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Thread: WiFi D/U ratio

  1. #1

    Default WiFi D/U ratio

    I'm new to inSSIDer, but I have a question that I have not been able to get an answer to anywhere else.

    How many dB difference does there need to be between my network (the desired, or "D") and any potentially interfering network (the undesired, or "U")?

    At home, my wireless router is set to 40 MHz and just a few others, all set to 20 MHz. It's in a fairly rural setting, but I'd like to be a good neighbor and not step on anyone.

    In a different location, there are three wireless networks (with different SSIDs) from the same organization on the same channel. Is this a good practice, or should they be spreading them out (potentailly occupying the entire 2.4 GHz band)?

  2. Default

    There isn't an easy answer for this. I think if you follow "channel re-use" recommendations you will be fine. I have seen 15-20dB separation between the two values as a recommendation but this is pretty exceptional. This is for enterprise-grade WLAN deployments. You'll want the highest of dB separation possible.

    Keep in mind that it is better to reuse the exact same channel than it is to overlap the channel. The reasoning behind this is that the APs can hear each other properly and wait their turns to talk.

    There are a lot of good articles that you'll be able to find by searching for WLAN Channel Reuse. Here is a pretty good article Cisco High Density Wireless LAN Design Guide

  3. #3

    Default

    Thanks for the info!

    I assumed that I would want both my wireless networks to be clear of each other so they can be used separately but simultaneously. I thought that was the point of different channels. I'm doing this to keep my "n" devices separate so that they can operate at higher speed and so that B and G devices don't drag down the speed of the AP. Is that a good idea, and/or the best way to implement it?

  4. Default

    If you have 2 11n APs (wireless routers) put them each on channels 1 (primary) and 11 (primary). If you are in a somewhat rural setting I wouldn't worry too much about stomping on anyone.

    If you don't have any 11b devices, disable rates 1,2 5.5 and 11. That will bring up the speed of the network significantly. Disabling g may help some but there are still a lot of non-11n wi-fi devices out there still.

    Interestingly enough about the 11n bonded channel APs, they'll only use the 40MHz when they have to. That means that the client must be compatible and it is demanding a lot of traffic.

  5. #5

    Default

    Thanks again. I'll give those channels a try.

    BTW, when I scan my neighborhood, I see 20-30 dB difference between my AP and my neighbors. (They're lower, of course.) In your earlier comment did you think that 15-20 dB separation was unusually high or low?

    I don't think my AP allows dropping of certain data rates, but it shoulddn't be a problem. I'll be moving the potential fast connections to the n-only AP. Any remaining -g clients will only be checking email or other internet-related sources.

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