SOURCEFORGE » RALF » 2015 Quantitative analysis of RF signals

h3. 1. Definition of inputs and ways to compute the outputs - Theory

+1. Display of the power spectrum+

p=. !Signal_to_power_spectrum.png!

+Figure 9: Computation of the Power Spectrum+

The incoming signal passes through the "power spectrum block" of LabView. The power spectrum of the given signal is then displayed.

+2. Computation of the power of the useful signal+

p=. !Power_Spectrum_to_power.png!

+Figure 10: Computation of the Power of the useful signal+

The value of the autocorrelation of the signal taken at 0 gives the total power of the signal. If the signal is noisy, the result will be the power of the useful signal added to the one of the noise. Generally, the power of the useful signal is much higher than the power of the noise. Therefore, this model is valid when the power of the noise is much lower than the one of the useful signal. This model is only valid for the [[2. Simulation|simulation]], it will be modified in subsection [[3. Moving from simulation to acquisition of real signals]].

+3. Computation of the power of the noise+

The noise will be known for the [[2. Simulation|simulation]], therefore, its power will be known and the signal-to-noise ratio will be approximated by dividing the measured power of the useful signal by the power of the noise.

+4. Display of the constellation+

p=. !Signal_to_constellation.png!

+Figure 11: Display of the constellation+

The signal is demodulated with the appropriate demodulation parameters.

+5. Computation of the error measurements+

Now, let’s have a look to digital results. We want to observe the constellation of the signal and some results like mean error vector magnitude or mean phase error. Our signal analyser does not determine automatically what is the constellation used to transmit the signal, we have to know it before and to enter it in the program as a parameter. Then we can observe the received constellation, the mean error vector magnitude, the mean phase error, and the mean magnitude error. 

!evm.gif!