Rohde & Schwarz SMBV100B, User Manual

Page: 265 / 1030

Adding Noise and Predistortions, and Impairing the Signal
R&S
®
SMBV100B
263 User Manual 1178.4460.02 ─ 03
●
The value units:
–
The values related to the RF outputs are displayed in dBm
– The values related to the baseband outputs - in dB
Remote command:
[:SOURce<hw>]:AWGN:DISP:MODE
on page 799
Set Noise Power Via
In "Additive Noise" mode, selects the way the noise power is determined.
The following correlation applies:
"C/N or S/N"= ("E
b
/N
0
")*(f
bit
/B
sys
) , where:
●
"C/N or S/N" is the carrier/noise ratio
●
"E
b
/N
0
" is the ratio of bit energy to noise power density
●
"Bit Rate "f
bit
= "Symbol Rate" x Modulation Value
●
B
sys
is the system bandwidth.
See also Chapter 4.1.2, "About the AWGN Generator" , on page 255.
Remote command:
[:SOURce<hw>]:AWGN:POWer:MODE
on page 799
Reference Mode
Selects whether the carrier or the noise power is kept constant if the C/N or Eb/N0 ratio
is changed.
In the common case, the instrument keeps the carrier power and adjusts the noise
power accordingly. Some test cases however, for example the 3GPP Base Station
Tests (TS
25.141), specify explicitly the noise power. These test cases require that the
noise power is permanently set as a function of the base station power class, whereas
the carrier power is variable.
Remote command:
[:SOURce<hw>]:AWGN:POWer:RMODe
on page 799
Bit Rate
In "Additive Noise" mode, indicates the bit rate used for converting C/N or S/N to E
b
/N
0
.
Tip: For digitally modulated signals, select the bit rate before or after channel coding,
as required.
See also Chapter 4.1.2, "About the AWGN Generator" , on page 255.
Remote command:
[:SOURce<hw>]:AWGN:BRATe
on page 800
Carrier/Noise Ratio, Signal/Noise Ratio
In "Additive Noise" and "CW Interferer" mode, sets the carrier/noise, signal/noise or
signal/interferer ratio.
Whether a configuration of C/N or S/N is enabled, depend on the selected output Show
Powers for Output .
●
In "Reference Mode > Carrier": sets the noise power. It does not affect the power of
the useful signal, i.e. the carrier power remains constant.
Thus the power of the c noise signal or the
power of the output signal
changes.
Adding Noise to the Signal