title: How to improve Bluetooth distance measuring using RSSI?
body: <p>For my project I need to estimate the distance between a Smartphone and a bluetooth module. The Estimation doesn't have to be very precise. I only need to determine the distance with a margin of error of about <code>50cm</code>. </p>
  
  <p>I did test the RSSI of two bluetooth modules at distance-steps of 10 cm. I measured the RSSI 5 times for each step and got the average of the 5 measurements. The averages are shown in the graph below:</p>
  
  <p><img src="https://i.stack.imgur.com/ZJBM1.png" alt="Blue and Red lines resemble the two bluetooth modules"></p>
  
  <p>The red and blue lines resemble the two Bluetooth modules. You can see that the results are not very linear. One of the reasons for this is interference, so i searched for ways to tackle the interference issue. Two ways i found are:</p>
  
  <ul>
  <li><p>Signal Noise Ratio(SNR): <a href="https://stackoverflow.com/questions/20416218/understanding-ibeacon-distancing/20434019#20434019">Understanding ibeacon distancing</a></p></li>
  <li><p>ratio of the iBeacon signal strength (<code>rssi</code>) over the calibrated transmitter power (<code>txPower</code>). The <code>txPower</code> is the known measured signal strength in <code>rssi</code> at <code>1 meter</code> away: <a href="http://www.princeton.edu/~achaney/tmve/wiki100k/docs/Signal-to-noise_ratio.html" rel="nofollow noreferrer">http://www.princeton.edu/~achaney/tmve/wiki100k/docs/Signal-to-noise_ratio.html</a></p></li>
  </ul>
  
  <p>However i don't really understand how the above techniques would be used to get more accuracy. For SNR i need the Noise value, how do i even get the Noise value? </p>
  
  <p>For ratio <code>rssi</code>/<code>txPower</code>, I can get the <code>txPower</code> by simply measuring the <code>rssi</code> at <code>1 meter</code> from the module. So I know all the needed values. But I don't know what to do from here on out. How do i use these values to get a more accurate distance estimations?</p>
  
  <p>Are there any other techniques i can use to improve accuracy?</p>