Optimization of duty cycles for LED based indoor positioning system

In this paper, an optimal duty cycle, which increases packet delivery ratio (PDR) and reduces probability of collision is designed for packet transmission in an indoor positioning system based on a multiple LED estimation model (MLEM). MLEM improves positioning accuracy by identifying positions of overlap regions where light footprints from multiple LEDs. In MLEM, asynchronous LED transmitters send positional information at the same frequency, amplitude, and wavelength. Consequently, in an LED overlap region, transmitted packets collide and therefore are lost. Methods to avoid packet collision in this region are considered and based on keeping the hardware simple, packet-based pulse duration multiplexing is optimized to provide a time based pseudo-orthogonality between packets. Initial experiments showed a PDR of 0.5 in the overlap region. However, by defining the boundary conditions for non-persistent packet collisions, an exhaustive search for the optimal packet transmission configuration is carried out in this work. Results show that the optimum points occur at 0.09 and 0.1 duty cycles. The use of this optimal duty cycles improved PDR to 0.9 for transmission in the overlap region.