Abstract
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.
Highlights
Sensor networks consisting of small sensors that have the abilities of detection, data processing, and communication have attracted much attention owing to the development of wireless communications and electric devices [1, 2]
The optical power captured by the nth cube retroreflectors (CCRs) is expressed as cos2 θs,n 4r2 tan2 cos θf θc,n where θc,n represents the angle between the center of the beam and the axis of the link and dc represents the effective diameter of CCR
Where i represents the number of CCRs deciding 1, ts represents the local threshold of the sensor, t f represents the threshold at the fusion center
Summary
Sensor networks consisting of small sensors that have the abilities of detection, data processing, and communication have attracted much attention owing to the development of wireless communications and electric devices [1, 2]. The use of passive transmitters such as the corner cube retroreflector (CCR), which do not have a light source in the sensor itself, is attractive for improving the power efficiency of the sensor. Karakehayov proposed an optical wireless sensor network system where the transceiver and CCR have a one-to-one correspondence. H0/H1 Figure 1: Optical wireless sensor network model with CCRs. performance, shorten decision time, and provide other benefits [6]. We note that this one-to-many correspondence between the transceiver and CCR has been neither proposed nor evaluated in any other paper In this figure, the local decision made on each CCR stream is communicated to the decision system. We confirm that BER is improved by using collective decision rather than majority decision
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