Rohde & Schwarz SMM100A, User Manual

Page: 270 / 1088

Adding noise and predistortions, and impairing the signal
R&S
®
SMM100A
270 User Manual 1179.1341.02 ─ 05
This setting also influences:
●
The way the interfering parameters are displayed, e.g. if the SNR value is defined
as C/N or as S/N.
●
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 863
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 5.1.2, "About the AWGN generator" , on page 262.
Remote command:
[:SOURce<hw>]:AWGN:POWer:MODE
on page 863
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 863
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 5.1.2, "About the AWGN generator" , on page 262.
Remote command:
[:SOURce<hw>]:AWGN:BRATe
on page 863
Carrier/Noise Ratio, Signal/Noise Ratio
In "Additive Noise" and "CW Interferer" mode, sets the carrier/noise, signal/noise or
signal/interferer ratio.
Adding noise to the signal