Pilot Channel PN Assignment

The pilot channel carries no data, but it is used by the subscriber unit to
acquire the system and assist in the process of soft handoffs, synchronization,
and channel estimation. A separate pilot channel is transmitted for
each sector of the cell site. The pilot channel is uniquely identified by its PN
offset or rather its PN short code that is used.
The PN sequence has some 32,768 chips that, when divided by 64, result
in a total of 512 possible PN codes that are available for use. The fact that
512 potential PN short codes to pick from almost ensures that no problems
will be associated with the assignment of these PN codes. However, some simple rules must be followed in order to ensure that no problems are
encountered with the selection of the PN codes for the cell and its surrounding
cell sites.

Numerous perturbations exist for how to set the PN codes, but it is suggested
that a reuse pattern be established for allocating the PN codes. The
rational behind the establishment of a reuse pattern lies in the fact that it
will facilitate the operation of the network for maintenance and growth. In
addition, when adding a second carrier, the same PN code should be used
for that sector.
Table 3-8 can be used for establishing the PN codes for any cell site in the
network. The method that should be used is to determine whether you want
to have a 4, 7 ,9, or 19 reuse pattern for the PN codes.
The suggested PN reuse pattern is an N  19 pattern for a new PCS system,
as shown in Figure 3-32. If you are overlaying the CDMA system on to a cellular system, an N  14 pattern should be used when the analog system
utilizes an N  7 voice channel reuse pattern.
Please note that not all the codes have been utilized in the N 19 pattern.
The remaining codes should be left in reserve for use when a PN code problem
arises. In addition, a PN_INC value of 6 is also recommended for use.

The PN short code used by the pilot is an increment of 64 from the other
PN codes and an offset value is defined. The Pilot_INC is the value that is
used to determine the amount of chips or rather the phase shift that one
pilot has versus another pilot.
The method that is used for calculating the PN offset is using the equations
in the following example.

Pilot_INC is valid from the range of 0 to 15. Pilot_INC is the PN
sequence offset index and is a multiple of 64 chips. The subscriber unit uses
the Pilot_INC to determine which are the valid pilots to be scanned.
Included in the example is a simple table that can be used to determine the
Pilot_INC as a function of the distance between reusing sites.