Device-to-device (D2D) content sharing, as a promising solution to rapidly growing mobile data traffic, is facing serious security issues. Hence, how to ensure its security is a challenging and meaningful work. Covert communication is regarded as an emerging and cutting-edge security technique for its higher level of security and less need for channel state information (CSI), and accordingly, has attracted wide attention. However, it is not easy to directly apply covert communication to D2D content sharing to ensure both security and efficiency. In this paper, a novel covert communication model is constructed in D2D content sharing scenario, where the co-channel interference (CCI) introduced by spectrum reusing is exploited as the cover of contents, so that the contents are hidden from the warden. Then, we propose a secure and efficient resource allocation scheme to ensure both security and efficiency of D2D content sharing by addressing the following two issues: i) In order to guarantee the robustness of our scheme, covert constraints are learnt by analyzing the detection performance at the warden, i.e., the security of D2D content sharing is guaranteed even considering some extremely adverse environments. ii) The joint spectrum allocation and power control is modeled as a two-sided matching problem and then reformulated as an one-to-one matching game based on the principle of mutual benefit, in order to ensure the quality of service (QoS) requirements of both D2D pairs and cellular users. Then, a covert constraints guaranteed resource allocation algorithm based on Gale-Shapley algorithm is proposed. Its properties, such as stability, optimality, convergence and complexity are analyzed. Extensive simulation results are provided to verify the theoretical analyses and demonstrate the efficiency of our proposed algorithm, which has at least 7.63% performance gain compared with some existing approaches and no more than 4.83% performance loss compared with the exhaustive search.

In this paper, we investigate the secure content delivery issue for device-to-device networks based on the trust evaluation mechanism and covert communication model. Specifically, in order to stimulate the lasting and rational cooperation among mobile devices, we propose a trust evaluation mechanism, where the trust degree between two mobile devices can be obtained through historical assessed values. Simultaneously, a covert communication model is introduced to guarantee the undetectability of content delivery, which helps to stop malicious wardens adopting some coming external attacks. In this way, the availability and dependability of content sharing, as well the confidentiality and integrity of transmitted contents cam be guaranteed. Then, combining security-aware metrics, in terms of trust degree and covert rate, with physical layer transmission performances, in terms of achievable rate and successful delivery probability, we propose the definition of secrecy-aware effective rate to serve as a guidance on the joint optimization issue of content delivery mode selection and resource management, which is formulated as a social welfare maximization problem. To solve the complex problem tactfully, it is decoupled into two subproblems, i.e., mode selection which is a many-to-one matching problem, and resource management which is a one-to-one matching problem. By analyzing the interaction between two issues, a novel hierarchical stable matching algorithm is proposed to obtain three-dimension stable matching results. Its properties, such as stability, convergence, optimality, and complexity, are theoretically analyzed and proved. Finally, extensive numerical results are provided to demonstrate the advantages of our proposed algorithms.

Device-to-device (D2D) multicast content sharing has become a promising technology to improve the services within a local area. This paper investigates the problem of cluster formation (i.e., cluster head (CH) selection and user grouping) for D2D multicast content sharing in cellular networks. Each cluster consists of one CH and multiple content requesters (CRs). Firstly, the selected CHs should be able to serve as many CRs as possible. To achieve this, they should have higher physical-social centrality and should not stay physically close to each other. Secondly, the issue of user grouping is modeled as a social-aware rate maximization problem, where social-aware rate is introduced to ensure the physical link quality and to stimulate an efficient cooperation between the CHs and CRs. In order to solve the optimization problem in a decentralized and low-complexity way, we propose a matching and coalition approach. Specifically, the optimization problem is transformed into a two-sided many-to-one matching game with externality, and a distributed user grouping algorithm is proposed to obtain a stable matching result. Considering the performance gap resulted from the externality, the problem is then transformed into a coalition formation game. Without loss of generality, a user grouping optimization algorithm with user transfer and merging is proposed. Moreover, some properties, e.g., the convergence, stability and complexity, of the proposed algorithms are discussed. Finally, the performance of our proposed scheme is evaluated by extensive simulations based on the comparisons with other schemes.

With the rapid growth of mobile data traffic, device-to-device (D2D) content sharing has attracted wide attention. However, due to the openness of wireless channel, D2D content sharing may be detected by a malicious warden. In this paper, covert communication is used to address the security issue of D2D content sharing in dedicated mode. Specifically, when D2D pair wants to share covert content without being detected, other D2D pairs who reuse the same resource block (RB) transmit with random power to produce co-channel interference confusing the warden. We derive the optimal threshold and the expected detection error rate of warden under the cases where the number of D2D pairs reusing the same RB is various. Extensive numerical results show that increasing the number and transmission power of D2D pair can reduce the probability of content sharing being detected and better guarantee D2D content sharing security in dedicated mode.