Wireless Link - 225 meters

Discussion in 'General Wireless Discussion' started by alkit, Jan 30, 2013.

  1. alkit

    alkit Occasional Visitor

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    Hi,

    After much experimentation, I finally managed to set up a wireless link between my house and my friend's apartment.

    Equipment on my side:
    Ubiquiti Bullet 2 CPE device connected to a 24dbi 2.4ghz grid antenna mounted on my roof

    In between:
    225 meters total distance between the 2 antennas. Around 2 or 3 thick trees. They are too high to get line of site.

    Friend's flat:
    Arc FreeStation 2.4Ghz 15dbi Panel CPE device

    I have managed to establish a link at around -65 dBm and have CCQ at 70-100%.
    The problem is that the speeds I am getting are terrible. Max speed goes to 3Mbps. This speed is crazy slow for file transfers.

    What factors could I look for that could be causing the bad rate? I know my antenna has been sitting around for a while - could it be a fault with the antenna? Could it be something to do with the Ubiquiti device?

    Please advise the best way forward to improve this connection speed.
     
  2. stevech

    stevech Part of the Furniture

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    -65dBm or better, if present on both ends of the link, should be much faster than 3Mbps. What's the link bit rate indicated? 11n it would be 6Mbps link rate or better.

    signal strength at both ends: if -65 or better, you can't blame the antennas. I would use a lower gain antenna than that dish unless you have a way to keep that dish pointed correctly in windy conditions. At that gain, it's about 3-5 degree beamwidth- darned sensitive.

    Is there a long coax cable in this setup? If so, did you account for its losses? Best to use an outdoor bridge co-located at the antenna. But again, -65dBm, no matter, is a good signal strength. Though most WiFi devices have about the same link bit rate for any particular signal strength (RSSI), you should look at what that vendor promises at -65.

    If the other end is poorer than -65, there's a problem.

    Have you eliminated the possibility that +/- 3 channels of what you're using there's a very busy WiFi user? Streaming/FTPing, etc?
     
    Last edited: Jan 31, 2013
  3. thiggins

    thiggins Mr. Easy Staff Member

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    How are you measuring "speed"?

    If you run a long ping, what does your packet loss look like?
     
  4. alkit

    alkit Occasional Visitor

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    I am copying a file across the network. I get max 370KBps transfer speed.

    No packet loss on over a minute of pinging. Once or 2 longish ping times, but the rest under 6ms.
     
  5. alkit

    alkit Occasional Visitor

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    To answer your questions:
    Link shows Tx/Rx Rate: 48/54. But the 2nd value goes down to 6 when sending a file to the client.
    There is no long coax cable. Dish has its own 0.5m cable plugged directly into the Ubiquiti CPE device, outdoors.
    I have tried all the 3 channels. 1 and 11 are very clean on both sides, so doesn;t seem to be the issue.

    However, I have noticed that on the AP side, signal strength is around -74dbm. Not sure why this differs from the client side which is -65dbm?

    I did also try aim the antenna better, however, all that has done is now decrease my CCQ rate. It now fluctuates all over the place (going as low as 50%), and I do not know what caused that.

    Thanks for the help!
     
  6. stevech

    stevech Part of the Furniture

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    " But the 2nd value goes down to 6 when sending a file to the client."

    This is odd. The link rate goes down when there's heavy traffic. To me, that sounds like bad WiFi hardware. Or the RSSI isn't the truth. The link rate can reduce during flows because of high bit error rates on the link, so the WiFi firmware slows down to try to get back to a reasonable bit error rate. But with good signal strengths, this shouldn't happen.

    There's another possibility: There's an ACK Timeout setting in WiFi. May not be user-changeable in your system. The timeout is supposed to be long enough to accommodate a round trip delay of x microseconds, where x is the round trip distance (in time of flight at 1nanosecond per ft.). If the time out is too small you'll see reduced speeds.

    There could also be non-WiFi signals interfering - such as an analog audio sender, baby camera, etc. Cure for these is to move to channel 1, 6 or 11.

    These are guesses.
     
    Last edited: Jan 31, 2013

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