SMIQ
Digital Standard GSM/EDGE
1125.5555.03
E-9
2.303
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 Random 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
7
6
5
4
3
2
1
0
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 slot number
= +
×
1 14
Example: PN9 generator in slot 1 with start value 15hex = 10101 binary.
1
0
DATA
EXOR
1
1
0
0
0
0
0
The resulting output sequence is
1010100000010100101011110010
etc.
