Security optimisation of exposure region-based beamforming with a uniform circular array

This paper investigates the impact of a uniform circular array (UCA) in the context of wireless security via exposure region-based beamforming. An improvement is demonstrated for the security metric proposed in our previous paper, namely, the spatial secrecy outage probability (SSOP), by optimizing the configuration of the UCA. Our previous paper focused on formalizing the SSOP concept and exploring its applicability using a uniform linear array example. This paper proposes the UCA as a superior candidate because it is more robust against the effects of mutual coupling. The UCA's SSOP configuration is explored and a special expression is derived from the general expression for the first time, and a closed-form upper bound is then generated to facilitate analysis. By carefully designing the UCA structure particularly the radius, an SSOP optimization algorithm is derived and explored for mutual coupling. It is shown that the information leakage to eavesdroppers is reduced while the legitimate user's received signal quality is enhanced due to the use of beamforming

Cooperative communication in wireless networks: algorithms, protocols and systems

Current wireless network solutions are based on a link abstraction where a single co-channel transmitter transmits in any time duration. This model severely limits the performance that can be obtained from the network. Being inherently an extension of a wired network model, this model is also incapable of handling the unique challenges that arise in a wireless medium. The prevailing theme of this research is to explore wireless link abstractions that incorporate the broadcast and space-time varying nature of the wireless channel. Recently, a new paradigm for wireless networks which uses the idea of 'cooperative transmissions' (CT) has garnered significant attention. Unlike current approaches where a single transmitter transmits at a time in any channel, with CT, multiple transmitters transmit concurrently after appropriately encoding their transmissions. While the physical layer mechanisms for CT have been well studied, the higher layer applicability of CT has been relatively unexplored. In this work, we show that when wireless links use CT, several network performance metrics such as aggregate throughput, security and spatial reuse can be improved significantly compared to the current state of the art. In this context, our first contribution is Aegis, a framework for securing wireless networks against eavesdropping which uses CT with intelligent scheduling and coding in Wireless Local Area networks. The second contribution is Symbiotic Coding, an approach to encode information such that successful reception is possible even upon collisions. The third contribution is Proteus, a routing protocol that improves aggregate throughput in multi-hop networks by leveraging CT to adapt the rate and range of links in a flow. Finally, we also explore the practical aspects of realizing CT using real systems.PhDCommittee Chair: Sivakumar, Raghupathy; Committee Member: Ammar, Mostafa; Committee Member: Ingram, Mary Ann; Committee Member: Jayant, Nikil; Committee Member: Riley, Georg

Physical layer security (PLS) solutions for passive eavesdropping in wireless communication

An absolute secured wireless communication is unattainable. Nevertheless, communication models must be secure and unique across each layer of the model. The physical layer is the easiest layer through which information leaks, due to its broadcast nature. The security in the physical layer, measured as secrecy capacity, is subdivided into keyed and keyless security models. In practice, the eavesdropper’s evasive and obscure random wireless channel model makes it difficult to optimise keyless security measure at the physical layer. Considering this practical challenge, the objective of this work is to use novel keyless approaches to reduce the ability of an illegitimate user to access the transmitted message via the physical layer. Physical layer security (PLS) was achieved through the deployment of unmanned aerial vehicles (UAV), intelligent reflecting surfaces (IRS), and communication sensing as security enablers in this thesis. The UAV operates with interfering signals while the IRS and sensing techniques optimise respective inherent properties leading to higher PLS performance. The thesis presents solutions to the parametric design of UAV, IRS, and wireless sensing technologies for PLS functionality. Designs and analysis herein follow from analytical derivations and numerical simulations. Specifically, the thesis presents a novel average secrecy rate formulation for passive eavesdropping with a reception rate upper bound by that of the legitimate receiver. The keyless PLS assessed from the formulations guaranteed positive rates with the design of a broadcast interfering signal delivered from a UAV. Based on the verification of the positive secrecy rate with passive eavesdropping, a swarm of UAVs improved the PLS of the communication system delivering more interfering signals. Furthermore, the functionalities of the interference driven UAV swarm were miniaturised with a system of aerial IRS. By harnessing inherent channel dynamics, a novel non-iterative design of the aerial IRS system was presented as a panacea to PLS requirements. Finally, the thesis presents the analysis of a legitimate receiver with a novel noise and interference filter as a sensing mitigation technique. The filter enhanced PLS by enabling the legitimate receiver to effectively extract desired information

Beam scanning by liquid-crystal biasing in a modified SIW structure

A fixed-frequency beam-scanning 1D antenna based on Liquid Crystals (LCs) is designed for application in 2D scanning with lateral alignment. The 2D array environment imposes full decoupling of adjacent 1D antennas, which often conflicts with the LC requirement of DC biasing: the proposed design accommodates both. The LC medium is placed inside a Substrate Integrated Waveguide (SIW) modified to work as a Groove Gap Waveguide, with radiating slots etched on the upper broad wall, that radiates as a Leaky-Wave Antenna (LWA). This allows effective application of the DC bias voltage needed for tuning the LCs. At the same time, the RF field remains laterally confined, enabling the possibility to lay several antennas in parallel and achieve 2D beam scanning. The design is validated by simulation employing the actual properties of a commercial LC medium