Simulating Fading, Adding Noise and Predistortions, and Impairing the Signal
R&S
®
SMW200A
418User Manual 1175.6632.02 ─ 30
For a correct measurement of the noise power within the system bandwidth, we recom-
mend that you measure the channel power with a signal analyzer.
In the "Additive Noise" mode, the output signal is the signal with the noise distribution.
Hence, the power level at the RF output corresponds to the carrier+noise power (see
Figure 6-3).
The noise power of digitally modulated signal is characterized by the parameter E
b
/N
0
indicating the ratio of bit energy to noise power density. The correlation to the SNR is
as follows:
C/N or S/N = (E
b
/N
0
)*(f
bit
/B
sys
), where B
sys
is the system bandwidth.
Bit Rate f
bit
= "Symbol Rate" * Modulation Value
Where the bit rate value is retrieved from?
The parameter "AWGN > Noise Power / Output Results > Bit Rate" indicates the value
used by the C/N or E
b
/N
0
calculation. The value is retrieved automatically depending
on the configured baseband signal:
●
For signals generated by the "Custom Digital Mod", the bit rate is determined by
the selected standard
(see parameter "Custom Dig Mod > General" > "Symbol Rate" and "Custom Dig
Mod > Modulation Type").
●
For signals generated in accordance to a digital standard, the bit rate is often a
standalone parameter.
Some test cases however, for example the 3GPP base station tests (TS 25.141),
specify the E/N settings that apply to channel-coded data or block segments. Set
the parameter "Bit Rate" to the required value, e.g. the bit rate before or after chan-
nel coding.
Understanding the displayed information
The following example explains the impact of the AWGN settings on the signal and
noise parameters.
See Figure 6-3 for an example of an AWGN generation with the following configuration:
●
Default "System Configuration"
Adding Noise to the Signal
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