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Báo cáo hóa học: " Adaptive Subchip Multipath Resolving for Wireless Location Systems"

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: Adaptive Subchip Multipath Resolving for Wireless Location Systems | Hindawi Publishing Corporation EURASIP Journal on Applied Signal Processing Volume 2006 Article ID 25431 Pages 1-16 DOI 10.1155 ASP 2006 25431 Adaptive Subchip Multipath Resolving for Wireless Location Systems Nabil R. Yousef 1 2 Ali H. Sayed 1 and Nima Khajehnouri1 1 Electrical Engineering Department University of California Los Angeles CA 90095-1594 USA 2 Newport Media Inc. Lake Forest CA 92630 USA Received 31 May 2005 Revised 3 November 2005 Accepted 8 December 2005 Reliable positioning of cellular users in a mobile environment requires accurate resolving of overlapping multipath components. However this task is difficult due to fast channel fading conditions and data ill-conditioning which limit the performance of least-squares-based techniques. This paper develops two overlapping multipath resolving methods adaptive and nonadaptive and shows how the adaptive solution can be made robust to the above limitations by extracting and exploiting a priori information about the fading channel. Also the proposed techniques are extended when there are antenna arrays at the base station. Simulation results illustrate the performance of the proposed techniques. Copyright 2006 Hindawi Publishing Corporation. All rights reserved. 1. INTRODUCTION Wireless propagation suffers from multipath conditions. Under such conditions the prompt ray may be succeeded by multipath components that arrive at the receiver within short delays. If this delay is smaller than the duration of the pulse shape used in the wireless system i.e. the chip duration Tc in CDMA systems then the rays overlap. When this situation occurs it results in significant errors in the estimation of the time and amplitude of arrival of the prompt ray. Figure 1 illustrates the combined impulse response of a two-ray channel using a conventional pulse shape in a CDMA IS-95 system in two situations. In the second situation where the pulses overlap the location of the peak is obviously delayed relative to the location of .