Visible light indoor positioning system based on gain difference between tilted multiple optical receivers

Novel concept for integrating visible light produced by LEDs with indoor positioning using tilted multiple optical receivers is presented in this paper. Generally, positioning system based on visible light communication (VLC) estimates transmission distance through received signal strength (RSS), which is based on intensity modulation and direct detection (IM/DD) method. In order to estimate position using trilateration through transmission distances, receiver needs to know the positions of three or more reference nodes. Thus, the system has limitation that optical receiver should receive signals from at least three different transmitters without interference. For this reason, a carrier allocation or TDM technique have been utilized and positioning area is limited by overlapped area of different transmitters. Furthermore, additional information on characteristics of transmitter, which have a decisive effect on signal strength, is required even though the inter-cell interference problem is solved because the characteristics of transmitters can be varied for different indoor environments. We propose an artificially tilted multiple optical receivers structure to control incidence angle gain and positioning algorithm using the received power difference. PDs are densely placed, thus, transmission distances between LED and PDs and radiation angles are the same. Inter-cell interference is fundamentally removed and positioning area is extended when compared with previous researches. In order to estimate the position, the transmitter's location code from single LED was received using multiple optical receivers. The validity of the proposed scheme was experimentally demonstrated by determining the local position of single transmitter and angle gain profile of receivers.