Last Modified: January 9, 2017

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.

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.

Trigger (start) time of the **Y** array.

**Default: **0.0

Time interval between data points in the **Y** array.

**Default: **1.0

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.

The ideal oversampled waveform. Wire the **detected complex waveform** parameter of MT Demodulate CPM to this parameter.

Trigger (start) time of the **Y** array.

**Default: **0.0

Time interval between data points in the **Y** array.

**Default: **1.0

The window over which impairments are measured.

Index of the first sample of the measurement window.

**Default: **0

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: **-1

Error conditions that occur before this node runs. The node responds to this input according to standard error behavior.

**Default: **no error

A value that indicates which set of equations is used to represent impairments.

In the equations in the following table,
$I$ is the real component and
$Q$ is the imaginary component of each sample in the **input complex waveform**.
${I}^{\prime}$ and
${Q}^{\prime}$ are the real and imaginary components of the corresponding sample in the **output complex waveform**.
${I}_{\circ}$ is **I DC Offset (%)** / 100, and
${Q}_{\circ}$ is **Q DC Offset (%)** / 100.

Name | Description |
---|---|

Vertical Shear | The definition uses the following equations for I/Q impairments: ${I}^{\prime}=a*\text{\hspace{0.17em}}I+\text{\hspace{0.17em}}{I}_{\circ}$ ${Q}^{\prime}=a*\mathrm{sin}\left(\phi \right)\text{\hspace{0.17em}}*\text{\hspace{0.17em}}I+\text{\hspace{0.17em}}b*\text{\hspace{0.17em}}\mathrm{cos}\left(\phi \right)\text{\hspace{0.17em}}*\text{\hspace{0.17em}}Q+\text{\hspace{0.17em}}{Q}_{\circ}$ where φ is the specified quadrature skew, in radians
$\gamma $ = 10 $a=\gamma *\text{\hspace{0.17em}}b$ $b=\sqrt{\frac{2}{1+{\gamma}^{2}}}$ In matrix form, these equations are represented by $\left[\begin{array}{c}{I}^{\prime}\\ {Q}^{\prime}\end{array}\right]=S\left[\begin{array}{c}I\\ Q\end{array}\right]+\left[\begin{array}{c}{I}_{\circ}\\ {Q}_{\circ}\end{array}\right]$ where $S=\left[\begin{array}{cc}a& 0\\ a*\mathrm{sin}\phi & b*\mathrm{cos}\phi \end{array}\right]$ |

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 * ${I}^{\prime}=I*\text{\hspace{0.17em}}\sqrt{\gamma}-Q*\left(\frac{\phi}{2}\right)+{I}_{\circ}$ ${Q}^{\prime}=-I*\left(\frac{\phi}{2}\right)+Q*\left(\frac{1}{\sqrt{\gamma}}\right)+{Q}_{\circ}$ where
$\gamma $ = 10 φ is the specified quadrature skew, in radians In matrix form, these equations are represented by $\left[\begin{array}{c}{I}^{\prime}\\ {Q}^{\prime}\end{array}\right]=S\left[\begin{array}{c}I\\ Q\end{array}\right]+\left[\begin{array}{c}{I}_{\circ}\\ {Q}_{\circ}\end{array}\right]$ where $S=\left[\begin{array}{cc}\sqrt{\gamma}& -\phi /2\\ -\phi /2& \frac{1}{\sqrt{\gamma}}\end{array}\right]$ |

**Default: **Vertical Shear

The measured quadrature skew of the complex waveform in degrees.

Number of samples per symbol in the modulated complex waveform.

**Default: **16

The measured magnitude error as a percentage. Magnitude error is the magnitude difference between the ideal and the actual measured symbol locations.

The RMS impairment value calculated over the **impairment measurement window**.

The peak impairment value measured over the **impairment measurement window**.

Index of the symbol having the peak magnitude of impairment.

The impairment value for each individual symbol.

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**.

The DC offset of the I waveform, expressed as a percentage of the largest I or Q value in the symbol map.

The DC offset of the Q waveform, expressed as a percentage of the largest I or Q value in the symbol map.

The offset, in dB, of the constellation origin from its ideal location.

The measured ratio of I gain to Q gain, in dB.

The measured phase error in degrees. Notice that the phase offset is removed by the demodulator and is excluded from this measurement.

The RMS impairment value calculated over the **impairment measurement window**.

The peak impairment value measured over the **impairment measurement window**.

Index of the symbol having the peak magnitude of impairment.

The impairment value for each individual symbol.

The measured error vector magnitude (EVM) expressed as a percentage.

The RMS impairment value calculated over the **impairment measurement window**.

The peak impairment value measured over the **impairment measurement window**.

Index of the symbol having the peak magnitude of impairment.

The impairment value for each individual symbol.

The measured modulation error ratio in dB.

**Where This Node Can Run: **

Desktop OS: Windows

FPGA: Not supported