resource allocation mechanism and secure transmission scheme considering both security requirements of both cellular users and D2 D users with the aid of new technologies proposed in 5G mobile communications.In the case where only security requirements of cellular users are considered,the unsolved problems are presented as follows: 1)there is no the resource allocation mechanism considering security requirements of cellular users except for both reliability requirements of cellular users and D2 D pairs;2)the current research on physical layer security of the cellular downlink in D2D-enabled network is only limited to the point-to-point scenario.To resolve the problems above,this paper exploits the physical layer security in D2D-enabled cellular network to achieve or improve its secure communication with the support of National 863 project program and the National Natural Science Foundation program.According to the different security requirements of the transmitted traffic over direct D2 D links,this paper studies physical layer security in D2D-enabled cellular network in the two different scenarios mentioned above,which is based on the interference between these hybrid links and the artificial noise scheme.The first two researches are studied in the case where the security requirements of both cellular users and D2 D users are simultaneously considered,whereas the later two researches are studied in the case where only security requirements of cellular requirements are considered.The main research results are summarized as follows:1.Aiming at the difference of their priorities of both cellular users and D2 D users,a secure access control strategy for D2 D communications underlaying cellular networks based on the secrecy outage probability(SOP)is proposed,which minimizes the SOP of the reused D2 D transmitter subject to the security requirement of the cellular user.Firstly,a candidate selected set of D2 D users sharing the same resource block based on the channel direction information(CDI)is determined to guarantee the reliable communication of the cellular user.Next,the transmission power of each D2 D user in the candidate selected set is optimized to achieve its minimum SOP.Finally,the D2 D transmitter with the minimum SOP is allowed to access to the cellular network.Simulation results show that the proposed strategy could improve the security performance of both the cellular user and the D2 D user subject to the reliable communication of the cellular user.2.Aiming at how to design the reasonable resource allocation mechanism and secure transmission scheme considering the security requirements of both cellular users and D2 D users with the aid of new technologies proposed in 5G mobile communications,a secure transmission scheme based on the artificial noise is proposed for D2 D communications underlaying full-duplex cellular networks,and a secure power allocation scheme to maximize the overall secrecy rate of both cellular users and D2 D users is presented.The full-duplex base station transmits the artificial noise to guarantee the secure communications for both cellular links and D2 D links when it receives the signals from cellular uplinks.Improving the transmission power of cellular users or D2 D users will degrade the secrecy rate of the other kind user,although will improve itself secrecy rate obviously.Hence,a secure power allocation scheme to maximize the overall secrecy rate of both cellular users and D2 D users is presented subject to security requirements of cellular users.Simulation results are conducted to evaluate the effectiveness of the proposed scheme.3.Aiming the tradeoff between the reliability requirements of cellular users and D2 D users and the security requirements of cellular users,an opportunistic access control scheme based on wireless channels is proposed,and an interference threshold optimization method is presented.The interference brought by these hybrid links is employed to improve the security performance of cellular users subject to the reliability requirements of both cellular users and D2 D users.We consider a scenario,in which multiple D2 D pairs could simultaneously share the same resource block with a specific cellular user.We utilize the channel direction information or channel gains to characterize the strength of the interference among cellular users and D2 D users in two respectively different scenarios: I)the base station being equipped with multi-antennas;II)the base station being equipped with a single antenna.According to the reliability requirements of both cellular users and D2 D users,the proposed scheme could guarantee their reliability requirements by designing the interference thresholds,and further could combat eavesdroppers while keeping the legitimate cellular user as non-intrusive as possible,regarding D2 D users as friendly jammers in a non-collaborative way.To further support the performance of this hybrid network,we next present a two-dimension search algorithm to obtain the optimal interference thresholds to minimize the connection outage probability(COP)of D2 D users subject to the secrecy requirements of cellular users.Finally,simulation results are presented to validate the effectiveness of our proposed scheme.4.Aiming at the current research on physical layer security of the cellular downlink in D2D-enabled network only limited to the point-to-point scenario,a secure transmission scheme of the cellular downlink based on the artificial noise assisted scheme in D2D-enabled network is proposed,and the system-level performance of this hybrid network is investigated.We consider a case in which each base station has no channel state information(CSI)from D2 D transmitters which are generally deployed in the cell edge.To guarantee the secure communication of the cellular user,each base station employs the artificial noise assisted transmission strategy.Firstly,we derive the closed-form and asymptotic expressions of the secrecy outage probability of the cellular link in different scenarios: I)eavesdroppers having no multi-user decedability;II)eavesdroppers having the multi-user decedability.Then,we comprehensively discuss the impacts of main system parameters on the security performance of the cellular user to provide some system design guidance.To characterize the reliable communication of the typical D2 D link,the closed-form and asymptotic expressions of the connection outage probability are respectively derived and some comprehensive analysis are presented.Finally,simulation results are provided to validate the effectiveness of theoretical analysis.