Hence these codes are split up into groups; there are 64 scrambling code groups, where each
group consists of 8 primary scrambling codes. It would be beneficial to reduce the search candidates,
in order to speed up the cell search time.
In an effort to provide a strategy for the UE to be able to efficiently search the nearest cell??™s primary
scrambling code, the three-step method was introduced [21??“23]. The first step is aimed at determining
the time slot synchronization of the strongest (possibly nearest) NodeB. This is accomplished
by detecting the P-SCH, since it is a Golay sequence repeated every time slot. The same P-SCH code
is used for all NodeBs.
Once time slot synchronization is obtained, we can proceed to Step 2. Here frame synchronization
is achieved by detecting the S-SCH. Recall the S-SCH transmits a different synch code every time
slot which can be used to determine where the UE is with respect to the frame boundary. The SCH
codes are constructed such that their cyclic shifts are unique. By this, we mean a nonzero cyclic shift
less than 15 of any of the SCH codes is not the same as some cyclic shift of any other SCH codes. The
sequence of the S-SCH codes is used to encode the 64 scrambling code groups mentioned earlier.
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