Optimal Relaying Function And Security Performance In Relay-eavesdropper Channel With Orthogonal Component

Wireless communication is widely used for its mobility and convenience and it has a great promotion to the development of economy and livelihood. But its nature of broadcast makes itself at the risk of being wiretapped because everyone could receive the signal during the cover of signal. So we need secure communication. The thesis studies secure communication from information theoretic viewpoint. In particular channel model, the destination receives as much information as possible from the source, which is called the'availability'of communication. And making the eavesdropper receives as little information as possible is called the'security'of communication.This thesis studies the four-terminal relay-eavesdropper channel with orthogonal receive components (the relay-destination and relay-eavesdropper channel is a separate channel). The perfect secrecy rate of the AF (Amplify and Forward) scheme in the orthogonal Gaussian relay-eavesdropper channel has been derived. But conventional AF is not the optimal strategy for such a channel because it does nothing but repeating the received signal. At this background, we suppose a piecewise linear AF strategy and optimize the relay function to get a larger secrecy rate than conventional AF in the orthogonal channel. Then we give numerical results under a simulated channel model. The secrecy rates achieved by the piecewise linear AF are computed and its relay function is optimized for a series of designed parameters. It can be concluded that piecewise linear AF can get a great improvement compared with conventional AF by relay function optimizing.During the optimizing, we find that secrecy rate do not get the most when the power of relay gets its most. So we use a power-allocation parameter to achieve greater secure performance. To study the power allocation, we still use the same channel model described before. Also, we derive the calculating and optimizing method to get the best-power-allocation strategy and do simulations to compare the best power-allocation and equal power-allocation. And we find power-allocation is an effective way to improve secure performance in PLAF strategy. When the relay is at the midpoint between source and destination, the best power-allocation is equal power-allocation.