Security-embedded opportunistic user cooperation with full diversity

As a promising technique for wireless networks, cooperative communications is coming to maturity in both theory and practice. The main merit of the cooperation technique is its capability in providing additional transmission links to harvest the spatial diversity gain at the physical layer. However, due to the broadcast nature of wireless medium, the diversity gain can be also freely achieved at the potential eavesdropper if the cooperation is performed blindly. To solve this problem, we propose a security-embedded opportunistic user cooperation scheme (OUCS) in this paper. The OUCS first defines a concept called secrecy-providing capability (SPC) for both the source and the cooperative relays. By comparing the values of SPC of these nodes, the OUCS jointly decides whether to cooperate and with whom to cooperate from the perspective of physical layer security. The secrecy outage performance of the OUCS is then derived. From the results we prove that full diversity can be achieved (i.e., the diversity order is N + 1 for N cooperative relays), which outperforms existing alternatives. Finally, numerical results are provided to validate the theoretical analysis