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Cell search procedure

WCDMAasynchronous system

Goal of search process

Synchronize to the system

Demodulate PCCPCH (Primary Common

Control PHY Channel)

Procedure initiated every time thephone is turned on

Subdivided into four steps

Acquisition of slot synchronization

Acquisition of frame synchronization

Determination of the PrSC

Resolution of the PCCPCH TTI ambiguity (TTI =20ms)

If the acquired system is the home

systemend of the procedure

If the acquired system in not the home

systemprocedure may be restarted

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Note 1. To demodulate PCCPCH the UE

Needs to determine proper PrSC and

proper code offset

Note 2. There are 512 codes and 38400

possible offsetssize of search space is~ 20 million possibilities

Note 3. Four step process allows for quick

pruning of the search space

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Step 1TS synchronization

Accomplished through the search for P-SCH (Primary SynchronizationChannel)

P-SCH uses 256 bit long code at the beginning of each time slot

Each TS is 0.67ms (15 TS make 10ms frame)

All cells (Node Bs) in the network use the same P-SCH code

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P-SCH radio frame

UE may receive P-SCH

from multiple cells

It will key on the

strongest one

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Step 3: PrSC identification

There are 512 PrSC arranged in 64 groups with 8 codes in each group

S-SCH points to one of 64 groups reducing the search to 8 PrSC candidates

PrSC is 38400 long and it is aligned with the beginning of the radio frame

By convolving single radio frame with 8 possible candidates, the mobile determinesPrSC of the cell

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PrSC establishes the cell

identity. Once mobile

determines the PrSC it can

decode the information

associated with a given cell

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Step 4: Decoding of PCCPCH

Broadcast channel (BCH) is sent over PCCPCH in 20 ms TTI

BCH aligned with beginning of every other frame

Mobile determines the beginning if PCCPCH through simple CRC checks

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Once PCCPCH is decoded, the mobile has acquired the system and it may register

Note: BCH is the only transport channel mapped to PCCPCH