introduction to WIMAX

[Virus King]

can any body plz tell me about wimax. why there is boom if wimax instead of cdma.
i searched through many sites but still not cleared



can any body guide me in simple way.


virus king

 

[sameerbabu]

wimax is for fizxed wireless, cdma for mobile wireless.
Both targets difrernt applications.U cannot compare them as such

 

[mindrover]

Virus King,


Found this on the web. I hope it helps,

mindrover

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What advantages will WiMax offer over existing 3G, MyWireless and iBurst infrastructure. The main difference seems to be the radio access method being used.

WiMax will use OFDM (orthogonal frequency division multiplexing) as opposed to the usual CDMA (code division multiple access) method used by cellphones, 3G, MyWireless, iBurst and others. CDMA suffers from two serious problems: Mulitpath interference and the so-called "near-far" problem.

Multipath interference occurs when signals from the base station bounces off trees, building etc before arriving at the CPE (customer premises equipment). It becomes very difficult (and very expensive) to recover the original signal when this happens. CDMA radios use multiple antennas to try and reduce multipath interference. (Thats why your 802.11b access point should have 2 antennas).

The "near-far" problem occurs when one CPE is near the base station and one CPE is far for the base. In a CDMA system the transmitted power reaching the base from the the CPEs should be exactly the same to reduce interference. To achieve this the near CPE must reduce its transmit power and the far CPE should increase its transmit power. (That's why your cellphone lasts longer when your close to the base). Because the power cannot be matched *exactly* interference does occur. This causes a slowdown in speed and a reduction in base cell size. What this means to you and me is that when someone connects from, say 10Km, to the base, he slows the connection for everybody else on that base.

OFDM (also used by the newer 802.11g WiFi) eliminates both the problems mentioned above. For the techies out there: This is done by applying a inverse FFT (Fast Fourier Transform) on the signal before transmission. Multiple carriers are used (up to 800) to spread the signal over a wide band (typically 6MHz). When multipaths exist the problem can be isolated to a single carrier and removed. One quote I saw somewhere states "OFDM fixes a frequency problem in the frequency domain".

You can actually use this multipath capability to propagate your signal: the signal will bounce off buildings and trees to your CPE. This is called NLOS (non line of sight) operation. Cooooooool!

A few vendors like NextNet, Alvarion and Airspan are starting to offer pre WiMax systems which employ OFDM. The ranges and speeds are indeed *very* impressive (up to 8K NLOS, 30K LOS). Unfortunatly I read somewhere Intel moved back the chipset release to mid 2006 and WiMax certified products will only be available in 2007. Sigh.
Reply With Quote

 

[flatulent]

802.16 will eventually replace 802.11 but not for a while.

 

[fm_com_28]

the standard IEEE802.16e is now for mobile applications not only fixed .[/quote]

 

[ricksidd]

The only reason for WiMAX to come in a big way is the economies of scale which the WiMAX( a consortium of more than 300 companies) is going to enjoy ultimately benefitting the consumer. The WiMAX certification will ensure the conformity to standard as well interoperability among vendors.

The mobile version 802.16e is going to enjoy the patronage of Intel by which you will be carrying laptops with inbuilt "WiMAX' like you do have inbuilt WiFi.

These scopes are missing in other technologies....

Sidd

 

[yasiranwar86]

go to wiki pedia its nice for intro

 

[cydi]

check out port-70.blogspot.com. Lots of articles on WiMax

 

[Communications_Engineer]

802.16 will eventually replace 802.11 but not for a while.

No chance. Perhaps you are ill informed

 

[sajjadhyd]

can any one help me in my project which is about wimax and its implemementation on hardware... using microcontrollere