Data rate (Therotical vs Actual)

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Hi,This is a general question , Theortically 802.11n offer upto 450 or 600 Mbps ,Why the actual data rate  is  below this rate ?
How the  value  600 or 450 Mbps theorotically calculated ? 
When we Say 600 ,does it mean RX is 300 and TXis 300 ?
What would be the actual value approximately ?
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Posted 2 years ago

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Nathaniel Moore, Employee

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Hi Sim,

I wrote an article covering this very topic here:

Hope this helps.

Kind regards,

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There is a lot that goes into achieving a certain modulation rate, but that doesn't necessarily transfer into actual throughput due to wireless overhead and contention for airtime. Wireless is a shared medium similar to an ethernet hub in a very basic analogy. The more AP(s) and clients using the same channel that you can receive and demodulate will slow your throughput as you have to contend for air time against more station's transmissions. is a great resource as is the MCS Chart by Andrew von Nagy at 

For example: 

450Mbps is the data rate for a radio transmitting with 3 spacial streams and able to modulate and demodulate the wireless frames at 64-QAM 5/6 modulation/coding with 40MHz channel width AND short guard interval. 

600Mbps would be the same except you add another spacial stream. Unfortunately, I do not recall any enterprise manufacture producing a 802.11n radio with four spacial stream capability. Cisco's 3500 series was capable of 3 spacial streams. The IEEE standard provided for up to four spacial streams. Which sounds great but most clients don't have more than 3 spacial streams. Most portable devices have one or two spacial streams. 

On top of all the physics to be able to modulate and demodulate 64-QAM 5/6 with at least an Signal to Noise Ratio of 28dBm. That is also IF you can utilize 40MHz channels without running into DFS events or channel overlap.

I hope this helps a bit. 

Todd S. 
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mr bee

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These are theoretical values (perfect conditions), 150 Mbps per stream (using 40 MHz channels and optimal settings) in one direction at the same time (half duplex). So depending on the number of radio's you can get 4x150Mbps=600Mbps on IEEE 802.11n.