User Guide

PAMS
Technical Documentation
NHD–4
System Overview
Page 3–26
Original 11/97
Interleaver
12345
12
34
5 Interleaver
Data In Data Out
CDMA08.DRW
Figure 24. Interleaver
Interleaving is the process of shuffling the data before transmission with a
corresponding un–shuffle on the receiving end. The purpose is to spread the bit
errors. Bit errors tend to come in bursts due to fading, rather than uniformly spread
in time. Interleaving provides a more uniform bit error distribution so that one burst
of errors will not wipe out a whole digital word but only individual bits that can be
corrected by the convolutional decoding.
PN Code Generation
Pseudorandom Noise (PN)Sequences
Pattern = 1001011
00 1
1
10 0 0
01 0 0
CDMA09.DRW
Figure 25. PN Code generator
The illustration above is a highly simplified version of a PN code generator. It will
be left to the reader to fill in the blank registers. This generator will start repeating
after 7 bits. A CDMA long code register is 42 bits long and the short code register
15 bits long.