Visible Light Communication (VLC) systems employ visible light for communication that occupy the spectrum from 380 nm to 750 nm corresponding to a frequency spectrum of 430 THz to 790 THz . The low bandwidth problem in RF communication is resolved in VLC because of the availability of the large bandwidth as Illustrated. The VLC receiver only receives signals if they reside in the same room as the transmitter, therefore the receivers outside the room of the VLC source will not be able to receive the signals and thus, it has the immunity to security issues that occurs in the RF communication systems. As a visible light source can be used both for illumination and communication, therefore, it saves the extra power that is required in RF communication. Keeping in view the above advantages, VLC is one of the promising candidates because of its features of non-licensed channels, high bandwidth and low power consumption.
Potential applications of VLC include Li-Fi, vehicle to vehicle communication, robots in hospitals, underwater communication and information displayed on sign boards. The Li-Fi uses visible light for communication to provide high speed internet up to 10Gbits/s. VLC can be used in vehicular communication for lane change warning, precrash sensing and traffic signal violation warning to avoid accidents. These applications require communication with low latency which is provided by VLC because of its high bandwidth and easier installation due to the existing presence of vehicle lights and traffic signals.
The features of high bandwidth, non-interference with the radio waves in electromagnetic sensitive areas and non-hazardous to health has made visible light communication an attractive technique for future communication. Li-Fi is 250 times faster than its analogous Wi-Fi, which uses radio frequency for communication. Potential applications of VLC include Li-Fi, visible light ID system, Hospital robots, underwater communication and traffic communication systems. All of these applications have made VLC an attractive area of research.
ARCHITECTURE OF VLC
The two integral parts of the VLC system: the transmitter and receiver generally consist of three common layers. They are the physical layer, MAC layer and application layer. The reference model of the VLC communication system. In IEEE 802.15.7, only two layers (such as PHY and MAC) are defined for Simplicity.
The tasks performed by Medium Access Control (MAC) layer include :
(1) Mobility support,
(2) Dimming support,
(3) Visibility support,
(4) Security support,
(5) Schemes for mitigation of flickering,
(6) Color function support,
(7) Network beacons generation if the device is a coordinator,
(8) VPAN disassociation and association support,
(9) Providing a reliable link between peer MAC entities.
The topologies supported by the MAC layer are peer-to-peer, broadcast and star. The communication in the star topology is performed using a single centralized controller.
VLC is one of the promising candidates for communication because of the rapid development of the solid state lighting. However, certain challenges that exist and must be addressed are listed as follows:
a. Integration of the VLC with the already existing communication standards such as Wi-Fi etc.
b. The issue of interference with ambient light sources.
c. The mobility issues such as handover should be properly considered in VLC.
d. To improve the communication system performance by specifying Forward Error Correction schemes.
e. Interference between the different devices using VLC is expected in the future because of an increase in the number of VLC devices.