Sunday, 20 September 2015

Design and Research - Wireless Components

Hello Everyone,

Today I'm gonna discuss about distribution of bands and classification of frequencies used by various versions of standards of Wi-Fi.

To begin with, Bands refers to the intervals in the frequency domains to separate types of waves based on their nature and properties!

Source - Cisco Network Engineering 3 Chapter 4 Slide (Wireless Concepts)

 we are particularly looking at sub-domains of radio frequency domain. The above classification is very similar to the various subnets under one subnet in networking...
Above is the chart, that will help you visualize the facts I'm presenting:

Therefore, just taking Wi-Fi into account, it uses the frequency bamds allocated by International Telecommunication Union - Radiocommunication Sector (ITU - R) on Radio Frequency (RF) Spectrum. It typically uses UHF, SHF, and recently adopted EHF ( Microwave sub domains) for transmission of data signals. under the Radio Waves (main) domain.

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2.4GHz  under UHF (Ultra High Frequency)

This frequency is used by many other standards as well such as Bluetooth, Cellular Broadband, UHF Television, Microwave ovens, GPS Systems etcetera.
The main advantage of UHF transmission is the short wavelength that is produced by the high frequency. The size of transmission and reception antennas is related to the size of the radio wave. The UHF antenna is stubby and short. Smaller and less conspicuous antennas can be used with higher frequency bands.
The major disadvantage of UHF is its limited broadcast range, often called line-of-sight between the TV station's transmission antenna and customer's reception antenna, as opposed to VHF's longer broadcast range.
UHF is widely used in two-way radio systems and cordless telephones, whose transmission and reception antennas are closely spaced. Transmissions generated by two-way radios and cordless telephones do not travel far enough to interfere with local transmissions. Public safety, business communications and personal radio services such as GMRS, PMR446, and UHF CB are often found on UHF frequencies as well as IEEE 802.11 wireless LANs ("WiFi"). The widely adapted GSM and UMTS cellular networks use UHF cellular frequencies. A repeater propagates UHF signals when a distance greater than the line of sight is required. - Source : Wikipedia

Standard               Max Speed               Backward Compatibility
802.11                  2 Mb/s                      N/A
802.11b                11 Mb/s                    N/A
802.11g                54 Mb/s                    802.11b

But sooner or later, while advancements were being brought to the UHF utilization, we felt the need to move to more higher frequency to avoid the noise/interference caused by other applications using the same freq to minimize collisions. Therefore, SHF came into play.

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5GHz under SHF (Super High Frequency)

SHF frequencies occupy a "sweet spot" in the radio spectrum which is currently being exploited by many new radio services. They are the lowest frequency band where radio waves can be directed in narrow beams by conveniently sized antennas so they do not interfere with nearby transmitters on the same frequency, allowing frequency reuse. 
The size of SHF waves allow large reflections from metal objects the size of automobiles, aircraft, and ships, and other vehicles. Thus, the narrow beamwidths possible with high gain antennas and the low atmospheric attenuation as compared with higher frequencies make SHF the main frequencies used in radar. Attenuation and scattering by moisture in the atmosphere is a factor at the high end of the band. - Source : Wikipedia 

Standard               Max Speed               Backward Compatibility
802.11a                54 Mb/s                     N/A
802.11n                600 Mb/s                   802.11 a/b/g( can be mixed with 2.4GHz)
802.11ac               1300 Mb/s                 802.11 a/n 

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60 GHz under EHF (Extra High Frequency)
Note* Line of sight only 
Compared to lower bands, radio waves in this band have high atmosphericattenuation; they are absorbed by the gases in the atmosphere. Therefore, they have a short range and can only be used for terrestrial communication over about a kilometer. In particular, signals in the 57–64 GHz region are subject to a resonance of the oxygen molecule and are severely attenuated. Even over relatively short distances, rain fade is a serious problem, caused when absorption by rain reduces signal strength. In climates other than deserts absorption due to humidity also has an impact on propagation. While this absorption limits potential communications range, it also allows for smaller frequency reuse distances than lower frequencies. The short wavelength allows modest size antennas to have a small beam width, further increasing frequency reuse potential. - Source : Wikipedia

Standard               Max Speed               Backward Compatibility
802.11ad                7 Gb/s                       802.11 a/b/g/n/ac ( can me mixed with 2.4. 5 GHz)

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Wi-Fi IEEE Standards chart
 Note* Supporting a mixed environment limits the expected data rates.
Classification on basis of Frequencies

Above images source : Cisco Network Engineering 3 Chapter 4 Slide (Wireless Concepts)

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Tomorrow I will be discussing something about Wi-Fi certifications and a brief comparision of Wifi with LAN. Also we will be looking at how does a client associates and exchanges information with an Access Point.

That's all for today, thank you very much for reading.

**You are welcome to comment, share your views and provide me further suggestions.
*** If you find anything that is incorrect or is wrongly presented, please feel free to comment.
Thank you

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