title: AT+CSQ network percentage formula from rssi
body: <p>Does anyone knows <strong>formula for calculating GSM network coverage into percents (0 .. 100) from rssi</strong>? It should be safe for 8bit AVR microcontroller CPU, without hardcore math operations like log or division by something that's not 2^n (bitshift is preferred). Creating array with 32 possible percentage values is poor solution.</p>
  
  <p>possible rssi values (0..31 is valid values):</p>
  
  <pre><code>0 -113 dBm or less
  1 -111 dBm
  2...30 -109... -53 dBm
  31 -51 dBm or greater
  99 not known or not detectable
  </code></pre>
  
  <p>Approximate values i want:</p>
  
  <pre><code>RSSI    %
  0   0
  1   3
  2   6
  3   10
  4   13
  5   16
  6   19
  7   23
  8   26
  9   29
  10  32
  11  36
  12  39
  13  42
  14  45
  15  48
  16  52
  17  55
  18  58
  19  61
  20  65
  21  68
  22  71
  23  74
  24  78
  25  81
  26  84
  27  87
  28  90
  29  94
  30  97
  31  100
  99  ?
  </code></pre>
  
  <p>I'm out of ideas, so please advise me! Thanks for Your time!</p>