The Capacity Analysis in the Secure Cooperative Communication System

With the characteristic of spatial diversity and low cost, cooperative system is a tendency for the future communications. In the wireless communication system, there exist degradation factors such as signal fading, multipath transmission, signal inferences, bandwidth limitation and so on. In addition to these degradation factors, the wireless transmission is not a secure environment. The information might be leaked during the transmission. Currently, the issues of privacy and security have become increasingly important for the mobile users. Traditionally, the security scheme is applied to the higher network layer. Encryption can be complex and difficult without infrastructure. It is not suitable to apply to the equipment with low computing resources, such as Internet of Things (IoT) application. Within information theoretic security characterizes the fundamental ability of the physical layer to provide a secure transmission. Hence, this work concentrates on the secure cooperative communication system. Based on the Shannon third theorem on channel capacity, this work analyzes the secrecy capacity between the source station and the destination station. For a practical situation in the system, the scenario includes multiple source stations, multiple relay stations, multiple destination stations, and eavesdroppers. For the positive secrecy rate consideration, the maximum mutual information between the source station and the destination station and the minimum mutual information between the source station and the eavesdropper should be held. To ensure a secure communication, the derived theoretical solution could be applied to find the optimal relay assignment. Beyond the relay selection, some issues related to the secure cooperative communication are suggested for the future researches in the final.