User Guide

ManualsBrandsNokia ManualsCell Phone2180

Technical Documentation

NHD–4

System Overview

PAMS

Page 3–37

Original 11/97

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Short Code Spreading

The Forward Channel is spread one–more–time. The final spreading uses a Short

Code that is 215 (32,768) bits long, runs at 1.2288 Mbps and repeats every 26.667

msec. As previously stated all base stations use the same set of Walsh codes, a

short code combined with an “offset” mask allows each base station to have a

unique identification. These “PN Offsets” are separated by multiples of sixty–four

1.2288 Mbps clock chips which allows 512 unique time offsets for base station

identification (32768 bits / 64 bits = 512 offsets). By XOR’ing the Walsh encoded

channels with the offset short code, each base station can reuse all 64 Walsh codes

and be uniquely identified from other adjacent cells using the same CDMA

frequency channel.

Forward Link Channel Format

First of all remember the word “Channel” means a different “PN Code Sequence”

and not a different frequency for this part of the discussion.

A base station transmitter signal is a composite of at least 4 and as many as 42

different channels depending on interference and the Rho of the mobiles. Rho is a

figure of merit for specifying: percentage of transmitted power that correlates to the

ideal code.