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Thread: 5 GHz - 40+ MHz bandwith - Adjacent channel interference?

  1. #1

    Question 5 GHz - 40+ MHz bandwith - Adjacent channel interference?

    First of all - Wi-Spy DBx + Chanalyzer is a fantastic product - Thanks for that!

    Now, we're seeing more and more AC-capable home-wifi-routers with 40 and 80 MHz bandwith - soon to be 160Mhz! My question is this:

    Case:
    1 wifi-network with SSID: MegaWidth (5 GHz - 80 MHz channelwidth - operating on channels 36, 40, 44, 48)
    1 wifi-network with SSID: MiniWidth (5 GHz - 20 MHz channelwidth - operating on channel 40)

    Will there be adjacent channel-interference in this case or is it categorized as co-channel?

    What if the case is both are 80 MHz channelwidth? Co-channel or adjacent channel?

    I've also seen the word "control-channel" I think it was - what does that actually imply?

  2. #2
    Join Date
    Feb 2012
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    On the Beach in Florida
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    In North America there are 24 20 MHz wide 802.11ac channels. They do not overlap. Consumer routers have only 9 channels. The control channel is used for handshaking, etc. When wide channels are configured, their actual use is negotiated using the control channel.

    Keep in mind that by using wide channels, the effective number of channels is reduced.
    160 MHz = 1 channel; 80 MHz = 2 channels; 40 MHz = 4 channels; 20 MHz = 9 channels

    What happened to the other15 channels? Those channels are restricted to devices capable of dynamic frequency selection (DFS) so the wi-fi signal does not interfere with radar operating on those frequencies.

    Code:
    
    
    802.11ac Channels
    
    Width     Valid Channel Numbers
    
    
    20 MHz	36, 40, 44, 48, 52, 56, 60, 64, 100, 104, 108, 112, 116, 120, 124, 128, 132, 136, 140, 144, 149, 153, 161, 165
    
    40 MHz	38, 46, 54, 62, 102, 110, 118, 126, 134, 142, 151, 159
    
    80 MHz	42, 58, 106, 122, 138, 155
    
    160 MHz	50, 114
    
    
    DFS channels are in red.  They are not available in consumer grade equipment.
    
    
    Last edited by ua549; 11-24-2015 at 10:34 AM.
    Old Mod by the Sea

  3. #3

    Default

    Thanks for that ua549 - that clears up the controlchannel - and I was wondering why consumergrade-products doesn't carry DFS-channels. Maybe it's the price vs quality

    What about my case?
    When reading http://www.metageek.com/training/res...ongestion.html it clearly states there's adjacent channel congestion in 2.4 GHz and that's a very bad thing. But I haven't seen any articles that deal with my stated scenario/case. I can't find info whether they'll share the network (co-channel-congestion) or actually be adjacent channel congestion.

  4. #4
    Join Date
    Feb 2012
    Location
    On the Beach in Florida
    Posts
    380

    Default

    Because the channels in the 5 GHz band do not overlap, there is no adjacent channel interference.
    Congestion becomes an issue when using wide channels.

    DFS certified equipment costs are significantly higher (thousands of dollars) than non-DFS certified equipment.
    Last edited by ua549; 11-25-2015 at 07:35 AM.
    Old Mod by the Sea

  5. #5

    Default

    Perfect! Thanks! And sorry for mixing terminology

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