Implementing the 5Hz Noise Bandwidth

 The standards documents [4] specify that the white gaussian noise sources should output a noise bandwidth of B_n=5Hz corresponding to a time of 0.1s between samples i.e.a 10Hz sampling frequency. This is because both TDEV and MTIE are functions of the power spectral density of the noise generated by the model as shown in equations (4.6) and (4.11). By equation (5.6) the power spectral density of the white gaussian noise sources are inversely proportional to the noise bandwidth, B_n. It is important to specify a value of B_n to be used. However, using SPW it is not possible to use a noise source with a 10Hz sampling frequency (i.e. a 5Hz bandwidth). This is because the minimum sampling frequency must be at least twice the passband edge frequency of all the filters being simulated. It was also necessary that the time error data produced by the simulation had a minimum sampling frequency of 30Hz, as described in section 2.4.3.

In order to satisfy the above two conditions, the SPW multi-rate interpolate block was utilised. Such a block increases the sampling frequency of its input signal by a factor of N by inserting N-1 zero valued points between each two consecutive data samples. Two white gaussian noise signal with a sampling frequency of 10Hz were interpolated up to a sampling frequency of 30Hz to provide the two 5Hz bandwidth noise sources for the model.