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1. A Reconfigurable Antenna-Based Solution for Stationary Device Authentication in Wireless Networks

   https://doi.org/10.1155/2012/545783  

   Mookiah, Prathaban; Dandekar, Kapil R. (January 2012, International Journal of Antennas and Propagation)

   null (Ed.)

   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. 

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2. Experimental Results of Novel DoA Estimation Algorithms for Compact Reconfigurable Antennas

   https://doi.org/10.1155/2017/1613638  

   Paaso, Henna; Hakkarainen, Aki; Gulati, Nikhil; Patron, Damiano; Dandekar, Kapil R.; Valkama, Mikko; Mämmelä, Aarne (January 2017, International Journal of Antennas and Propagation)

   null (Ed.)

   Reconfigurable antenna systems have gained much attention for potential use in the next generation wireless systems. However, conventional direction-of-arrival (DoA) estimation algorithms for antenna arrays cannot be used directly in reconfigurable antennas due to different design of the antennas. In this paper, we present an adjacent pattern power ratio (APPR) algorithm for two-port composite right/left-handed (CRLH) reconfigurable leaky-wave antennas (LWAs). Additionally, we compare the performances of the APPR algorithm and LWA-based MUSIC algorithms. We study how the computational complexity and the performance of the algorithms depend on number of selected radiation patterns. In addition, we evaluate the performance of the APPR and MUSIC algorithms with numerical simulations as well as with real world indoor measurements having both line-of-sight and non-line-of-sight components. Our performance evaluations show that the DoA estimates are in a considerably good agreement with the real DoAs, especially with the APPR algorithm. In summary, the APPR and MUSIC algorithms for DoA estimation along with the planar and compact LWA layout can be a valuable solution to enhance the performance of the wireless communication in the next generation systems. 

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3. ROBin: Known-Plaintext Attack Resistant Orthogonal Blinding via Channel Randomization

   Pan, Y and (April 2020, IEEE INFOCOM 2020)

   Orthogonal blinding based schemes for wireless physical layer security aim to achieve secure communication by injecting noise into channels orthogonal to the main channel and corrupting the eavesdropper’s signal reception. These methods, albeit practical, have been proven vulnerable against multiantenna eavesdroppers who can filter the message from the noise. The venerability is rooted in the fact that the main channel state remains stasis in spite of the noise injection, which allows an eavesdropper to estimate it promptly via known symbols and filter out the noise. Our proposed scheme leverages a reconfigurable antenna for Alice to rapidly change the channel state during transmission and a compressive sensing based algorithm for her to predict and cancel the changing effects for Bob. As a result, the communication between Alice and Bob remains clear, whereas randomized channel state prevents Eve from launching the knownplaintext attack. We formally analyze the security of the scheme against both single and multi-antenna eavesdroppers and identify its unique anti-eavesdropping properties due to the artificially created fast changing channel. We conduct extensive simulations and real-world experiments to evaluate its performance. Empirical results show that our scheme can suppress Eve’s attack success rate to the level of random guessing, even if she knows all the symbols transmitted through other antenna modes. 

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4. Reinforcement Learning Based Power-Optimal Usage of Beamforming Antenna Array for Multi-Way Wireless Communication in Vehicular Traffic Environments

   Suhasini Kommarraju and Abhijit Chatterjee (August 2022, Midwest Symposium on Circuits and Systems)

   There has been recent work on the design of antenna arrays for beamforming in dynamic evolving environments such as in vehicle-to-vehicle communication systems. A key problem is that of determining how to optimally use a large antenna array to communicate with multiple spatially located vehicles in dynamically changing channel conditions with minimal co-channel interference while minimizing overall power consumption of the wireless system. We envision disjoint subsets of antennas in the array being used to direct beams concurrently to different vehicles. The number of antennas, gain and phase of each RF-chain driving an antenna are optimized dynamically using a constrained quadratic cost formulation encompassing channel quality, interference and power consumption. This quadratic optimization problem is solved using behavior constrained bandit algorithm, a reinforcement learning based technique. A gaussian kernel is used to perform data clustering of vehicle environment and resulting solutions, allowing quick bootstrapping of the bandit solver to find optimal array configurations in real-time vehicle environments. Simulation studies prove the viability of the proposed scheme. 

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5. On Secrecy Performance of RIS-Assisted MISO Systems Over Rician Channels With Spatially Random Eavesdroppers

   https://doi.org/10.1109/TWC.2023.3348591  

   Shi, Wei; Xu, Jindan; Xu, Wei; Yuen, Chau; Lee_Swindlehurst, A; Zhao, Chunming (August 2024, IEEE Transactions on Wireless Communications)

   Reconfigurable intelligent surface (RIS) technology is emerging as a promising technique for performance enhancement for next-generation wireless networks. This paper investigates the physical layer security of an RIS-assisted multiple-antenna communication system in the presence of random spatially distributed eavesdroppers. The RIS-to-ground channels are assumed to experience Rician fading. Using stochastic geometry, exact distributions of the received signal-to-noise-ratios (SNRs) at the legitimate user and the eavesdroppers located according to a Poisson point process (PPP) are derived, and closed-form expressions for the secrecy outage probability (SOP) and the ergodic secrecy capacity (ESC) are obtained to provide insightful guidelines for system design. First, the secrecy diversity order is obtained as 2α2 , where α2 denotes the path loss exponent of the RIS-to-ground links. Then, it is revealed that the secrecy performance is mainly affected by the number of RIS reflecting elements, N, and the impact of the number of transmit antennas and transmit power at the base station is marginal. In addition, when the locations of the randomly located eavesdroppers are unknown, deploying the RIS closer to the legitimate user rather than to the base station is shown to be more efficient. Moreover, it is also found that the density of randomly located eavesdroppers, λe , has an additive effect on the asymptotic ESC performance given by log2(1/λe) . Finally, numerical simulations are conducted to verify the accuracy of these theoretical observations. 

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