Adaptive cancellation of periodic noise and multipath dispersion in an infrared wireless CDMA system

IR is specified as an option for IEEE 802.11 wireless LAN standards because, the IR band has abundant, unregulated bandwidth, enabling rapid deployment at low cost. IR systems do not interfere (EMI) with RF systems. However, limitations over power emission levels (IEC825), noise due to ambient lighting and multipath dispersion remain as hurdles in high-speed environments. Especially, the IR signal is severely impaired by high frequency interference produced by fluorescent lights with electronic ballast in indoor LAN environments. Spread spectrum techniques improve the performance in this scenario at the expense of increased bandwidth. In this paper, an adaptive FIR filter is trained to cancel both the multipath dispersion and the fluorescent light interference in an IR system. From analytical and simulation results, it is shown that the adaptive filter greatly enhances the inherent noise rejection capability of CDMA systems. Analytical and simulation results show 7 dB improvement in SINR and 10-15 times improvement in BER.