A Visible Light Positioning system using Frequency Division Multiple Access with square waves

In this paper, a Visible Light Positioning (VLP) system using Frequency Division Multiple Access (FDMA) with square waves is presented. For the multiple access technology, the properties of square waves in the frequency domain is exploited. Neighboring LEDs will use multiples of the ground frequency of the first LED where the receiver performs a Fast Fourier Transform (FFT) and retrieves the Received Signal Strength (RSS) for every LED. In order to facilitate implementation, the LEDs are transmitting pilot tones in a non-synchronized way to the receiver, and thus requiring no backbone network. The positioning algorithm uses the RSS to perform triangulation and finds the position by taking the least square fit. Practical results show that this VLP system has position errors smaller then 10 cm when an photodiode is used which has a Field Of View (FOV) of 70°. Simulation results show that when a photodiode with a FOV of 90° is applied, the position error can drop to a few centimeter within the entire test bench surface. The key advantage of the system is the use of unsynchronized low bandwidth transmitters, leading to an easy implementation using current high efficiency LED drivers.