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Theory of 300 mbps

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Earlier there used to be only one antenna to transmit or receive. Now we have multiple antennas to transmit(multiple output) or receive(multiple input): MIMO, which uses the technique of spatial division multiplexing [Continous flow of data: stream; when multiple streams of data are sent simultaneously via the same channel]

802.11n products are denoted by TxR:S where :

“T” is the number of transmit radio chains (sent     by the AP    ), and

“R” is the number of receive  radio chains (received by the client), and

"S" is the number of spatial  streams      (the common number of antennas in use by the tranmitter and receiver)

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when an antenna transmits continous flow of data (stream), we call it a stream

when the same antenna is able to transmit multiple streams together, via the same channel: SDM

'Assuming' a clear signal, a two spatial stream link will achieve twice the throughput of a single spatial stream in the same channel. So, its important to ensure that we are getting high SNR. This is because, the amount of information that can be carried by a signal depends on the signal-to-noise ratio, or SNR, typically expressed in decibels (dB). The greater the SNR the more information is carried on the signal and recovered by the receiver.

Each                spatial stream                             provides data rate up to 150 Mbps

So, system with two spatial streams                            will  support      up to 300 Mbps

So, system with two antennas (which can transmit at same time) will  support      up to 300 Mbps

So, if an AP and Client has three antennas but 'two' antennas can transmit at the same time, the AP should be able to provide 300 mbps in the ideal situations

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Both, the AP and the client must be able to send and receive the info being exchanged between each other.

If AP is using two antennas, two antennas must be used by the client also !

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Without channel bonding,      one   wireless channel is 20 mhz wide for        max of 075 mbps of throughput.

With    channel bonding,       one   wireless channel is 40 mhz wide for         max of 150 mbps of throughput.

With    channel bonding,        two   wireless channels can provide                 max of 300 mbps of throughput.

With    channel bonding,        three wireless channels can provide                 max of 450 mbps of throughput.

So, it should be clear by now, that how come by combining two such channels, each channel using channel bonding, we can achieve max of 300 mbps of throughput.

Interestingly, the IEEE 802.11n specification offers options for up to four spatial streams, though as of now there are no systems available with this feature !

1 antenna = 1 transtmitter = 1 spatial stream

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‎01-22-2014 06:29 AM
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New Member

Hi,

 

I can see in the WLAN client status showing 300 mbps. But when I test the throughput it is attaining only 20 to 25 mbps. why?

I have testing this with Lwapp AP and Autonomous AP also.