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.
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.
The broadcast nature of the wireless medium makes the communication over this medium vulnerable to eavesdropping. This report considers the problem of secret communication between two nodes, over a fading wireless medium, in the presence of a passive eavesdropper. The assumption used is that the transmitter and its helpers (amplifying relays) have more antennas than the eavesdropper. The transmitter ensures secrecy of communication by utilizing some of the available power to produce ‘artificial noise’, such that only the eavesdropper’s channel is degraded. Two scenarios are considered, one where the transmitter has multiple transmit antennas, and the other where amplifying relays simulate the effect of multiple antennas. The channel state information (CSI) is assumed to be publicly known, and hence, the secrecy of communication is independent of the secrecy of CSI.
The broadcast nature of the wireless medium makes the communication over this medium vulnerable to eavesdropping. This paper considers the problem of secret communication between two nodes, over a fading wireless medium, in the presence of a passive eavesdropper. The assumption used is that the transmitter and its helpers (amplifying relays) have more antennas than the eavesdropper. The transmitter ensures secrecy of communication by utilizing some of the available power to produce 'artificial noise', such that only the eavesdropper's channel is degraded. Two scenarios are considered, one where the transmitter has multiple transmit antennas, and the other where amplifying relays simulate the effect of multiple antennas. The channel state information (CSI) is assumed to be publicly known, and hence, the secrecy of communication is independent of the secrecy of CSI.
In this article, a new relay-aided secure communication system is investigated, where a transmitter sends signals to a destination via an amplify-and-forward (AF) relay in the presence of an eavesdropper. We consider a general system configuration, where the source, relay, destination, and eavesdropper are all equipped with multiple antennas. In the practical scenarios of unknown eavesdropper's channel state information (CSI) and uncertainty of the eavesdropper's location, we aim to maximize the expected value of the system secrecy rate over the presumed distribution of the eavesdropper's channels, by exploiting the artificial noise (AN) transmitted by the source and relay nodes. The system design issue is formulated as a nonconvex stochastic optimization problem with a source transmission power constraint and a nonconvex relay transmission power constraint. A novel computational method is proposed to solve this challenging problem. The new method is developed based on an exact penalty function method together with a parallel stochastic decomposition algorithm. Numerical simulations are performed to study the effectiveness of the proposed scheme at various locations of the eavesdropper. Simulation results show that for most cases, secure communication can be achieved without the CSI knowledge of eavesdropper's channels, and the achievable secrecy rate follows the trend of a benchmark system where the eavesdropper's full CSI is available. In particular, the achievable system secrecy rate increases with the number of antennas at the legitimate users. Moreover, the optimal power allocated for the transmission of the AN increases with the system signal-to-noise ratio. The proposed computational method achieves a higher system secrecy rate than a conventional penalty function based approach.
We consider the problem of secret communications between two nodes over a wireless link in the presence of multiple passive eavesdroppers which may collude. Both the transmitter and the receiver are assumed to have multiple antennas and the multiple colluding eavesdroppers are modeled by an eavesdropper with multiple antennas. Communication is secret if the eavesdropper is unable to decode the message whereas the receiver can decode the message without making any errors. Thus, we deal with the problem of secrecy in a MIMO scenario. It is shown how the transmitter can use the multiple antennas to add artificially generated noise to the information signal such that the artificial noise only degrades the eavesdropper's channel. Thus, even if the eavesdropper has a 'better' channel than the receiver, secret communication is made possible by selectively degrading the eavesdropper's channel. The secrecy of communication is achieved by exploiting the physical characteristics of the wireless medium and it is independent of the secrecy of channel state information (CSI)
This paper addresses physical layer security in MIMO communications over frequency selective wireless channels in the presence of passive eavesdroppers, i.e. the associated channels are unknown to the legitimate transmitter. Signalling is based on orthogonal frequency division multiplexing (OFDM). Spatial beamforming is performed to improve the quality of the legitimate link. With the aim of confusing the eavesdroppers, a fraction of the available power is allocated to transmit artificial noise. Frequency diversity is shown to significantly improve secrecy. A probabilistic analysis of secrecy is presented.
Achieving secure transmission in wireless network is a significantly important research topic. Classic cryptography encrypts a confidential message to an unreadable cipher message. Thus only the authentic receiver with correct secrecy key is able to decrypt the message. However, with the growing computational capability of adversaries, the requirement of secrecy key generation and distribution is getting stringent. Another method to achieve wireless security, which has attracted much attention in recent years, is through physical layer processing, named physical layer security. In a typical wiretap channel model consisting of a transmitter, a legal receiver and an adversary (illegal receiver), early works have proven that it is possible to achieve positive secrecy rate using multiple antenna techniques, such as beamforming, at the transmitter. In this thesis, we focus on two types of malicious behaviors of the adversary: passive eavesdropping and active attack. For the passive eavesdropping, we first consider the multi-input-single-output (MISO) wiretap channel, in which the legitimate transmitter utilizes the artificial noise aided precoding strategy to maximize the achievable secrecy rate of the channel. Both scenarios of known and unknown channel state information (CSI) for the eavesdropper channels are considered. By deriving the closed-form expression of ergodic secrecy rate, we prove that there exists an optimal power ratio between the information signal and the artificial noise. We then extend our study to a four-node fading channel model in a wireless relay network, which includes two single-antenna users, one single-antenna eavesdropper and one relay node equipped with multiple antennas. By studying the decode-and-forward (DF) scheme, cooperative jamming (CJ) scheme and one proposed hybrid relay scheme, relay-and-jamming (RJ), we aims to find the optimal relay scheme with the condition that the transmitter and the relay node are under individual power constraints and the CSI of the illegitimate channel is only statistically known. Our analysis shows that the hybrid RJ scheme is optimal when the transmitter has a relatively small power budget and/or the transmitter is far away from the intended receiver. Besides the passive eavesdropping, the adversary could also choose the active attack. The pilot spoofing attack is one active attack conducted by the adversary during the channel estimation phase of the legitimate transmission. In practical systems, the pilot signals are usually known \textit{a priori} and repeatedly used information. In this attack, an intelligent adversary spoofs the transmitter on the estimation of CSI by sending the identical pilot signal as the legitimate receiver. By doing so, the adversary could obtain a larger channel rate in the data transmission phase, and also drastically weaken the strength of the received signal at the legitimate receiver if the adversary utilizes large enough power. Due to the serious consequences caused by such an attack, we first propose an energy ratio detector (ERD) that explores the asymmetry of received signal power levels at the transmitter and the legitimate receiver when the attack occurs. Our analysis shows that the ERD could provide very high probability of detection with certain requirement on the false alarming probability. Furthermore, we design a two-way training based scheme to provide not only attack detection but also secure transmission. The two-way training based detector (TWTD) exploits the intrusive component created by the adversary, followed by a secure beamforming-assisted data transmission. In addition to the good detection performance, our scheme could estimate both legitimate and illegitimate channels, with which the beamforming could be designed for data transmission.