Optical Wireless network basics | Optical Wireless Tutorial
This page covers optical wireless network basics. The optical wireless tutorial compares short range (directed and diffused) and long range optical wireless technologies and mentions difference between them. Advantages and disadvantages of optical wireless system are also mentioned.
Broadband wireless internet market is booming. We know that broadband wireless works on RF spectrum which is very scarse resource. Moreover due to increase in number of subscribers for wireless networks, spectrum congestion has become a bottlenack. Moreover licensing requirements as well as un-suitability of certain RF bands have pioneered the developed of optical wireless communication system. Unlike conventional wireless system which operates using RF waves, optical wireless system works either using infrared waves or light waves.
Optical wireless system operates using wavelength ranging from 1330 nm to 1550 nm. These are most common wavelength used in optical fiber system. It requires Line of Sight communication between transmitter and receiver.
Figure-1 depicts typical optical wireless system. As shown it consists of optical transmitter and optical receiver part. Optical transmitter consists of optical WDM Multiplexer, driver and LED/Laser device. Optical receiver consists of optical WDM Demultiplexer and detector circuit using PIN diode or Avalanche diode.
Optical WDM multiplexes the different wavelength channels for simultaneous transmission. It does demultiplexing operation for reception and separation at the receiving end.
There are different topologies supported in optical wireless system viz. point to point, point to multi-point and ring bus. These are the configurations using which optical wireless components are connected.
Difference between Short range and Long range optical wireless
Based on the distance and data rate specifications, optical wireless system is divided into short range and long range optical wireless systems. Moreover short range transmission system is further divided into directed system and diffused system. In directed system line of sight (LOS) is must while in diffused LOS is not needed. Following table compares these two and mentions difference 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.|
|Atmospheric channel effect||lower||higher|
Advantages of Optical Wireless System
Following are the advantages of optical wireless system:
• It is immune to interference.
• It is highly secure as optical waves do not penetrate the walls.
• It provides higher data rate due to huge bandwidth available on fiber cable.
• As it operates using ISM unlicensed bands, license related issues are not required to be tackled with.
• Optical wireless network is used as best complement technology along with RF based wireless network.
• Data transfer rate of upto 10 Gbps can be achieved.
• It can cover distance of upto 1000 meters.
• It can make use of cheaper optical fiber cables and components.
Disadvantages of Optical Wireless System
Following are the disadvantages of optical wireless system:
• Break in the optical line of sight link leads to huge loss of data.
• Moreover atmospheric conditions can lead to link failures. The typical examples are dense smoke, kites, birds, rain etc.