Nonstationary noise cancellation in infrared wireless receivers

Infrared is attracting much attention for indoor wireless access due to its enormous bandwidth, inherent privacy and low cost. Intensity modulated, directly detected infrared schemes do not experience multipath fading. However, ambient noise due to artificial lighting has been the major concern in infrared wireless systems in indoors. Conventionally, static or low frequency noise due to conventional light sources is removed using optical high pass filters. Nonetheless, interference from fluorescent lights equipped with electronic ballasts has periodic interference components up to 1 MHz and, cannot be filtered easily. In this paper, soft DSP filters are proposed to cancel the harmonics, ambient noise, and uncorrelated signal structures. Nonstationary noise is cancelled with an adaptive denoising filter, and a comb filter cancels interference from the electronic ballasts. Adaptive soft filters have the advantage that they can be easily updated and track the variations in noise characteristics. Simulation results show promising improvement in noise cancellation even under very low and varied SNR and noise source conditions.