Optical CDMA codes for an indoor localization system using VLC

This paper describes the use of optical Code Division Multiple Access (CDMA) codes for an indoor localization system using Visible Light Communication. VLC uses Intensity Modulation and Direct Detection (IM/DD) so the CDMA codes can be used as baseband signals which makes the driving electronics less complex. In order to keep the installation cost low, a backbone network between the LEDs is not present. This makes it an asynchronous CDMA system where the cross- correlation is random and can in some cases introduces large distance errors. There are two groups of Optical CDMA codes namely uni- and bi- polar. When bipolar codes are used, the receiver should be equipped with an appropriated High Pass Filter (HPF). The results show that there is no large difference in cross- correlation between the codes but bipolar codes can reduce the distance error and so the position error even when there is static surrounding light like e.g. sunlight.