• Hello!

    I want to know on which radio/antenna an 802.11n access point sends management and control frames. 

    An 802.11a/b/g access point will use only one of its diversity antennas to transmit these frames. 

    But how behaves a .11n access point? For example a 3x3:3 access points with 1Mbps as lowest data rate. Which of it's three antennas will it use to send management and control frames?

  • Because I don't received a reply I want to push my question and add some details.

    I ask this question because a customer wants to install a single AP with two different high gain antennaes that point into different directions. Independent from the hidden node problem, I think there can be problems with the management and control frames. 

    [<---10dbi antenna] [Accesspoint] [10 dbi antenna --->]

    From my perspective an 802.11a/b/g access point will transmit Beacons and other management/control frames only on one of its antennas. Am I right?

    How behaves an 802.11n accesspoint with lowest data rate of 1Mbps or an .11n  (6,5Mbps+) rate as lowest basic data rate.

  • I don't remember seeing a restriction on an  AP only using one of its antennas for this purpose, but it kind of makes sense.

    However, it would seem like this solution would be creating a hidden node (the AP) for half of the clients.   Antennas in totally opposite directions would also eliminate any advantage of multiple streams or  beam-steering.

    I don't work with many MIMO radios, but this seems totally backwards to me.

  • Spatial diversity in a/b/g systems was used to eliminate multi-path signal cancelation on the receive side only. For transmit the AP typically would use the antenna which received the best(RSSI) from the STA it is communicating with.

    MIMO adds transmit beamforming and multiple data streams to the mix which means that you’ll really never know what antenna/s were used to send a packet.

    Tony using 2 directionals pointed in 2 separate directions from the same radio, no in all cases, never, all antennas used on a single AP radio/radio chain need to be identical and have identical aim if they are directional.


  • Hi Guys, 

    thank you for you replys.

    I  don't want to install a solution  like that because of hidden node problem and performance loss due to missing diveristy and/or multiple radios. 

    I was primarily interessted in how an 802.11n access point transmits frames with different speeds. 



  • All management frames are at the lowest basic rate, uni-cast traffic is sent to the STA at the rate the AP received the last data frame from the STA at.


  • Sirkozz,

    I have seen a few variations in this behavior with various AP's, but I can't recall the details at the moment.

    If the Wi-Fi Alliance had items like this as part of their test suites, then there would be more uniformity in the behavior.  Otherwise they wouldn't get certified. 

    Our devices don't require high throughput, so I just wish they were ALL consistent.

  • Howard,

    I was speaking generically, not about a single vendor, but this does bring up a major downfall of this forum; the dichotomy between studying and the real world.

    Hint, hint CWNP, maybe you need to split the board into a CWNP side and a “real-world” wireless side?


Page 1 of 1
  • 1