Research Of Positioning Schemes In Visible Light Communication Networks With Dense Cells

Indoor positioning is playing an important role in the security monitoring, object tracking and indoor navigation. There are many indoor positioning technologies including ultra-wide band (UWB), radio frequency identification (RFID), wireless local area network (WLAN) and Bluetooth. However, they all have limitations. Radio frequency-based positioning technologies are not secure due to its diffraction property. High cost of UWB equipment makes it not suitable for broader use. The spectrum that Bluetooth uses is vulnerable to interference. An unprecedented opportunity for visible light communication (VLC) and visible light positioning (VLP) is brought by the introduction of white LEDs for illumination and extensive research has been done. However,there are limitatioins for dense cells which may appear in large pblic facilities like airport. So two visible light positioning schemes are present in this paper:·Integral space time coding (ISTC)-based VLP is proposed for dense small cell deployment.Considering that specific positioning messages can be suitably combined with the layout of the LED lights, ISTC-based VLP integrates the multidimensional information from dense cells into 2-dimensional information corresponding to the position on the detection surface, namely,dimension reduction. Three positioning determination mechanisms,Mapping table mechanism (MTM), mapping function mechanism (MFM)and iterative calculation mechanism (ICM) are proposed to get the position from the measured values. The simulation and experiment results show that ISTC-based VLP can work well in visible light communication networks with dense cells and positioning accuracy can be improved by an order of magnitude by using this scheme comparing with the traditional positioning schemes.·VLP based on orthogonal frequency division multiplexing(OFDM) signals and reference points database is present in this paper.Comparing with ISTC-based VLP, this scheme in not limited by the layout of the LEDs on the ceilings, and this scheme can also realize 3-dimensional positioning. There are two main steps of this scheme. The first step is allocating different subcarriers to different LEDs, and getting a positioning result from the received signal by using multilateration. The second step is to establish a reference database around the positioning result from the first step and improve the positioning result. This scheme can improve the flexibility of the transmitters and lower the requirement for the controler of the transmitter. As demonstrated in the simulations and the experiment, the proposed scheme improves the positioning accuracy by about 24% comparing with the positioning scheme only using OFDM signals. The time cost of the proposed scheme is only about 20% of the positioning scheme only using reference points database.