SINR Calculation

The SINR is defined as the power of a certain signal of interest divided by the sum of the interference power (from all the other interfering signals) and the power of some background noise. NetSim models an ideal receiver whose noise figure (NF) is zero.

The background thermal noise in dBm at room temperature is given by:

\[\begin{equation} P\;(\text{dBm}) = -174 + 10 \times \log_{10}(\Delta f) \end{equation}\]

\[\begin{equation} P\;(\text{mW}) = 10^{\left(\frac{P\;(\text{dBm})}{10}\right)} \end{equation}\]

Where \(\Delta f\) is the Bandwidth in Hz.

  • 802.15.4, \(\Delta f\) = 5 MHz

  • 802.11a, b, g, \(\Delta f\) = 20 MHz

  • 802.11n, \(\Delta f\) = 20 MHz or 40 MHz

  • 802.11 ac, \(\Delta f\) = 20 / 40 / 80 / 160 MHz

Therefore, SINR is calculated as:

\[\begin{equation} SINR\;[\text{dB}] = 10 \times \log_{10}\!\left(\frac{\text{Received power [mW]}}{\text{Interference Noise [mW]} + \text{Thermal Noise [mW]}}\right) \end{equation}\]

NOTE: Floating numbers may lose precision when converting from dBm to mW or vice versa (Ref: https://msdn.microsoft.com/en-us/library/c151dt3s.aspx). Hence

  • If the received power (in mW) is less than 0.0001 then it is assumed to be zero.

  • If the received power (in mW) is 0 then dBm value is \(-10000.0\) not \(-\infty\)

  • While adding two powers, decimal points after fifth digit is ignored. Ex: 2.0000005+3.0000012 = 5.0