Monitoring Signal Characteristics
R&S
®
SMW200A
622User Manual 1175.6632.02 ─ 30
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Chapter 6.2, "Adding Noise to the Signal", on page 415
Baseband leveling principle
In the R&S SMW, signal routing is performed in the digital domain, i.e. before the I/Q
modulation and the RF upconversion. This implementation ensures a lossless signal
addition with high precision. In the digital domain however, real RF levels do not exist.
To let you define baseband signals with different average levels, the R&S SMW intro-
duces the concept of baseband leveling. This principle bases on a relative leveling of
the baseband signals in the digital domain.
By default, when two identical baseband signals are added, they are output at the RF
output with the equal average levels. To set a relative level between the baseband sig-
nals, use one of the possible alternatives, e.g:
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Enable "Baseband > Baseband Offsets > Gain".
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In MIMO configurations, select "Fading > Fading Settings" and adjust the MIMO
correlation matrix.
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In non-MIMO configurations, enable "Fading > Summation Ratio A/B".
9.2.2.1 Why Is a Power Level Surveillance Important
When routing the signal to the I/Q output connectors of the instrument, adding signals
from several baseband sources and/or applying baseband power offsets or fading the
signal, the signal power is an important parameter.
For example, when measuring the power after fading the peak and RMS power values
can fluctuate significant due to the varying channel state information (CSI) of the fading
process. The retrieving of correct measurement results for the faded signal requires
not only a suitable acquisition point but also a sufficient (long enough) measurement
time to allow the power results to converge reliable values for the long channel state
information. Similar situation and requirements apply when measuring the carrier
power and the carrier+noise power before and after an AWGN block.
Use the observed information for an evaluation and verification of the correct signal
processing throughout the instrument and for a correct adjustment of the power set-
tings at the connected device.
The power values observed in the "Baseband Power Simulation" dialog are suitable as
control mechanism. The values cannot be modified to influence the power and level
control in the instrument.
9.2.2.2 Defining Suitable Acquisition Points
The Figure 9-17 shows an overview of the possible signal acquisition points.
Querying Information on the Baseband Power Levels
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