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Tuyển tập báo cáo các nghiên cứu khoa học quốc tế ngành hóa học dành cho các bạn yêu hóa học tham khảo đề tài: Research Article LCMV Beamforming for a Novel Wireless Local Positioning System: Nonstationarity and Cyclostationarity Analysis | Hindawi Publishing Corporation EURASIP Journal on Advances in Signal Processing Volume 2007 Article ID 98243 12 pages doi 10.1155 2007 98243 Research Article LCMV Beamforming for a Novel Wireless Local Positioning System Nonstationarity and Cyclostationarity Analysis Hui Tong Jafar Pourrostam and Seyed A. Zekavat Department of Electrical and Computer Engineering Michigan Technological University 1400 Townsend Drive Houghton MI 49931 USA Received 24 June 2006 Revised 29 January 2007 Accepted 21 May 2007 Recommended by Kostas Berberidis This paper investigates the implementation of a novel wireless local positioning system WLPS . WLPS main components are a a dynamic base station DBS and b a transponder both mounted on mobiles. The DBS periodically transmits ID request signals. As soon as the transponder detects the ID request signal it sends its ID a signal with a limited duration back to the DBS. Hence the DBS receives noncontinuous signals periodically transmitted by the transponder. The noncontinuous nature of the WLPS leads to nonstationary received signals at the DBS receiver while the periodic signal structure leads to the fact that the DBS received signal is also cyclostationary. This work discusses the implementation of linear constrained minimum variance LCMV beamforming at the DBS receiver. We demonstrate that the nonstationarity of the received signal causes the sample covariance to be an inaccurate estimate of the true signal covariance. The errors in this covariance estimate limit the applicability of LCMV beamforming. A modified covariance matrix estimator which exploits the cyclostationarity property of WLPS system is introduced to solve the nonstationarity problem. The cyclostationarity property is discussed in detail theoretically and via simulations. It is shown that the modified covariance matrix estimator significantly improves the DBS performance. The proposed technique can be applied to periodic-sense signaling structures such as the WLPS RFID .
