Performance analysis of indoor infrared wireless networks utilising PPM CDMA

Abstract

A hybrid based on pulse position modulation code division multiple access (PPM CDMA) is studied in the context of the indoor infrared LAN. The utilisation of optical orthogonal codes (OOC) as signature sequences is investigated. Original results are presented illustrating the improvement in bit rate achieved by utilising PPM CDMA rather than on-off keying (OOK) CDMA. It is demonstrated that there exists an optimum PPM order, at a given number of users. Original results are presented that evaluate the dispersion in the optical diffuse infrared channel and its effects on optical orthogonal codes (OOC). A new equalisation technique is introduced and analysed in the context of this channel. The method is shown to be effective in reducing the resultant intersymbol interference (ISI). Illustrative examples are given on an isolated pulse and a typical OOC. The results indicate that good performance can be achieved with minimum hardware overheads.