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.
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.
The Ill-posed security theoretical framework for guaranteeing wireless physical-layer security is proposed in the paper, by introducing the concept of ill-posed.Firstly,the ill-posed security transforms non-unique and instability of solutions into information redundancy,which transforms the original problem into two randomized problems with redundancy combining the theory of perturbation. The framework includes the first kind ill-posed secure theory based on non-unique solutions and the second kind ill-posed secure theory based on instable solutions of an ill-posed problem.The first one utilizes the non-uniqueness of ill-posed problem to introduce redundancy for the transmitted precoding parameters,which is used to randomize transmitted signals for guaranteeing physical-layer security.The second one utilizes the instability of ill-posed problem to introduce redundancy for the transmitted precoding parameters,which can be used to guarantee physical-layer security at a little cost of legitimate users' performance.Secondly,the security of the proposed framework is measured by using secrecy capacity with imperfect channel statement information.At last,some typical examples are researched under the theoretical framework of ill-posed security.The results reveal that the existing signal processing based physical-layer security methods are all the special cases of the framework.
Wireless communications are naturally exposed to important security risks due to their broadcast nature. In contrast with wired communications, no physical medium is isolating the transmission surroundings to a specific path. Traditional methods to reach the goals of communications security rely on algorithms at protocol stack level, which are based on mathematically derived cryptographic protocols. With the tremendous proliferation of wireless devices, and the increase in computational power available for decryption, traditional cryptographic measures may be compromised. To protect communications at the lowest level, physical layer (PHY) security methods have been proposed recently. These techniques aim to ensure secure communications by exploiting the unique characteristics of the physical medium between communicating nodes, effectively reducing the decryption capabilities of an eavesdropper to intercept transmissions. This thesis explains within a general framework the most important PHY layer security schemes. First we explore approaches which utilize the knowledge of the unique channel between communicating nodes to distort a transmitted signal with various kinds of randomizations, in such a way that the intended receivers are unaffected by the distortion, but any other observer will be exposed to it. These techniques, however, introduce several trade-offs between transmission resources and the effectiveness in achieving secrecy. Of particular interest for this investigation is a class of methods which can be referred to as "security enhancing techniques", in which minimal priors about the potential eavesdroppers locations and capabilities are assumed. In this thesis, a wave-based approach to the communication secrecy problem is introduced. An interesting perspective is provided by studying the relation between electromagnetic theory and information theory, the so-called electromagnetic information theory. This allows to properly identify the unavoidable limitations imposed by the laws of electromagnetics to our ability to communicate securely. The proposed model can be extended to the analysis of different signal distortion methodologies and different channel conditions. The resulting approach is highly relevant to the study of PHY layer security methods since it is physically fundamental as well as architecture independent, which leads to a consolidating point of view of the secrecy problem. In addition, the thesis presents computer simulation results which shed insight on the security possibilities and limitations of three different security scenarios, which are termed MISO (multiple-input, single-output) (with single eavesdropper), MISOME (multiple-input, single-output, multiple eavesdropper), and MIMOME (multiple-input, multiple-output, multiple-eavesdropper).
Secure wireless communication has always been a hot research topic due to the vulnerabilities associated with wireless channel. Physical layer aspects to secure wireless communication, based on the information-theoretic security and signal processing methods have gained much recognition over the last decade. Specifically, artificial noise (AN) methods are assumed to be good means for providing security against potential eavesdroppers in multi-input multi-output (MIMO) systems and/or relay systems. However, there are still a large number of nodes which do not have multi-antennas or support sophisticated protocols in wireless networks. In this paper, a novel AN-aided method is proposed to secure wireless communications between the legitimate users (not equipped with multiple antennas) in the presence of an eavesdropper. In this proposed method frequency selective property of wireless channel is exploited. The basic principle is same in which transmitter generate random AN signal utilizing some of the transmission power to confuse eavesdropper. However artificial noise is generated in such a way that it appears to be zero at the sampling time, only for the legitimate receiver while degrading eavesdropper's channel. Artificial noise is specified using the channel state information (CSI) of the legitimate users' link. However, the secrecy of proposed scheme doesn't depend on the secrecy of CSI. Extensive simulation suggests that the proposed scheme can effectively utilized for securing wireless transmissions.
Security capacity improvement is always the implementation goal of physical layer security, which can be achieved by deliberate randomization based on differentia and uniqueness of wireless channels through signal processing method. An information-guided randomization secure transmission scheme is proposed combined with a spatial modulation system in which information can be carried by receiving antennas index but actually by channel differentia. Randomization is generated along with channel modulation procedure realized by corresponding preprocessing to transmitting signals. We provide three approaches for designing preprocessing weights under different constraint conditions. The former two can only be used when the number of receiving antennas is less than transmitting and have a tradeoff with varying degrees between receiving performance and security. The third one then relaxes the limits via generalized spatial modulation and can be used for arbitrary antennas configuration but with a receiving performance compromise. Lastly, results of performance analysis and numerical evaluation show that the proposed secure scheme is effective to prohibit the eavesdropper from intercepting information.
Wireless physical layer key generation is a remarkable technology for physical layer security. The security of key generation is not guaranteed in existing wireless physical layer key generation schemes if the eavesdropper is less than half a wavelength away from the legitimate node, which called non-secure zones problem. To address this problem, this paper proposes a Wireless physical layer key generation scheme based on unscheduled forwarding signal (WKG-UFS). Specifically, the legitimate communication nodes send random signals to each other within a coherent time. Then, the received signals are forwarded back within the coherent time after a random time interval. The legitimate nodes estimate the equivalent channel based on the final received signal and generate the secure key. Since eavesdropper does not know the original signals sent by the legitimate communication nodes, the channel feature cannot be effectively estimated. The results of theoretical analysis and experimental simulation show that the proposed scheme can effectively reduce the threat of eavesdropping on secure communication. Besides, since the time intervals for receiving and forwarding signals are variable, it can also effectively resist active attacks which by manipulating the channel.
Due to the limited reciprocity of wireless channel, most existing physical-layer security method based on channel characteristics is implemented by repeatedly interacting to generate consistent keys, which resulting in large overhead. This paper proposes a secure transmission scheme based on equivalent channel which is built by random scrambling codes generated from channel characteristics. To improve efficiency and reliability, the legitimate senders scramble the encoded signal and the receivers mitigate the non-reciprocal effect by channel decoding, rather than interacting information to obtain consistent scrambling codes. The channel capacity and security capacity of the scheme are analyzed and simulated in Rayleigh channel model. The results show that the difference of channel characteristics significantly degrade the eavesdropper's receiving performance, so that the received signal cannot be decoded correctly.