MT Add Phase Noise
- Updated2023-02-17
- 5 minute(s) read
MT Add Phase Noise
Models and applies common sources of phase noise present in communications systems components. This node creates phase noise by first generating white noise and then applying a 1/f (inverse f) filter to specify the noise shape. The output of the filter is scaled such that the generated noise density is equal to the specified offset frequency. The phase component of the input signal is then modulated by the filtered noise.
Inputs/Outputs
input complex waveform
The modulated complex baseband waveform data.
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.
offset frequency
The offset frequency, in hertz (Hz), for the noise density. This is the frequency at which the 1 Hz bandwidth spectral density of the ideal inverse-f noise waveform is equal to specified noise density. Valid entries for this parameter must be in the range 0.7 mHz to fs/2, where fs is the sampling frequency (1/dt) of the input complex waveform.
Default value: 0.2
noise density
The single sideband noise contribution in a 1 Hz bandwidth relative to the total power at the specified offset frequency.
Default value: -120 dBc/Hz
inverse f exponent for noise shape
The exponent of the desired 1/f curve. The inverse f curve specifies the spectral shape of the phase noise. Valid values are -3.0 to 3.0, inclusive.
Default value: 2
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
seed in
A seed for the noise sample generator. Set this value to -1 (xFFFFFFFF) to reseed the noise generator with a random seed. The random signal generator is reseeded on the first call to this node and when reset? is set to TRUE. When reset? is FALSE, seed in is ignored on subsequent calls.
Default value: -1 (xFFFFFFFF)
reset?
A Boolean that determines whether this node reuses the noise shaping filter and reseeds the noise generator on subsequent calls.
| TRUE | Designs or redesigns noise-shaping IIR filter and reseeds the noise generator using the seed in value. |
| FALSE | Reseeds the noise generator using the previously designed IIR filter, with the seed out parameter, upon each subsequent call. This node always resets on first call. |
Default value: TRUE
output complex waveform
The signal-plus-noise complex baseband waveform data returned by this node.
t0
Trigger (start) time of the Y array.
Default value: 0
dt
Time interval between data values 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.
seed out
The seed used in the subsequent call to this node when reset? set to FALSE.
error out
Error information.
The node produces this output according to standard error behavior.
Multiregion Inverse f Rolloff Noise
Multiregion inverse f rolloff noise shapes can be implemented by calling MT Add Phase Noise multiple times in series on a signal, with each call defining the inverse f rolloff and desired level at a specific offset frequency. When combining individual MT Add Phase Noise nodes in this way, consider the following:
- Wire the seed out parameter from a previous call to the seed in parameter of a subsequent call to reduce the likelihood of correlation between the individual noise sources.
- The overall noise spectrum shape in a particular offset frequency region is the sum of contributions from the individual noise sources in that region. As such, at any particular offset frequency, a noise contribution from one source can overwhelm the contribution from another source.