A distinctive method to improve the security capacity of backscatter wireless system

Backscatter communication system is the backbone of many low cost and low power distributed wireless systems. This paper studies the physical layer security (PLS) performance of a backscatter system which contains several relays and an eavesdropper. We discuss the conditions for a positive secrecy rate of the system in two different situations. First, in the case of known information of eavesdropper, we use a sub-optimal relay selection method to secure backscatter communication and maximize the secrecy rate. The simulation results prove the suboptimal scheme with low complexity achieves the same effects as the optimal one. But the transmission rate is very low due to the difference between the main channel and eavesdropper channel is too little, so we put forward the second distinctive method. Second, without knowing any information of eavesdropper, we adopt the artificial noise (AN) technique to reduce the received signal to interference noise (SINR) of eavesdropper, and came to a conclusion that under the condition of the same system model, adding a weak AN greatly improves the secrecy rate compared to situation one, and it doesn't required to obtain any information of eavesdropper. In small power of this type of communication system, this method is also effective.