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 Restless Watchdog: Selective Quickest Spectrum Sensing in Multichannel Cognitive Radio Systems Husheng Li | Hindawi Publishing Corporation EURASIP Journal on Advances in Signal Processing Volume 2009 Article ID 417457 12 pages doi 2009 417457 Research Article Restless Watchdog Selective Quickest Spectrum Sensing in Multichannel Cognitive Radio Systems Husheng Li Department of Electrical Engineering and Computer Science The University of Tennessee Knoxville TN 37996 USA Correspondence should be addressed to Husheng Li husheng@ Received 26 January 2009 Revised 29 May 2009 Accepted 8 July 2009 Recommended by K. Subbalakshmi Selective quickest spectrum sensing which monitors the spectrum activity in multiple channels is studied for multichannel cognitive radio systems with nonnegligible channel switching time blind period . The spectrum sensor needs to detect the emergence of primary users as quickly as possible. Due to hardware limitation it is assumed that only a subset of frequency channels can be monitored simultaneously. The problem of controlling the monitoring procedure is studied in the frameworks of dynamic programming DP . System states and cost functions are defined. Cost-to-go functions for DP are derived simplified and approximated based on which control policies are derived. Numerical results are provided to demonstrate the proposed algorithms. Copyright 2009 Husheng Li. This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited. 1. Introduction In recent years cognitive radio 1 2 has attracted intensive studies since it helps to solve the underutilization problem of frequency spectrum 3-5 . Significant progress has been made for standardizing . IEEE 6 7 and implementing . XG radio system 8 the cognitive radio. In a cognitive radio system secondary users without license can use frequency channels that are not being used by primary users with license . However when primary users .