Spatial ODAC performance for indoor environment

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.