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Using WNCS to Resolve Missing Neighbor Cells in an Ericsson UMTS System
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Using WNCS to Resolve Missing Neighbor
Cells in an Ericsson UMTS System
UMTS Performance Team
Central Region RF Planning and Engineering
2
Overview
Retainability performance has been poor in Ericsson UMTS
markets since P2 upgrade in early June, 2006.
There are many contributing issues, some have been resolved and
others are being addressed. Here is a list of most issues that are
or have been contributors to poor Retainability performance:
RNC module restarts addressed in CU2, resolved Sleeping cell addressed in CU2, CU4, and upcoming CU8,
current performance is good.
Corrupted target 2G LAC on Ericsson RNC CU6 currently being tested, deployment expected this coming week.
Old firmware on air cards issue has been escalated. New sites in pre-launched phases negatively impacting commercial
system performance Needs to be managed more closely Missing neighbors Use WNCS to identify missing neighbor
relationships or overshooting sectors.
3
Handover in Connected Mode List Events
Intra-Frequency Handover
Event 1a Add cell to Active Set
Event 1b Delete cell from Active Set
Event 1c Replace worst cell in Active Set
Event 1d Change best cell in Active Set
Inter-Frequency or Inter-RAT Handover
Event 2d Current used frequency is below threshold, start Compressed Mode
Event 2f Current used frequency is above threshold, stop Compressed Mode
Event 6a UE transmit power is above threshold, start Compressed Mode
Event 6b UE transmit power is below threshold, stop Compressed Mode
* Not all events are listed
4
Using Event Data in WNCS
WNCS Wide-Band CDMA Neighbor Cell Support
Active
Set
A B
C
RNC
WNCS uses the event data processed by the RNC for normal mobility
management to evaluate neighboring cell relationships. WNCS is used
to:
Identify missing neighboring cell relationships Identify radio link failures Provide data to determine when cells are overshooting their coverage
OSS-RC
5
Example Process of Troubleshooting DCR, Statistics
Use CNN, Watchmark Prospect, or Business Objects to
Determine Retainabilty performance.
* This example uses CNN
6
Example Process of Troubleshooting DCR, Daily Report Missing Neighbors
Missing Neighbor report shows cells that have at least 1 occurrence of
the pmNoSysRelSpeechNeighbr being incremented in a 15 minute period
between 5:00 a.m. and 11:00 p.m. each day.
Counter Name pmNoSysRelSpeechNeighbr
Description Number of system disconnects of a speech call for the best cell in the active set due to unknown measured cell (missing neighbor relation).
Condition Network initiated call release of speech calls due to inability to include an non-valid cell in the active set. The counter shall be incremented for the best cell in the active set prior to the call release. Note: This counter is only incremented in the SRNC.
MO Class UtranCell
Counter Type PEG
ST CS, PS
Unit -
7
WNCS Explanation How are we using this tool?
WNCS is part of the Radio Network Optimization (RNO) tool.
It is similar to the NCS tool in the Ericsson GSM OSS.
We set up a measurement for the Dallas area for all cells in all RNCs.
The measurement ran from 6:00 a.m. to 10:00 a.m. on Sept 7, 2006.
Once the measurement was complete, we performed the following:
Opened the WNCS Overview Report. Sorted on Dropped Calls in descending order. Investigated each cell starting from the cell with the most dropped
calls, then the cell with the next most dropped calls, etc.
For our investigation we used the WNCS Probable Neighbor Cell Report to determine what cell relation might be missing.
We also used a mapping tool similar to Mapinfo, CNN, and a database of the markets configuration and neighbor relation data in our investigation.
8
WNCS Report Basics
Launch the RNO application from the OSS RC Workspace menu, Select the Recording Results
tab, double-click on the report you wish to open.
9
Example First Scenario, slide 1
Cell DXU0775Z has 29 drops in the
WNCS Overview Report.
When we use the WNCS Probable
Neighbor Cell Report for DXU0775Z,
we learn that there are 18 Possible
Radio Links Addition attempts; these
are *Event 1a occurrences that did not
happen because the cell was not
defined as a neighbor.
The 18 Possible Radio Link Additions
Could have come from 4 possible cells.
Best Cell
CPICH Ec/No
reportingRange1a
Candidate Cell
timeToTrigger1a
hysteresis1a
MEASUREMENT
REPORT to RNC
Time
* It is possible that Events 1c or 1d rather than
Event 1a could have happened.
Event 1a Add cell to Active Set Event 1b Delete cell from Active Set Event 1c Replace worst cell in Active Set Event 1d Change best cell in Active Set
10
Example First Scenario, slide 2
29 Drops
In WNCS
Overview
Report
18 Possible
Radio Link
Addition
attempts
4 Possible
Cells based
on Scrambling
Code 308
WNCS
suggests
what cell
is missing
based on
distance,
uses Lat.
Long.
Note: WNCS may not have all the information
required to make the correct prediction.
11
Example First Scenario, slide 3
DXU0775Z is the cell that shows drops due
to missing neighbors on WNCS.
WNCS suggested that DXU2164Z be
added as a neighbor to DXU0775Z.
The dark blue sector is DXU0775Z. The green sectors are DXU0775Zs neighbors.
The royal blue sectors are undefined neighbors to DXU0775Z.
12
Example First Scenario, slide 4
If in this case the Event 1d trigger point
was met , and if the signal strength of
DXU1264Z exceeded the value of
releaseConnOffset the system would
release the call and a user perceived drop
would occur.
releaseConnOffset is typically set to 12 dB
Best Cell
CPICH Ec/No
Another Cell in AS
timeToTrigger1d
hysteresis1d
MEASUREMENT
REPORT to RNC
Description:
Threshold, for a cell to be included in the Active Set, when the connection is released due to an inclusion rejection. If UE enters a new cell area, and the quality Ec/No of the new cell is ReleaseConnOffset dB above the quality of the best cell in the Active Set, and for any reason, the new cell cannot be included in the Active Set, then Handover algorithms will ask for UE connection release. The reason is that it is not permitted to stay (with an established connection) in a cell area without being power controlled by the cell serving that area. The UE may cause interference in the uplink.
Range: -3 - +12 dB
Default: 12 dB
Resolution: 0.5 dB
13
Example Second Scenario, slide 1
We set up a measurement for the Dallas area for all cells in all RNCs.
The measurement ran from 4:00 p.m. to 9:00 p.m. on Sept 5, 2006.
Once the measurement was complete, we performed the following:
Opened the WNCS Overview Report. Sorted on Dropped Calls in descending order. Investigated each cell starting from the cell with the most dropped
calls, then the cell with the next most dropped calls, etc.
For our investigation we used the WNCS Probable Neighbor Cell Report to determine what cell relation might be missing.
We also used a mapping tool similar to Mapinfo, CNN, and a database of the markets configuration and neighbor relation data in our investigation.
WNCS is part of the Radio Network Optimization (RNO) tool.
It is similar to the NCS tool in the Ericsson GSM OSS.
14
Example Second Scenario, slide 2
Cell DXU1512X has 495 drops in the
WNCS Overview Report.
When we use the WNCS Probable
Neighbor Cell Report for DXU1512X,
we learn that there are 240 Possible
Radio Links Addition attempts; these
are *Event 1a occurrences that did not
happen because the cell was not
defined as a neighbor.
The 240 Possible Radio Link Additions
Could have come from 4 possible cells.
Best Cell
CPICH Ec/No
reportingRange1a
Candidate Cell
timeToTrigger1a
hysteresis1a
MEASUREMENT
REPORT to RNC
Time
* It is possible that Events 1c or 1d rather than
Event 1a could have happened.
Event 1a Add cell to Active Set Event 1b Delete cell from Active Set Event 1c Replace worst cell in Active Set Event 1d Change best cell in Active Set
15
Example Second Scenario, slide 3
495 Drops
In WNCS
Overview
Report
240 Possible
Radio Link
Addition
attempts
4 Possible
Cells based
on Scrambling
Code146
WNCS
suggests
what cell
is missing
based on
distance,
uses Lat.
Long.
Note: WNCS may not have all the information
required to make the correct prediction.
16
Example Second Scenario, slide 4
The dark blue sector is DXU1512X. The green sectors are DXU1512Xs neighbors.
The royal blue sectors are undefined neighbors to DXU1512X.
RNC Border
DXU1512X is the cell that shows drops due
to missing neighbors on WNCS.
No WNCS suggestions make sense.
Looking at the site data on this map
shows that DXU1547X has a
Scrambling Code of 146 and is close
to DXU 1512X.
This is a new site from a pre-launch
phase.
Slide 16
17
Example Second Scenario, slide 5
If in this case the Event 1d trigger point
was met and if the signal strength of
DXU1547X exceeded the value of
releaseConnOffset the system would
release the call and a user perceived drop
would occur.
releaseConnOffset is typically set to 12 dB
Best Cell
CPICH Ec/No
Another Cell in AS
timeToTrigger1d
hysteresis1d
MEASUREMENT
REPORT to RNC
Description:
Threshold, for a cell to be included in the Active Set, when the connection is released due to an inclusion rejection. If UE enters a new cell area, and the quality Ec/No of the new cell is ReleaseConnOffset dB above the quality of the best cell in the Active Set, and for any reason, the new cell cannot be included in the Active Set, then Handover algorithms will ask for UE connection release. The reason is that it is not permitted to stay (with an established connection) in a cell area without being power controlled by the cell serving that area. The UE may cause interference in the uplink.
Range: -3 - +12 dB
Default: 12 dB
Resolution: 0.5 dB
Thats All Folks
For now anyway