Reconfigurable antennas for wireless network security

Prathaban Mookiah

doi:10.17918/etd-3645

Large scale proliferation of wireless technology coupled with the increasingly hostile information security landscape is of serious concern as organizations continue to widely adopt wireless networks to access and distribute critical and confidential information. Private users also face more risks than ever as they exchange more and more sensitive information over home and public networks through their ubiquitous wireless-enabled laptops and hand held devices. The fundamental broadcast nature of wireless data transmission aggravates the situation, since unlike wired networks, it introduces multiple avenues for attack and penetration into a network. Though several traditional mechanisms do exist to protect wireless networks against threats, such schemes are a carryover from the traditional wire based systems. Hence vulnerabilities continue to exist, and have been repeatedly demonstrated to be susceptible to failure under different circumstances. The resulting uncertainties have led to a significant paradigm shift in the design and implementation of wireless security in recent times, among which wireless channel based security schemes have shown the most promise. Channel based security schemes are rooted on the simple fact that a legitimate user and an adversary cannot be physically co-located and hence the underlying multi-path structure corresponding to the two links cannot be the same. However most wireless systems are constrained in terms of bandwidth, power and number of transceivers, which seriously limit the performance of such channel based security implementations. To overcome these limitations, this thesis proposes a new dimension to the channel based security approach by introducing the capabilities of reconfigurable antennas. The main objective of this work is to demonstrate that the ability of reconfigurable antennas to generate different channel realizations that are uncorrelated between different modes will lead to significant improvements in intrusion detection rates. To this end, two different schemes that make use of channels generated by a reconfigurable antenna are proposed and evaluated through measurements. The first scheme is based on associating a channel based fingerprint to the legitimate user to prevent intrusion. The three main components of this scheme are i ) a fingerprint derived from the different modes of the antenna, ii ) a metric to compare two fingerprints and iii ) a hypothesis test based on the proposed metric to classify intruders and legitimate transmitters. The second scheme relies on monitoring the statistics of the channels for the legitimate transmitters' links since any intrusion will result in an observable change in the channel's statistics. The problem is posed as a generalized likelihood ratio test (GLRT) which responds to any change in the channel statistics by a large spike in the likelihood ratio's value. The detector's performance is studied as a function of pattern correlation coefficient for both schemes to provide insights on designing appropriate antenna modes for better performance. Moreover this thesis takes a holistic approach to studying the antenna based security schemes. A novel channel modeling approach which combines the cluster channel model and site specific ray tracer results is proposed and validated to facilitate the analysis of such schemes through simulations without resorting to comprehensive channel measurements. This approach is motivated by the lack of an intuitive and simple channel model to study systems that use reconfigurable antennas for any application. Finally the design of a metamaterial based substrate that can help miniaturize antenna arrays and reconfigurable antennas is presented. The magnetic permeability enhanced metamaterial's capability to miniaturize an antenna's size while maintaining an acceptable level of isolation between elements in an array is experimentally demonstrated. The benefits gained in a wireless communication system that uses a patch antenna arrray built on this substrate is quantified in terms of mean effective gain, correlation between the antennas and channel capacity through channel measurements. Despite their capability to significantly improve spectral efficiency, the widespread adoption of reconfigurable antennas in wireless devices has been hampered by their complexity, cost and size. The work presented in this thesis is therefore intended to serve as a catalyst to the widespread adoption of reconfigurable antenna technology by i ) adding value to such antennas by utilizing them for enhancing system security and ii ) providing a mechanism to miniaturize them to facilitate their integration into modern space constrained wireless devices.

Reconfigurable antennas for wireless network security

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Reconfigurable antennas for wireless network security

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