LiFi Tutorial: Understanding Protocol, Working, and Applications

LiFi (Light Fidelity) is a cutting-edge wireless communication technology that uses visible light to transmit data at high speeds. With the growing demand for faster, more secure, and efficient communication systems, LiFi is emerging as a powerful alternative to traditional radio-frequency-based systems like WiFi. This LiFi tutorial describes LiFi protocol layers, how LiFi works, and its various applications.

Introduction

LiFi is short for “Light Fidelity”. It works on the principle of Visible Light Communication (VLC). The network is also referred to as VPAN or VLC Personal Area Network. VLC transmits data by intensity modulation, using LEDs and Laser diodes (or photo detectors) at the transmit and receive ends respectively. It operates in the 380 nm to 780 nm optical band, which is visible light, hence the name VLC.

The VLC standard or VPAN standard defines three classes of devices: infrastructure, mobile, and vehicle. These devices operate in one of the three topologies mentioned below. The different devices have different coverage ranges, data rates, and other requirements.

It works in three modes as mentioned above in figure-1.

• Star Topology: Communication is established between a central controller (i.e., coordinator) and devices.
• Peer-to-Peer Topology: One of the devices should become the coordinator at the time of establishing association.

Each device or coordinator has a unique 64-bit address. A device can also use a 16-bit address upon request when establishing association with a coordinator.

How LiFi Works

LiFi (Light Fidelity) is a wireless communication technology that uses visible light, infrared, or ultraviolet light to transmit data between devices. Instead of using radio waves like WiFi, LiFi relies on modulating the intensity of light emitted by a light source such as an LED (Light Emitting Diode). The data is transmitted through variations in light intensity that are too rapid for the human eye to detect.

A photodetector on the receiving device captures these changes in light and converts them back into electronic data.

Key steps in how LiFi works are as follows:

• LED Light Source: LiFi communication begins with an LED light source that emits visible light. These LEDs can quickly modulate light at extremely high speeds, encoding binary data (1s and 0s) through light intensity variations.
• Modulation: The light emitted by the LED is modulated, meaning its intensity is varied in a way that carries information. This can be done in millions of cycles per second (high frequencies), allowing the transmission of large amounts of data.
• Transmission: The modulated light beam is then sent from the LED light source to the receiving device. The changes in light intensity represent the binary data being transmitted.
• Photodetector: The receiving device is equipped with a photodetector that captures the modulated light. The photodetector senses the rapid changes in light intensity and converts these changes back into electronic signals.
• Decoding: The electronic signals are then decoded into digital data (1s and 0s) by the receiver. This data can be in the form of text, images, or video, depending on the application.
• Data Processing: Finally, the received data is processed and used by the end device, such as a smartphone, laptop, or IoT device.
• LiFi can be used for two-way communication, meaning that both the transmitter (LED) and receiver (photodetector) can exchange data simultaneously.

LiFi Protocol Stack

LiFi (Light Fidelity) technology uses visible light for wireless communication and has a layered protocol structure similar to traditional wireless communication systems.

The figure-2 depicts protocol stack used in a typical VPAN device. As shown, the protocol stack consists of PHY, MAC, and upper layers. The physical layer houses the light transceiver. A PHY switch housed in the PHY layer interfaces with an optical SAP which connects it to the optical medium. The optical medium is composed of one or multiple optical sources or optical detectors (e.g., laser diodes or photodiodes).

The MAC layer provides channel access for all types of data and control message transmissions. The upper layer consists of the network layer and application layer. The network layer takes care of providing network configuration, network manipulation, message routing, etc. The application layer provides the intended functionality as needed by the VPAN or LiFi device.

DME (Device Management Entity) is also supported by the LiFi or VPAN network architecture. It facilitates interfacing between the dimmer and PHY/MAC.

LiFi Physical Layer

The physical layer in LiFi handles the modulation and transmission of data using light waves. It is responsible for the following:

• Modulation Techniques: Transforming digital data into a modulated signal for transmission using light.
• LED Transmitter and Photodetector Receiver: LEDs are used to emit modulated light, and photodetectors receive and convert this light back into electrical signals.
• Line-of-Sight Communication: The physical layer also manages the line-of-sight nature of the communication, ensuring that light signals are properly transmitted and received.

In LiFi, three major modulation techniques are used in the physical layer, namely OOK (On-Off Keying), VPPM (Variable Pulse Position Modulation), and CSK (Color Shift Keying).

There are three types of physical layer configurations supported in VLC or LiFi System Viz. PHY-I, PHY-II, PHY-III. Different rates can be achieved in different configurations. They can be used indoor or outdoor.

LiFi MAC Layer

The MAC layer in LiFi is responsible for controlling how multiple devices share the same light medium and ensuring that data is transmitted efficiently without collisions. Its key roles include the following:

• Frame Control: The MAC layer divides data into frames for transmission and manages retransmission in case of errors.
• Channel Access: It controls when devices can transmit, preventing collisions between multiple devices attempting to send data simultaneously.
• Error Detection: It ensures that any errors in transmission are detected, and corrupted frames are retransmitted.

LiFi’s MAC layer is similar to the MAC layers used in wireless communication technologies like WiFi but is optimized for light-based transmission, where factors such as interference from ambient light and line-of-sight conditions are considered.

The MAC layer takes care of resource management, i.e., allocation of channels, IDs, as well as entire network management.

LiFi Modulation Types: OOK, VPPM, CSK

As mentioned, there are different modulation schemes used in different physical layer modes. OOK stands for On-Off Keying, VPPM stands for Variable Pulse Position Modulation, and CSK stands for Color Shift Keying.

• On-Off Keying (OOK):
  • Working: Uses binary signals where 1 is represented by the LED being ON and 0 by it being OFF.
  • Advantage: Simple, low-power consumption.
  • Disadvantage: Limited data rate due to the binary nature of the signaling.
• Variable Pulse Position Modulation (VPPM):
  • Working: Uses variable timing of light pulses to encode data, which can be combined with dimming.
  • Advantage: Allows simultaneous data transmission and light dimming control.
  • Disadvantage: More complex than OOK.
• Color Shift Keying (CSK):
  • Working: Uses different colors (wavelengths) to represent different symbols. A combination of red, green, and blue LEDs is used for higher data rates.
  • Advantage: High data rates due to color multiplexing.
  • Disadvantage: Requires more complex hardware and LED systems.

Together, these layers and modulation schemes make LiFi a powerful technology for high-speed, light-based wireless communication.

Applications of LiFi or VLC system

There are many applications of LiFi or VLC systems as lighting and data communications. Typical among them are lighting, signboards, street lights, vehicles, and traffic signals or lights. The figure mentions the emerging application of LiFi for internet data communication. It has also become popular due to the wide adoption of IoT-based technologies.

Benefits of LiFi System

Following are the benefits of the LiFi system:

• It transfers data very rapidly.
• It transfers data securely as it can be used in Line of Sight mode of optical signal. It does not pierce through the walls and hence it cannot be easily intruded upon by hackers.
• It uses much lower power for transmission compared to other systems such as WiFi.

Conclusion

LiFi offers a unique blend of speed, security, and efficiency, positioning it as a game-changing technology for the future of wireless communication. Its use of light instead of radio waves opens up new possibilities for applications in smart homes, healthcare, underwater communication, and more. As LiFi continues to evolve, its potential to complement and even surpass traditional wireless technologies becomes more apparent. This LiFi tutorial is very useful for beginners who would like to understand the basic concepts of LiFi technology, its features, working operation, and LiFi network architecture components.