Research On Resource Allocation For Physical Layer Security In Large-Scale MIMO Relaying Systems

The broadcast nature of the wireless channel gives rise to more and more information security problems. Traditionally, wireless security is guaranteed through high layer encryption. With the development of interception techniques, encryption becomes more complex, leading to high computation burden. Inspired by information theory, physical layer security is introduced into wireless communications to guarantee secure communication by using wireless channel characteristics, i.e., fading, noise and interference. This paper considers a large-scale multiple-input multiple-output(LS-MIMO) relaying system, where an information source sends the message to its intended destination aided by an LS-MIMO relay, while a passive eavesdropper tries to intercept the information forwarded by the relay. The advantage of a large scale antenna array is exploited to enhance wireless security.Firstly, under imperfect CSI, a thorough secrecy performance analysis and comparison are given under amplify-and-forward(AF) and decode-and-forward(DF) relaying schemes. Furthermore, asymptotical analysis is carried out to provide clear insights on the secrecy performance for such an LS-MIMO relaying system.Then, a resource allocation algorithm is proposed that aims at maximizing the secrecy outage capacity of DF LS-MIMO relaying system. We propose an relay transmit power allocation scheme in the sense of maximizing the secrecy outage capacity, and derive the close-form expression for the optimal power at the relay. What's more, a joint source transmit power, relay transmit power, and time allocation scheme and the corresponding algorithm are given. Simulations results validate the effectiveness of the proposed joint resource allocation scheme.Finally, taking green communication into consideration, we optimize the secrecy energy efficiency of AF LS-MIMO relaying system. The relay transmit power is optimized in the sense of maximizing the secure energy efficiency. By using the property of fractional programming, the relay power allocation algorithm is derived. Furthermore, two energy-efficient power allocation schemes are proposed through maximizing the secrecy energy efficiency with joint or distributed source and relay power constraints, respectively. It's proved that the scheme with joint power allocation performs better than the one with distributed power allocation, but they asymptotically approach the same saturated energy efficiency.