Wireless Access

Contributor II

wireless radios and airtime


I am trying to understand how the multipe radios work together and clients communicate simultaneously. 

Suppose I have AP-225 which supports a/b/g/n/ac. It is 3x3 MIMO and 3 antennas each for both 2.4 and 5 GHz. Now I am trying to understand the following:

- Does it have 3 antennas each for 2.4 Ghz and 5 Ghz and each has transmit & receive capability?

- If a client connect on g 2.4Ghz , does it connect to one antenna? Can another user connect to same antenna with timeshare? Or, does all three antenna work together to handle all 2.4 Ghz clients simultaneously? How does timeshare work.

- If a client connect on ac 5 Ghz to the same AP, does the 5 Ghz radio work separately from 2.4 Ghz and does not wait for free time ? 

- If another 5 Ghz n client connect to this ap can it work together with the first client since it has MIMO technology?

- How does channel bonding work in this case?




Guru Elite

Re: wireless radios and airtime

Start here:  http://en.wikipedia.org/wiki/MIMO


*Answers and views expressed by me on this forum are my own and not necessarily the position of Aruba Networks or Hewlett Packard Enterprise.*
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Contributor II

Re: wireless radios and airtime

I now have some idea about MIMO. But I still have few questions:


- AP-225 has six antennas? Do they all work simultaneously for transmit and receive to a single client at a time? Since we stil don't have MU-MIMO..

- if the antenas are specific for transmit and receive then how many for each purpose in both bands?

MVP Expert

Re: wireless radios and airtime

This is how Medium Access Control works in 802.11


Channel Bonding:



 Spatial Multiplexing in 802.11n/ac Wave 1 allows you use simultaneously several antennas at the same time but only to one device at a time , in ac wave 2 then will be able to take advantage of MU-MIMO

2015-01-16 15_10_02-www.arubanetworks.com_pdf_technology_whitepapers_wp_Designed_Speed_802.11n.pdf.png


Please read this document

Thank you

Victor Fabian
Lead Mobility Architect @WEI
All-Decade MVP 2020

Re: wireless radios and airtime

AP-225 has six antennas, three on each band.  See http://community.arubanetworks.com/t5/Unified-Wired-Wireless-Access/Inside-ArubaNetworks-AP-225-AP225-11ac/td-p/119041 for a look under the cover.


Until MU-MIMO, WiFi is a half-duplex medium.  The extra antennas are used either to beamform or to add bandwidth on the same packet transmission.  How many are used, and how, depends on how good the client is.  Because the multiple antennas allow faster rates, packets take less time to transmit and the medium becomes free for use by another client sooner, so that is how they speed things up.


Contributor II

Re: wireless radios and airtime

Thanks you! This is good information. However, I do not see anything explicitly written for 3 antennas in 2.4 GHz and 3 antennas for 5 GHz. Does 3x3 MIMO means 3 antennas for 2,4 and 3 for 5 GHz. ?

MVP Expert

Re: wireless radios and airtime

You are correct, 2x2 APs would have 2 antennas per radio, 3x3 would have 3 antennas per radio, etc. The 225 has 6 antennas total, 3 are 2.4GHz and 3 are 5Ghz antennas. The 224 shows only three external connectors, but that is because both radios' antennas are diplexed onto a single connector (so that each connector handles both 2.4Ghz and 5Ghz frequencies, which is why you need dual-band external antennas). 

Jerrod Howard
Distinguished Technologist, TME
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