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RSSI / noise / etc.

Discussion in 'DD-WRT Firmware' started by bigjohns, Dec 7, 2005.

  1. bigjohns

    bigjohns Network Guru Member

    So, I do a survey of my wireless lan and see this information. Now, one network has RSSI of -88, the other -79, and both have noise of -94. Can someone give me a simple explanation of what all this means?

  2. gaster

    gaster Network Guru Member

    Zero is a perfect signal and -100 is the worst so the -79 is the better of those two, but that's still not that great.
  3. gaster

    gaster Network Guru Member

    I was talking about RSSI
  4. pewter

    pewter Network Guru Member

    hi johns,

    in a nutshell:
    you get the important information if you subtract the values of rssi and noise.
    to simplify things we leave the leading - for all numbers out of our
    consideration, for the moment...
    in your example:

    94 (dbi) - 79 (dbi) = 15 (dbi)


    94 (dbi) - 88 (dbi) = 6 (dbi)

    the results show the available signalstrength.
    for comparison, you need at least 10dbi to establish a solid 11mbit connection.

  5. bigjohns

    bigjohns Network Guru Member

    Thanks! That helps alot!
  6. PacoSS

    PacoSS Network Guru Member

    pewter where can we see more information about this?

    I think that a table with the dbi needed for each speed would be greatly appreciated in this forum, maybe as an sticky post.

  7. pewter

    pewter Network Guru Member

    the answer is simple enough to put it in a table.
    if you're in a lab. in a laboratory the lower bounds are:

    6 Mbit @ 2 dB
    9 Mbit @ 3 dB
    12 Mbit @ 4 dB
    18 Mbit @ 6 dB
    24 Mbit @ 10 dB
    36 Mbit @ 14 dB
    48 Mbit @ 19 dB
    54 Mbit @ 23 dB

    this is theory. really.
    because if you're insisting to live in a more comfortable environment,
    like your own aparment for instance, things aren't that simple anymore.
    (like a lot of things become somewhat dodgy once you actually do live in
    you're own apartment, now that i come to think of it... where was i? ah, yes.)

    in real life jitter will make it hard to get anything working below 5db.
    i found that 10db will do for a 11mbit, about 30db for a 54mbit connection. (and as you all know, the actual transferrate you can reasonably hope to get is something altogether different)

  8. pewter

    pewter Network Guru Member

    this is for g-standard...

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