Performance of infrared transmission systems under ambient light interference

Optical transmission systems are mainly impaired by the shot noise induced by ambient light, the transmitted optical power limitations (high path losses), the channel bandwidth limitations owing to multipath dispersion and the interference produced by artificial light sources. Several modulation and encoding schemes have been proposed for this channel and their performance has been studied and presented by several authors while neglecting the effects of the artificial light interference. The work reported extends the previous analysis by taking into account the optical power penalty induced by artificial light interference. An analytical approach is used to estimate this. In practical systems, the effect of the interference is usually mitigated using electrical highpass filters. In the paper the combined effect of interference and highpass filter is evaluated. The presented results show that the interference produced by fluorescent lamps driven by electronic ballasts induce high power penalties in OOK and L-PPM systems, even when electrical highpass filtering is used, for data rates up to 10 Mbit/s. For the interference produced by incandescent lamps and fluorescent lamps driven by conventional ballasts, the power penalty induced in OOK systems can be effectively reduced using highpass filtering, while PPM is very tolerant to that interference even without any highpass filtering. The major conclusion is that artificial light interference have to he considered both in system design and performance evaluation.