MT Measure CPM Quadrature Impairments
- Updated2023-02-17
- 6 minute(s) read
MT Measure CPM Quadrature Impairments
Measures and reports quadrature impairments over a single user-specified window. This node must be called once for each measurement window. This node calculates continuous phase modulation (CPM) quadrature impairments on a point-by-point basis on the oversampled waveform.
Inputs/Outputs
recovered complex waveform
The time-aligned and oversampled complex waveform data after matched filtering, frequency offset correction, and phase offset correction. Wire the recovered complex waveform parameter of MT Demodulate CPM to this parameter.
t0
Trigger (start) time of the Y array.
Default value: 0.0
dt
Time interval between data points in the Y array.
Default value: 1.0
Y
The complex-valued signal-only baseband modulated waveform. The real and imaginary parts of this complex data array correspond to the in-phase (I) and quadrature-phase (Q) data, respectively.
detected complex waveform
The ideal oversampled waveform. Wire the detected complex waveform parameter of MT Demodulate CPM to this parameter.
t0
Trigger (start) time of the Y array.
Default value: 0.0
dt
Time interval between data points in the Y array.
Default value: 1.0
Y
The complex-valued signal-only baseband modulated waveform. The real and imaginary parts of this complex data array correspond to the in-phase (I) and quadrature-phase (Q) data, respectively.
impairment measurement window
The window over which impairments are measured.
start index
Index of the first sample of the measurement window.
Default value: 0
width
Number of symbols over which to measure impairments. A value of -1 (default) measures impairments over all symbols. Positive values must be two or greater.
Default value: -1
error in
Error conditions that occur before this node runs.
The node responds to this input according to standard error behavior.
Default value: No error
impairment definition
A value that indicates which set of equations is used to represent impairments.
In the equations in the following table, is the real component and is the imaginary component of each sample in the input complex waveform. and are the real and imaginary components of the corresponding sample in the output complex waveform. is I DC Offset (%) / 100, and is Q DC Offset (%) / 100.
| Vertical Shear |
The definition uses the following equations for I/Q impairments:
where φ is the specified quadrature skew, in radians = 10(IQ gain imbalance/20)
In matrix form, these equations are represented by
where
|
| Axis Shear |
With this option selected, this node uses an impairment definition that simplifies the conversion between measured impairments and their inverse impairments. For example, you may want to measure the I/Q impairments of a system and compensate for those impairments by applying the inverse impairments to the generated or received waveform. Using the Axis Shear definition, given a measured skew and imbalance (in dB), the inverse impairments are -1.0 * skew and -1.0 * imbalance. This definition uses the following equations for IQ impairments:
where = 10(IQ gain imbalance/20) φ is the specified quadrature skew, in radians In matrix form, these equations are represented by
where
|
Default value: Vertical Shear
quadrature skew
The measured quadrature skew of the complex waveform in degrees.
samples per symbol
Number of samples per symbol in the modulated complex waveform.
Default value: 16
magnitude error
The measured magnitude error as a percentage. Magnitude error is the magnitude difference between the ideal and the actual measured symbol locations.
RMS measurement
The RMS impairment value calculated over the impairment measurement window.
peak measurement
The peak impairment value measured over the impairment measurement window.
peak symbol index
Index of the symbol having the peak magnitude of impairment.
individual symbol measurements
The impairment value for each individual symbol.
DC offset measurements
The measured DC offset of the I or Q waveforms as a percentage of the largest I and Q value in the symbol map of the recovered complex waveform.
I
The DC offset of the I waveform, expressed as a percentage of the largest I or Q value in the symbol map.
Q
The DC offset of the Q waveform, expressed as a percentage of the largest I or Q value in the symbol map.
origin offset
The offset, in dB, of the constellation origin from its ideal location.
IQ gain imbalance
The measured ratio of I gain to Q gain, in dB.
phase error
The measured phase error in degrees. Notice that the phase offset is removed by the demodulator and is excluded from this measurement.
RMS measurement
The RMS impairment value calculated over the impairment measurement window.
peak measurement
The peak impairment value measured over the impairment measurement window.
peak symbol index
Index of the symbol having the peak magnitude of impairment.
individual symbol measurements
The impairment value for each individual symbol.
EVM
The measured error vector magnitude (EVM) expressed as a percentage.
RMS measurement
The RMS impairment value calculated over the impairment measurement window.
peak measurement
The peak impairment value measured over the impairment measurement window.
peak symbol index
Index of the symbol having the peak magnitude of impairment.
individual symbol measurements
The impairment value for each individual symbol.
modulation error ratio
The measured modulation error ratio in dB.
error out
Error information.
The node produces this output according to standard error behavior.