Biblio

Communication systems across a variety of applications are increasingly using the angular domain to improve spectrum management. They require new sensing architectures to perform energy-efficient measurements of the electromagnetic environment that can be deployed in a variety of use cases. This paper presents the Directional Spectrum Sensor (DSS), a compressive sampling (CS) based analog-to-information converter (CS-AIC) that performs spectrum scanning in a focused beam. The DSS offers increased spectrum sensing sensitivity and interferer tolerance compared to omnidirectional sensors. The DSS implementation uses a multi-antenna beamforming architecture with local oscillators that are modulated with pseudo random waveforms to obtain CS measurements. The overall operation, limitations, and the influence of wideband angular effects on the spectrum scanning performance are discussed. Measurements on an experimental prototype are presented and highlight improvements over single antenna, omnidirectional sensing systems.

Visible light communication (VLC) is an important alternative and/or complementary technology for next generation indoor wireless broadband communication systems. In order to ensure data security for VLC in public areas, many studies in literature consider physical layer security (PLS). These studies generally neglect the reflections in the VLC channel and assume no inter symbol interference (ISI). However, increasing the data transmission rate causes ISI. In addition, even if the power of the reflections is small compared to the line of sight (LoS) components, it can affect the secrecy rate in a typical indoor VLC system. In this study, we investigate the effects of ISI and reflected channel components on secrecy rate in multiple-input single-output (MISO) VLC scenario utilized null-steering (NS) and artificial noise (AN) PLS techniques.

Cognitive radio primary network secure communication strategy based on secondary user energy harvesting and primary user destination assistance is investigated to guarantee primary user secure communication in cognitive radio network. In the proposed strategy, the primary network selects the best secondary user to forward the traffic from a primary transmitter (PT) to a primary receiver (PR). The best secondary user implements beamforming technique to assist primary network for secure communication. The remaining secondary transmitters harvest energy and transmit information to secondary receiver over the licensed primary spectrum. In order to further enhance the security of primary network and increase the harvested energy for the remaining secondary users, a destination-assisted jamming signal transmission strategy is proposed. In this strategy, artificial noise jamming signal transmitted by PR not only confuses eavesdropper, but also be used to power the remaining secondary users. Simulation results demonstrate that, the proposed strategy allows secondary users to communicate in the licensed primary spectrum. It enhances primary network secure communication performance dramatically with the joint design of secondary user transmission power and beamforming vectors. Furthermore, physical layer security of primary and secondary network can also be guaranteed via the proposed cognitive radio primary network secure communication strategy.

This article investigates the beamforming method selection in artificial-noise-aid (AN-aid) multiuser multiple-input-single-output (MU-MISO) broadcast wiretap systems in slow fading channel environment. We adopt beamforming pre-coding matrix with artificial noise to achieve secure multiuser communication and optimize system performance, and compare the secure transmission performance of two beamforming methods. To overcome the complexity of this model, a novel optimization scheme expressed using semi-closed-form expressions and Monte Carlo method is employed to derive the relationship between transmission parameters and secure transmission performance. This scheme would help us to analyses performance of different beamforming methods.

In cognitive radio network, the primary user (PU) network and the secondary user (SU) network interfered with each other because of sharing the spectral resource. Also interference among multi-downlinks in SU network decreased the sum rate in SU network and the eavesdropper in PU network decreased the secrecy rate in PU network. Focusing on above problem, this paper raised two channel selection and beamforming methods based on singular value decomposition (SVD) and uplink-downlink duality respectively, and then analyzed the performance of them in physical layer security.

Cooperative MIMO communication is a promising technology which enables realistic solution for improving communication performance with MIMO technique in wireless networks that are composed of size and cost constrained devices. However, the security problems inherent to cooperative communication also arise. Cryptography can ensure the confidentiality in the communication and routing between authorized participants, but it usually cannot prevent the attacks from compromised nodes which may corrupt communications by sending garbled signals. In this paper, we propose a cross-layered approach to enhance the security in query-based cooperative MIMO sensor networks. The approach combines efficient cryptographic technique implemented in upper layer with a novel information theory based compromised nodes detection algorithm in physical layer. In the detection algorithm, a cluster of K cooperative nodes are used to identify up to K - 1 active compromised nodes. When the compromised nodes are detected, the key revocation is performed to isolate the compromised nodes and reconfigure the cooperative MIMO sensor network. During this process, beamforming is used to avoid the information leaking. The proposed security scheme can be easily modified and applied to cognitive radio networks. Simulation results show that the proposed algorithm for compromised nodes detection is effective and efficient, and the accuracy of received information is significantly improved.

In this paper, an improved cooperative jamming (CJ) strategy is developed for physical layer (PHY) security in a multi-hop wireless communication system which employs beamforming in the last hop. Users are assigned to independent groups based on the merger-and-split rule in a coalition game. The secrecy capacity for a valid coalition is a non-convex optimization problem which cannot easily be solved. Therefore, restrictions are added to transform this into a convex problem, and this is solved to obtain a suboptimal closed-form solution for the secrecy capacity. Simulation results are presented which show that the proposed strategy outperforms other methods such as non-cooperation, relay cooperation, and previous CJ approaches in terms of the secrecy capacity. Further, it is shown that the proposed multi-hop solution is suitable for long distance communication systems.

This paper considers the physical layer security for the cluster-based cooperative wireless sensor networks (WSNs), where each node is equipped with a single antenna and sensor nodes cooperate at each cluster of the network to form a virtual multi-input multi-output (MIMO) communication architecture. We propose a joint cooperative beamforming and jamming scheme to enhance the security of the WSNs where a part of sensor nodes in Alice's cluster are deployed to transmit beamforming signals to Bob while a part of sensor nodes in Bob's cluster are utilized to jam Eve with artificial noise. The optimization of beamforming and jamming vectors to minimize total energy consumption satisfying the quality-of-service (QoS) constraints is a NP-hard problem. Fortunately, through reformulation, the problem is proved to be a quadratically constrained quadratic problem (QCQP) which can be solved by solving constraint integer programs (SCIP) algorithm. Finally, we give the simulation results of our proposed scheme.

We investigate large wireless networks subject to security constraints. In contrast to point-to-point, interference-limited communications considered in prior works, we propose active cooperative relaying based schemes. We consider a network with nl legitimate nodes and ne eavesdroppers, and path loss exponent α ≥ 2. As long as ne2(log(ne))γ = o(nl) holds for some positive γ, we show one can obtain unbounded secure aggregate rate. This means zero-cost secure communication, given a fixed total power constraint for the entire network. We achieve this result with (i) the source using Wyner randomized encoder and a serial (multi-stage) block Markov scheme, to cooperate with the relays, and (ii) the relays acting as a virtual multi-antenna to apply beamforming against the eavesdroppers. Our simpler parallel (two-stage) relaying scheme can achieve the same unbounded secure aggregate rate when neα/2 + 1 (log(ne))γ+δ(α/2+1) = o(nl) holds, for some positive γ, δ.