Spatial ODAC performance for indoor environment

Abstract

The optical digital to analog conversion (ODAC) concept was introduced as a method able to cope with light-emitting diode's (LED) non-linear characteristic and dimming constraints. The approach is similar to an electrical digital-to-analog converter (DAC), where several digital bit streams are weighted in order to represent an analog signal. This technique enables simple on-off modulation schemes, which are able to take full advantage of the LEDs non-linear characteristic and also allow pulse-width modulation (PWM) dimming to be employed for combined lighting and communication means. Unlike electrical DACs, and ODAC has a reconstruction error that depends not only on the bit depth of the converter, but also on the system set-up. This paper presents simulation results able to show the reconstruction error performance as a function of space, luminaire placement, LED's half power angle (HPA) and photo detector field of view (FOV). The set-up assumes multipath due to reflections and low bit rates. Important conclusions point out for necessary precautions concerning the LED's and photo detector's characteristics, which are linked to the number of LED luminaires inside the room and the uniformity of the lighting conditions.