Operating Manual Vol 1 - ES Documentation

SMIQDigital Standard PDC2.17.2 PN Generators as Internal Data SourceIndependent PN generators (Pseudo Noise) can be selected for each slot as data source for data fieldsDATA, SACCH, RCH and SI. These PN generators provide pseudo-random bit sequences of differentlength 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 shiftregisters.The following figure gives an example of a 9 bit generator with feedbacks after register 4 and 0 (output).EXOR8 7 6 5 4 3 2 1 0 DATAThe pseudo-random sequence of a PRBS generator is clearly defined by the number of registers andthe feedback. The following table describes all PRBS generators available:Table 2-30PRBS generators for PDCPRBS generator Length in bits Feedback after9 bit 2 9 -1 = 511 Register 4, 011 bit 2 11 -1 =2047 Register 2, 015 bit 2 15 -1 = 32767 Register 1, 016 bit 2 16 -1 = 65535 Register 5, 3, 2, 020 bit 2 20 -1 = 1048575 Register 3, 021 bit 2 21 -1 = 2097151 Register 2, 023 bit 2 23 -1 = 8388607 Register 5, 0PN generators PN9,11,15,20 and PN23 are configured according to CCITT Rec. 0.151/152/153. Theoutput sequence is inverted for generators PN15 and PN23.The start value of the PN generators is different in the slots and equalsstart value = 1+ 14hex × slotnumberExample: PN9 generator in slot 1 with start value 15hex = 10101 binary.EXOR00001 010 1 DATAThe resulting output sequence is 1010100000010100101011110010 etc.1125.5555.03 2.281E-9