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1. Reconfigurable Antenna Assisted Intrusion Detection in Wireless Networks

   https://doi.org/10.1155/2013/564503  

   Mookiah, Prathaban; Walsh, John M.; Greenstadt, Rachel; Dandekar, Kapil R. (October 2013, International Journal of Distributed Sensor Networks)

   null (Ed.)

   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. 

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2. 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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3. 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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4. Linear Polarization Optimization for Wideband MIMO Systems With Reconfigurable Arrays

   https://doi.org/10.1109/TWC.2023.3297130  

   Castellanos, Miguel R.; Heath, Robert W. (March 2024, IEEE Transactions on Wireless Communications)

   Reconfigurable arrays mold the propagation en- vironment to benefit wireless systems. We use single-port polarization-reconfigurable antennas in a wideband multiple- input multiple-output (MIMO) system and demonstrate the efficacy of reconfiguration techniques based on analytical channel models. We apply a double-directional channel model to show that polarization reconfiguration acts as an additional precoding step on an unpolarized channel. We use Jensen’s inequality to upper bound the spectral efficiency and leverage the relaxed objective to derive closed-form expressions for the optimal polarization angles at each antenna. We also derive upper bounds on the performance of a polarization reconfigurable system and develop an efficient procedure for polarization reconfiguration that aims to maximize these upper bounds. Numerical results show that the proposed simplified methods achieve near-optimal in wideband MIMO settings. 

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5. Reconfigurable Antenna Multiple Access for 5G mmWave Systems

   https://doi.org/10.1109/ICCW.2018.8403609  

   Almasi, Mojtaba Ahmadi; Mehrpouyan, Hani; Matolak, David; Pan, Cunhua; Elkashlan, Maged (May 2018, 2018 IEEE International Conference on Communications Workshops (ICC Workshops))

   This paper aims to realize a new multiple access technique based on recently proposed millimeter- wave reconfigurable antenna architectures. To this end, first we show that integration of the existing reconfigurable antenna systems with the well-known non-orthogonal multiple access (NOMA) technique causes a significant degradation in sum rate due to the inevitable power division in reconfigurable antennas. To circumvent this fundamental limit, a new multiple access technique is proposed. The technique which is called reconfigurable antenna multiple access (RAMA) transmits only each user's intended signal at the same time/frequency/code, which makes RAMA an inter-user interference-free technique. Two different cases are considered, i.e., RAMA with partial and full channel state information (CSI). In the first case, CSI is not required and only the direction of arrival for a specific user is used. Our analytical results indicate that with partial CSI and for symmetric channels, RAMA outperforms NOMA in terms of sum rate. Further, the analytical result indicates that RAMA for asymmetric channels achieves better sum rate than NOMA when less power is assigned to users that experience better channel quality. In the second case, RAMA with full CSI allocates optimal power to each user which leads to higher achievable rates compared to NOMA for both symmetric and asymmetric channels. The numerical computations demonstrate the analytical findings. 

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