STRICTLY CONFIDENTIALMarch, 2006

SCRAMBLING CODE PLANNING STRATEGY

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Scrambling Code Planning StrategyScrambling Code Groups

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Scrambling Code Group

Scra

mbl

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Scrambling Code Planning StrategyCell search procedure, synchronisation time and battery life

Stage 3 requires more processing complexity since the CPICH is spread over the entire timeslot length (P-SCH and S-SCH are only transmitted in the first 10% portion of each slot).

Cell_DCH state synchronisation is the main concern (the process is simplified since UE knows which scrambling codes to look for).

Trade-off between the number of operations that the handset is required to perform (impacts battery life) and acquisition time:

Processing complexity depends on number and length of correlations that the UE needs to perform. Correlations in Stage 2 are shorter than in stage 3.

Acquisition time depends on number of errors in stages 2 and 3. When an error occurs UE will have to attempt synchronisation again. Stage 3 error probabilities are lower than stage 2.

Stage 1 Slot Synchronisation

Stage 2 Frame Synchronisation & Group Detection

Stage 3 Scrambling Code Identification

(P-SCH)

(S-SCH)

(CPICH)

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Scrambling Code Planning StrategyFrame and slot structures for CPICH, P-SCH and S-SCH

P–SCH

S–SCH

CPICH

1 Time Slot = 0.67ms, 2560 chips

1 Frame = 10ms

0.067ms, 256 chips

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Scrambling Code Planning StrategyStrategy background

Battery life is an important issue in UMTS due to the complexity of the technology. Use of UE battery should be optimised to lengthen the active life of the handset and improve user perception and potential revenues.

Neighbour cell scrambling codes can be distributed in different ways that can modify the number of operations required and the error probabilities in stages 2 and 3 of the synchronisation process. Two extreme planning strategies would be:

Each neighbour cell belongs to a different code group. Stage 2 of the synchronisation process will identify the cell almost completely and stage 3 will only confirm that the cell detected uses the expected scrambling code (the network provides information about the neighbour cell codes while in Cell_DCH state). Lowest number of operations required to acquire synchronisation (lowest battery consumption).

All neighbour cells belong to the same code group. Stage 2 will merely provide frame synchronisation and therefore stage 3 will have to correlate with all possible codes to identify the cell. Lowest probability of error in synchronisation process (lowest time to acquire synchronisation).

Simulations show that scrambling code plans using between 2 and 4 codes per group provide good complexity properties without major increase in synchronisation time.

Using the same scrambling code group in all the sectors of each base station will ensure that the neighbour list will contain in most of the cases 2 or 3 codes per group.

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Scrambling code groups allocated as follows:Group 0 (SC 0–7): reserved for temporary use such as test, integration and special events;

Groups 1 to 50 (SC 8–407): available for normal planning purposes;

Group 51 (SC 408–415): used for in-building cells;

Groups 52 to 63 (SC 416–511): reserved for future growth.

Sectors of the same site use the first codes of each group.

Neighbour sites should be assigned scrambling codes from different groups.

Strategy aims at providing neighbour lists containing between 2 and 4 codes per scrambling code group, minimizing the number of operations the UE needs to perform in the cell search procedure and saving battery life.

Synchronisation times achieved are also acceptable from a network operation point of view.

2-sector sites where a new sector might be installed in the future should be assigned 3 scrambling codes (1 unused – for future sector).

Scrambling Code Planning StrategyStrategy description

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