Variable pulse position modulation (VPPM) is a new modulation scheme that supports simultaneously illumination with dimming control and communication. In this paper, the transmitter, optical wireless channel, and receiver structure of VPPM were modeled mathematically, and their error performance for examining the communication performance according to dimming level and data rate was analyzed. The results highlight the need for careful consideration of the tradeoff between the dimming flexibility and communication performance according to the channel condition in VPPM.
Visible light communication (VLC) is an emerging communication paradigm that supports illumination and data transmission simultaneously. To provide dimming control functionality, a range of dimmable modulation methods have been exploited. Among them, the variable pulse position modulation (VPPM) scheme, which is deployed using the IEEE 802.15.7 VLC standard is very simple and easy to implement. On the other hand, it has a limited data rate because it just uses binary PPM for data transmission. This study proposes the M-ary VPPM (M-VPPM) scheme to increase the data rate of the VPPM scheme. To evaluate the performance of this scheme, the modelling of the transmitter, optical wireless channel and the receiver for M-VPPM are provided. In addition, the error probability according to the dimming ratio and modulation order was analysed mathematically. The simulation results showed that the analytical bounds on the error probability are tight, which provides key insights into the performance trade-off of M-VPPM in a dispersive VLC channel environment.
Recently, indoor LED lighting can be considered for constructing green infra with energy saving and additionally providing LED-IT convergence services such as visible light communication (VLC) based location awareness and navigation services. For example, in case of large complex shopping mall, location awareness to navigate the destination is very important issue. However, the conventional navigation using GPS is not working indoors. Alternative location service based on WLAN has a problem that the position accuracy is low. For example, it is difficult to estimate the height exactly. If the position error of the height is greater than the height between floors, it may cause big problem. Therefore, conventional navigation is inappropriate for indoor navigation. Alternative possible solution for indoor navigation is VLC based location awareness scheme. Because indoor LED infra will be definitely equipped for providing lighting functionality, indoor LED lighting has a possibility to provide relatively high accuracy of position estimation combined with VLC technology. In this paper, we provide a new VLC based positioning system using visible LED lights and image sensors. Our system uses location of image sensor lens and location of reception plane. By using more than two image sensor, we can determine transmitter position less than 1m position error. Through simulation, we verify the validity of the proposed VLC based new positioning system using visible LED light and image sensors.
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