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Intrusion detection is a challenging problem in wireless networks due to the broadcast nature of the wireless medium. Physical layer information is increasingly used to protect these vulnerable networks. Meanwhile, reconfigurable antennas are gradually finding their way into wireless devices due to their ability to improve data throughput. In this paper, the capabilities of reconfigurable antennas are used to devise an intrusion detection scheme that operates at the physical layer. The detection problem is posed as a GLRT problem that operates on the channels corresponding to the different modes of a reconfigurable antenna. The performance of the scheme is quantified through field measurements taken in an indoor environment at the 802.11 frequency band. Based on the measured data, we study the achievable performance and the effect of the different control parameters on the performance of the intrusion detection scheme. The effect of pattern correlation between the different modes on the scheme's performance is also analyzed, based on which general guidelines on how to design the different antenna modes are provided. The results show that the proposed scheme can add an additional layer of security that can significantly alleviate many vulnerabilities and threats in current fixed wireless networks. 

Applying channel information for user authentication is gaining attention in the area of wireless network security. Similarly, reconfigurable antennas capable of generating multiple decorrelated channel realizations have become increasingly popular in wireless systems. In this paper we propose and evaluate a channel-based authentication scheme that applies the capabilities of a pattern reconfigurable antenna for improved performance in user authentication. Field measurements of the channel frequency response employing such an antenna were performed to quantify the performance of the proposed scheme. Based on these measurements, we show the effect of correlation that exists between the different modes on the authentication performance. Furthermore, the performance gain that can be achieved by the scheme is studied as a function of the number of antenna modes. Offline mode analysis is performed to give a loose upper bound on performance while online mode analysis results are presented to quantify achievable authentication performance in realtime. A general guideline on how to choose the different elements of the decision metric in order to realize better performance for physical layer-based authentication schemes based on any diversity scheme is also developed.