2.9 Standardization of Visible Light Communication
The standard of visible light communication is important in practical application to
avoid the mutual interference between different product and the problem due to
interchangeability are expected when the different communication methods is used.
Although the VLC does not infer with RF signal but it is necessary to consider the
interference between the VLC devices against existing infrared devices.
In effort of standardization the VLC. Currently we have JEITA (Japan
Electronic and Information Technology) standards and IEEE standards which working
on the specification of PHY and MAC layers for VLC. VLCC (Visible Light
Communication Consortium) working on visible light communication standards. In
2007, VLCC proposed two visible light standard to JEITA and the two proposals
became JEITA standard in June 2007 (Haruyama, 2008).
Therefore, the proposed VLC standard at JEITA is the most fundamental
standard in the free space visible light optical communication system. The objective of
the proposed JEITA CP-1221 standard is to present and indicator in order to prevent
the interference between different optical communication equipments and define a
minimum necessary requirement in various visible light communication applications
(Haruyama, 2008).
The visible light communication system standard of JEITA CP-1221 proposed
assumes the range of the wavelength of the light of a visible light communication to be
380nm-780nm, and allows an arbitrary wavelength range of each application in 1 nm
accuracy. The standard uses the subcarrier method by modulating the light intensity by
a specific frequency. Therefore, by using a different subcarrier frequencies,
interference can be avoided.
However the second proposed standard JEITA CP-1222 (Shinichiro Haruyama,
2008). differs from JEITA CP-122. It is retricts the subcarrier frequency t 28.8kHz and
it specifically suggests using SC-4PPM as modulation scheme. Thus, its requires
cyclic redundancy checks for error detection and correction (Haruyama, 2008).