This study investigates the framework of associating multiple‐input–multiple‐output (MIMO) beamforming with secure code to achieve unconditional secure communications in the wireless passive eavesdropping environment. The schemes are based on a two‐step method under Wyner's wiretap channel model. First, with MIMO transmit beamforming, one can utilise the spatial degree of freedom to cripple eavesdroppers’ interceptions even when he does not know the eavesdropper's channel state information. Consequently, by taking the threshold characteristics of the secure code, the legitimate receivers will continue to extend an average bit error rate advantage over eavesdroppers when they share similar conditions (background noise power and channel gains). By this way, the proposed system could achieve almost zero information obtained by the eavesdroppers while still keeping rather lower error transmissions for the main channel. A profound theoretical analysis for the MIMO advantage channel and the exact closed‐form expressions of secrecy outage probability for the secure code joint system are presented. The authors launch extensive experiments to verify the proposed security systems and demonstrate its feasibility and implement ability.
This study investigates the framework of associating multiple‐input–multiple‐output (MIMO) beamforming with secure code to achieve unconditional secure communications in the wireless passive eavesdropping environment. The schemes are based on a two‐step method under Wyner's wiretap channel model. First, with MIMO transmit beamforming, one can utilise the spatial degree of freedom to cripple eavesdroppers’ interceptions even when he does not know the eavesdropper's channel state information. Consequently, by taking the threshold characteristics of the secure code, the legitimate receivers will continue to extend an average bit error rate advantage over eavesdroppers when they share similar conditions (background noise power and channel gains). By this way, the proposed system could achieve almost zero information obtained by the eavesdroppers while still keeping rather lower error transmissions for the main channel. A profound theoretical analysis for the MIMO advantage channel and the exact closed‐form expressions of secrecy outage probability for the secure code joint system are presented. The authors launch extensive experiments to verify the proposed security systems and demonstrate its feasibility and implement ability.
This paper investigated unconditional secure communications in a passive eavesdropping (PE)wireless environment via a two-step method under Wyner's model. Firstly, with MIMO transmit beamforming, one can utilize the spatial degree of freedom (DoF) to cripple eavesdroppers' interceptions even though the eavesdropper's CSI is unknown. Consequently, note that the legitimate receivers will still continue to enjoy an advantage channel over eavesdroppers when they share similar conditions (background noise power, channel gains), we approach Eve's optimal bit error rate bound as a bridge to unit the beamforming end with the security codes. Followed by such effective security code, the proposed system could achieve almost error-free transmissions for the main channel while zero information obtained by the eavesdroppers and the unconditional security system was built. We launched extensive experiments to verify the proposed security systems and demonstrated its feasibility and implement ability.
This study analyses the physical layer security in the wiretap channel for multiple‐input–multiple‐output transmit‐beamforming (TB) systems with maximal ratio combining (MRC) receivers. The TB is designed to maximise the signal‐to‐noise ratio (SNR) at the main receiver output. The authors assume that both legitimate and eavesdropper receivers have the knowledge of their own channel state information (CSI). Furthermore, they consider that the transmitter has the full CSI of the main channel and does not have the CSI of the eavesdropper's channel. At the eavesdropper, two combining methods are considered: (i) MRC technique and (ii) selection combining method. They derive closed‐form expressions for the exact secrecy outage probability (SOP) and the probability of strictly positive secrecy capacity. Expressions of the asymptotic SOP and the asymptotic ε ‐outage secrecy capacity are also derived. The secrecy diversity order and the secrecy SNR gain are then obtained.
This chapter considers securing wireless communications at the physical layer using multiple antennas. In particular, the multiple antenna (MIMO) wiretap channel is presented and its secrecy capacity is provided. Further investigation of the high-SNR characterization of the secrecy capacity, i.e., secure degrees of freedom, reveals that the secrecy capacity of the MIMO wiretap channel does not scale with the transmit power when the eavesdropper has an advantage over the legitimate transmitter in the number of antennas. An external multi-antenna cooperative jammer terminal is introduced to the channel model in order to improve its secrecy capacity scaling with power. The secure degrees of freedom for this new multi-terminal multi-antenna channel is characterized. While for these models the eavesdropper channel state information is known at the legitimate terminals, the chapter next removes this assumption and presents results that utilize multiple antennas in order to provide secure communications irrespective of the eavesdropper channel state. An achievable strong secrecy rate and the secure degrees of freedom characterization for the MIMO wiretap channel when the eavesdropper channel is arbitrary, varying, and unknown at the legitimate terminals are presented. Finally, the extension of this model to the two-user multiple access MIMO wiretap channel is considered and its secure degrees of freedom region is characterized. Introduction The wiretap channel and the notion of secrecy capacity, introduced in [1] and generalized by [2], have provided the framework for physical layer design for wireless channels with information theoretic guarantees against eavesdropping. A natural model in wireless communications is one which utilizes multiple antennas for transmission and reception at each node. The improvement in secrecy rate that can be obtained using multiple antennas in a point-to-point channel with an eavesdropper has been studied extensively in several references, including [3, 4]. Specifically, the secrecy capacity of the Gaussian model consisting of a multiple antenna legitimate transmitter, a multiple antenna legitimate receiver, and a multiple antenna eavesdropper, termed the multiple-input multiple-output (MIMO) wiretap channel, has been identified in full generality in [5, 6].
The issues of the physical layer security are studied, where one transmitter (Alice), one full‐duplex (FD) legitimate receiver (Bob) and one multi‐antenna jammer (Charlie) are considered to defend against multiple passive and non‐colluding eavesdroppers (Eves), for multiple‐input multiple‐output wiretap channels. With the assumption that the complete channel state information (CSI) for main channels and the statistical CSI for Eves' channels are available, an improved secrecy transmission design is proposed to minimise the secrecy outage probability (SOP), under the minimum secrecy rate requirement. In addition to integrating artificial noise aided transmit beamforming and multi‐antenna cooperative jammer to impair Eves' channels, which is widely used in many existing works, a FD legitimate receiver is applied together to further enhance physical layer security. Based on the basic probability theory and convex optimisation, the accurate closed‐form expression of the SOP is derived, and the impacts on secrecy performance are described, including the qualities of main channels, the Alice's transmit power and the number of Eves. Numerical results show that the proposed scheme using the FD Bob can significantly enhance the system security, as compared with that employing the half‐duplex Bob.
The use of multiple‐antenna arrays has attracted much attention for the physical layer security of wireless systems, where the so‐called artificial‐noise solution can be applied to enhance the communication confidentiality. In the first part of this study, the authors consider secure communication over a multiple‐input single‐output Rayleigh‐fading channel in the presence of a multiple‐antenna eavesdropper – referred to as a multiple‐input single‐output multiple‐eavesdropper (MISOME) wiretap channel. Specifically, secure beamforming with artificial noise is treated when the transmitter has access to full channel state information (CSI) of a legitimate channel but only partial CSI of an eavesdropper channel. First, the optimal power allocation between the information‐bearing signal and artificial noise (or simulated interference) is derived to maximise the achievable secrecy rate in the presence of a weak or strong eavesdropper. Then, the first‐order optimal power allocation strategy is developed in a switched fashion by selecting the best of weak‐ and strong‐eavesdropper solutions for a general eavesdropping attack, and a closed‐form expression is derived for the ergodic secrecy rate achieved by secure beamforming with this switched power allocation in the MISOME wiretap channel. The numerical results show that the switched power allocation is a simple but effective approach that nearly achieves the optimal secrecy rate.
This paper examines linear beamforming methods for secure communications in a multiuser wiretap channel with a single transmitter, multiple legitimate receivers, and a single eavesdropper, where all nodes are equipped with multiple antennas. No information regarding the eavesdropper is presumed at the transmitter, and we examine both the broadcast MIMO downlink with independent information, and the multicast MIMO downlink with common information for all legitimate receivers. In both cases the information signal is transmitted with just enough power to guarantee a certain SINR at the desired receivers, while the remainder of the power is used to broadcast artificial noise. The artificial interference selectively degrades the passive eavesdropper's signal while remaining orthogonal to the desired receivers. We analyze the confidentiality provided by zero-forcing and optimal minimum-power beamforming designs for the broadcast channel, and optimal minimum-MSE beamformers for the multicast channel. Numerical simulations for the relative SINR and BER performance of the eavesdropper demonstrate the effectiveness of the proposed physical-layer security schemes.