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: Opportunistic Carrier Sensing for Energy-Efficient Information Retrieval in Sensor Networks | EURASIP Journal on Wireless Communications and Networking 2005 2 231-241 2005 Hindawi Publishing Corporation Opportunistic Carrier Sensing for Energy-Efficient Information Retrieval in Sensor Networks Qing Zhao Department of Electrical and Computer Engineering University of California Davis CA 95616 USA Email qzhao@ Lang Tong School of Electrical and Computer Engineering Cornell University Ithaca NY 14853 USA Email ltong@ Received 26 January 2005 We consider distributed information retrieval for sensor networks with cluster heads or mobile access points. The performance metric used in the design is energy efficiency defined as the ratio of the average number of bits reliably retrieved by the access point to the total amount of energy consumed. A distributed opportunistic transmission protocol is proposed using a combination of carrier sensing and backoff strategy that incorporates channel state information CSI of individual sensors. By selecting a set of sensors with the best channel states to transmit the proposed protocol achieves the upper bound on energy efficiency when the signal propagation delay is negligible. For networks with substantial propagation delays a backoff function optimized for energy efficiency is proposed. The design of this backoff function utilizes properties of extreme statistics and is shown to have mild performance loss in practical scenarios. We also demonstrate that opportunistic strategies that use CSI may not be optimal when channel acquisition at individual sensors consumes substantial energy. We show further that there is an optimal sensor density for which the opportunistic information retrieval is the most energy efficient. This observation leads to the design of the optimal sensor duty cycle. Keywords and phrases sensor networks distributed information retrieval opportunistic transmission energy efficiency. 1. INTRODUCTION A key component in the design of sensor networks is the process by which .
