Study On Secrecy Capacity For Two Classes Of Wiretap Channels

With the wide usage of the wireless networks nowadays,the security of wireless communication has become a crucial issue.Due to the open nature of the wireless channel,the wireless links are more vulnerable to eavesdropping.However,in the dynamic wireless network,the traditional cryptography faces many challenges in handling the security problem,such as complex key distribution and management.By contrast,information theoretic secrecy guarantees secure communication against the eavesdropper even with unlimited computational power,not requiring any shared key beforehand.The basic idea of the information theoretic secrecy is to use the inherent randomness of the physical medium(including noises and channel fluctuations due to fading)and exploit the difference between the channel to a legitimate receiver and the channel to an eavesdropper to benefit the legitimate receiver.As the fundamental theoretic research of information theoretic secrecy,in this dissertation we give several constructions to the secrecy capacity for the two-way wiretap channel and the binary input Gaussian wiretap channel.Firstly,regarding that the joint secrecy is impossible in some scenarios of two-way wiretap channel,we propose the one-sided secrecy constraint for two-way wiretap channel.Under this secrecy constraint,an achievable secrecy rate region is derived for the general twoway wiretap channel.In addition,outer bounds on the secrecy capacity region are established for two classes of two-way wiretap channel.Particularly,the secrecy capacity regions are characterized for the XOR channel and the degraded Gaussian two-way wiretap channel,respectively.Secondly,we propose the individual secrecy for two-way wiretap channel.With the individual secrecy,we obtain an achievable secrecy rate region for the general two-way wiretap channel and the outer bounds for two classes two-way wiretap channel.The achievable secrecy rate region with individual secrecy is demonstrated to be strictly larger than that with joint secrecy.Most notably,we establish the secrecy capacity of the degraded Gaussian twoway wiretap channel.Thirdly,considering the benefit of feedback for multi-user secure communications,we investigate the two-way wiretap channel with feedback and propose the one-sided secrecy constraint of many transmissions.Utilizing the Markov block coding,an achievable secrecy rate region for two-way wiretap channel with feedback is derived and demonstrated to be lager than that for the two-way wiretap channel without feedback.Moreover,we obtain anouter bound on the secrecy capacity for the general two-way wiretap channel.Forthly,we investigate the effect of output quantization on the secrecy capacity of the binary-input Gaussian wiretap channel.Four cases are under consideration:(1)Both of the legitimate receiver and the wiretapper have unquantized outputs;(1)Both of the legitimate receiver and the wiretapper have binary quantized outputs;(3)The legitimate receiver has binary quantized outputs,while the wiretapper has unquantized outputs;(4)The legitimate receiver has unquantized outputs,while the wiretapper has binary quantized outputs.The close-form expressions of the secrecy capacity are obtained for case(1)and(2),respectively;the upper bounds on the secrecy capacity are established for case(3)and(4),respectively.By comparison,we conclude that the secrecy capacity of case(4)is larger than that of case(1)and(2).In the low SNR(of the main channel)region,the secrecy capacity of(1)is larger than that of(2),while as the SNR increases,the secrecy capacity of(2)tends to overtake.