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Applies adaptive feedforward software equalization using the least-mean-squared (LMS) algorithm to the QAM-demodulated input complex waveform. Sets the length of the feedforward equalizer in symbols.

Note  

This node assumes that the input sample rate is an even integer multiple of the symbol rate. The even integer multiple must match the samples per symbol element of the QAM system parameters cluster.

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input complex waveform

The modulated complex baseband waveform data.

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t0

Trigger (start) time of the Y array.

Default: 0.0

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dt

Time interval between data points in the Y array.

Default: 1.0

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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.

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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.

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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: 16

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symbol map

An ordered array that maps each Boolean symbol to its desired coordinates in the complex plane. The number of states in the array must be 2 N , where N is the number of bits per symbol.

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equalizer length

The duration of the feedforward equalizer filter in symbols.

Note  

The actual length of the feedforward equalizer is given by the following equation:

N = equalizer length (symbols) × samples per symbol + 1

When reset? is set to TRUE, use this parameter to create the N-tap feedforward equalizer with default initial conditions. The default feedforward equalizer coefficients are thereby specified by the Dirac delta impulse response:

c ( n ) = δ ( n N 2 ) , n = 0 .. N-1

when reset? is set to TRUE.

Default: 1

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training bits

The binary-valued training bits that train the feedforward equalizer during the training phase when the reset? parameter is set to TRUE. This parameter is ignored when reset? is set to FALSE.

Note  
  • Ensure that the duration of training is long enough to allow the feedforward equalizer to converge before switching to a decision-directed adaptation.
  • When working with M-ary modulation schemes {M>2, or bits per symbol>1} in which symbols represent groups of bits, the specified training bits must start on a symbol boundary.
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error in

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

Default: no error

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feedforward equalizer (lms) parameters

The feedforward equalization parameters, which define the equalizer tap spacing (symbol spaced/fractionally spaced) and convergence rate during training and steady-state.

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taps per symbol

The tap-spacing of the equalizer coefficients array, relative to one symbol duration. For error-free operation, set this parameter value to be a factor of the samples per symbol passed from MT Generate System Parameters.

Note  

Modulation nodes use two types of equalizers that are distinguished by their tap spacing: symbol-spaced or fractionally-spaced. A symbol-spaced (T-spaced) equalizer has

taps per symbol = 1,

which means that every tap of the equalization filter spans the time duration of one symbol.

A fractionally-spaced (T/N-spaced) equalizer has

taps per symbol > 1.

For example, a T/2-spaced equalizer has taps per symbol = 2, meaning that every two taps of the equalization filter span the time duration of one symbol.

Default: 1

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delta (training)

The convergence parameter for feedforward equalization during the training phase. This value adapts the feedforward equalizer coefficients for the duration of the training period when reset? is set to TRUE.

Default: 0.01

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delta (steady state)

The steady-state convergence parameter for adapting the equalizer coefficients during the decision-directed phase. Use this value for adapting the feedforward equalizer coefficients when reset? is set to FALSE.

Default: 0.01

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reset?

A Boolean that determines whether to continue feedforward equalization using the previous iteration states. This node always resets on first call.

TRUE Resets the internal state, restarts, and trains the equalizer.
FALSE Continues feedforward equalization using the previous iteration states. This node assumes that the input complex waveform is phase-continuous with the previous iteration.

Default: TRUE

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output complex waveform

The equalized oversampled waveform generated from the feedforward equalizer as a result of adaptation. This waveform consists of the oversampled data that are compensated for the channel impulse response with zero intersymbol interference. Wire this parameter to the corresponding instance of MT Measure Quadrature Impairments to make modulation measurements such as modulation error ratio (MER) and error vector magnitude (EVM).

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t0

Trigger (start) time of the Y array.

Default: 0

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dt

Time interval between data values in the Y array.

Default: 1.0

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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.

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error

The instantaneous per symbol error in the output of the adaptive feedforward equalizer filter.

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equalizer coefficients out

The adaptive feedforward equalizer filter coefficients when equalization is complete for the current iteration.

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output bit stream

The recovered bit stream generated from the adaptive feedforward equalizer. The recovered bit stream is phase-aligned with the output complex waveform at the equalizer output. Wire this parameter to MT Measure Quadrature Impairments for performing modulation measurements such as modulation error ratio (MER) and error vector magnitude (EVM), or to MT Calculate BER after Trigger for making bit error rate (BER) measurements.

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error out

Error information. The node produces this output according to standard error behavior.