Visible Light Communication (VLC) is a technique for communicating information using visible light. There are several advantages to using VLC over conventional wireless communication that relies on radio frequency (RF) signals. First, the visible light spectrum (with wavelengths in the range 380 nm to 780 nm) is not regulated or restricted for use by regulatory agencies. Second, the visible light spectrum is less “crowded” than the available RF spectrum because visible light is local and does not permeate physical obstacles, such as buildings and walls. Thus, unlike RF signals, which can interfere with other RF signals in the general vicinity, VLC signals from a VLC light source only interfere with other visible light sources that are within a line of sight of a device receiving the VLC signal. Third, a VLC receiver can determine the location of the source of the VLC signal using an image sensor. Thus, a device that includes a VLC receiver can use the VLC signal to determine the position of the device indoors where RF signals from global positioning systems can be unreliable. Fourth, VLC light sources can be included in existing light fixtures that produce lighting in indoor and outdoor spaces because humans cannot perceive the modulation of the light source used to encode information in the VLC signals.
VLC signals can be encoded in various ways. One particular example is pulse width modulation (PWM) in which information is encoded by turning on and off the light source using a number of cycles per second that his greater than human eyes can perceive (e.g., greater than 150 Hz). Information encoded in the VLC signals can be used in different ways, including determining the position of the device that receives the VLC signals.
USPTO Backgrounds
USPTO Backgrounds