MT ASK Feedforward Equalizer (LMS) (Specify coefficients)
Applies adaptive feedforward software equalization using the least-mean-squared (LMS) algorithm to the ASK-demodulated input complex waveform. Allows you to specify equalizer coefficients or their initial conditions.
 (Specify coefficients).png)
input complex waveform
The modulated complex baseband waveform data.
t0
Trigger (start) time of the Y array.
Default: 0.0
dt
Time interval between data points in the Y array.
Default: 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.
ASK system parameters
Parameter values defining the ASK system. Wire the ASK system parameters cluster of MT Generate ASK System Parameters (M) or MT Generate ASK System Parameters (map) to this cluster. Do not alter the values.
symbol map
An ordered array that maps each symbol to its desired level. The number of ASK levels 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.
equalizer coefficients in
The filter coefficients for initializing the feedforward equalizer. The time span of this array (in symbols) is given by the following equation:
size(equalizer coefficients in) / taps per symbol
For best performance and minimization of intersymbol interference, ensure that the time span (in symbols) of the equalizer coefficients filter is greater than the time span (in symbols) of the channel filter.
- The equalizer coefficients in array must contain an odd number of elements.
- The values specified here are used by the equalizer only when reset? is set to TRUE or on the first call to this node. Otherwise, this node maintains an internal buffer of the equalizer coefficients resulting from completion of the previous call.
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.
- 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.
error in
Error conditions that occur before this node runs. The node responds to this input according to standard error behavior.
Default: no error
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.
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.
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
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
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
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
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).
t0
Trigger (start) time of the Y array.
Default: 0
dt
Time interval between data values in the Y array.
Default: 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.
error
The instantaneous per symbol error in the output of the adaptive feedforward equalizer filter.
equalizer coefficients out
The adaptive feedforward equalizer filter coefficients when equalization is complete for the current iteration.
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.
error out
Error information. The node produces this output according to standard error behavior.
