Optimal Resource Allocation For The Orthogonal Relay Eavesdropper Channel

Due to the open nature of wireless medium, the wireless communication is very convenient and particularly vulnerable to security threats. The cooperation between transmitter and intended receiver can improve the communication efficiency. However, the messages that transmitted by the untrusted nodes are easy vulnerable to interference or eavesdropping, which makes it difficult to be guaranteed for the security of wireless communication. In this thesis, we study the security performance of single-user channel from information theoretic viewpoint.The gaussian orthogonal untrusted relayr channel is investigated. We assume that there is an eavesdropper at the relay node who has access everything that the relay node knows. The source node transmits signals with the relay node and the destination node in channel 1, the relay node transmits signals with destination node in channel 2, channel 1 and channel 2 are orthogonal. The achievable secrecy rate is derived based on analyzing the gaussian orthogonal untrusted relay channel. Under the limit of the total channel resource, the maximum of the achievable secrecy rate is obtained through optimizing the resource allocation. In the Gaussian orthogonal untrused relay channel, there exists a unique optimum bandwidth or power to achieve the maximum secrecy rate and a higher secrecy rate can be achieved using the optimal resource allocation strategy than the maximum resource allocation strategy.In next station, we consider single-user OFDM wiretap channel with an external cooperative jammer (CJ), where the CJ helps the destination interference the eavesdropper. We further consider a special case: the network with a CJ and the achievable secrecy rate is derived. The source power and CJ power are optimized over all sub-carriers to maximize the sum secrecy rate under a total system power constraint. The simulation results indicate that the secrecy rate with optimal resource allocation is higher than the network without a CJ with optimal resource allocation. From the result, the network with an external CJ using optimal resource allocation can makes the security performance improve greatly.