SMIQ
Digital Standard IS-95 CDMA
1125.5555.03
E-9
2.135
2.12.3
PN Generators as Internal Data Source for Reverse Link
Different PN (Pseudo Noise) generators can be selected as data source for modulation data in the two
reverse link modes. These PN generators provide pseudo random bit sequences of different lengths or
periods which is why they are also called PRBS generators (Pseudo Random Binary Sequence).
The data sequences are so-called sequences of maximum lengths that are generated by means of
feedback shift registers.
The following schematic shows the 9 bit generator with feedback to registers 4 and 0 (output).
8
7
6
5
4
3
2
1
0
DATA
EXOR
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 2-16 PN generators for IS-95 reverse link
PRBS generator
Length in bits
Feedback to
Start value
9 bits
2
9
-1 = 511
Register 4, 0
1100 0100 1
11 bits
2
11
-1 =2047
Register 2, 0
1100 0100 111
15 bits
2
15
-1 = 32767
Register 1, 0
1100 0100 1110 001
16 bits
2
16
-1 = 65535
Register 5, 3, 2, 0
1100 0100 1110 0011
20 bits
2
20
-1 = 1048575
Register 3, 0
1100 0100 1110 0011 1111
21 bits
2
21
-1 = 2097151
Register 2, 0
1100 0100 1110 0011 1111 0
23 bits
2
23
-1 = 8388607
Register 5, 0
1100 0100 1110 0011 1111 000
PN generators PN9,11,15,20 and PN23 are designed according to CCITT Rec. 0.151/152/153. The
output sequence is inverted for generators PN15 and PN23.
Example: PN9 generator in slot 1 with start value 110001001 (binary)
1
1
DATA
EXOR
0
0
0
1
0
0
1
The resulting output sequence is
110001001100010001000
etc.
