In this paper, we investigate the security of cellular networks using cooperative jamming with imperfect wiretap channel status information (CSI). Firstly, the CSI of the eavesdropper is considered imperfect and modeled as a sphere with a certain center and a radius which is the estimated channel of eavesdropper, and then the optimization of the worst-case secrecy rate is given. Secondly, using semidefinite relaxation (SDR) and a search method, the SDR-based scheme is proposed to maximize the secrecy rate. To reduce the complexity, a second scheme to optimize the ratio between interference to the eavesdropper and to the legitimate user, which is transmitted by jammers, is introduced. Finally, the numerical results demonstrate the excellent performance of the two strategies, and the performance of the low-complexity scheme is very close to that of the SDR-based scheme.

This work studies the security enhancement and social relationship model in heterogeneous D2D and cellular network with an adaptive jamming. Different from traditional physical layer securities that optimize secrecy capacity, we investigate strategies based on reduction of compromised secrecy region (CSR). Specifically, we firstly format the outage probability while taking fading channel effects into consideration and we build a novel social relationship model evaluated by social interactions and physical secrecy outage probability. Then three strategies for adaptive jamming are proposed to reduce CSR at various levels of channel states in the presence of joint cellular user and adaptive jammer beam-forming. Finally, numerical approximation and results validate the proposed CSR optimization strategies for joint artificial noise from cellular user and adaptive jammer and our scheme could reduce CSR efficiently.

In this paper, we investigate the Physical Layer Security (PLS) of a multiple friendly jammers and multiple users wireless system in Device-to-Device (D2D) communications underlaying cellular networks with an eavesdropper. The aim is to maximize the increase of secrecy capacity of the entire system through optimal power allocation and jamming matching under various practical constraints. Firstly, the total increase secrecy capacity of D2D pairs with the help of jamming is derived, then we obtain optimal jamming power for each D2D pair and formulate the D2D pairs and jammers matching problem in the weighted bipartite graph via designing the Kuhn-Munkres (KM) algorithm. Finally, numerical results demonstrate that our scheme could greatly improve the secrecy performance of heterogeneous D2D and cellular networks.

In this paper, we study the secret-key capacity of the secure cooperative network using the collaborative amplify-andforward (AF) relays to form a beamforming system through the physical layer. The closed-form expression of secret-key capacity is firstly given to prove the the secret-key capacity is not only achievable but can be designed and optimized by beamforming vector formed by AF relays. Furthermore, three beamforming solutions are proposed to maximize the secret-key capacity under the total relay power constraint. The first solution, maximum secret-key capacity (MSKC) beamforming solution, is aimed towards two-level optimization problems and performed by using the semidefinite relaxation (SDR) technique. This solution is the closest to the optimal solution of original problem, but its complexity is very high because of the SDPs. To decrease the complexity, the signals at all eavesdroppers are forced to be zero, producing the second solution named zero-forcing (ZF) beamforming solution. However, the ZF beamforming solution does not work when the number of eavesdroppers is larger than that of relays. The third solution, lower bound maximum secretkey capacity (LB-MSKC) beamforming solution, is designed to make up the loss. It simplifies the original problem to a one-level optimization problem by relaxing the eavesdroppers, and it can still work well when the number of eavesdroppers is larger than that of relays. Simulation results are presented to illustrate the proposed solutions.

This paper exploits physical layer network coding (PNC) and friendly jamming to improve their physical layer security in wireless two-hop cooperative communications, consisting of one source-destination pair with the help of multiple intermediate nodes in the presence of one eavesdropper. By sending a jamming signal carrying a random binary message from the selected jammer and utilizing the PNC at the selected relay node, the system can avoid the disadvantage of the friendly jamming to the source-relay channel and do good to the relay-destination channel, thereby achieving better secrecy rate. Assuming global channel state information available and memoryless adversaries, we seek to minimize the secrecy outage probability with the optimal relay and jammer selection. Numerical simulation results show that our schemes outperform the conventional approaches in wireless cooperative communications.

In this paper, we investigate the physical layer security scheme in heterogeneous Device-to-Device (D2D) and cellular networks. More specifically, we aim to optimize the secrecy capacity of D2D users in a single cell where the D2D users share downlink resource with cellular users. We assume that base station is equipped with multiple antennas while other nodes are equipped with single antenna, and the eavesdropper is intending to wiretap the information of D2D user. Base station transmits artificial noise as the jamming-aided signal to degrade the wiretap channel such that the security capacity of D2D user could be improved. First, we design the precoding matrix of artificial noise to make sure that the wiretap channel would be degraded while D2D link and cellular link are not influenced. Second, the precoding matrix of desired information signal of cellular link is designed in order to satisfy the quality demand of cellular link. In this part, we propose three schemes according to different criteria. Finally, the optimal power allocation algorithm is provided. Simulation results demonstrate that our scheme could efficiently improve the secrecy capacity of D2D user while the quality demand of cellular user is satisfied.