1. Calculate the power in the transmitted signal, 'SignalPower':
If 'X' represents the transmitted signal waveform, then the
following MATLAB code will calculate the signal power:
N = length(X);
SignalPower = X*X'/N;
2. Estimate the noise power based on the signal-to-noise ratio
specified in the AWGN function call. For example, in the Communication SystemToolbox , we can use
y = awgn(x,snr)
Where snr = SignalPower/Noise Power.
Since, we know Signal Power from 1 and know the value of snr from the AWGN function-call, the noise power can be calculate thereafter.
3. Calculate the total power in the received signal using the same
method as that for 'X' above.
4. Calculate the interference power as follows:
InterferePower = TotalPower - NoisePower - SignalPower;
5. Calculate the Carrier-To-Interference Ratio in dB as follows:
CIR = 10*log10(SignalPower/InterferePower);
Best Answer
The "sinr" function computes the ratio of total received power from a signal source to total received power from non-signal sources plus noise. The algorithm re-uses the "sigstrength" function to compute total received power from each source and this calculation includes path loss. Please take a look at this function for implementation details.
The "sinr" function does not perform any interference modelling of multipath and does not calculate constructive/destructive interference of waveforms. It is important to note that the "sinr" function does model signal level interference but *does not *model wave interference. Wave interference refers to the constructive or destructive effects of the superposition of multiple waves. When multipath propagation occurs, multiple copies of the same signal reach the receiver and may undergo wave interference. Above, I mentioned that the "sinr" function is computing a ratio of signal source power to non-signal source power. Those non-signal sources are considered interference sources (in some contexts they would be called jammers).
Please take a look at the following example:
https://www.mathworks.com/help/releases/R2019b/phased/examples/sinr-map-for-a-5g-urban-micro-cell-test-environment.html
This scenario models a cell network where each base station is operating on the same frequency. The SINR value at each point on the map is computed with the nearest base station being the desired signal source, and all other base stations being interference sources. The cloverleaf pattern in the original example is caused by each marker containing three sectored cells with directional antenna patterns.
Our treatment of SINR is consistent with the following page which introduces it and gives a key to interpret SINR values:
https://wiki.teltonika-networks.com/view/SINR
The main Wikipedia article is good too:
https://en.wikipedia.org/wiki/Signal-to-interference-plus-noise_ratio