Layered Space-Time Coding Using LED Array for Image-Sensor-Based Visible Light Communications

This paper demonstrates the feasibility of layered space-time coding (STC) in an outdoor image-sensor-based (IS-based) visible light communication (VLC) system. We examined that for low-resolution IS-based VLC channel where intensity modulated signals from two different light emitting diodes (LEDs) are detected at one pixel on the image plane, STC allows to decouple them, thus receiving data with no errors. Consequently, STC offers extending the transmission distance. In the layered STC presented here, additional bit streams are aligned in the 2(n) x 2(n) LED array for increasing the transmission rate per symbol duration for the case where the spatial resolution is improved. A prototype of three layered STC is built with an 8 x 8 LED array, where each of the LEDs is modulated at 1 kbps and a high-speed camera with IS operating at 1000 fps. Our experimental results validate that additional bit streams (layer-2 and -3), aligned in the layer-1 STC matrix pair, are extracted with no errors when the receiver comes within 155m and 55 m, respectively, from the LED array, without decreasing 210m of the transmission distance of layer-1 bit stream.