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HOME » 3G » HOW DOES A UE(MOBILE) DETECTS THE SCRAMBLING CODE OF THE CELL, WHEN IT IS SWITCHED ON?

How does a UE(mobile) detects theScrambling code of the cell, when it isswitched on?

When the UE(mobile phone) is switched on, it does not have any ide a regarding the Primary scrambling code that is

used in the cell and it is not having any synchronization with the net work.

Now lets have a look at how the UE gets the time slot synchronization and learns about Primary Scrambling code of 

the Cell.

When the UE is switched on, initially it will be trying to attain time slot synchronization. For that it will start listening to

Primary Synchronization Channel (P-SCH). The slot timing of the cell can be obtained by receiving the primary

synchronization channel (P-SCH) and detecting peaks in the output of a filter that is matched to this universal

synchronization code. This P-SCH is sent during the first 256 chips of every slot. the whole slot is 2560 chips long.

Thus the UE can identify when a time slot starts, i.e by decoding the first 256 chips, but still the UE cannot determine

the slot number and hence it doesn’t have an idea regarding the radio frame boundary also.In UMTS there are 15

time slots in each radio frame.Each radio frame is of 10ms duration.Thereafter the UE correlates the received signal from the secondary synchronization channel (S-SCH) with all

secondary synchronization codes (SSC), and identifies the maximum correlation value. The S-SCH is also only sent

during the first 256 chips of every slot. One SSC is sent in every time slot. There are 16 different SSCs, and they

can form 64 unique secondary SCH sequences. One sequence consists of 15 SSCs, and these sequences are

arranged in such a way that in any nonzero cyclic shift less than 15 of any of the 64 sequences is not equivalent to

some other sequence. This means that once the UE has identified 15 successive SSCs, it can determine the code

group used as well as the frame boundaries (i.e., frame synchronization).

But now also the UE doesn’t know the Primary scrambling code of the cell. But the UE knows the Scrambling code

group. Now the question could be what is a Scrambling code group?

There are 512 Primary scrambling codes available in downlink, and these are divided into 64 groups,.i.e 8

scrambling codes per group(512/8=64). Once the UE determines the scrambling code group, it starts picking -up

each scrambling codes and tried to decode the P-CPICH channel, and for one particular scrambling code , the UE

would be able to decode the channel properly. And the UE assumes this as the cell scrambling code.

 And later it starts decoding the P-CCPCH channel for understanding the SIB information.

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7/30/2019 How does a UE(mobile) detects the Scrambling code of the cell, when it is switched on_ « 3G And 4G Networks

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