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: Optical Wireless Sensor Network System Using Corner Cube Retroreflectors | EURASIP Journal on Applied Signal Processing 2005 1 39-44 2005 Hindawi Publishing Corporation Optical Wireless Sensor Network System Using Corner Cube Retroreflectors Shota Teramoto Department of Electrical Engineering Tokyo University of Science 2641 Yamazaki Noda Chiba 278-8510 Japan Tomoaki Ohtsuki Department of Electrical Engineering Tokyo University of Science 2641 Yamazaki Noda Chiba 278-8510 Japan Email ohtsuki@ Received 18 March 2004 Revised 16 September 2004 We analyze an optical wireless sensor network system that uses corner cube retroreflectors CCRs . A CCR consists of three flat mirrors in a concave configuration. When a light beam enters the CCR it bounces off each of the three mirrors and is reflected back parallel to the direction it entered. A CCR can send information to the base station by modulating the reflected beam by vibrating the CCR or interrupting the light path the most suitable transmission format is on-off keying OOK . The CCR is attractive in many optical communication applications because it is small easy to operate and has low power consumption. This paper examines two signal decision schemes for use at the base station collective decision and majority decision. In collective decision all optical signals detected by the sensors are received by one photodetector PD and its output is subjected to hard decision. In majority decision the outputs of the PDs associated with the sensors are subjected to hard detection and the final data is decided by majority decision. We show that increasing the number of sensors improves the bit error rate BER . We also show that when the transmitted optical power is sufficiently large BER depends on sensor accuracy. We confirm that collective decision yields lower BERs than majority decision. Keywords and phrases corner cube retroreflector optical wireless sensor network collective decision majority decision. 1. INTRODUCTION Recently sensor networks consisting of small sensors that have
