An in-Depth Survey of Visible Light Communication Based Positioning Systems <s> Frequency Division Multiplexing <s> The performance of time division multiplexing and frequency division multiplexing protocols for light emitting diode light emitting diode (IPS) designs using visible light emitting diode lights is evaluated. The impact of timing synchronisation errors on the localisation accuracy of IPS designs is also determined. <s> BIB001 </s> An in-Depth Survey of Visible Light Communication Based Positioning Systems <s> Frequency Division Multiplexing <s> Visible Light Communication (VLC) technology using light emitting diodes (LEDs) has been gaining increasing attention in recent years as it is appealing for a wide range of applications such as indoor positioning. Orthogonal frequency division multiplexing (OFDM) has been applied to indoor wireless optical communications in order to mitigate the effect of multipath distortion of the optical channel as well as increasing data rate. In this paper, we investigate the indoor positioning accuracy of optical based OFDM techniques used in VLC systems. A positioning algorithm based on power attenuation is used to estimate the receiver coordinates. We further calculate the positioning errors in all the locations of a room and compare them with those of single carrier modulation scheme, i.e., on-off keying (OOK) modulation. We demonstrate that OFDM positioning system outperforms its conventional counterpart. <s> BIB002
Frequency division multiplexing (FDM) introduces complexity in designing the demultiplexer. However, with the advantage of asynchronous positioning, many systems used FDM. In these systems, the light in different LED base stations will be modulated to transmit at different frequencies. TDM and FDM used in VLC based positioning systems were compared in BIB001 and the authors came to the conclusion that the positioning accuracy provided by FDM is greater than that of TDM. It is worth noting that the simulation in BIB001 was conducted with the assumption that any two LEDs have a timing synchronization error of 10%. In BIB002 , the advantage of using OFDM, which is a specialized FDM, in an indoor VLC based positioning system was investigated. With OFDM, the visible light from different LEDs could be modulated at low symbol rates and thus the intersymbol interference, which might degrade the positioning accuracy, was mitigated. The simulation results showed that for the same system, using OFDM could achieve twice as much positioning accuracy compared to using OOK with TDM. Notice that in BIB002 the effect of intersymbol interference was clear since a high data rate up to 25 Mbps was assumed.