Research On Improving Secrecy Capacity In Physical-layer Security

The broadcast nature of wireless channel has brought great challenge tocommunication security. Currently using cryptosystems such as symmetric key andpublic key depend on two conditions to achieve security. Firstly, bit-error rate inphysical layer should equal to zero. Secondly, the attacker with limited computingpower cannot crack the password in limited time. Shannon proposed “perfect secrecy”which brings no limit in the attacker’s computing power. Perfect secrecy is based onideal physical layer though. Later research in wireless channel proves that withreasonable constraint even noise and fading will not compromise perfect secrecy.Research in this area is generally called physical-layer security or information-theoreticsecurity.Secrecy capacity is an import parameter in wire-tap channel without fading. Withfading imposed, perfect secrecy can only be achieved with some probability; thereforethe outrage probability becomes another import parameter for security system.The essence of improving secrecy capacity is to introduce differential channelswhich legitimate user has better SNR than eavesdropper. Based on wire-tap channelwith Rayleigh fading, this paper proposes a new jamming method——ring jamming.The method needs an ideal directional antenna which significantly reduces SNR ofeavesdropper while keep the SNR of legitimate user invariant. The outrage probabilitydepends on the power of signal, jammer and relative position of users. Theoretically,outrage probability decreases except locations near legitimate receiver. This paper hassimulated the numeric results in finite area and it shows that this active jammingmethod can significantly reduce outrage probability and improve the secrecy capacity.In the presence of multiple receiver, ring jamming based method also reaches goodperformence. In addition, an area called secure communicaiton area can be constructedusing this method.