Reducing the Effects of Artificial Light Interference in Wireless Infrared Transmission Systems

The performance of wireless infrared transmission systems for indoor use is severely impaired by the noise and interference induced by natural and artificial ambient light. In order to combat the effects of ambient light on the system performance, both optical filtering and electrical filtering is usually adopted. However, even when resorting to these techniques, the optical power penalty imposed by the interference may be very large. In particular, the interference produced by fluorescent lamps driven by electronic ballasts imposes very large optical power penalties on systems operating at data rates up to a few tens of Mbps. In this paper, a different technique to overcome the penalty induced by artificial light interference is analysed. This technique explores the different optical spectra of the transmitted signal and the artificial light and the characteristics of optical filtering to cancel the interfering signal. Some aspects of its implementation are also discussed. The results obtained with this approach are shown to be much better than those obtained through electrical high-pass filtering.