Rohde & Schwarz SMU200A - Page 324

Instrument Function
R&S
®
SMU200A
304Operating Manual 1007.9845.32 ─ 15
"E
b
/N
0
"
The noise level is set on the basis of the value entered for the ratio of bit
energy to noise power density.
The associated C/N or S/N value is displayed. The correlation between
the two values is as follows:
C/N or S/N = (E
b
/N
0
)*(f
bit
/B
sys
), where
f
bit
is the Bit rate (Symbol rate x Modulation value)
B
sys
is the System bandwidth
With "Custom Dig Mod" signals, the bit rate used for calculation is defined
by the selected standard in the "Custom Digital Mod" dialog.
With "Digital Standard" signals, the bit rate to be used for calculating the
E
b
/N
0
can be entered at "Bit Rate".
Some test cases with the 3GPP base station tests (TS 25.141) specify,
for example, E/N settings that apply to channel-coded data or block seg-
ments.
SCPI command:
[:SOURce<hw>]:AWGN:POWer:MODE on page 575
Reference Mode - AWGN
(Additive Noise and CW Interferer, Display Mode set to RF)
Select reference mode if the C/N or Eb/N0 ratio is changed.
"Carrier"
If the C/N value or E
b
/N
0
value changes, the carrier level is kept constant
and the noise level is adjusted. This is the standard procedure for meas-
uring the bit error rate versus the noise power.
"Noise"
If the C/N value or E
b
/N
0
value changes, the noise level is kept constant
and the carrier level is adjusted.
Some test cases of 3GPP Base Station Tests (TS 25.141) specify, for
example, that the noise power be permanently set as a function of the
base station power class, whereas the carrier power is variable.
SCPI command:
[:SOURce<hw>]:AWGN:POWer:RMODe on page 576
Bit Rate - AWGN
(Additive Noise only)
Sets or indicates the bit rate used for converting C/N or S/N to E
b
/N
0
.
With "Custom Digital Mod" signals, the bit rate used is indicated here. It is defined by the
choice of the standard in the "Custom Digital Mod" menu.
With "Digital Standard" signals, the bit rate used for converting C/N or S/N to E
b
/N
0
is set
here.
When generating a "Digital Standard", it is thus possible to select which bit rate is to be
used for calculating the ratio of bit energy to noise power density, e.g. the bit rate before
or after channel coding.
SCPI command:
[:SOURce<hw>]:AWGN:BRATe on page 570
Carrier/Noise Ratio / Signal/Noise Ratio
(Additive Noise and CW Interferer only)
Impairment of Digital I/Q Signal and Noise Generator - AWGN/IMP Block