Ericsson Accessibility KPI Opitimization - 2G
Ericsson Accessibility KPI Opitimization - 2G
Ericsson Accessibility KPI Opitimization - 2G
Prepared By
Makavana Sachinkumar
Nidhi Bakshi
S Ramya
Jaya Ram T K
agenda
Accessibility Definition;
Accessibility KPI;
Random Access;
SDCCH Congestion;
SDCCH Drop;
TCH Blocking;
Setup SDCCH
SDCCH Call Processing
SDCCH Assignment command
(Assign TCH, FACCH)
Assignment complete FACCH/TCH
FACCH/TCH Alerting TCH Assignment and
FACCH/TCH Completion
Connect
Connect Ack FACCH/TCH
Accessibility KPI
– ACCMIN - ACCMIN controls the access threshold to the system, Often the setting of
ACCMIN is decided by non-technical reasons, A low setting of ACCMIN can cause RA
failures, TCH drops and bad quality and A high setting of ACCMIN can stop users
accessing the system resulting in lost revenue.
– MAXRET - MAXRET controls the number of Random Access retries allowed when the MS
accesses the system, A lower setting of MAXRET can improve RA performance but also
result in MSs not being able to access the system.
– TX - the randomness in the time interval between each of these access request is
defined by the parameter TX.
RANDOM ACCESS SUCCESS RATE
• Root causes for degradation
• Actions /Resolution:
– Check for BCCH / BSIC plan for RACH success rate affected cells .
– Improve weak coverage areas by physical optimization.
– Check for correct ACCMIN based on clutter and CRO based on boundaries.
– Do the complete BTS health check and replace the faulty / suspected HW.
– Set the appropriate MAXRET and TX values.
SDCCH CONGESTION
• SDCCH is a control channel and is used for system signaling (UL/DL) during
Location Updating, IMSI Attach, IMSI Detach, Mobile Originated Calls,
Mobile Terminated Calls, SMS and etc. In short SDCCH plays a big part in
call setup process as the call setup attempts go from a successful
Random Access to TCH via SDCCH.
– MAXNOSDCCHTRX – this parameter limits the max number of SDCCHs that can be
defined in a cell.
– INCRSDCCHCAP – needs to be set to 1 to leverage the benefit of MAXNOSDCCHTRX
parameter.
– T3212 - Periodic location update timer value.
– CRH, CRO & PT - Cell reselection hysteresis, cell reselection offset and Penalty timer -
Too high value of CRH can result in SDCCH drops and too less may increase load on
SDCCH.CRO, PT can also be used to delay reselection in LAC borders.
SDCCH CONGESTION
• Root causes for degradation
– High volume of LAU
– High volume of SMS
– High volume of Call Setup
• Actions /Resolution:
– Add an extra SDCCH/8 if blocking occurs continuous for a certain period of time
– Check for T3212 (Periodic location update timer) value.
– Verify cell Accmin value. Too high value may result in high SD usage.
– Check for CRH at cell in LAC boundaries.
– Verify MAXNOSDCCHTRX – this parameter limits the max number of SDCCHs that can be
defined in a cell. Note : INCRSDCCHCAP needs to be set to 1 to change the
MAXNOSDCCHTRX parameter.
SDCCH Drop
• A drop on SDCCH does not mean a failed call set-up since it can be used
for procedures that require an SDCCH like a location area update or SMS.
– DHA - Controls the activation of Dynamic Half Rate Allocation Root causes for
degradation.
– SCLD - Subcell load distribution.
– LOL - Path loss threshold. It defines the OL subcell coverage border in terms of the
pathloss from the serving cell.
– CLS - Cell load sharing
– KOFFSETP - Signal strength positive offset in dB when evaluating K-cells.
– HCS - Hierarchical Cell Structures
TCH Blocking
• Root causes for degradation
– High HR traffic
– Over utilized resources (TRX)
– Sleeping TRX
– Wrong LOL & SCLD settings
– CLS feature switched off
– Nearby site availability Issue
– Need to check Transcoder setting
• Actions /Resolution:
– High HR traffic. - Check for DHA setting for AMR and tune it.
– Over utilized TRX - Check for adding additional TRX
– Check for sleeping TRX.
– CLS – Cell load sharing can be used. Wrong parametric settings can cause congestion.
– Adjust the KOFFSETP of neighbor cell ( Low traffic ) to push the traffic towards it, reduces TCH
blocking.
– Tried all the options, then plan for fourth sector, else go for a new site to offload.
– Hierarchical Cell Structures (HCS) - provides a mechanism whereby the traffic may be directed
towards cells belongings to the lower layer, so as the lower layer cells can serve all the traffic with
sufficient signal strength.
TCH Assignment SUCCESS RATE
• The TCH assignment success rate measures how often a call set-up,
ordered by the MSC, has been successful.
– Overlaid/Underlaid Subcells - The fundamental idea is that traffic close to the site is
moved to the Overlaid subcell while traffic closer to the edge of the cell is carried on the
Underlaid.
– AMR Half-rate (AHR) - Possibility of doubling the AMR capacity by using AHR instead of
AFR. DHA allocates AMR HR at call set-up and handover when few idle TCHs remain in
the cell.
– CLS – Cell load sharing - Helps avoiding congestion at pre-defined load
– Hierarchical Cell Structures (HCS) - provides a mechanism whereby the traffic may be
directed towards cells belongings to the lower layer, so as the lower layer cells can serve
all the traffic with sufficient signal strength.
– Expansions need to be planned in advance – Before capacity is needed.