Operating Manual Vol 1 - ES Documentation

SMIQDigital Standard IS-95 CDMA2.12.3 PN Generators as Internal Data Source for Reverse LinkDifferent PN (Pseudo Noise) generators can be selected as data source for modulation data in the tworeverse link modes. These PN generators provide pseudo random bit sequences of different lengths orperiods 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 offeedback shift registers.The following schematic shows the 9 bit generator with feedback to registers 4 and 0 (output).EXOR8 7 6 5 4 3 2 1 0 DATAThe pseudo random sequence of a PRBS generator is determined by the number of registers and thefeedback. The following table describes all available PRBS generators:Table 2-16PN generators for IS-95 reverse linkPRBS generator Length in bits Feedback to Start value9 bits 2 9 -1 = 511 Register 4, 0 1100 0100 111 bits 2 11 -1 =2047 Register 2, 0 1100 0100 11115 bits 2 15 -1 = 32767 Register 1, 0 1100 0100 1110 00116 bits 2 16 -1 = 65535 Register 5, 3, 2, 0 1100 0100 1110 001120 bits 2 20 -1 = 1048575 Register 3, 0 1100 0100 1110 0011 111121 bits 2 21 -1 = 2097151 Register 2, 0 1100 0100 1110 0011 1111 023 bits 2 23 -1 = 8388607 Register 5, 0 1100 0100 1110 0011 1111 000PN generators PN9,11,15,20 and PN23 are designed according to CCITT Rec. 0.151/152/153. Theoutput sequence is inverted for generators PN15 and PN23.Example: PN9 generator in slot 1 with start value 110001001 (binary)EXOR10010 001 1 DATAThe resulting output sequence is 110001001100010001000 etc.1125.5555.03 2.135E-9