For the wiretapping in wireless communication system, this paper proposes an eigenvalue decomposition method for wireless physical layer security. In the method, firstly, the channel state information matrix is decomposed into sub-channels by eigenvalue decomposition. Secondly, we choose the sub-channels with bigger eigenvalue to transmit useful signal and the one with the smallest eigenvalue is transformed into a random channel. Then, the received signal of legitimate receiver becomes steady, while eavesdropper's turns random. The simulations show that, by choosing the characteristic, the method can decrease the demands of legitimate channel state, and keep the eavesdropper's error probability at a high level, so as to increase the system security. We can get the conclusion that the eigenvalue decomposition method can prevent wiretapping and increase wireless physical layer security between the transmitter and legitimate receiver effectively.
For the wiretapping in wireless communication system, this paper proposes an eigenvalue decomposition method for wireless physical layer security. In the method, firstly, the channel state information matrix is decomposed into sub-channels by eigenvalue decomposition. Secondly, we choose the sub-channels with bigger eigenvalue to transmit useful signal and the one with the smallest eigenvalue is transformed into a random channel. Then, the received signal of legitimate receiver becomes steady, while eavesdropper's turns random. The simulations show that, by choosing the characteristic, the method can decrease the demands of legitimate channel state, and keep the eavesdropper's error probability at a high level, so as to increase the system security. We can get the conclusion that the eigenvalue decomposition method can prevent wiretapping and increase wireless physical layer security between the transmitter and legitimate receiver effectively.
For the wire-tapping in wireless communication system,this paper presented an encrypting method based on channel multipath delay-time information to ensure the security of physical layer in wireless communication system.In this method,the transmitter made the time to transmit symbol random with channel multipath delay-time information that estimated,and made the received signal of legitimate receiver stronger at the synchronization location.So the legitimate could receive the information normally.While the received signal of eavesdropper turned random for different channel information,such as phase and range.Then the eavesdropper couldn't recover the information with the random received signal,and the error probability was high,which increased the security of legitimate receiver.The simulations show that the method can keep the eavesdropper's error probability at a high level,so as to increase the system security.Finally,it comes to the conclusion that this method can ensure the security of physical layer in wireless communication system with channel multipath.
This paper proposes a new channel state based secure wireless communication mechanism to realize secure communication with a pre-equalization function in a physical layer. Researches of physical layer security have been proposed to achieve secure communication in physical layers. On the contrary, there are a few issues where terminals in a same direction can receive a message, overhead due to complex control mechanisms, special hardware, etc. This paper focusses on practical wireless communication environment, where multi-path signals are received at a receiver. It is common knowledge that a channel state according to multi-path signals is different when a position of a receiver is different. The transmitter of proposed scheme transmits an optimized signal to a receiver with pre-equalizing the signal according to the channel state between the transmitter and the receiver. Therefore, only the receiver that has the same channel state for the pre-equalizing can obtain the high quality signal from the transmitter, and can demodulate the signal correctly. As a result, eavesdroppers around the transmitter cannot equalize the received signal before a demodulation process for the received signal because they exist at a different place of the receiver. The numerical results show that the proposed scheme can realize secure communication in typical wireless channel models. It means that a legitimate receiver can demodulate a signal correctly and eavesdroppers suffer from demodulation errors. As a result, we can find that the proposed scheme can utilize a channel state as an encryption key in physical layer security communication.
Due to the broadcast nature, wireless links are open to malicious intrusions from outsiders, which makes the security issues a critical concern in the wireless communicationsover them. Physical-layer security techniques, which are based on the Shannon’s unconditional secrecy model, are effective in addressing the security issue while meeting the required performance level. According to the Wyner’s wiretap channel model, to achieve unconditionally security communication, the first step is to build up a wiretap channel with better channel quality between the legitimate communication peers than that of the eavesdropper; and the second step is to employ a robust security code to ensure that the legitimate users experience negligible errors while the eavesdropper is subject to 0.5 error probability. \nMotivated by this idea, in this thesis, we build wiretap channels for the single antenna systems without resorting to the spatial degree in commonly observed the multiple-input multiple-output (MIMO) systems. Firstly, to build effective wiretap channels, we design a novel scheme, called multi-round two-way communications (MRTWC). By taking feedback mechanisms into the design of Low Density Parity Check (LDPC) codes, our scheme adds randomness to the feedback signals from the destination to keep the eavesdropper ignorant while adding redundancy with the LDPC codes so that the legitimate receiver can correctly receive and decode the signals. Then, the channel BERs are specifically quantified according to the crossover probability in the case of Binary Symmetric Channel (BSC), or the Signal to Noise Ratio (SNR) in the case of AWGN and Rayleigh channels. Thus, the novel scheme can be utilized to address the security and reliability. Meanwhile, we develop a cross-layer approach to building the wiretap channel, which is suitable for high dynamic scenarios. By taking advantage of multiple parameters freedom in the discrete fractional Fourier transform (DFRFT) for single antenna systems, the proposed scheme introduces a distortion parameter instead of a general signal parameter for wireless networks based on DFRFT. The transmitter randomly flip-flops the uses of the distortion parameter and the general signal parameter to confuse the eavesdropper. An upper-layer cipher sequence will be employed to control the flip-flops. This cryptographic sequence in the higher layer is combined with the physical layer security scheme with random parameter fipping in DFRFT to guarantee security advantages over the main communication channel. \nAs the efforts on the second step, this thesis introduces a novel approach to generate security codes, which can be used for encoding with low complexity by taking advantage of a matrix general inverse algorithm. The novel constructions of the security codes are based on binary and non-binary resilient functions. With the proposed security codes, we prove that our novel security codes can ensure 0.5 error probability seen by the wiretapper while close to zero by the intended receiver if the error probability of the wiretapper’s channel is over a derived threshold. Therefore, the unconditionally secure communication of legitimate partners can be guaranteed. It has been proved mathematically that the non-binary security codes could achieve closer to the security capacity bound than any other reported short-length security codes under BSC. \nFinally, we develop the framework of associating the wiretap channel building approach with the security codes. The advantages between legitimate partners are extended via developing the security codes on top of our cross-layer DFRFT and feedback MRTWC security communication model. In this way, the proposed system could ensure almost zero information obtained by the eavesdroppers while still keeping rather lower error transmissions for legitimate users. Extensive experiments are carried out to verify the proposed security schemes and demonstrate the feasibility and implement ability. An USRP testbed is also constructed, under which the physical layer security mechanisms are implemented and tested. Our study shows that our proposed security schemes can be implemented in practical communications settings.
The unstable characteristic of ill-conditioned system is used to guarantee wireless security in this paper. The use of ill-conditioned theory to protect wireless transmissions is proposed as a way to secure wireless networks at physical layer. Firstly, the problem of randomized transmission is converted to that of solving ill-conditioned equation to guarantee wireless transmissions with inherent low-probability-of interception (LPI). Secondly, a conditional ill-conditioned optimization function is constructed. The function of legitimate node is stable because of its matched channel. But the function of eavesdropper is randomized because that she has not the legitimate conditions, which relate to the wireless medium contains domain-specific information. In this context, we propose a security scheme for wireless security in time-variant channels. In this scheme, the variable part of channels is converted to additional conditions, which can be solved by optimizing parameters. In contrast to conventional physical-layer security techniques, the scheme exploits the redundancy of ill-conditioned problem's solutions instead of array redundancy for deliberate signal randomization, which effectively randomizes the eavesdropper's received signals but not the authorized receiver's signals. Extensive simulations and analysis results show that our proposed scheme is useful for securing wireless transmissions.
As a promising technology, physical layer security (PLS) enhances security by leveraging the physical characteristics of communication channels. However, it commonly takes the legitimate user more effort to secure its data, compared to that required by the eavesdropper to intercept the communication. To address this imbalance, we propose a physical layer deception (PLD) framework, which applies random deceptive ciphering combined with orthogonal frequency-division multiplexing (OFDM) to deceive eavesdroppers with falsified information, preventing them from wiretapping. While ensuring the same level of confidentiality as traditional PLS methods, the PLD approach additionally introduces a deception mechanism, which remains effective even when the eavesdropper has the same knowledge about the transmitter as the legitimate receiver. Through detailed theoretical analysis and numerical simulations, we prove the superiority of our method over the conventional PLS approach.
In this paper, we propose a novel approach for providing secure wireless communications in transmit-receive diversity systems. In this approach, we precode the information-bearing signal with a uniquely generated randomized eigenvector-based jamming signal to impair the eavesdropper's received signal, while the main channel, the link between the transmitter and the desired receiver, remains unaffected. Unlike existing methods, our approach can be applied to any antenna array configuration, even when the receiver and eavesdropper utilize more antennas than the transmitter, with no benefits to the eavesdropper's information detection capability from employing more antenna elements. Moreover, our proposed approach can provide more degrees of freedom for the jamming signal, significantly increasing the provided level of security. Additionally, our scheme does not assume any knowledge about the eavesdropper or even the number of collaborating eavesdroppers. Our simulation results show a secrecy capacity increase of about 7 bits/s/Hz for a 4 x 4 antenna configuration under typical transmit power constraints, which results in significant improvement in security performance and enables physically secure wireless communications.