Application of complementary sequences in indoor wireless infrared communications

The performance of a direct sequence spread spectrum based infrared wireless communication system in multipath channels depends very much on the aperiodic correlation properties of the spreading sequences used. Ideally, the aperiodic auto-correlation functions of the spreading sequence should have zero sidelobes in order to eliminate multipath dispersion. Unfortunately, no such ideal sequences exist in the binary field when data modulation is applied. A spread spectrum technique is proposed, based on a binary modulation scheme. Instead of one spreading sequence, a pair of complementary sequences is transmitted simultaneously such that the sum of their aperiodic auto-correlation and cross-correlation functions at the correlator outputs are impulsive or near impulsive. The system modelling, bit error rate analyses, generation and selection of the appropriate binary complementary pairs, with multipath dispersion and fluorescent light interference taken into consideration, are presented. Results show that the proposed scheme is able to remove the degradations due to these two channel impairments almost completely.