Chapter 3
GSM Asynchronous Mode Operation
RF generator
130
4460 GSM System Option and 4468 EDGE System Option
Version 12.20
Parameters of the
modulation area
The modulation of the RF signal to be generated is set in this area of the menu.
Modulation —
Selection field.
Selections possible: GMSK, none or AM.
Data —
Selection field to specify the ‘data payload’ to be transmitted. Further
details regarding the structure of a GSM time slot can be found in section
“Time
slots and bursts” on page 110
.
Selections possible:
– 0...0 (i.e. all bits are ‘zeros’),
– 1...1 (i.e. all bits are ‘ones’),
– 1010... (i.e. the sequence will start with a ‘one’ and the current bit will
always be the inverted value of the previous bit),
– 11001100... (i.e. the sequence will start with two ‘ones’ and the current two
bits will always be the inverted value of the previous two bits),
– 11110000... (i.e. the sequence will start with four ‘ones’ and the current four
bits will always be the inverted value of the previous four bits),
– 1...10...0 (i.e. the sequence will start with eight ‘ones’ and the current eight
bits will always be the inverted value of the previous eight bits),
– PRBS-9 (i.e. a
),
NOTE
Setting “none” means that the RF output signal generated by the 4400 will be
unmodulated, i.e. a pure carrier sine wave.
NOTE
When “none” has been selected on this field, all other entry fields of this
menu area will not be available.
NOTE
The modulation setting also affects measurements in the analyzer: If GMSK is
selected, the analyzer will attempt to demodulate the signal; phase and fre-
quency error are shown with respect to a GMSK-modulated signal. Adversely,
if no modulation is selected in the generator, the analyzer shows the results
assuming that the input signal is unmodulated as well.
NOTE
The AM selection is available only if the AM Modulation Option is installed
and if Signal type is set to “continuous”. For more information regarding AM
see below.