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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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