Optical wireless sensor network system using corner cube retroreflectors (CCRs)

We analyze the optical wireless sensor network system using corner cube retroreflectors (CCRs). A CCR consists of three concave mirrors. 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 sends information towards a base station modulating the reflected beam by operation of vibrating CCR or shielding of light pass, and one can transmit an on-off-keying (OOK) modulated optical signal. In optical communications, a CCR is attractive, because it is small size, ease of operation, and low power consumption. In this analysis, we evaluate two decisions at the fusion center, the collective decision and the majority decision. The collective decision is that all the information detected by the sensors is collected by one photodetector (PD), and then the hard decision is done. The majority decision is that each information detected by the sensor is respectively received by each PD, the hard detection is done for each PD output, and decided by majority. We show that the bit error rates (BERs) of the systems are improved as the number of sensors increases. We also show that when the transmitted optical power is adequately large, the BERs of the systems depend on the accuracy of the sensors. We confirm that the BERs of the systems using the collective decision are better than those of the systems using the majority decision.