Scrambling Codes

o# possible D/L scrambling codes = 2  

-1 = 262143

oScrambling codes divided  into 512 

sets

n1 primary scrambling code and 15 

secondary scrambling codes

nSo, there are 512 x 16 = 8192 codes

oEach cell is allocated one and only 

primary scrambling code

nThe primary CCPCH (Common Control 

Physical CHannel)  is Tx always using 

this primary scrambling code

nOther D/L physical channels can be Tx 

with either the PSC or SSC from the set 

associated with the PSC of the cell

CELL SEARCH PROCEDURE

During the cell search, the UE searches for a cell and 

determines the downlink scrambling code and frame 

synchronisation of that cell.

The cell search is typically carried out in three steps:

Step 1:

Slot synchronisation

During the first step of the cell search procedure the UE uses the

SCH's primary synchronisation code

to acquire slot synchronisation to a cell.

This is typically done with a single matched

filter (or any similar device) matched to the

primary synchronisation code which is

common to all cells. 

Step 2:

Frame synchronisation and code-group 

identification

During the second step of the cell search procedure, the 

UE uses the

SCH's secondary synchronisation code to find frame 

synchronisation and identify the code group of the cell 

found in the first step. 

This is done by correlating the received signal

with all possible secondary synchronisation code

sequences, and identifying the maximum

correlation value.

Step 3:

Scrambling-code identification

During the third and last step of the cell search procedure, the UE determines the exact primary scrambling code used by the found cell.

After the primary scrambling code has been identified,

the Primary CCPCH can be detected and the system- 

and

cell specific BCH information can be read.