3grpess_annex2
DESCRIPTION
Initial Parameter Paning, 3G Nokia WCDMATRANSCRIPT
HSDPA BrainstormingTrainer notes on Annex 2
This optional module can be used for internal trainings or customized customer trainings, Extra time need to be allocated for this module if it is presented
If used, this module replaces the existing module 11. “Initial Parameter Planning”
For internals, it corresponds to chapters “Scrambling Code Planning”, “Neighbour List Planning” and “Location , Routing and Service Area Planning” in the 3G Radio Planning Guide.
Company Confidential
Initial Parameter Planning
Company Confidential
Scrambling Code Planning
Introduction
512 Primary scrambling codes are organised into 64 groups of 8
Each Primary scrambling code has 15 Secondary scrambling codes
Each Primary & Secondary scrambling code has left and right Alternate scrambling codes
Scrambling code planning refers to assigning the Primary scrambling codes
Each cell is assigned 1 Primary scrambling code
Scrambling code planning strategies can be defined that maximise the number of neighbours belonging to the same code group, or that maximise the number of neighbours that belong to different code groups
The difference between the two strategies remains unquantified in the field and is likely to depend upon UE implementation
Scrambling code planning requires co-ordination at international borders
Scrambling code planning can be completed independantly for each RF carrier
Scrambling code planning can be completed using a radio network planning tool or a home made tool
Scrambling code plan should account for future network expansion
Company Confidential
Air-Interface BCCH Synchronisation (I)
Search for Primary Synchronisation Channel (P-SCH)
Same chip sequence within every timeslot of every cell of every operator
Chip sequence has length of 256 chips
Provides slot synchronisation
CP
CP
CP
P-SCH
Step 1 is the same for all scrambling code planning strategies
Company Confidential
Air-Interface BCCH Synchronisation (II)
Different series of 15 chip sequences for each code group
Each chip sequence has a length of 256 chips
Select 1 out of 64 => relatively large probability of error
Relatively low UE processing requirement relative to step 3
Only necessary to identify 3 consecutive chip sequences to identify code group
Provides frame synchronisation and identifies Primary scrambling code group
Cs1
Cs2
Cs15
Cs1
Emphasis is placed on Step 2 if scrambling code plan maximises the number of neighbours with different scrambling code groups
Company Confidential
Air-Interface BCCH Synchronisation (III)
Select 1 out of 8 => relatively low probability of error
Relatively high UE processing requirement relative to step 2
Not necessary to correlate complete 38400 chip frame to identify scrambling code
CPICH
38400 Chips = 10 ms radio frame
Emphasis is placed on Step 3 if scrambling code plan maximises the number of neighbours with the same code group
Company Confidential
Example Strategy – with issues (I)
TCELL parameter defines the time offset between the P-SCH and S-SCH transmitted by different cells belonging to the same Node B
TCELL parameter usually defines time offsets of 0, 256 and 512 chips for the 3 cells belonging to a 1+1+1 Node B
Cs
Cs
Example Strategy – with issues (II)
If the scrambling code plan assigns codes belonging to the same code group to all cells belonging to the same RF carrier of a Node B then both the P-SCH and S-SCH are the same for all cells
In this case, TCELL could be set to 0 for all cells
This would allow UE to combine signals from multiple cells when in softer handover areas, i.e. the signal to noise ratio is improved and the decoding reliability improves
Cs
Cs
Cell 2
Cell 3
HOWEVER, in practise this strategy has issues and should not be used
some UE interpret the reception of a single P-SCH and S-SCH as meaning that there is only 1 scrambling code to identify instead of 3.
Company Confidential
* © Nokia Siemens Networks Presentation / Author / Date
Impact of Neighbour List Combining (I)
When a UE is in soft handover then the RNC combines the neighbour lists belonging to the active set cells
It is necessary that duplicate scrambling codes do not appear within those lists
Checks should be made to ensure that cells within potential active sets do not have different neighbours with the same scrambling code
Active Radiolink
Active Radiolink
Example scrambling code clash scenario 1
SC100
SC100
* © Nokia Siemens Networks Presentation / Author / Date
Impact of Neighbour List Combining (II)
Checks should be made to ensure that no cells are neighboured to two or more cells which have neighbour lists including the same scrambling code for different target cells
Active Radiolink
SC100
SC100
Company Confidential
Example Scrambling Code Plan
Area with 12 Node B
Strategy has been to minimise the number of code groups used in neighbouring cells
Two code groups enough up to 15 neighbours
6
7
20
1
2
0
24
23
8
10
4
17
11
25
3
18
5
19
9
22
21
15
14
13
IntraFreqNcell
ScrCode
UE
Recommendations
Isolation between cells assigned the same scrambling code should be maximised
isolation between cells assigned the same scrambling code sufficiently great to ensure that a UE never simultaneously receives the same scrambling code from more than 1 cell
isolation between cells assigned the same scrambling code sufficiently great to ensure that a UE never receives a scrambling code from one cell while expecting to receive the same scrambling code from second cell
Scrambling code planning should maximise the number of neighbours belonging to the same scrambling code group. But a different scrambling code strategy can be accepted as long as the operator is made aware of the theoretical trade-offs
Specific scrambling codes should be excluded from the plan to allow for future network expansion.
The same scrambling code plan should be assigned to each RF carrier
Scrambling code planning should be completed in conjunction with neighbour list planning
Scrambling code audits should be completed in combination with neighbour list audits
Checks should be made to ensure that no cells are neighboured to two or more cells which have neighbour lists including the same scrambling code for different target cells
Company Confidential
Neighbour List Planning
Introduction
Neighbour lists:
3G intra-frequency
3G inter-frequency
3G inter-system
2G inter-system
High quality neighbour lists are critical to the performance of the network
Neighbour lists are usually refined during pre-launch or post-launch optimisation
Neighbour list planning should be as accurate as possible
Impact upon pre-launch optimisation has to be recognised
Pre-launch optimisation often limited to specific drive route which may not identify all neighbours
Neighbour list tuning usually achieves the greatest gains during pre-launch optimisation
Optimisation tools based upon RNC logging can also be used to refine neighbour lists subsequent to launch
Company Confidential
3G Intra-Frequency Neigbour Lists
Intra-frequency neighbours are used for cell re-selection, soft handover, softer handover and intra-frequency hard handover
Missing neighbours result in unnecessarily poor signal to noise ratios
Excessive neighbours
may lead to important neighbours being deleted during soft handover
Intra-frequency neighbour lists are combined for both intra-RNC and inter-RNC soft handover (assuming inter-RNC soft handover is supported)
Intra-frequency neighbour lists are transmitted in SIB11 and dedicated measurement control messages
CPICH Ec/Io
Time
Missing neighbours can be identified from UE log files as a decrease in CPICH Ec/Io until connection drops and then cell selection allows sudden improvement
Example SC200 missing from neighbour list associated with SC100
UE movement
Company Confidential
Neighbour List Combining
Intra-Frequency Neighbours
When a UE is in soft handover then the neighbour lists belonging to each of the active set cells are combined
Not all vendors offer neighbour list combining
The RNC generates a new intra-frequency neighbour list after every active set update procedure (events 1a, 1b and 1c)
The RNC transmits the new intra-frequency neighbour list to the UE if the new list differs from the existing list
Active set cells
Neighbour cells which are common to three active set cells
Neighbour cells which are common to two active set cells
Neighbour cells which are defined for only one active set cell
Generating a combined intra-frequency neighbour list
Update
Parameters
WCELL
ADJS
WBTS
RNC
HOPS
100
32
RT
NRT
HSDPA
Structure of databuild
RAS05 ADJS parameters
3GPP allows the network to specify a maximum of 32 intra-frequency cells for the UE to measure
Serving cell + 31 Intra-frequency neighbours when not in soft handover
2-3 serving cells + 30-29 neighbours in soft handover
Size of SIB11 can limit the number of neighbours for cell re-selection
Company Confidential
3G Inter-Frequency Neigbour Lists
Inter-frequency neighbours are used for inter-frequency cell re-selection and inter-frequency handover
The Nokia RNC allows a maximum of 48 inter-frequency neighbours to be defined with a maximum of 32 on any one RF carrier
3GPP specifies that a max. of 32 inter-frequency neighbours can be broadcast in SIB11
Nokia does not support
inter-frequency handover from CELL_FACH
inter-frequency handover while anchoring an RNC
The Nokia RNC instructs the UE to measure neighbours from one RF carrier at a time for inter-frequency hard handover
UE in CELL_DCH are only informed of Inter-Frequency Neighbours when necessary
Excessive neighbours
may lead to important neighbours being deleted during soft handover
Inter-frequency neighbours are usually introduced after the network has been launched and so refining them is usually a post launch optimisation task
Company Confidential
Neighbour List Combining
Inter-Frequency Neighbours
When a UE is in intra-RNC soft handover then the neighbour lists belonging to each of the active set cells are combined
Neighbour lists are not combined for inter-RNC soft handover because the Nokia RNC does not support inter-frequency neighbour signalling across the Iur
Not all vendors offer neighbour list combining
Neighbour lists are not updated once compressed mode measurements have begun, i.e. inter-frequency neighbour lists are dependant upon the active set cells when inter-frequency handover is triggered
Neighbour cells which are common to three active set cells
Neighbour cells which are common to two active set cells
Neighbour cells which are defined for only one active set cell
Generating a combined inter-frequency neighbour list
Inter-Frequency Neighbour List
Parameters
WCELL
ADJI
WBTS
RNC
HOPI
100
48
RT
NRT
Structure of databuild
RAS05 ADJI parameters
Size of SIB11 can limit the number of neighbours for cell re-selection
Company Confidential
3G Inter-System Neigbour Lists
GSM neighbours are used for inter-system cell re-selection and inter-system handover
3GPP specifications allow a maximum of 32 inter-system neighbours to be defined
Inter-system neighbours are broadcast in SIB11 for cell re-selection and are transmitted in dedicated measurement control messages for inter-system handover
Nokia does not support
inter-system handover from CELL_FACH
inter-system handover while anchoring an RNC
The Nokia RNC instructs the UE to measure all GSM neighbours for RSSI measurements but one specific neighbour for BSIC verification
Excessive neighbours
may lead to important neighbours being deleted during soft handover
GSM neighbour lists can be based upon existing BSC 2G neighbour lists when sites are co-sited
If an operator has both GSM900 and DCS1800 networks then it is possible to define inter-system neighbours only for the GSM900 layer or only for the DCS1800 layer
Company Confidential
Neighbour List Combining
Inter-System Neighbours
When a UE is in intra-RNC soft handover then the neighbour lists belonging to each of the active set cells are combined
Neighbour lists are not combined for inter-RNC soft handover because the Nokia RNC does not support inter-system neighbour signalling across the Iur
Not all vendors offer neighbour list combining
Neighbour lists are not updated once compressed mode has begun, i.e. inter-system neighbour lists are dependant upon the active set cells when inter-system handover is triggered
Neighbour cells which are common to three active set cells
Neighbour cells which are common to two active set cells
Neighbour cells which are defined for only one active set cell
Generating a combined inter-system neighbour list
Inter-System Neighbour List
Parameters
WCELL
ADJG
WBTS
RNC
HOPG
100
32
RT
NRT
Structure of databuild
RAS05 ADJG parameters
Size of SIB11 can limit the number of neighbours for cell re-selection
Company Confidential
Maximum Neighbour List Lengths (I)
SIB11 is used to instruct UE which cells to measure in RRC Idle, CELL_FACH and CELL_PCH
TS25.331 includes a contradiction made by 3GPP, i.e. SIB11 should be able to accommodate information regarding 96 cells, but SIB11 cannot exceed 3552 bits and this is insufficient to accommodate information regarding 96 cells
If a Nokia RNC is configured with a cell which is configured with more neighbours than SIB11 can accommodate then the cell is blocked and an alarm is raised
Nokia has issued RNC Technical Note 46 to specify that when Hierarchical Cell Structure is disabled, a maximum of 47 cells should be configured. This is a worst case figure and in general more cells can be included
Maximum Size of SIB 11
Adjs
Adji
Adjg
Company Confidential
Maximum Neighbour List Lengths (II)
The size of SIB11 can be estimated from the number of intra-frequency, inter-frequency and inter-system neighbours
The quantity of data associated with each neighbour can vary depending upon which information elements are included
Example for intra-frequency neighbours
Maximum Neighbour List Lengths (III)
Expression can be generated to identify whether or not a particular combination of neighbours is likely to exceed the capacity of SIB11
RAS05 includes parameters ADJS, ADJI and ADJG parameters:
AdjsSIB
AdjiSIB
AdjgSIB
These parameters allow larger neighbour lists to be defined for CELL_DCH by specifying whether or not specific neighbours should be included in SIB11
Company Confidential
2G Inter-System Neigbour Lists (I)
BSC inter-system neighbours are used for inter-system cell re-selection and inter-system handover
Nokia’s implementation of the BSS allows the definition of 32 UMTS FDD neighbours
The definition of 3G neighbours has an impact upon the maximum number of GSM neighbours which can be defined within the BSC
Without 3G neighbours
With 3G neighbours
Without common BCCH
With common BCCH
2G Inter-System Neigbour Lists (II)
When a UE is in GSM idle mode, GPRS packet idle mode or GPRS packet transfer mode then it reads the 3G neighbour list from SI2quater and PSI3quater system information messages
When a UE is in GSM connected mode then it reads the 3G neighbour list from measurement information messages which are sent on the SACCH
The length of a single SI2quater message is not sufficient to accommodate 32 inter-system neighbours
A single SI2quater message is able to accommodate 10 3G neighbours. This means that it is beneficial if 3G neighbour lists can be limited to a length of 10
If multiple SI2quater messages are required then the UE must wait until it has received the complete set before it is able to make a cell re-selection decision
If neighbours are missing then UE may fail inter-system handovers and may remain on the GSM system longer than necessary
If 3G sites are co-sited with 2G sites then 3G neighbour lists configured within the BSC can be based upon the existing 2G neighbour lists
Company Confidential
Typical Neighbour List Lengths
Some examples
Company Confidential
Introduction
Location Areas (LA) and Routing Areas (RA) are used by the core network to track the location of a UE
LA are used by the CS domain whereas RA are used by the PS domain
Each core network service domain has its own independent state machine for each UE
The main CS service states are CS-DETACHED, CS-IDLE and CS-CONNECTED
The main PS service states are PS-DETACHED, PS-IDLE and PS-CONNECTED
UE Non-Access Stratum
LA and RA are handled by the Non-Access Stratum layer within the UE and core network
Not registered
Node B
Access Stratum
Non-Access Stratum
Company Confidential
Location Areas
A UE in CS IDLE state does not have to update the CS core of its location when moving within a LA
a LA consists of cells belonging to one or more RNCs that are connected to the same CN node, i.e. one MSC/VLR
The minimum size of a Location Area (LA) is a single cell
The maximum size of a LA is the collection of cells connected to a single VLR
The mapping between a LA and its associated RNCs is handled by the MSC/VLR
The mapping between a LA and its cells is handled by the RNC
A LA is identified globally using a Location Area Identification (LAI)
The LAI is a concatenation of the Mobile Country Code (MCC), Mobile Network Code (MNC) and Location Area Code (LAC)
2 Bytes => 65336 values
00 00 and FF FE values are reserved
Company Confidential
Routing Areas
A UE in PS IDLE state does not have to update the PS core of its location when moving within a RA
a RA consists of cells belonging to one or more RNCs that are connected to the same CN node, i.e. one SGSN
The minimum size of a Routing Area is a single cell
A RA is always contained within a single LA
it is possible for RA and LA to be defined to be equal
The mapping between a RA and its associated RNCs is handled by the SGSN
The mapping between a RA and its cells is handled by the RNC
A RA is identified globally using a Routing Area Identification (RAI)
The RAI is a concatenation of the LAI and the Routing Area Code (RAC)
1 Byte => 256 values
Company Confidential
Paging Channel
Transport Block Size =
(equation from TS 25.331)
Maximum Transport Block Set Size = 1 * 80 = 80 bits
Nokia RAN provides an 8 kbps PCH transport channel on the S-CCPCH
8 kbps is sufficient to include a single paging record per 10 ms
A single cell can thus page 100 UE per second
S-CCPCH can be shared with the FACH-c and FACH-u but PCH always has priority
Paging completed over either a Location Area, Routing Area, RNC or Cell
Utilisation of paging capacity is maximised when paging is completed over a Cell
URA_PCH RRC state not currently supported and so paging does not occur over a URA
Company Confidential
Strategies (I)
Small LA/RA
Improves paging capacity because each IDLE state paging message is broadcast by fewer cells
Increase in network signalling due to increased quantity of updates resulting from mobility
Potential decrease in mobile terminated connection establishment success rate
(Potential decrease in mobile originated connection establishment success rate)
LA and RA can be planned to be relatively large while levels of traffic are not too great
Acceptable to plan location area across multiple RNC
Generates paging per RNC for UE which are in RRC Connected Mode
LA and RA commonly planned to be of equal size
Cell
Strategies (II)
Possible to plan 2G and 3G networks using the LAI and RAI
Requires unique 2G and 3G Cell Identities (CI)
Cell Global Identification (CGI) defined by
core network is not able to distinguish between the two networks for paging purposes and both 2G and 3G paging appears on both the 2G and 3G networks
less chance of a UE missing a paging message when it is completing inter-system cell re-selection
increased quantity of paging on both systems and a requirement to co-ordinate cell identities. In practice it may be difficult to implement the same location areas for 2G and 3G as a result of them not having the same coverage areas and not all sites being co-sited
CGI must be unique
Strategies (III)
LA and RA boundaries used for the 2G system are likely to be relatively mature and may have already been optimised in terms of their locations
This means that they provide a good starting point for the definition of 3G LA and RA boundaries.
LA and RA boundaries should not run close to and parallel to major roads nor railways otherwise there is a risk of relatively large numbers of updates.
Likewise, boundaries should not traverse dense subscriber areas
Cells which are located at a LA or RA boundary and which experience large numbers of updates should be monitored to evaluate the impact of the update procedures.
It is only necessary to decrease the size of a RA area relative to a LA if there is a large quantity of paging from the PS service domain
LA and RA boundaries should be accounted for during the cluster identification task associated with pre-launch optimisation
Clusters should be defined such that LA and RA boundaries are crossed during drive tests. This helps to verify that the update procedures are successful and do not have a significant impact upon services
Company Confidential
Service Areas
A Service Area (SA) is identified globally using its Service Area Identifier (SAI)
The SAI is a concatenation of
MCC + MNC + LAC + Service Area Code (SAC)
Service areas are used for emergency service calls
The SAC can be configured on a per cell basis with a value equal to the cell identity (CI). This helps to simplify system design
RAN04 introduces the Service Area Broadcast (SAB) feature which makes use of a third S-CCPCH and Service Area Codes for SAB (SACB)
A specific SAC can be assigned to multiple cells within a location area whereas a SACB must be unique for each cell within a location area.
AdjsQoffset1 or
AdjsQoffset2 included
CPICH transmit
power included
Both
No
Neither
Yes
averag
This optional module can be used for internal trainings or customized customer trainings, Extra time need to be allocated for this module if it is presented
If used, this module replaces the existing module 11. “Initial Parameter Planning”
For internals, it corresponds to chapters “Scrambling Code Planning”, “Neighbour List Planning” and “Location , Routing and Service Area Planning” in the 3G Radio Planning Guide.
Company Confidential
Initial Parameter Planning
Company Confidential
Scrambling Code Planning
Introduction
512 Primary scrambling codes are organised into 64 groups of 8
Each Primary scrambling code has 15 Secondary scrambling codes
Each Primary & Secondary scrambling code has left and right Alternate scrambling codes
Scrambling code planning refers to assigning the Primary scrambling codes
Each cell is assigned 1 Primary scrambling code
Scrambling code planning strategies can be defined that maximise the number of neighbours belonging to the same code group, or that maximise the number of neighbours that belong to different code groups
The difference between the two strategies remains unquantified in the field and is likely to depend upon UE implementation
Scrambling code planning requires co-ordination at international borders
Scrambling code planning can be completed independantly for each RF carrier
Scrambling code planning can be completed using a radio network planning tool or a home made tool
Scrambling code plan should account for future network expansion
Company Confidential
Air-Interface BCCH Synchronisation (I)
Search for Primary Synchronisation Channel (P-SCH)
Same chip sequence within every timeslot of every cell of every operator
Chip sequence has length of 256 chips
Provides slot synchronisation
CP
CP
CP
P-SCH
Step 1 is the same for all scrambling code planning strategies
Company Confidential
Air-Interface BCCH Synchronisation (II)
Different series of 15 chip sequences for each code group
Each chip sequence has a length of 256 chips
Select 1 out of 64 => relatively large probability of error
Relatively low UE processing requirement relative to step 3
Only necessary to identify 3 consecutive chip sequences to identify code group
Provides frame synchronisation and identifies Primary scrambling code group
Cs1
Cs2
Cs15
Cs1
Emphasis is placed on Step 2 if scrambling code plan maximises the number of neighbours with different scrambling code groups
Company Confidential
Air-Interface BCCH Synchronisation (III)
Select 1 out of 8 => relatively low probability of error
Relatively high UE processing requirement relative to step 2
Not necessary to correlate complete 38400 chip frame to identify scrambling code
CPICH
38400 Chips = 10 ms radio frame
Emphasis is placed on Step 3 if scrambling code plan maximises the number of neighbours with the same code group
Company Confidential
Example Strategy – with issues (I)
TCELL parameter defines the time offset between the P-SCH and S-SCH transmitted by different cells belonging to the same Node B
TCELL parameter usually defines time offsets of 0, 256 and 512 chips for the 3 cells belonging to a 1+1+1 Node B
Cs
Cs
Example Strategy – with issues (II)
If the scrambling code plan assigns codes belonging to the same code group to all cells belonging to the same RF carrier of a Node B then both the P-SCH and S-SCH are the same for all cells
In this case, TCELL could be set to 0 for all cells
This would allow UE to combine signals from multiple cells when in softer handover areas, i.e. the signal to noise ratio is improved and the decoding reliability improves
Cs
Cs
Cell 2
Cell 3
HOWEVER, in practise this strategy has issues and should not be used
some UE interpret the reception of a single P-SCH and S-SCH as meaning that there is only 1 scrambling code to identify instead of 3.
Company Confidential
* © Nokia Siemens Networks Presentation / Author / Date
Impact of Neighbour List Combining (I)
When a UE is in soft handover then the RNC combines the neighbour lists belonging to the active set cells
It is necessary that duplicate scrambling codes do not appear within those lists
Checks should be made to ensure that cells within potential active sets do not have different neighbours with the same scrambling code
Active Radiolink
Active Radiolink
Example scrambling code clash scenario 1
SC100
SC100
* © Nokia Siemens Networks Presentation / Author / Date
Impact of Neighbour List Combining (II)
Checks should be made to ensure that no cells are neighboured to two or more cells which have neighbour lists including the same scrambling code for different target cells
Active Radiolink
SC100
SC100
Company Confidential
Example Scrambling Code Plan
Area with 12 Node B
Strategy has been to minimise the number of code groups used in neighbouring cells
Two code groups enough up to 15 neighbours
6
7
20
1
2
0
24
23
8
10
4
17
11
25
3
18
5
19
9
22
21
15
14
13
IntraFreqNcell
ScrCode
UE
Recommendations
Isolation between cells assigned the same scrambling code should be maximised
isolation between cells assigned the same scrambling code sufficiently great to ensure that a UE never simultaneously receives the same scrambling code from more than 1 cell
isolation between cells assigned the same scrambling code sufficiently great to ensure that a UE never receives a scrambling code from one cell while expecting to receive the same scrambling code from second cell
Scrambling code planning should maximise the number of neighbours belonging to the same scrambling code group. But a different scrambling code strategy can be accepted as long as the operator is made aware of the theoretical trade-offs
Specific scrambling codes should be excluded from the plan to allow for future network expansion.
The same scrambling code plan should be assigned to each RF carrier
Scrambling code planning should be completed in conjunction with neighbour list planning
Scrambling code audits should be completed in combination with neighbour list audits
Checks should be made to ensure that no cells are neighboured to two or more cells which have neighbour lists including the same scrambling code for different target cells
Company Confidential
Neighbour List Planning
Introduction
Neighbour lists:
3G intra-frequency
3G inter-frequency
3G inter-system
2G inter-system
High quality neighbour lists are critical to the performance of the network
Neighbour lists are usually refined during pre-launch or post-launch optimisation
Neighbour list planning should be as accurate as possible
Impact upon pre-launch optimisation has to be recognised
Pre-launch optimisation often limited to specific drive route which may not identify all neighbours
Neighbour list tuning usually achieves the greatest gains during pre-launch optimisation
Optimisation tools based upon RNC logging can also be used to refine neighbour lists subsequent to launch
Company Confidential
3G Intra-Frequency Neigbour Lists
Intra-frequency neighbours are used for cell re-selection, soft handover, softer handover and intra-frequency hard handover
Missing neighbours result in unnecessarily poor signal to noise ratios
Excessive neighbours
may lead to important neighbours being deleted during soft handover
Intra-frequency neighbour lists are combined for both intra-RNC and inter-RNC soft handover (assuming inter-RNC soft handover is supported)
Intra-frequency neighbour lists are transmitted in SIB11 and dedicated measurement control messages
CPICH Ec/Io
Time
Missing neighbours can be identified from UE log files as a decrease in CPICH Ec/Io until connection drops and then cell selection allows sudden improvement
Example SC200 missing from neighbour list associated with SC100
UE movement
Company Confidential
Neighbour List Combining
Intra-Frequency Neighbours
When a UE is in soft handover then the neighbour lists belonging to each of the active set cells are combined
Not all vendors offer neighbour list combining
The RNC generates a new intra-frequency neighbour list after every active set update procedure (events 1a, 1b and 1c)
The RNC transmits the new intra-frequency neighbour list to the UE if the new list differs from the existing list
Active set cells
Neighbour cells which are common to three active set cells
Neighbour cells which are common to two active set cells
Neighbour cells which are defined for only one active set cell
Generating a combined intra-frequency neighbour list
Update
Parameters
WCELL
ADJS
WBTS
RNC
HOPS
100
32
RT
NRT
HSDPA
Structure of databuild
RAS05 ADJS parameters
3GPP allows the network to specify a maximum of 32 intra-frequency cells for the UE to measure
Serving cell + 31 Intra-frequency neighbours when not in soft handover
2-3 serving cells + 30-29 neighbours in soft handover
Size of SIB11 can limit the number of neighbours for cell re-selection
Company Confidential
3G Inter-Frequency Neigbour Lists
Inter-frequency neighbours are used for inter-frequency cell re-selection and inter-frequency handover
The Nokia RNC allows a maximum of 48 inter-frequency neighbours to be defined with a maximum of 32 on any one RF carrier
3GPP specifies that a max. of 32 inter-frequency neighbours can be broadcast in SIB11
Nokia does not support
inter-frequency handover from CELL_FACH
inter-frequency handover while anchoring an RNC
The Nokia RNC instructs the UE to measure neighbours from one RF carrier at a time for inter-frequency hard handover
UE in CELL_DCH are only informed of Inter-Frequency Neighbours when necessary
Excessive neighbours
may lead to important neighbours being deleted during soft handover
Inter-frequency neighbours are usually introduced after the network has been launched and so refining them is usually a post launch optimisation task
Company Confidential
Neighbour List Combining
Inter-Frequency Neighbours
When a UE is in intra-RNC soft handover then the neighbour lists belonging to each of the active set cells are combined
Neighbour lists are not combined for inter-RNC soft handover because the Nokia RNC does not support inter-frequency neighbour signalling across the Iur
Not all vendors offer neighbour list combining
Neighbour lists are not updated once compressed mode measurements have begun, i.e. inter-frequency neighbour lists are dependant upon the active set cells when inter-frequency handover is triggered
Neighbour cells which are common to three active set cells
Neighbour cells which are common to two active set cells
Neighbour cells which are defined for only one active set cell
Generating a combined inter-frequency neighbour list
Inter-Frequency Neighbour List
Parameters
WCELL
ADJI
WBTS
RNC
HOPI
100
48
RT
NRT
Structure of databuild
RAS05 ADJI parameters
Size of SIB11 can limit the number of neighbours for cell re-selection
Company Confidential
3G Inter-System Neigbour Lists
GSM neighbours are used for inter-system cell re-selection and inter-system handover
3GPP specifications allow a maximum of 32 inter-system neighbours to be defined
Inter-system neighbours are broadcast in SIB11 for cell re-selection and are transmitted in dedicated measurement control messages for inter-system handover
Nokia does not support
inter-system handover from CELL_FACH
inter-system handover while anchoring an RNC
The Nokia RNC instructs the UE to measure all GSM neighbours for RSSI measurements but one specific neighbour for BSIC verification
Excessive neighbours
may lead to important neighbours being deleted during soft handover
GSM neighbour lists can be based upon existing BSC 2G neighbour lists when sites are co-sited
If an operator has both GSM900 and DCS1800 networks then it is possible to define inter-system neighbours only for the GSM900 layer or only for the DCS1800 layer
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Neighbour List Combining
Inter-System Neighbours
When a UE is in intra-RNC soft handover then the neighbour lists belonging to each of the active set cells are combined
Neighbour lists are not combined for inter-RNC soft handover because the Nokia RNC does not support inter-system neighbour signalling across the Iur
Not all vendors offer neighbour list combining
Neighbour lists are not updated once compressed mode has begun, i.e. inter-system neighbour lists are dependant upon the active set cells when inter-system handover is triggered
Neighbour cells which are common to three active set cells
Neighbour cells which are common to two active set cells
Neighbour cells which are defined for only one active set cell
Generating a combined inter-system neighbour list
Inter-System Neighbour List
Parameters
WCELL
ADJG
WBTS
RNC
HOPG
100
32
RT
NRT
Structure of databuild
RAS05 ADJG parameters
Size of SIB11 can limit the number of neighbours for cell re-selection
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Maximum Neighbour List Lengths (I)
SIB11 is used to instruct UE which cells to measure in RRC Idle, CELL_FACH and CELL_PCH
TS25.331 includes a contradiction made by 3GPP, i.e. SIB11 should be able to accommodate information regarding 96 cells, but SIB11 cannot exceed 3552 bits and this is insufficient to accommodate information regarding 96 cells
If a Nokia RNC is configured with a cell which is configured with more neighbours than SIB11 can accommodate then the cell is blocked and an alarm is raised
Nokia has issued RNC Technical Note 46 to specify that when Hierarchical Cell Structure is disabled, a maximum of 47 cells should be configured. This is a worst case figure and in general more cells can be included
Maximum Size of SIB 11
Adjs
Adji
Adjg
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Maximum Neighbour List Lengths (II)
The size of SIB11 can be estimated from the number of intra-frequency, inter-frequency and inter-system neighbours
The quantity of data associated with each neighbour can vary depending upon which information elements are included
Example for intra-frequency neighbours
Maximum Neighbour List Lengths (III)
Expression can be generated to identify whether or not a particular combination of neighbours is likely to exceed the capacity of SIB11
RAS05 includes parameters ADJS, ADJI and ADJG parameters:
AdjsSIB
AdjiSIB
AdjgSIB
These parameters allow larger neighbour lists to be defined for CELL_DCH by specifying whether or not specific neighbours should be included in SIB11
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2G Inter-System Neigbour Lists (I)
BSC inter-system neighbours are used for inter-system cell re-selection and inter-system handover
Nokia’s implementation of the BSS allows the definition of 32 UMTS FDD neighbours
The definition of 3G neighbours has an impact upon the maximum number of GSM neighbours which can be defined within the BSC
Without 3G neighbours
With 3G neighbours
Without common BCCH
With common BCCH
2G Inter-System Neigbour Lists (II)
When a UE is in GSM idle mode, GPRS packet idle mode or GPRS packet transfer mode then it reads the 3G neighbour list from SI2quater and PSI3quater system information messages
When a UE is in GSM connected mode then it reads the 3G neighbour list from measurement information messages which are sent on the SACCH
The length of a single SI2quater message is not sufficient to accommodate 32 inter-system neighbours
A single SI2quater message is able to accommodate 10 3G neighbours. This means that it is beneficial if 3G neighbour lists can be limited to a length of 10
If multiple SI2quater messages are required then the UE must wait until it has received the complete set before it is able to make a cell re-selection decision
If neighbours are missing then UE may fail inter-system handovers and may remain on the GSM system longer than necessary
If 3G sites are co-sited with 2G sites then 3G neighbour lists configured within the BSC can be based upon the existing 2G neighbour lists
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Typical Neighbour List Lengths
Some examples
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Introduction
Location Areas (LA) and Routing Areas (RA) are used by the core network to track the location of a UE
LA are used by the CS domain whereas RA are used by the PS domain
Each core network service domain has its own independent state machine for each UE
The main CS service states are CS-DETACHED, CS-IDLE and CS-CONNECTED
The main PS service states are PS-DETACHED, PS-IDLE and PS-CONNECTED
UE Non-Access Stratum
LA and RA are handled by the Non-Access Stratum layer within the UE and core network
Not registered
Node B
Access Stratum
Non-Access Stratum
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Location Areas
A UE in CS IDLE state does not have to update the CS core of its location when moving within a LA
a LA consists of cells belonging to one or more RNCs that are connected to the same CN node, i.e. one MSC/VLR
The minimum size of a Location Area (LA) is a single cell
The maximum size of a LA is the collection of cells connected to a single VLR
The mapping between a LA and its associated RNCs is handled by the MSC/VLR
The mapping between a LA and its cells is handled by the RNC
A LA is identified globally using a Location Area Identification (LAI)
The LAI is a concatenation of the Mobile Country Code (MCC), Mobile Network Code (MNC) and Location Area Code (LAC)
2 Bytes => 65336 values
00 00 and FF FE values are reserved
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Routing Areas
A UE in PS IDLE state does not have to update the PS core of its location when moving within a RA
a RA consists of cells belonging to one or more RNCs that are connected to the same CN node, i.e. one SGSN
The minimum size of a Routing Area is a single cell
A RA is always contained within a single LA
it is possible for RA and LA to be defined to be equal
The mapping between a RA and its associated RNCs is handled by the SGSN
The mapping between a RA and its cells is handled by the RNC
A RA is identified globally using a Routing Area Identification (RAI)
The RAI is a concatenation of the LAI and the Routing Area Code (RAC)
1 Byte => 256 values
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Paging Channel
Transport Block Size =
(equation from TS 25.331)
Maximum Transport Block Set Size = 1 * 80 = 80 bits
Nokia RAN provides an 8 kbps PCH transport channel on the S-CCPCH
8 kbps is sufficient to include a single paging record per 10 ms
A single cell can thus page 100 UE per second
S-CCPCH can be shared with the FACH-c and FACH-u but PCH always has priority
Paging completed over either a Location Area, Routing Area, RNC or Cell
Utilisation of paging capacity is maximised when paging is completed over a Cell
URA_PCH RRC state not currently supported and so paging does not occur over a URA
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Strategies (I)
Small LA/RA
Improves paging capacity because each IDLE state paging message is broadcast by fewer cells
Increase in network signalling due to increased quantity of updates resulting from mobility
Potential decrease in mobile terminated connection establishment success rate
(Potential decrease in mobile originated connection establishment success rate)
LA and RA can be planned to be relatively large while levels of traffic are not too great
Acceptable to plan location area across multiple RNC
Generates paging per RNC for UE which are in RRC Connected Mode
LA and RA commonly planned to be of equal size
Cell
Strategies (II)
Possible to plan 2G and 3G networks using the LAI and RAI
Requires unique 2G and 3G Cell Identities (CI)
Cell Global Identification (CGI) defined by
core network is not able to distinguish between the two networks for paging purposes and both 2G and 3G paging appears on both the 2G and 3G networks
less chance of a UE missing a paging message when it is completing inter-system cell re-selection
increased quantity of paging on both systems and a requirement to co-ordinate cell identities. In practice it may be difficult to implement the same location areas for 2G and 3G as a result of them not having the same coverage areas and not all sites being co-sited
CGI must be unique
Strategies (III)
LA and RA boundaries used for the 2G system are likely to be relatively mature and may have already been optimised in terms of their locations
This means that they provide a good starting point for the definition of 3G LA and RA boundaries.
LA and RA boundaries should not run close to and parallel to major roads nor railways otherwise there is a risk of relatively large numbers of updates.
Likewise, boundaries should not traverse dense subscriber areas
Cells which are located at a LA or RA boundary and which experience large numbers of updates should be monitored to evaluate the impact of the update procedures.
It is only necessary to decrease the size of a RA area relative to a LA if there is a large quantity of paging from the PS service domain
LA and RA boundaries should be accounted for during the cluster identification task associated with pre-launch optimisation
Clusters should be defined such that LA and RA boundaries are crossed during drive tests. This helps to verify that the update procedures are successful and do not have a significant impact upon services
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Service Areas
A Service Area (SA) is identified globally using its Service Area Identifier (SAI)
The SAI is a concatenation of
MCC + MNC + LAC + Service Area Code (SAC)
Service areas are used for emergency service calls
The SAC can be configured on a per cell basis with a value equal to the cell identity (CI). This helps to simplify system design
RAN04 introduces the Service Area Broadcast (SAB) feature which makes use of a third S-CCPCH and Service Area Codes for SAB (SACB)
A specific SAC can be assigned to multiple cells within a location area whereas a SACB must be unique for each cell within a location area.
AdjsQoffset1 or
AdjsQoffset2 included
CPICH transmit
power included
Both
No
Neither
Yes
averag