Research On Physical Layer Security Based On Compound Wiretap Channels

Due to the broadcast nature of the wireless channels, the radio transmission is more vulnerable to noise and attacks from unexpected eavesdroppers. Therefore, the security of wireless communications has attracted broad attention from experts all over the world. Traditionally, cryptographic protocols have been designed and implemented to provide security in the upper layers, based on the assumption of an error-free link in the physical layer. However, this assumption does not apply to all scenarios, especially in wireless situations. What is more, the eavesdroppers’ computers today are easier to solve the problems with high computational complexity, which makes the situation more complicated. Information-theoretic principles have been applied in physical layer security to make sure of secure communication. The simplest network is the model of wiretap channel, where there is a transmitter, a legitimate receiver and an unauthorized receiver. The transmitter wishes to communicate a private message to the receiver, while the eavesdropper tries to wiretap. By taking the advantage of all the channel state information, perfect secrecy can be achieved.Based on some existing treatises on physical layer security, two novel models of compound wirtap channels are analysed. A Nakagami-m fading, which is a more flexible distribution in matching experimental data than the log-normal, Rayleigh or Rician distributions, is assumed in the first model of compound wiretap channels. Moreover, there are multiple receivers in the presence of multiple eavesdroppers and even some colluding eavesdroppers. The second model is based on the first one, where the transmitter equips with multiple antennas and uses an outdated version of the feedback information.The secrecy outage probability and the average secrecy ca pacity are derived in the first model of compound wiretap channels. Both analytical and asymptotic results are given. Numerical results show that there is a n increase in the secrecy performance when there is a higher fading coefficient, and fewer receivers or eavesdroppers. Moreover, Similar results can also be achieved by non-colluding eavesdroppers. For the second model, the secrecy outage probability is derived and its analytical and asymptotic results are also given as well. It is shown that a higher outdated correlation coefficient or more transmit antennas can lead to higher secrecy performance. In addition, the impact of the outdated correlation coefficient on secrecy increases with its own value, while the counterpart of the numbers of the transmit antennas turns out to be the opposite. Both of them are non-linear process, which shows that it is better for the system disigners to consider about all the parameters when facing a situation of secure transmission.