MT Measure QAM Quadrature Impairments

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 QAM 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.

input bit stream

The demodulated bit stream from the output bit stream parameter of MT Demodulate QAM.

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.

Standard Error Behavior

Default value: No error

QAM system parameters

Parameter values defining the QAM system. Wire the QAM system parameters cluster of MT Generate QAM System Parameters (M) or MT Generate QAM System Parameters (map) to this cluster. Do not alter the values.

samples per symbol

An even number of samples dedicated to each symbol. Multiply this value by the symbol rate to determine the sample rate.

Note The demodulation and detector nodes use timing recovery, which is optimized for four or more samples per symbol.

Default value: 16

symbol map

An ordered array that maps each symbol to its desired coordinates in the complex plane. The number of QAM states in the array is 2^N, where N is the number of bits per symbol. The vector length for the symbols farthest from the origin is 1.

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

reset?

A Boolean that determines how the node handles bits from partial symbols in the input bit stream.

TRUE	Discards bits making up incomplete symbols.
FALSE	Saves the leftover bits and starts with them on the next iteration.

Default value: TRUE

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.

quadrature skew

The measured quadrature skew of the complex waveform in degrees.

IQ gain imbalance

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