Secure Communication for Spatially Sparse Millimeter-Wave Massive MIMO Channels via Hybrid Precoding

In this paper, we investigate secure communication over sparse millimeter-wave (mm-Wave) massive multiple-input multiple-output (MIMO) channels by exploiting the spatial sparsity of legitimate user's channel. We propose a secure communication scheme in which information data is precoded onto dominant angle components of the sparse channel through a limited number of radio-frequency (RF) chains, while artificial noise (AN) is broadcast over the remaining nondominant angles interfering only with the eavesdropper with a high probability. It is shown that the channel sparsity plays a fundamental role analogous to secret keys in achieving secure communication. Hence, by defining two statistical measures of the channel sparsity, we analytically characterize its impact on secrecy rate. In particular, a substantial improvement on secrecy rate can be obtained by the proposed scheme due to the uncertainty, i.e., 'entropy', introduced by the channel sparsity which is unknown to the eavesdropper. It is revealed that sparsity in the power domain can always contribute to the secrecy rate. In contrast, in the angle domain, there exists an optimal level of sparsity that maximizes the secrecy rate. The effectiveness of the proposed scheme and derived results are verified by numerical simulations

RINGO: a novel ring polarimeter for rapid GRB followup - art. no. 62695M

We describe the design and construction of a novel optical ring-polarimeter (RINGO) for the Liverpool Telescope. The instrument is designed for rapid (< 5 minutes) followup observations of Gamma Ray Bursts in order to measure the early time polarization and its evolution for the first time. Sensitivity calculations and data reduction procedures are described, and the results of on-sky commissioning presented. The instrument is now on the telescope and in routine use during GRB followup. © (2006) COPYRIGHT SPIE--The International Society for Optical Engineering

Reconfigurable Intelligent Surfaces for 6G Systems: Principles, Applications, and Research Directions

This is the submitted version of the paper accepted by IEEE Communications Magazine made available on arXiv under a Creative Commons (CC BY) Attribution License). In this paper, we have answered four critical questions in RIS/IRS. More importantly, we have pointed out several promising research directionsThis work was supported in part by the National Key Research and Development Project under Grant 2019YFE0123600, in part by the Research Fund of National Mobile Communications Research Laboratory, Southeast University (No.2021B01) and the Fundamental Research Funds for the Central Universities. M. Di Renzo’s work was supported in part by the EU-H2020 projects ARIADNE (871464) and RISE-6G (101017011). The work of M. Chen is supported by the National Natural Science Foundation of China under Grant 61871128. The work of Y. Hao is supported by EPSRC EP/R035393/1. The work of A. L. Swindlehurst is supported by U.S. National Science Foundation grant ECCS2030029 L. Hanzo would like to acknowledge the financial support of the European Research Council’s Advanced Fellow Grant QuantCom (Grant No. 789028)

The Effects of Array Calibration Errors on DF-Based Signal Copy Performance

This paper studies the effect of array calibration errors on the performance of various DF (direction finding) based signal copy algorithms. Unlike blind copy methods, this class of algorithms requires an estimate of the directions of arrival (DOAs) of the signals in order to compute the copy weight vectors. Under the assumption that the observation time is sufficiently long, the following algorithms are studied: classical beamforming, least squares, total least squares, linearly constrained minimum variance beamforming, and structured stochastic estimation. Expressions for the mean-square error of the signal estimates are derived as a function of the calibration errors for both the case where the DOAs are known precisely and for the case where the DOAs must be estimated. This work was supported by a contract from E-Systems, Inc., Greenville Division (Dr. William A. Gardner, Principal Investigator), and by the National Science Foundation under grant MIP-9110112. 1. Introduction An im..