Bandwidth and power allocation for Gaussian orthogonal untrusted relay channel

The Gaussian orthogonal untrusted relay channel is investigated in this paper. We assume that there is an eavesdropper at the relay node which can access everything that the relay node knows. The source node transmits signals to the relay node and the destination node in channel 1, the relay node transmits signals to destination node in channel 2, channel 1 and channel 2 are orthogonal. The achievable secrecy rate is derived firstly. Under the limit of the total channel resource, the maximum achievable secrecy rate is obtained through optimizing the resource allocation. Of the Gaussian orthogonal untrusted 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 this optimal resource allocation strategy than the maximum resource allocation strategy.