Modulation methods for wireless infrared transmission systems: performance under ambient light noise and interference

The major aspects that impair the performance of optical wireless transmission systems are the shot noise induced by the steady ambient light level, transmitted optical power limitations (high path losses), channel bandwidth limitations due 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. The work reported in this paper extends the previous analysis by taking into account the optical power penalty induced by artificial light interference. An analytical approach is used to estimate the optical power penalty induced by artificial light interference. In practical systems, the effect of the interference is usually mitigated using electrical high- pass filters. In this paper the combined effect of interference and high-pass filter is evaluated by resorting to simulation. The presented results show that interference produced by fluorescent lamps driven by electronic ballasts induce high power penalties in OOK and PPM systems, even when high-pass filtering is used. 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 high-pass filtering, while PPM is very tolerant to that interference even without any high-pass filtering.