Pilot PN Codes and PN Offsets
Definition: The Pseudo-random Noise (PN) codes used to spread all the signal transmitted from a given base station.
Note: There are actually two pilot PN codes used to spread the base-to-mobile forward-link channels. One PN code is used in the "in-phase" arm or element and a second PN code is used in the "quadrature" element of a Quadrature Phase Shift Keying (QPSK) spreading circuit as depicted in the figure below.
Pilot PN Codes and PN Offsets
Application: The pilot PN code generators use 15 stage linear shift registers and extra circuitry to generate two augmented PN code which have a period of exactly 215 or 32,768 chips. These codes are each offset by an integer multiple of 64 chips. The 64-chip intervals between offsets allows 32,768/64 or 512 offsets. One of the possible 512 pilot offsets is assigned to each base station and allows the mobiles to identify that base station by its offset.
The zero offset pilot produces the 15th zero, the zero added to increase the PN period to exactly 215, every even numbered second in GPS time. The nth offset produces this 15th zero n times 64 chips after the zero offset does.
Pilot PN Codes and PN Offsets
Example: The pilot PN spreading circuit used in IS-95 is shown in the figure below. 
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