Basics of WiMax and OFDMA

WiMAX 

World-wide Interoperability for microwave access [WiMAX]

As broadband wireless networks encompass various services such as www, voice, video and data network traffic becomes very dynamic and unbalanced between the Uplink and Down-link stream volumes.

To provide the highest transport efficiency in broadband network TDD [Time Division Duplex] is preferred over FDD [frequency division Duplex] because it offers more flexibility in changing up-link and down-link bandwidth ratio.

WiMAX is one of the wireless standard as wi-fi(wireless-fidelity) and is of standard (IEEE 802.16) for the 10 to 66 Ghz range. WiMAX and wi-fi both standards have different applications. 

WiMAX is a long range system, covering many kilometers that uses licensed or unlicensed spectrum to deliver point-to-point connection to the Internet from an ISP( Internet Service Provider) to an end user. Different 802.16 standards provide access to a network from mobile to fixed. Where as wi-fi is a shorter range system, typically hundreds of meters that uses unlicensed spectrum to provide access to a network. 

 The licensed spectrum for WiMAX profile is: 2.3 Ghz, 2.5 Ghz and 3.5 Ghz. 

One of the Advantages of WiMAX is spectral efficiency. VOIP ( Voice over Internet Protocol) is extra QOS ( Quality of Service) class for WiMAX technology.

WiMAX works on OFDMA scheme (Orthogonal Frequency Division Multiplexing).

OFDMA:

Orthogonal Frequency Division Multiple Access.

It is a multiplexing technique that subdivides the bandwidth in to multiple frequency sub-carriers. Here the input data stream is divided in to several parallel sub-streams of reduced data rate and each sub-stream is modulated and transmitted on a separate Orthogonal Sub carrier.

• It is a multi-user version of the popular Orthogonal Frequency Division Multiplexing (OFDM) digital modulation scheme. multiple access is achieved in OFDMA by assigning subsets of subcarriers to individual users.
• It is MIMO (multiple input and multiple output) friendly and advantage of channel frequency selecting.

 Advantage over TDM :

• It Allows simultaneous low-data-rate transmission from several users.
• Lower maximum transmission power for low data rate users.

Other Advantage :

• Flexibility of deployment across various frequency bands with little needed modification to the air interface.
• Averaging interference from neighboring cells, by using different basic carrier permutations between users in different cells.
• Enables Single Frequency Network coverage, where coverage problem exists and gives excellent coverage.

 
The WiMAX forum for this has published three Licensed Spectrum profile: 

2.3 Ghz, 2.5 GHz and 3.5 Ghz.

USES of OFDMA:

1.at IEEE 802.16 wireless MAN standard [WiMAX] .
2. at IEEE 802.20 mobile wireless MAN standard.
3. Ultra mobile Broadband [UMB] , Qualcomm.

-DR