RFOptical Wireless Network Basics
Advertisement
This page provides an introduction to optical wireless networks. It compares short-range (directed and diffused) and long-range optical wireless technologies, highlighting their differences. The advantages and disadvantages of optical wireless systems are also discussed.
The broadband wireless internet market is experiencing rapid growth. While broadband wireless traditionally relies on the RF spectrum, this resource is becoming increasingly scarce. Spectrum congestion, driven by a growing number of wireless network subscribers, has become a significant bottleneck. Moreover, licensing requirements and the unsuitability of certain RF bands have spurred the development of optical wireless communication systems.
Unlike conventional wireless systems that use RF waves, optical wireless systems operate using either infrared or light waves. These systems typically use wavelengths ranging from 1330 nm to 1550 nm, which are commonly used in optical fiber systems.
A key requirement for optical wireless communication is a Line of Sight (LOS) connection between the transmitter and receiver.
Figure 1: Typical Optical Wireless System
Figure 1 depicts a typical optical wireless system, comprising an optical transmitter and an optical receiver.
The optical transmitter includes an optical WDM Multiplexer, a driver, and an LED/Laser device. The optical receiver consists of an optical WDM Demultiplexer and a detector circuit using a PIN diode or an Avalanche diode.
The optical WDM multiplexer combines different wavelength channels for simultaneous transmission. The demultiplexer performs the reverse operation, separating the channels at the receiving end.
Optical wireless systems support various topologies, including point-to-point, point-to-multipoint, and ring bus configurations. These configurations define how the optical wireless components are interconnected.
Difference Between Short-Range and Long-Range Optical Wireless
Based on distance and data rate specifications, optical wireless systems are categorized into short-range and long-range systems. Short-range systems are further divided into directed and diffused systems. Directed systems require a Line of Sight (LOS), while diffused systems do not.
The following table compares these systems and highlights the differences between short-range and long-range optical wireless system types:
| Specifications | Short-range Optical Wireless | Long-range Optical Wireless |
|---|---|---|
| Data rate | 9600bps to 4Mbps | less than 10 Gbps |
| Coverage distance | less than 10 meters | less than 1000 meters |
| Transmitter (preferable) | LED diode | Laser diode |
| Receiver (preferable) | PIN diode | Avalance diode |
| Propagation | Can be LOS or diffused | It must be LOS |
| Transmitter power | lower | higher |
| Atmospheric channel effect | lower | higher |
Advantages of Optical Wireless System
The following are the advantages of optical wireless systems:
- Immunity to Interference: Optical wireless systems are resistant to interference.
- High Security: They are highly secure, as optical waves do not penetrate walls.
- Higher Data Rate: They offer higher data rates due to the large bandwidth available on fiber cables.
- Unlicensed Bands: As they operate using ISM unlicensed bands, there are no licensing issues.
- Complementary Technology: Optical wireless networks serve as an excellent complement to RF-based wireless networks.
- High Data Transfer Rate: Data transfer rates of up to 10 Gbps can be achieved.
- Long Coverage Distance: They can cover distances of up to 1000 meters.
- Cost-Effective: They can utilize cheaper optical fiber cables and components.
Disadvantages of Optical Wireless System
The following are the disadvantages of optical wireless systems:
- Line of Sight Dependency: A break in the optical line of sight link can lead to significant data loss.
- Atmospheric Sensitivity: Atmospheric conditions can cause link failures. Common examples include dense smoke, kites, birds, and rain.
