LTE- ACCESSIBILITY
Prepared (Subject resp)
1 (15)
No.
Deepak Gupta
Approved (Document resp)
Checked
Date
Rev
Reference
2017-02-28
LTE - ACCESSIBLITY OPTIMIZATION
LTE- ACCESSIBILITY
Prepared (Subject resp)
2 (15)
No.
Deepak Gupta
Approved (Document resp)
Checked
Date
Rev
Reference
2017-02-28
The Different Phases of Accessibility
Accessibility for the EUTRAN is a measure of the abilit y of a user to obtain an E-RAB from the system. The initial ERAB establishment process can be divided into the following phases:
• Random Access
• Paging
• RRC Connection Establishment
• S1 Signalling Connection Establishment
• Initial E-RAB Establishment or E-RAB Addition.
Note: Pls. note that Phase 1) Random Access & 2) Paging will have effect on end user experience but are not directly
reflected in Counter based KPI formula. Considering counter based Accessibility KPI, we have only 3 phases of
Accessibility, which are mentioned as below.
CSSR Formula:-
LTE- ACCESSIBILITY
Prepared (Subject resp)
3 (15)
No.
Deepak Gupta
Approved (Document resp)
Checked
Date
Rev
Reference
2017-02-28
1) Random Access:The UE uses the random access process to gain access to the cell for the following reasons:
 Initial access to the network from the idle state – R R C Connection E stablis hment
 Re-gain access to the network after radio link failure – R R C C onnection R e-es tablis hment
 During handover to gain synchronization with a new cell – Handover Ex ecution
Two types of RA procedures are defined:
 CBRA (Contention Based Random Access): pmRaAttCbra, pmRaSuccCbra
 CFRA (Contention Free Random Access): pmRaAttCfra, pmRaSuccCfra
Troubleshooting:
i)
Sleeping Cells:
Check whether the cell is a “Sleeping Cell”. Due to their nature Sleeping Cells are difficult to
detect and therefore cells in these conditions can remain out of service for long time periods
causing major service outages.

They do not report standard symptoms of failures in services e.g. hardware or software alarms

The Counter pmRaSuccCbra is very low or zero; then the cell is considered a sleeping cell
Resolution:

Lock/Unlock the cell.

Re-Start.
ii) Uplink Interference:
UL Interference can be either
Internal - Interference due to other UE’s in the cell.
External- Interference due to power supply sources.

Due to UL RSSI, RBS cannot detect/decode the request sent by UE. And so, UL RSSI has a great
impact on Accessibility performance.

‘pmRadioRecInterferencePwr’
is the measured Noise and Interference power on PUSCH &
‘pmRadioRecInterferencePwrPucch’
is the measured Noise and Interference Power on PUCCH.
These two counters can be used to identify if the noise floor of the cell is higher than it should
be. Ideally this counter should be measured at the lowest traffic hours (early morning hours for
most), to know the actual noise floor of the cell and perform further investigation to find the
root cause for the same.
LTE- ACCESSIBILITY
Prepared (Subject resp)
4 (15)
No.
Deepak Gupta
Approved (Document resp)
Checked
Date
Rev
Reference
2017-02-28
Resolution:

Checking Alarms & HW faults in case of high RSSI in low traffic hours(external interference),
auditing “pzeronominalpusch” ( -65,-103) & “pzeronominalpucch” (-120,-117)powers if the noise
floor is very high during the high traffic hours(internal interference).

preambleInitialReceivedTargetPower can be tuned to higher values, if the source of high RSSI is
unknown, so that the RACH preamble signal can rise above the noise floor.
iii) Preamble Issues:

High traffic on a cell can lead to conflicts between UEs and will impact the average call-setup
time and user perception. In the current versions for Ericsson system, we cannot increase the
RACH capacity, but in future versions, prachconfigurationindex can be tuned to increase the
capacity of cell from RACH perspective.

Preambles discarded for TA > CellRange: Counter for this is only available for CFRA, however it
can be used to have an idea of the performance of CBRA. Counter "pmRaFailCfraMsg1DiscOoc”
can be used to find the amount of discards because of TA > Cell-Range. Activating feature
“MaximumCellRange” and increasing “CellRange” parameter. RachRootSequence to be tuned
accordingly to accommodate 64 preambles.

RootSequenceIndex(RachRootSequence) Conflict: RSI hits nearby can lead to conflicts in
preambles detection in the concerned cells. RSI should be tuned considering the Cell Range, and
the respective difference should be maintained in the potential interfering cells.
MTD Signal Traces:
UPC_DL_MAC_CE_FI_SCHEDULE_RA_MSG2_REQ : Used to request creation of one RA Msg2 session to be scheduled for a subframe.
UPC_DL_MAC_CE_FI_SCHEDULE_RA_MSG2_CFM: Confirmation of above
UP_DLMACPE_CI_RA_MSG2_ALLOC_IND: Allocation information for messages on the common channel (TB description, L1 Control Description,
RAR Information
RACH_All_Traces.txt
2) RRC Connection Establishment:•
The RRC connection request message is sent to the eNodeB after the UE has performed initial cell selection and
detected the best cell
LTE- ACCESSIBILITY
Prepared (Subject resp)
5 (15)
No.
Deepak Gupta
Approved (Document resp)
Checked
Date
Rev
Reference
2017-02-28
•
The RRC connection establishment is always initiated by the UE but can be triggered by either the UE (Mobile
Originated) or the network (Mobile Terminated). The network triggers the RRC connection establishment
procedure by paging the UE.
RRC Setup Failure [%] = 100*(pmRrcConnEstabAtt-pmRrcConnEstabSucc) / (pmRrcConnEstabAtt)
Troubleshooting
i) Access fail due to overloading & High Loading :
The eNodeB may block the UE’s connection request by sending the “RRC Connection Reject”,
there will be no cause value signaled to the UE with RRC Connection Rejects.

Counters “pmRrcConnEstabFailHighLoad” & “pmRrcConnEstabFailOverload” will be stepped at
transmission of “RRC Connection Reject” during high load or overload circumstances.
Resolution:Change SC 556(numInitialAccessAndIncomingHo): Increase the maximum number of initial

accesses and incoming handovers that are allowed during a time window without triggering
the load control mechanism. (Comments)

Change EutranCellFDD.qRxLevMin to higher values, if the coverage is not an issue.

Change EutranFreqRelation.qOffsetCellEUtran: enable faster cell re-selection from loaded
cells towards other surrounding cells that satisfy the cell selection criteria.
ii) Access fail due to license Issue:
The number of failed-RRC-Connection-Establishments that are rejected due to lack of CUL
(Connected User License) are counted with the pmRrcConnEstabFailLic.
Resolution:
pmRrcConnEstabFailLic pegs only when the grace period(gracePeriodAvailable) has ended, and
during the duration when grace period is active, eNodeB is allowed to accept maximum number
of UEs(limited by DUL/eNB version). This can be found out using pmLicConnectedUsersMax and
the new license limit should be adjusted accordingly.
iii) RF Issues:
Radio i include radio interference, imbalance between the uplink (UL) and downlink (DL) quality,
weak coverage and the UE does not use the maximum transmit power.

During an RRC connection setup process, the eNodeB has not received any RRC connection setup
complete messages within the related timeout duration.
LTE- ACCESSIBILITY
Prepared (Subject resp)
6 (15)
No.
Deepak Gupta
Approved (Document resp)
Checked
Date
Rev
Reference
2017-02-28

At the eNodeB side, both the RRC connection setup success rate and the E-RAB setup Success
rate are low.
To be investigated:



Radio Interference: DL interference from neighboring cells, DL interference from external
systems, and UL interference need to be investigated. The counters that can be used to find out
the
same
are:
pmSinrPucchDistr,
pmSinrPuschDistr,
pmRadioUeRepCqiDistr,
pmRadioTxRankDistr, pmRadioRecInterferencePwrPucch.
eg: PUCCH received power should be around the pZeroNorminalPucchPwr (default:-117 dBm)
“pmRadioTbsPwrRestricted”
Cell
coverage
issues
can
be
detected
using
&
“pmbadcovevalreport”.
UEs trying to access the network in poor Downlink RF conditions can be determined by looking
for high pegs in “pmRrcConnEstabAttReatt”.
Resolution:-

Tuning
pZeroNorminalPucchPwr
depending
on
the
values
from
pmRadioRecInterferencePwrPucch
Tuning t300 in cases where, the radio conditions can be improved much and immediate results
are required in the success rate.
Change EutranCellFDD.qRxLevMin to higher values, if the coverage is not an issue.

Change EutranFreqRelation.qOffsetCellEUtran: enable faster cell re-selection towards better


cells.
iv) CCE Capacity:-
LTE- ACCESSIBILITY
Prepared (Subject resp)
7 (15)
No.
Deepak Gupta
Approved (Document resp)
Checked
Date
Rev
Reference
2017-02-28

pmPdcchCceUtil will give idea if high CCE utilization led to degradation in RRC Success Rate. If
the last bucket has high number of samples in the degraded hours, then surely problem is due
to lack of CCE resources.
Resolution:
Tuning pdcchCfiMode to the optimum value of 5(dynamic, max=3) can get best utilization of
the CCE resources with required control dimensioning.(pdcchLoadTarget)
L3 Traces:
te e all Ft_RRC_CONN_SETUP: Will printout out L3 messages related to the RRC Setup as well as internal information of the
triggered procedures and detailed info on failure cases
CTR Trace:
INTERNAL_PROC_RRC_CONN_SETUP: Generated for the RRC Connection Setup procedure to establish an RRC Connection. Contains
information about the request and result.
3) S1 Connection Establishment.
•
When setting up the E- RAB the ‘RRC CONNECTION SETUP COMPLETE’ message contains a piggybacked NAS ‘Attach
Request’ message. The RBS will send this message to the MME in the S1AP ‘INITIAL UE MESSAGE’ and increment
the ‘pmS1SigConnEstabAtt’ counter as illustrated below.
LTE- ACCESSIBILITY
Prepared (Subject resp)
8 (15)
No.
Deepak Gupta
Approved (Document resp)
Checked
Date
Rev
Reference
2017-02-28
Counters:pmS1SigConnEstabAtt
pmS1SigConnEstabSucc
Troubleshooting

MME overload can lead to s1 connection failures and this can be found using the
pmS1SigConnEstabFailMmeOvlMos counter. Investigation from MME end would be required in
this case. Using “st termpointtomme” status of connected MME can be checked, whether all are
up and running, as if one is inactive, the load will be on the other MME’s i n the pool.
LTE- ACCESSIBILITY
Prepared (Subject resp)
9 (15)
No.
Deepak Gupta
Approved (Document resp)
Checked
Date
Rev
Reference
2017-02-28

Find out if the degradation is from a certain hour, if yes, try to find out if any restarts or any
alarms on the node are evident from the logs.
Resolution:


Restarting the node.
Locking and Unlocking the cell.
Locking and unlocking the termpointtomme with the problematic MME.
TE Trace:
te e all Ft_S1AP_ASN: Will printout out messages related to the S1AP Setup as well as internal information of the triggered
procedures and detailed info on failure cases.
CTR trace:
INTERNAL_PROC_S1_SIG_CONN_SETUP: Generated for the S1 Signaling Connection Setup procedure to establish an S1 Signaling
Connection. Contains information about the request and result.
Eg: Enabling and decoding the S1AP_ASN traces will show us the cause of an S1 Setup failure. In the below
case, an incorrect PLMN id is defined (ENodeBFunction and EUtranCellFDD MOs).
4) E-RAB Establishment:A. Initial E-RAB Establishment
•
The Initial Context Setup procedure is triggered by the MME by sending the INITIAL CONTEXT SETUP REQUEST. This
message includes information regarding the default E-RAB to set up
LTE- ACCESSIBILITY
Prepared (Subject resp)
10 (15)
No.
Deepak Gupta
Approved (Document resp)
Checked
Date
Rev
Reference
2017-02-28
•
•
The eNodeB allocates resources for the first Data Radio Bearer (DRB). The eNodeB configures the UE by sending
message RRC CONNECTION RECONFIGURATION
The UE responds with RRC CONNECTION RECONFIGURATION COMPLETE and the procedure is completed after the
eNodeB has sent INITIAL CONTEXT SETUP RESPONSE to the MME.
Counters:
pmErabEstabAttInit
pmErabEstabSuccInit
B. Added E-RAB Establishment
•
•
•
The added bearer is established if the user requires different QoS of that offered by the initial bearer, or if the user
requires connectivity to different PDN. Added bearers are configured to run in parallel to the existing initial bearer
The added bearer establishment procedure is initiated by the network but may be requested by the UE
The eNodeB uses the E-RAB Setup Request to configure itself for the added bearer. The RRC Connection
Reconfiguration message provides the UE with information necessary to configure the added bearer.
Counters:pmErabEstabAttAdded
pmErabEstabSuccAdded
LTE- ACCESSIBILITY
Prepared (Subject resp)
11 (15)
No.
Deepak Gupta
Approved (Document resp)
Checked
Date
Rev
Reference
2017-02-28
i)
License for no. of ERAB's per user:
pmErabEstabFailInitLic/pmErabEstabFailAddedLic Gives the total number of license rejects
depending on the configuration on the eNodeB like “ Multiple Radio Bearer per user”.
ii) UL /DL GBR resources overload:

pmErabEstabFailGbrDlEnb & pmErabEstabFailGbrUlEnb gives the total number of failed
initial E-RAB setup attempts due to downlink/Uplink GBR overload for transport network
resources.
zzzTemp20 / zzzTemp21 are the parameters used to configure Uplink and Downlink
admission thresholds respectively. Check if they are set to default values, else tuning will be
required depending on the capacity and requirement. Also an audit of various Admission
Control parameters can be carried out
LTE- ACCESSIBILITY
Prepared (Subject resp)
12 (15)
No.
Deepak Gupta
Approved (Document resp)
Checked
Date
Rev
Reference
2017-02-28
iii) eNodeB Issue


With regards to hanging resources in eNb – a restart normally helps. With regards to faulty
RRU’s – if restarting the RRU doesn’t help, replacing the RRU is the option.
To find out particular UE issue, We ne ed to analyze CTR (Cell Traces) & EBM (MME).
iv) RF Issues:
Radio issues include radio interference, imbalance between the uplink (UL) and downlink (DL)
quality, weak coverage and the UE does not use the maximum transmit power.

During an RRC connection setup process, the eNodeB has not received any RRC connection setup
complete messages within the related timeout duration.

At the eNodeB side, both the RRC connection setup success rate and the E-RAB setup Success
rate are low.
To be investigated:



Radio Interference: DL interference from neighboring cells, DL interference from external
systems, and UL interference need to be investigated. The counters that can be used to find out
the
same
are:
pmSinrPucchDistr,
pmSinrPuschDistr,
pmRadioUeRepCqiDistr,
pmRadioTxRankDistr, pmRadioRecInterferencePwrPucch.
eg: PUCCH received power should be around the pZeroNorminalPucchPwr (default:-117 dBm)
“pmRadioTbsPwrRestricted”
Cell
coverage
issues
can
be
detected
using
&
“pmbadcovevalreport”.
UEs trying to access the network in poor Downlink RF conditions can be determined by looking
for high pegs in “pmRrcConnEstabAttReatt”.
LTE- ACCESSIBILITY
Prepared (Subject resp)
13 (15)
No.
Deepak Gupta
Approved (Document resp)
Checked
Date
Rev
Reference
2017-02-28
Resolution:-

Tuning
pZeroNorminalPucchPwr
depending
on
the
values
from
pmRadioRecInterferencePwrPucch
Tuning t300 in cases where, the radio conditions can be improved much and immediate results
are required in the success rate.
Change EutranCellFDD.qRxLevMin to higher values, if the coverage is not an issue.

Change EutranFreqRelation.qOffsetCellEUtran: enable faster cell re-selection towards better


cells.
v)
CCE Capacity:
pmPdcchCceUtil will give idea if high CCE utilization led to degradation in RRC Success Rate. If
the last bucket has high number of samples in the degraded hours, then surely problem is due
to lack of CCE resources.
Resolution:
Tuning pdcchCfiMode to the optimum value of 5(dynamic, max=3) can get best utilization of
the CCE resources with required control dimensioning.
L3 Traces:
te e all Ft_ERAB_SETUP - Will printout out L3 messages related to the ERAB setup as well as internal i nformation of the
triggered procedures and detailed info on failure cases.
CTR Trace:
INTERNAL_PROC_ERAB_SETUP: Generated for the ERAB setup procedure to establish additional ERABs. Contains information
about the request and result.
LTE- ACCESSIBILITY
Prepared (Subject resp)
14 (15)
No.
Deepak Gupta
Approved (Document resp)
Checked
Date
Rev
Reference
2017-02-28
5) Paging :-
i. S1 Paging
% S1 Paging discard rate: shows the discard rate of paging messages due to max
intensity of incoming S1AP Paging messages are forwarded to the eNodeB.
% S1 Paging discard rate = 10 0 * pmPagS1Discarded / pmPagS1Received
ii. Paging Discards by Cell:After the S1AP Paging message is correctly received and not discarded by RBS, it is routed to
one cell (pmPagReceived). An S1AP Paging message discarded as part of pmPagS1Discarded
will not cause this counter to be pegged.
When the cell fails to broadcast an RRC Paging within a certain time (pagingDiscardTimer),
e.g. due to congestion, the Paging is discarded and counter pmPagDiscarded is incremented
by the number of included Paging Records in the discarded Paging message.
pagingDiscardTimer(3s): The length of time a received paging is retained or queued in the
RBS before it is discarded. The timer should be set to the same (or smaller) value as the
paging resend timer in MME (T3413). This setting prevents the RB S from retaining or sending
an old paging after the re-sent copy is received from the MME.
.
%Cell Paging discard rate = 100 * pmPagDiscarded / pmPagReceived
iii. S1 Issues with the MME(MME Codes)
There can be issues where the paging attempts have reduced to Zero. A
restart can help in that case.
LTE- ACCESSIBILITY
Prepared (Subject resp)
15 (15)
No.
Deepak Gupta
Approved (Document resp)
Checked
Date
2017-02-28
Rev
Reference