Instrument Function
R&S
®
SMU200A
378Operating Manual 1007.9845.32 ─ 15
Multi carrier waveforms consisting of up to 512 carriers modulated by user-selectable
baseband signals can be created in order to simulate complex multi carrier scenarios with
different baseband signals (e.g. CDMA2000 or 3GPP FDD).
Waveform sample rate
The Arbitrary Waveform Generator includes a resampling unit that interpolates the input
samples to reach a target digital output I/Q sample rate before digital-to-analog conver-
sion (DAC). The input sample rate finput is given by the default sample rate tag of the
waveform file or is set by the user in the ARB panel.
The R&S SMU uses a 100 MHz system clock and a sample rate of 100 MSamples/s.
The resampling lowpass limits the signal bandwidth to a maximum of 1.36 x f
input
. Within
a bandwidth of 0.68 x f
input
the resampler lowpass is distortion-free. Thus, an externally
created waveform file have to provide a sample rate f
input
that is high enough for perfect
signal reconstruction.
For distortion-free resampling the lower bound of the required sample rate finput is cal-
culated by:
f
input
≥ Signal bandwidth / 0.68
In case of digital modulation this means that the oversampling factor (f
input
=symbol rate
x oversampling factor) that is applied for impulse forming is high enough.
The lower bound of the oversampling factor is given by:
oversampling factor ≥ signal bandwidth / (symbol rate x 0.68)
Example:
For the WCDMA standard 3GPP FDD with root raised cosine filter (α = 0.22) and a symbol
rate (chip rate) of 3.84 MHz the minimum oversampling factor is calculated as follow:
3.84 MHz x (1+0.22) / (3.84 MHz x 0.68) = 1.794
A modulation signal with a sample rate of 100 MHz is passed directly to the digital-to-
analog converter (DAC), i.e. the resampling unit is bypassed (see figure below). After the
DAC the signal is finally limited to a maximum bandwidth of 80 MHz.
Baseband Signal - Baseband Block
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