Equalizer (Custom IQ)
Equalizer Parameters
Define the type and length of the equalization filter (in symbols) and set the convergence (convergence determines the size of the steps used to reshape the equalization filter). For additional details about these parameters, see online help for convergence and filter length.
Adaptive equalization uses the measured signal to determine the coefficients of the equalization filter.
selects the adaptive equalization method to use with the measurement.
None: No equalization is applied to the signal.
Minimize Evm: The VSA software uses a least mean square algorithm and compares the measured signal against the reference signal on a subset of the samples per symbol, namely the decision points for EVM Error vector magnitude (EVM): A quality metric in digital communication systems. See the EVM metric in the Error Summary Table topic in each demodulator for more information on how EVM is calculated for that modulation format.. This is the legacy method of adaptive equalization.
Minimize Error Vector: The entire error vector is used (all sample points) for adaptive improvements to the equalization filter. While the least mean square algorithm is still used, this enhanced equalizer should result in better EVM in most cases compared to the Minimize EVM method. In some cases, Minimize EVM may provide better EVM results.
sets the length of the VSA's equalization filter.
sets the rate at which the equalization filter converges.
Adaptive Operations
If is set to , the VSA uses the results of the current measurement to update the filter coefficients for the next measurement. The VSA chooses coefficients that produce a modulation quality metric that is less impacted by the presence of linear distortion.
If is set to , the VSA does not update the filter coefficients. Instead, the VSA uses the last updated coefficients before selecting .
Select or at any time to continue or stop updating filter coefficients.
The VSA does not redefine the equalization filter to have a unit impulse response when is selected. Instead, the VSA will use the last updated filter coefficients.
When equalization is Reset (see About Adaptive Equalization for conditions that reset the equalization filter), the equalization filter has a unit impulse response. The length of the filter determines the position of the unit impulse response in the filter. The impulse is located in the center of the filter for short filter lengths. As the filter length increases, the impulse moves proportionally towards the start of the filter to handle channels with large delay-spread.
Select Reset at any time to redefine the equalization filter to have a unit impulse response.
Selecting a Frequency Span
For best results, make sure to select a frequency span that contains all energy of your signal. If significant energy from your signal falls outside of the displayed frequency span, equalization will not work on your signal.
Viewing Impulse Response or Frequency Response
View the impulse response or the frequency response of the equalized channel by clicking , and selecting Eq Impulse Response or Ch Frequency Response.
Equalization and Measurement Speed
The following parameters affect measurement speed when using adaptive equalization:
- Result Length
- Filter Length (for the equalization filter)
- Points / Symbol
See Also
