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Which of the following is the MINIMUM configuration tha…

A company is deploying a new wireless network and requires 800Mbps network throughput. Which of the following is the MINIMUM configuration that would meet
this need?

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A.
802.11ac with 2 spatial streams and an 80MHz bandwidth

B.
802.11ac with 3 spatial streams and a 20MHz bandwidth

C.
802.11ac with 3 spatial streams and a 40MHz bandwidth

D.
802.11ac with 4 spatial streams and a 160MHz bandwidth

Explanation:
Spatial streaming is used in wireless communications where multiple-input-multiple-output (MIMO) is being used. With MIMO, multiple antennas are used for
transmission and reception. MIMO was available in 802.11n but its capabilities have been extended in 802.11ac.
802.11ac supports a mandatory 80 MHz channel bandwidth for stations (vs. 40 MHz maximum in 802.11n), 160 MHz available optionally and more (up to 8) special
streams.
A single antenna and 80 MHz channel bandwidth provides a bandwidth of 433Mbps. In this question, we need a minimum bandwidth of 800Mbps. Two antennas
and 80 MHz channel bandwidth provides a bandwidth of 867Mbps and therefore meets the requirement.

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2 Comments on “Which of the following is the MINIMUM configuration tha…

  1. klt316 says:

    Go to https://www.sourceonetechnology.com/802-11ac-wireless-channel-bonding-mimo-spatial-streams-and-beamforming/… GREAT source to understand spatial streams and bandwidth. One of the charts there is important to know, and it’s easy to remember… 1 spatial stream @ 20MHZ is roughly 100Mbps (actually 86)… @ 40MHZ it doubles to 200Mbps… @ 80MHZ it doubles again to 400Mbps… and @ 160MHZ it doubles again to 800Mbps (actually 866), but these numbers are close enough! That’s easy to remember! Then complete the chart for 2 spatial streams start with 200Mbps @ 20MHZ and do the same as above, double @ 40, double again at 80, and double again at 160. Then for 3 spatial streams start with 300Mbps and do the same as above. And finally for 4 spatial streams start with 400Mbps and do the same doubling technique. Use this easy memorization and repetition to recreate the chart to figure out the bandwidth for various spatial streams and frequencies! Once you have a chart, for example on this question, simply cross reference 2 spatial streams @ 80MHZ and that shows you a bandwidth of 800Mbps, 3 spatial streams @ 20MHZ shows a bandwidth of 300Mbps, 3 spatial streams @ 40MHZ shows a bandwidth of 600Mbps, and 4 spatial streams @ 160MHZ shows a bandwidth of roughly 3.2Gbps. The question asks for a minimum of 800Mbps, so answer A is correct!




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