Digital Modulation
SMIQ
1125.5555.03
E-9
2.94
2.10.3
Internal PRBS Data and Pattern
The PRBS generators in the modulation coder provide pseudo random binary sequences (PRBS) of
different length and period. They are called sequences of maximum length and are generated by means
of feedback shift registers.
The following schematic shows the 9-bit generator with feedback from registers 4 and 0 (output).
8
7
6
5
4
3
2
1
0
SER DATA
EXOR
Fig. 2-53
9-bit PRBS generator
The pseudo random sequence of a PRBS generator is determined by the number of registers and the
feedback. The following table describes all available PRBS generators:
Table 2-11 PRBS generators of modulation coder
PRBS generator
Length in bit
Feedback to
9 Bit
2
9
-1 = 511
Register 4, 0
15 Bit
2
15
-1 = 32767
Register 1, 0
16 Bit
2
16
-1 = 65535
Register 5, 3, 2, 0
20 Bit
2
20
-1 = 1048575
Register 3, 0
21 Bit
2
21
-1 = 2097151
Register 2, 0
23 Bit
2
23
-1 = 8388607
Register 5, 0
PRBS data as a source for modulation data are selected in the menu via SOURCE - SOURCE PRBS.
The period is determined by PRBS LENGTH.
Other internal modulation data are available as simple data patterns such as 0s or 1s. Selection is via
SOURCE - SOURCE PATTERN.
Note:
With PRBS data or Pattern selected as source for modulation data, only external control
signals can be used. A combination with control signals from lists is not possible.
