1. VLC uses electromagnetic spectrum wavelengths 375 to 780 nm

2. VLC is known as long-range optical wireless communication.

3. VLC can transmit large amounts of data faster than Bluetooth

4. VLC has no electromagnetic interference

Select the correct answer using the code given below:

(a) 1, 2 and 3 only

(b) 1, 2, and 4 only

(c) 1, 3 and 4 only

(d) 2, 3, and 4 only

3. Ans: c

Explanation:

Optical wireless communication (OWC) 

Conventional radio frequency (RF) technique which has a regulated and licensed electromagnetic spectrum band, spanning from 30 kHz to 300 GHz. Due to an exponential increase in the wireless data traffic and advanced mobile devices, there are calamities that are emerging within the RF band. This increase leads to spectral crisis such as congestion and maximum data rates that are low relative to OWC. Recent developments and standardization of various RF technologies are not able to overcome these looming crisis

OWC spectral band is between 300 GHz and 30 000 THz (wavelength between 1 mm and 10 nm) of the electromagnetic spectrum, covering the infrared (IR), visible light, and ultraviolet (UV) light bands

OWC technology has an edge over the RF technology due to various factors. These factors include but are not limited to high energy efficiency, widely spread bandwidth which is free from regulation, intrinsic security, and low economical costs.

The categories are briefly explained by giving examples of OWC applications. 

• Ultrashort range category (typically about a range of 100 or less), OWC is used for optical communication between and within chips of integrated circuits (ICs).
•  Short-range category (typically within a distance of about 1 m), OWC is used to create communication links between the ever-present electronic equipment for daily use. The said equipment form the wireless personal area networks (WPANs). Such networks wirelessly interconnect electronic devices that are used around an individual’s personal work space. Moreover, the short range is used for the establishment of wireless body area networks (WBANs). WBAN is a network, which continually monitors the health of a patient by means of embedding one or more electronic devices within the body or surface mounting the device at a specific body part.
•  Medium-range category (typically up to 10 km) is concerned with, but not limited to, indoor infrared and communication within the visible light spectrum band which is commonly known as visible light communication (VLC).
• Long-range category Free-space optical communication (FSO)  communication which is also referred to as outdoor intrabuilding links, FSO communication, maximum data transfer rates up to 2.5 Gbps is possible, unlike the maximum data transfer rates of 622Mbps offered by RF communication systems.  FSO involves the optical transmission of voice, video, and data using air as the medium of transmission. 
• Ultralong range category (typically 4500 km to 10,000 km) is concerned with laser communication in space for intersatellite links.

In RF wireless communication systems, the scramble for spectrum is increasing by a very high magnitude yearly . To complement the conventional RF wireless communication systems is to explore other frequency bands in the electromagnetic spectrum, specifically the visible light band. This shift has led to the discovery of a potential and favorable wireless communication technique commonly referred to as VLC. 

VLC constitutes optical links, which enable visible light sources to be employed for transmission of data using air as the transmission medium. VLC technology uses visible light part of the light spectrum. It uses wavelength range from 380 nm to 750 nm (i.e. frequency range from 430 THz to 790 THz) for communication.

 For indoor application, the idea is that the existing illuminating devices are utilized to transmit data using the same energy which is being used for illumination. VLC is considered to be a medium-range communication technique. This is by virtue of propagation distance which is limited by the luminaries which in most cases are white light-emitting diodes (WLEDs).

Visible Light Communication (VLC) technology:

• The Visible Light Communication (VLC) technology uses light instead of radio frequency signals to transmit the data.
• The VLC technology uses the visible light spectrum (380 to 750 nanometers) to transmit data across a wireless network of communication. 
• VLC-based networks can be used to provide fast, and highly stable internet connections in smaller coverage zones of offices and homes. 
• The objective of VLC is to increase data rates in wireless communication and to have better performance of networks especially for indoor networks using light emitting diode (LED), lamps.
• LiFi or light fidelity is a subtype of VLC technology that uses light waves in the visible/invisible/infrared spectrum to transmit data. Harald Haas first introduced it in his 2011.
• Bluetooth has a transfer rate of up to 2.1 Mbps, while Lifi has the data transmission rate up to 224 Gbps.

A comparison between VLC and RF technologies 

• VLC offers a wireless communication service with an enormous bandwidth capable of transmitting at very high data rates. The VLC bandwidth is approximately ten thousand folds that of the entire RF bandwidth.
• The luminaires used for VLC systems are energy efficient as they use less power despite their high light intensity, and they also come at a very low cost. 
• The VLC systems are much safer compared to RF systems in the sense that there are minimal or no medical health complications caused by visible light. Emissions from RF equipment and devices may be harmful to humans and medical equipment if the radiation power exceeds a particular measure. 
• In VLC systems, there is no requirement for sophisticated antennas to transmit data from the light source through the air.
•  One more factor that makes VLC systems attractive over RF systems is that they have intrinsic security. The control of transmitted data in the physical layer is simple as communication is commonly in line of sight (LoS). This avoids invasion of the communication system by passive eavesdroppers. 
• In contrast to RF, visible light is not capable of penetrating solid surfaces such as walls. The incapability of wall penetration enables the creation of small cells to transmit without interference between cell locations (i.e., intercell interference).
• RF communications are prone to problems, such as lack of spectrum resources, electromagnetic interference , VLC employs the unlicensed frequency spectrum resources at 400–800 THz , which can provide a high data transmission rate and a strong resistance to electromagnetic interferences
• Dueto its appealing advantages, including abundant and unregulated spectrum resources, no electromagnetic interference (EMI) radiation and high security, visible light communication (VLC) using light-emitting diodes (LEDs) or laser diodes (LDs) has been envisioned as one of the key enabling technologies for 6G and Internet of Things (IoT) systems.

Hence, statement 2 is incorrect and 1, 3 and 4 are correct.

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