Rohde & Schwarz SMIQ02B - PN Generators as Internal Data Source; Table 2-31 PRBS Generators for GSM

SMIQ Digital Standard GSM/EDGE
1125.5555.03 E-92.303
2.18.2 PN Generators as Internal Data Source
Independent PN generators (Pseudo Noise) can be selected for each slot as data source for data field
DATA. These PN generators provide pseudo-random bit sequences of different length or period. That is
why they are also called PRBS generators (Pseudo R
andom Binary Sequence).
Data sequences are sequences of maximum length which are generated by means of feedback shift
registers.
The following figure gives an example of a 9 bit generator with feedbacks after register 4 and 0 (output).
8
765 4 3
2
10
DATA
EXOR
The pseudo-random sequence of a PRBS generator is clearly defined by the number of registers and
the feedback. The following table describes all PRBS generators available:
Table 2-31 PRBS generators for GSM
PRBS generator Length in bits Feedback after
9 bit 2
9
-1 = 511 Register 4, 0
11 bit 2
11
-1 =2047 Register 2, 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
PN generators PN9,11,15, 20 and PN23 are configured according to CCITT Rec. 0.151/152/153. The
output sequence is inverted for generators PN15 and PN23.
The start value of the PN generators is different in the slots and equals
start value hex slotnumber=+ ×114
Example: PN9 generator in slot 1 with start value 15hex = 10101 binary.
10
DATA
EXOR
1100 0 0 0
The resulting output sequence is 1010100000010100101011110010 etc.