wcdma scrambling code planning guide 2002

wcdma scrambling code planning guide 2002

1. 1 © NOKIA FILENAMs.PPT/ DATE / NN
COMPANY CONFIDENTIAL
Guide for DL Primary Scrambling
Code Planning
in 3G Radio Network

2. 2 © NOKIA FILENAMs.PPT/ DATE / NN
COMPANY CONFIDENTIAL
General
•Downlink Primary Scrambling code planning is part of Network
Planning activities
•DL code allocation is not done by system itself like UL code
•DL Primary Scrambling code info is needed for cell search
procedure in UE & in frame syncronization
•search step 1: slot syncronisation to a cell
•search step 2: frame syncronisation & code group identification
•search step 2: scrambling code identification
•Scrambling code Info is needed during
•call set up
•handover
•Codes are divided to Primary and secondary Scrambling codes
•Each cell is allocated one and only one primary scrambling code.
The primary CCPCH, primary CPICH, PICH, AICH and S-CCPCH
carrying PCH are always transmitted using the primary
scrambling code.
Most Important
step !

3. 3 © NOKIA FILENAMs.PPT/ DATE / NN
COMPANY CONFIDENTIAL
Code Specification & Parameters
•The primary scrambling codes consist of i=0…511 different
scrambling codes, the real code generate in system is 16*i (not
for secondary scrambling codes)
•Codes are seen differently for user compared to real RNC
implementation (see the picture in next page)
•The set of primary scrambling codes is further divided into 64
primary scrambling code groups, each consisting of 8 primary
scrambling codes. The j:th scrambling code group consists of
primary scrambling codes 16*8*j+16*k, where j=0..63 and
k=0..7. (see the picture in next page)
•Parameter Dictionary info (serving cell)
•Parameter Name: Primary downlink scrambling code
•Appreviated Name: PriScrCode
•Range and step: 0…511, step 1
•Neighbour parameters: InterFreqNcellScrCode,
IntraFreqNcellScrCode

4. 4 © NOKIA FILENAMs.PPT/ DATE / NN
COMPANY CONFIDENTIAL
k/j 0 1 2… 63
0 0 128 256 8064
1 16 144 272 8080
2 32 160 288 8096
3 48 176 304 8112
4 64 192 320 8128
5 80 208 336 8144
6 96 224 352 8160
7 112 240 368 8176
Codes 0 1 2… 63
0 0 8 16 504
1 1 9 17 505
2 2 10 18 506
3 3 11 19 507
4 4 12 20 508
5 5 13 21 509
6 6 14 22 510
7 7 15 23 511
Primary Scrambling Codes
•Here is how
Primary Scrambling
codes are seen for
Planning Engineer
(i=0…511)
•Here are real
primary Scrambling
codes implemented
in RNC
One Code
Group
16*i relation

5. 5 © NOKIA FILENAMs.PPT/ DATE / NN
COMPANY CONFIDENTIAL
•The allocation of DL Primary Scrambling code in neighbouring cells
is possible in many ways (not all supported in NetAct WCDMA
Planner)
•Random code planning approach: Use any codes from any groups
•slow cell search algorithm, no need to plan
•Use codes from different code groups
•slow cell search algorithm, no tool support
•All 64 code groups could be used
•Recommended approach : Minimize the number of used code
groups
•fast cell search algorithm, relative easy to plan
•There must be large enough separation (minimum reuse)
between two cells using the same scrambling code
•Recommended minimum reuse 64
•The cell search algorithm between different mobile manufacturers is
likely to be different
•The performance depends on the reliability of the search procedure in cell
search step 2 and 3
•UE power consumption difference between the strategies is
negligible relative to all the other processing the UE has to do
Scrambling Code planning methods

6. 6 © NOKIA FILENAMs.PPT/ DATE / NN
COMPANY CONFIDENTIAL
Recommended Planning Approach
•What ?
•Scrambling code planning
•Why ?
•Fast and reliable handover to neighbouring cells
•Where ?
•In all environments (Urban, suburban, rural, highways)
•How ?
•Minimize the number of used code groups
•Use all codes from every group
•Make sure that the code reuse is 64 !!!
•Use neighboring codes in neighboring cells, repeat the
codes until all codes have been used (see next slide)

7. 7 © NOKIA FILENAMs.PPT/ DATE / NN
COMPANY CONFIDENTIAL
Recommended Approach - Example
•Area with 12 BTS(1+1+1) sites
•Assign the codes such that code
groups form georaphic cluster
of cells.
•Two code groups enough up to
15 neighbours
•For 12 sites 5 code groups
needed
•The code planning is
independent for each carrier
layer => same codes could be
used
•Cell search time increases when
the number of neighbours is
high e.q. in Urban area
6
7
20
1
2
0 24
2
3
8
16
4
1
7
2
6
25
3
18
5
1
9
9
22
21
12
1
1
10
15
1
4
13
2
7
2
9
2
8
3
0
3
1
3
2
3
3
3
4
3
5
IntraFreqNcell
ScrCode
UE
PriScrCode
Cluster of cells
having 2 code
groups

8. 8 © NOKIA FILENAMs.PPT/ DATE / NN
COMPANY CONFIDENTIAL
•Basic DL Primary Scrambling code planning support is in
NetAct WCDMA Planner 4.0 (E4 2/2002)
•Tool assigns scrambling code to all the cells having the same
carrier
•Assignment is based on pilot coverage
•In each pixel there is info about pilot power of the own cell
and pilot power of the interfering cells
•Same scrambling code should be avoided if cells are
interfering each others
•Calculation process:
•Code can be transferred to network (interface between
Planner and RAC radio access configurator)
NetAct WCDMA Planner 4.0 Support
Main Input:
 List of Carriers
 Number of Covering Cells
 Range of Scrambling Codes
Main calculation Data:
 Pilot Power
 existing Cell’s Scrambling
Code if any
 Pathloss
Main Output:
 Scrambling Code for each cell

9. 9 © NOKIA FILENAMs.PPT/ DATE / NN
COMPANY CONFIDENTIAL
Conclusion
•The RAN system is working with all code planning
approaches
• It has affect to the cell search algorithm (time)
•Recommended approach (in all neighbour sets in all
environments):
•Minimize the number of used code groups
•Maximise the number of codes per group
•Same scrambling code plan can be assigned to each carrier
layer
•Optimisation activity is required to optimise the size of the
neighbor sets (depends on the environment) ie. large
enough to include all useful candidates but as small as
possible to help the synchronisation process