Is there a function that computes the Carrier-To-Interference Ratio in MATLAB 7.5 (R2007b)

I would like to compute the Carrier-To-Interference ratio in MATLAB, but I cannot find a function that calculates this figure of merit.

Answer 1

[MathWorks Support Team]

There is no function in MATLAB that calculates the Carrier-To-Interference Ratio (CIR) directly. It is possible, however, to calculate the CIR using other information that is available in the MATLAB code that models the communication system. The calculation might proceed as follows:

   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;     % assumes X is row vector

   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);