Walls Impede Wifi

Posted by Martin R on January 19, 2009
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i-263fe8bc0170b7546cafa8a6afb52604-wifi logo.gif

My experiments with the wifi installation in our house and the excellent Bredbandskollen TPTEST bandwidth tester (mainly for machines in Sweden) has taught me a few interesting things about wifi.

  • Your operating system may report the quality of the connection in percent or columns or somesuch. This is not directly proportional to the actual bandwidth you’re getting. One percentage estimate may correspond to a wide range of bandwidth figures.
  • The bandwidth of a wifi connection is extremely sensitive to obstacles such as walls, doors, even waste paper baskets.

I started with the access point sitting on the floor near the middle of our house, and got 7 Mbps. Then I moved it less than three meters onto the wall, thinking that a high placement would improve bandwidth. Instead it dropped to 3 Mbps. So I moved it onto the window ledge, one meter from its original placement, and got 9 Mbps. (Note that I get 11 Mbps when I use an ethernet cable instead of wifi.) None of the three placements has line-of-sight to my computer’s antenna.

Reminds me of the time when my work computer was off-line and I solved the problem by moving the system unit 15 cm.

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Comments

  1. #1 Lassi Hippeläinen
    January 19, 2009

    The waves see everything that conducts electricity, which in practise means metal. They may pass through a wall unhindered, but electric wires and plumbing inside the wall will change everything. So will metal furniture like wastepaper baskets.

    Note that the field won’t get absorbed, it will be reflected, causing interference. In some places the reflection adds to the original, in others it subtracts from it. If there are several reflecting items, the result is as messy as the waves in a harbour basin.

    The peaks and throughs are spaced one wavelength apart. At 2.3 GHz that means about 13 cm – if you move in the right direction.

  2. #2 Zeno
    January 19, 2009

    I’m afraid your otherwise useful advice can’t be applied in the U.S. Most of us move our electronic gear around in terms of inches, which are well known to be incompatible with centimeters. Yes, it’s a terrible problem. One hopes that someday someone will discover the equivalent placement (and re-placement) techniques in terms of inches (or even feet). But my experience with my math students suggests the difficulties may be insuperable.

  3. #3 DuWayne
    January 19, 2009

    Dammit Zeno, as if it wasn’t bad enough to have a Swede correcting our English. Now you want to display yet another aspect of American ignorance?

    I suppose next someone is going to imply the large percentage of Americans who can’t even name their representative in the house of representatives, or even one of their state’s senators.

  4. #4 DuWayne
    January 19, 2009

    Oops!

  5. #5 kai
    January 20, 2009

    Bragging time:

    I helped my sister install WiFi in her house. It turned out to be very difficult, her HP laptop would not communicate with encryption turned on and in particular was very particular about its exact placement relative to the base station—the only acceptable place being in an asymmetric position on her desk, much disturbing her sense of neatness.

    Of course, my PowerBook had perfect reception at any point in the building and ran with any combination of encryption settings.

    On the other hand I do not know who “my” MP is without looking it up. (But I do know how to do that.)