On The Optical Code Division Multiple Access Based Visible Light Positioning Systems

Indoor visible light positioning(VLP)technology has become increasingly popular in recent years due to its advantages such as immunity to electromagnetic interference,high positioning accuracy and high security,energy saving and environmental protection.The method to separate multiple signals at the receiver is one of the most significant point in VLP systems.Multiplexing technologies are widely used to distinguish different light-emitting-diode(LED)signals to visible light positioning.Typical multiplexing technologies include frequency division multiplexing(FDM),time division multiplexing(TDM),and code division multiplexing(CDM),where FDM systems need ideal filter design which is almost impossible in practical,and TDM systems require strict synchronization between transmitters and receivers.Different from FDM and TDM,CDM is able to separate multiple signals based on the correlation of spreading codes which has the advantages of strong anti-interference ability,random access,and free from receiving filter design.In addition,there exist problems to be solved in traditional received signal strength(RSS)based positioning systems,for example,Positioning performance at the edge zone and the corner zone suffers a lot from reflecting components.In this paper,an advanced visible light positioning method employing optical code division multiple access(OCDMA)is proposed,and the OCDMA based positioning algorithm is deducted based on traditional RSS positioning algorithm.In the proposed scheme,we use the correlation value between the received signal and local optical address code,rather than received power,for positioning purposes,which improves the system’s robustness when non-line-of-sight(NLOS)reflections are under consideration.For facilitate analysis,room is divided into three types of zone in the system simulation,called inner locations,edge locations,and corner locations.Simulation results show that the proposed approach based on OCDMA method can effectively mitigate the NLOS interference.The positioning error of more than 80% of the room area is less than 10 cm,and positioning accuracy of the edge locations improves significantly by 44.20%,and 56.84% for corner locations.Positioning accuracy can achieve 1～2 cm in the inner zone of the target room.Meanwhile,the maximum error at the edge of room can be limited within ～32 cm.