NPO Enabling:
VoL
oLTE
TE Trai
aini
ning
ng
Detailed Analysis for Radio
13 March 2017
1
© Nokia Solutions and Networks 2014
Contents
• VoLTE KPI Performance
• VoLTE KPI benchmarking
• VoL
VoLTE
TE Voice Quality
• VoLTE Radio Optimization
• Periodical CQI reporting
• QCI1 specific T310 and T31
T311
1 timers
• Voice quality analysis
• DRX – optimized algorithm
• PDCP discard timer & SN size
• High speed users
• VoL
VoLTE
TE Mobility
Mobi lity
• VoLTE Call Flow Analysis
• VoL
VoLTE
TE layering
layer ing
• Registration procedure
• SRVCC thresholds
• Mobile originated VoLTE call
• Mobile terminated VoLTE call
• SRVCC to 3G
2
© Nokia Solutions and Networks 2014
VoL
oLTE
TE KPI Perf
Performa
ormance
nce
3
© Nokia Solutions and Networks 2014
VoLTE KPI Benchmarking
Call setup success rate for QCI1
• VoLTE Call Setup Success KPI (LTE_5204c) measures both initial or an additional ERAB establishments for QCI1 voice bearer.
-
In practise, QCI1 E-RAB is usually setup after the non-GBR E-RAB for application data and SIP
signalling so the ‘additional’ E-RAB counters are typically incremented for VoLTE.
E-UTRAN E-RAB Setup Success Ratio, QCI1 (LTE_5204c) =
100*sum(ERAB_INI_SETUP_SUCC_QCI1 + ERAB_ADD_SETUP_SUCC_QCI1 - ERAB_REL_TEMP_QCI1)
sum(ERAB_INI_SETUP_ATT_QCI1 + ERAB_ADD_SETUP_ATT_QCI1)
-
4
ERAB_REL_TEMP_QCI1: number of temporary admitted QCI1 bearer release due to an
overbooking timer expiry (LTE2832 SRVCC due to admission control rejection), i.e. these bearers
were temporarily setup but not successfully handed over to UTRAN.
© Nokia Solutions and Networks 2014
LTE2832 SRVCC due to Admission Control Rejection
QCI1 bearer release due to an overbooking timer expiry
UE
• eNB establishes temporary the DRB
with QCI1 and configures the UE
with event B1 based measurements
within
RRC:ConnectionReconfiguration
• AC Overbooking Supervision Timer
expired before preparation phase
and thus, eNB releases E-RAB with
QCI1:
-
5
ERAB_REL_TEMP_QCI1 is
incremented on transmission of an
S1AP: E-RAB RELEASE INDICATION
message (eNB -> MME; 3GPP TS
36.413) due to an overbooking timer
expiry for a temporarily admitted QCI1
bearer.
© Nokia Solutions and Networks 2014
eNB
MME
S1AP: E-RAB SETUP REQUEST
QCI=1
Admission Control
rejection
Temporary overbooking
is possible
DRB with QCI1
establishment +
configuration event
B1
RRC Connection Reconfiguration
AC Overbooking
Supervision Timer
RRC Connection Reconfiguration
Complete
S1AP: E-RAB SETUP RESPONSE
DRB with QCI1
deactivation +
deconfiguration
event B1
RRC Connection
Reconfiguration
AC Overbooking
Supervision Timer
RRC Connection Reconfiguration
Complete
S1AP: E-RAB RELEASE
INDICATION
VoLTE KPI Benchmarking
Call setup success rate for QCI1
• KPI does not reflect the end user
experience in case of failures in
the following procedures:
6
-
RACH and RRC signalling
establishment
-
S1 signalling setup
-
Security and authentication
-
IMS bearer (QCI5) setup
-
SIP message delivery over radio
interface.
-
Mobility during E-RAB setup
© Nokia Solutions and Networks 2014
VoLTE Call Setup Success
GBR vs. non-GBR eRAB setup performance
• QCI1 E-RAB setup success
rate is slightly worse than nonGBR E-RAB setup success
rate due to following factors:
GBR and non-GBR E-RAB Setup Success (%)
E -R AB Se tu p A tt em pt s, QC I1
E -R AB Se tu p S uc ce ss Ra te
E -R AB Se tu p S uc ce ss Ra te ,Q CI 1
L in ea r ( E- RA B S et up At te mp ts , Q CI 1)
100.00
400 000
720 users - 15 MHz
99.90
99.80
350 000
Admission Control Threshold – 75%
600 users - 10 MHz
-
Much less QCI1 bearer setups
compared to data bearers and
thus, the weight of setups
attempted under poor radio
conditions is increased
-
If a handover becomes
necessary during E-RAB Setup,
the eNB may interrupt the
ongoing E-RAB Setup procedure
as specified in 36.413 (chapter
8.2)
300 000
99.70
)
(% 99.60
e
t
a
R 99.50
s
s
e
c
c 99.40
u
S
250 000
200 000
150 000
99.30
100 000
99.20
50 000
99.10
99.00
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Q
VoLTE Call Setup Failure due to Handover in Progress
MME bearer request handling
• 3GPP 36.413 (chapter 8.2): If a handover becomes necessary during E-RAB Setup, the
eNB may interrupt the ongoing E-RAB Setup procedure and initiate the Handover
Preparation procedure as follows:
-
The eNB shall send the E-RAB SETUP RESPONSE message in which the eNB shall indicate, if
necessary all the E-RABs fail with an appropriate cause value, e.g. , ”S1 intra system Handover
triggered”, “S1 inter system Handover triggered” or “X2 Handover triggered”.
• Therefore, MME needs to resend the E-RAB Setup Request when it receives the Path
Switch Request after the failed E-RAB setup (applies for E-RAB release or modify
procedure as well) – feature implemented in Nokia MME (NS15 onwards).
-
8
In case the SGW is changed due the HO then MME should send the Create Bearer Response
message to SGW indicating rejected E-RAB with cause 110 “Temporarily rejected due to
handover/TAU/RAU procedure in progress“.
© Nokia Solutions and Networks 2014
VoLTE Call Setup Failure due to Handover in Progress
PGW bearer request handling
• 3GPP TS 23.401: Upon reception of a rejection for an EPS bearer(s) PDN GW i nitiated
procedure with an indication that the request has been temporarily rejected due to
mobility procedure in progress, the PDN GW start a locally configured guard timer. The
PDN GW shall re-attempt, up to a pre-configured number of times, when either it
detects that the Tracking Area Update procedure is completed or has fail ed using
message reception or at expiry of the guard timer.
9
-
PDN GW which initiated the bearer related request (e.g.Create / Update / Delete Bearer
request) is supposed to handle the rejection by re-sending the request after handover is
completed.
-
Nokia PGW (NG3.2 onwards) has re-attempt mechanism, with the default value “handoverrejection-guard-timer-reattempt-count” = 2, i.e. when PGW receives the rejection, it will re-initiate
rejected EPS bearer procedure to MME.
© Nokia Solutions and Networks 2014
VoLTE Call Setup Failure due to Handover in Progress
Failure message sequence
S-eNB
T-eNB
MME
S-SGW
T-SGW
SIP:INVITE
SIP: TRYING
SIP: SESSION PROGRESS
Radio Handover in Progress
Create Bearer Request
Create Bearer Request (QCI1)
E-RAB Setup Request
E-RAB Setup Response (failure) Cause: X2-Handover-Triggered
PatchSwitchRequest
Create Bearer Response
(failure)
SIP: 503 Service Unavailable
10
© Nokia Solutions and Networks 2014
Cause: Temporarily Rejected due to Handover Procedure in
Progress
PGW
VoLTE Call Setup Failure due to Handover in Progress
Correct message sequence
T-eNB
S-eNB
MME
S-SGW
T-SGW
PGW
SIP:INVITE
SIP: TRYING
SIP: SESSION PROGRESS
Radio Handover in Progress
Create Bearer Request
Create Bearer Request (QCI1)
E-RAB Setup Request
E-RAB Setup Response (failure) Cause: X2-Handover-Triggered
PatchSwitchRequest
Create Bearer Response
Cause: Temporarily Rejected due to Handover Procedure in
(failure)
Progress
Create Session Request (QCI5)
Modify Bearer Request
Modify Bearer Response
Create Session Response
Patch Switch Request Ack
Delete Access Bearer in S-eNB and Session in S-SGW
SIP: PRACK
11
© Nokia Solutions and Networks 2014
Create Bearer Request
Create Bearer Request (QCI1)
R
e
tr
a
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s
m
i
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s
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o
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VoLTE Call Setup Failure in Poor Coverage
SIP message delivery failure
•
12
© Nokia Solutions and Networks 2014
The UL SIP message SESSION PROGRESS
(183) delivery is unsuccesful and thus, VoLTE call
setup fails.
-
IP packet including SIP message is more than 1500B
which leads to packet fragmentation in the application
layer (mandatory).
-
Under poor radio conditions, it takes too long time to
deliver the 1st piece of SIP message and therefore,
the 2nd piece of SIP message in eNB buffer is
discarded due to expiry of PDCP tDiscard timer.
-
The entire SIP message can NOT be concatenated in
application layer, which leads VoLTE call failure
-
Please note, in such case the UE doesn’t generate
new PDCP SN for buffered data which means that
data is kind of silently discarded and thus, eNB’s PM
counter or internal logs can’t reflect this failure.
-
QCI5 the parameter tDiscard is recommended to set
to “infinity” to overcome this issue under very poor UL
channel.
VoLTE KPI Benchmarking
Drop ratio for QCI1 – radio perspective
• VoLTE E-RAB QCI1 Drop Ratio (RAN View) KPI describes the ratio of abnormally
released (dropped) QCI1 E-RABs from RAN point of view.
-
Abnormal E-RAB drops which are initiated by eNB are only counted.
E-UTRAN E-RAB QCI1 Drop Ratio, RAN View (LTE_5572e) =
100*sum(ER AB _REL_HO_PART_QCI1 + ER AB _RE L_ENB_QCI1 - ERAB_REL_ENB_RNL_INA_QCI1 ERAB_REL_ENB_RNL_RED_QCI1 -ERAB_REL_ENB_RNL_RRNA_QCI1 - ERAB_REL_TEMP_QCI1)
sum(ERAB_REL_ENB_QCI1 + ERAB_REL_HO_PART_QCI1 + EPC_EPS_BEAR_REL_REQ_N_QCI1
+EPC_EPS_BEAR_REL_REQ_D_QCI1 + EPC_EPS_BEAR_REL_REQ_R_QCI1 +
EPC_EPS_BEAR_REL_REQ_O_QCI1 + ERAB_REL_EPC_PATH_SWITCH_QCI1 - ERAB_REL_TEMP_QCI1 +
ERAB_REL_SUCC_HO_UTRAN_QCI1 + ERAB_REL_SUCC_HO_GERAN_QCI1)
13
© Nokia Solutions and Networks 2014
VoLTE KPI Benchmarking
Drop ratio for QCI1 – end user perspective
• VoLTE E-RAB QCI1 Drop Ratio (user perspective) KPI describes the ratio of abnormally
released (dropped) QCI1 E-RABs from end user point of view.
-
Abnormal E-RAB drops initiated both by eNB and EPC are counted.
-
Call drops due to duplicated S1 connections and SRVCC during alerting are counted.
ERAB QCI1 drop ratio, user perspective (LTE_1263h) =
100 * SUM(EPC_EPS_BEAR_REL_REQ_R_QCI1 + EPC_EPS_BEAR_REL_REQ_O_QCI1 +
ERAB_REL_EPC_PATH_SWITCH_QCI1 + ERAB_REL_HO_PART_QCI1 + ERAB_REL_ENB_QCI1 ERAB_REL_ENB_RNL_INA_QCI1 - ERAB_REL_ENB_RNL_RED_QCI1 - ERAB_REL_ENB_RNL_RRNA_QCI1 ERAB_REL_TEMP_QCI1)
SUM(EPC_EPS_BEAR_REL_REQ_N_QCI1 + EPC_EPS_BEAR_REL_REQ_D_QCI1 +
EPC_EPS_BEAR_REL_REQ_R_QCI1 + EPC_EPS_BEAR_REL_REQ_O_QCI1 + ERAB_REL_ENB_QCI1 +
ERAB_REL_HO_PART_QCI1 + ERAB_REL_EPC_PATH_SWITCH_QCI1 - ERAB_REL_TEMP_QCI1 +
ERAB_REL_SUCC_HO_UTRAN_QCI1 + ERAB_REL_SUCC_HO_GERAN_QCI1)
14
© Nokia Solutions and Networks 2014
VoLTE Drop Call Rate
Duplicated S1 Connection
• Duplicated S1 connection occurs when the UE tries to
make HO from eNB-A cell to eNB-B cell but the HO fails
and following RRC connection re-establishment fails (no
LTE1617) and therefore, UE makes new RRC setup
attempt in eNB-B cell which causes new (duplicated) S1
connection establishment towards the MME
-
-
15
The MME notices that there are two S1 connections for the
UE and releases the old one (eNB-A). This release can be
done with cause: NORMAL release or RADIO, where the
latter causes dropped call counting (EPC initiated E-RAB
release due RNL)
After activation of LTE1617 there is no gain expected in
dropped call rate if the MME releases the duplicated S1
connection with NORMAL release cause (only gain on t he
reduced mute time).
© Nokia Solutions and Networks 2014
MME
eNB-B
UE
eNB-A
UE
VoLTE KPI Benchmarking
Drop ratio for QCI1 – active drops
• VoLTE E-RAB QCI1 Drop Ratio (active drops) KPI describes E-RAB QCI1 with data in
the queue drop ratio.
-
ERAB_REL_ENB_ACT_QCI1: number of released active E-RABs, i.e. when there was user data
in the queue at the time of release with QCI1 characteristics. The release is initiated by the eNB
due to radio connectivity problems.
-
E-RAB releases due to "No Radio Resources Available" initiated by eNB are counted as normal
releases from RAN perspective as drops are not resulted from any radio quality problems.
E-UTRAN E-RAB QCI1 with data in the queue drop ratio (LTE_5571f) =
100*sum(ERAB_REL_ENB_ACT_QCI1)
sum(ERAB_REL_ENB_QCI1 + ERAB_REL_HO_PART_QCI1 + EPC_EPS_BEAR_REL_REQ_N_QCI1 +
EPC_EPS_BEAR_REL_REQ_D_QCI1 + EPC_EPS_BEAR_REL_REQ_R_QCI1 +
EPC_EPS_BEAR_REL_REQ_O_QCI1 + ERAB_REL_EPC_PATH_SWITCH_QCI1 - ERAB_REL_TEMP_QCI1 +
ERAB_REL_SUCC_HO_UTRAN_QCI1 + ERAB_REL_SUCC_HO_GERAN_QCI1)
16
© Nokia Solutions and Networks 2014
VoLTE KPI Benchmarking
Active call drop counters
• Note that some network vendors are
counting only the drops when there is
data in the eNB buffer to be
transmitted to the UE in case of both
eNB triggered and EPC triggered
abnormal releases.
-
The difference is quite large between all
drops (during inactivity) and drops only in
case there is data in buffer as shown in
the graph on the right:
• 0.4%-0.8% for all drops
• 0.05%- 0.15% for only drops with data
in buffer
17
© Nokia Solutions and Networks 2014
ERAB DR, RAN View, QCI1, LTE_5572A
ERAB DR, QCI1 w/ data in buffer, LTE_5571B
1.00
0.90
0.80
0.70
0.60
0.50
%
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VoLTE Drop Call Rate
GBR vs. non-GBR drop calls
• QCI1 E-RAB drop rate is much
worse compared to non-GBR
traffic.
GBR and non-GBR E-RAB Drop Rate (%)
VoLTE Drops EPCinitiated
VoLTE Drops eNB initiated
E-RAB Drop Rate, UserPerspective (eNB pre-emptions excluded)
VoLTE Drop Rate
2.00
6 000
720 users - 15 MHz
1.80
Admission Control Threshold – 75%
1.60
600 users - 10 MHz
5 000
1.40
4 000
) 1.20
%
(
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#
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• VoLTE (QCI1) bearer drop rate
has an increasing trend up to
1.6% with increased voice
traffic.
-
The QCI1 session time (activity
time) is much longer compared
to the non-GBRQCI and
therefore, QCI1 is much more
sensitive to mobility related
performance challenges (too late
HO, too early HO, RRC reestablishments)
VoLTE KPI Benchmarking
Active Drops per Session Time
• The simple dropped call rate calculation
(drops/setup E-RABs per QCI) is not
necessarily a good metric due to the
extremely large difference in session
times between QCI1 (100s – 200s) and
Non-GBR : (0.5s – 1.5s)
• The QCI1 performance in terms of drops
per minute is much better compared to
the non-GBR, i.e. QCI1 performance
should be also monitored by active drops
per active in session time.
active drops per active minute QCI1
active drops per active minute non-GBR
non-GBR to QCI1 ratio
0.0035
0.003
© Nokia Solutions and Networks 2014
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VoLTE Drop Call Rate
DCR vs. Release Causes
iPhone6 VoLTE
launch
• After iPhone6/6Plus launched with
VoLTE enabled, the VoLTE calls
increased by 6 times.
• VoLTE drop rate KPI is stable with
~1.6% level with more call attempts.
• Howeve, abnormal VoLTE call release
distribution is as follows:
20
© Nokia Solutions and Networks 2014
-
~80% calls are caused by EPC release due to
Radio cause
-
~10% calls are caused by ENB release due to
Radio cause
-
~10% calls are caused by ENB release due to
Other cause
VoLTE KPI Benchmarking
SRVCC success ratio – UTRAN
• VoLTE SRVCC Success Ratio KPI describes inter-RAT HO to UTRAN with SRVCC
success ratio when the source eNB receives information that the U E is successfully
connected to the target cell (UTRAN).
-
This KPI is not triggered by load balancing cases to UTRAN.
-
Reception of an S1AP:UE CONTEXT RELEASE COMMAND message (source eNB <- MME;
3GPP TS 36.413) with Cause value "Radio Network Layer (Successful Handover)" indicates the
successful SRVCC handover. Otherwise, after HO guard timer expiration UE CONTEXT
RELEASE REQUEST is sent by eNB and drop call is counted by ERAB_REL_ENB_QCI1 and and
ERAB_REL_HO_FAIL_TIM_QCI1
E-UTRAN Inter RAT HO UTRAN with SRVCC Success Ratio (LTE_5564a) =
100*sum(ISYS_HO_UTRAN_SRVCC_SUCC)
sum(ISYS_HO_UTRAN_SRVCC_ATT)
21
© Nokia Solutions and Networks 2014
VoLTE KPI Benchmarking
SRVCC success ratio – GERAN
• VoLTE SRVCC Success Ratio KPI describes inter-RAT HO to GERAN with SRVCC
success ratio when the source eNB receives information that the U E is successfully
connected to the target cell (GERAN).
-
This KPI is not triggered by load balancing cases to UTRAN.
-
Reception of an S1AP:UE CONTEXT RELEASE COMMAND message (source eNB <- MME;
3GPP TS 36.413) with Cause value "Radio Network Layer (Successful Handover)" indicates the
successful SRVCC handover. Otherwise, after HO guard timer expiration UE CONTEXT
RELEASE REQUEST is sent by eNB and drop call is counted by ERAB_REL_ENB_QCI1 and
ERAB_REL_HO_FAIL_TIM_QCI1
E-UTRAN Inter RAT HO GERAN with SRVCC Success Ratio (LTE_5567a) =
100*sum(ISYS_HO_GERAN_SRVCC_SUCC)
sum(ISYS_HO_GERAN_SRVCC_ATT)
22
© Nokia Solutions and Networks 2014
SRVCC to WCDMA/GSM
SRVCC failure counter
• SRVCC failure counter
(ISYS_HO_UTRAN_SRVCC_FAIL or
ISYS_HO_GERAN_SRVCC_FAIL ) is
only triggered due to
TS1RELOCoverall expiry in
execution phase and does not give
an exact indication possible failure
case, i.e. SRVCC attempts may be
greater than the sum of SRVCC
success and SRVCC failures.
• Therefore, the exact failure scenario
needs to be checked with a cell trace
from both LTE and 3G side.
23
© Nokia Solutions and Networks 2014
SRVCC Failure Rate
t304 timer impact
• After increasing the t304InterRAT setting from 500ms (default) to 2000ms, the
SRVCC failure rate reduce ~13%, and QCI1 drop rate improvement can be
seen as well
TS1RELOCoverall = TDRX + T304 + T311 + T301 + TS1RELOCoverallDelta
LTE_5572a E-RAB QCI1 DR, RAN view
LTE_5562a Inter RAT HO Att, UTRAN, SRVCC
LTE_5563a Inter RAT HO FR, UTRAN, SRVCC
2.5
140
40
120
35
100
30
25
80
20
60
24
1.5
1
15
40
10
20
5
0
2
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-1
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0
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8
-2
5
0
© Nokia Solutions and Networks 2014
9
-2
5
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SRVCC to WCDMA/GSM
iPhone6 issues with container size limitation
• SRVCC might fail due to size of "source to transparent c ontainer" is more that 255
bytes in S1AP: HandoverRequired message and thus, RNC does not decode WCDMA
BTS ID correctly and voice call is dropped.
-
It could be caused by too big size of UE capability IE especially with Apple iPhones as it
supports lots of bands.
-
As a workaround in some networks, SRVCC to WCDMA is set to both PS + CS in LNADJW
(SRVCC HO indication) because Relocation Request from PS CN has correct information even
though CS CN request is not valid.
-
Another workaround could be the activation of LTE2324 Network requested UE capabilities
feature (FL15A) to limit UE capability information message size in case of CA is enabled in the
network.
-
LTE2324 is based on 3GPP functionality and introduces filtering of supported CA band
combinations on UE side:
•
25
upon eNB request, UE will report supported CA band combinations related only to bands used in Operator’s
network.
© Nokia Solutions and Networks 2014
SRVCC Benchmarking
SRVCC Success Rate
• SRVCC performance for
VoLTE has declining trend with
increased attempts.
SRVCC Success (%)
Inter RAT HO Attempts toUTRAN SRVCC
Inter RAT HOUTRAN with SRVCC Success Rate
95
20 000
720 users - 15 MHz
90
Admission Control Threshold – 75%
85
600 users - 10 MHz
-
18 000
16 000
80
14 000
75
12 000
)
(%70
s
s
e
c
c 65
u
S
10 000
8 000
60
6 000
55
4 000
50
2 000
45
40
0
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© Nokia Solutions and Networks 2014
4
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(#
s
t
p
m
e
tt
A
SRVCC is degraded due to an
issue in MSS not sending proper
cause code for successful
SRVCC HO and thus, SRVCC
success counter is not correctly
incremented.
• IMS network was not
supporting aSRVCC
-
Customized firmware was
created for the phones to do
CSFB instead of VoLTE
when the RSRP is less than
-115 dBm.
SRVCC
Handover interruption time
• There is a short interruption period during SRVCC, i.e. user can notice ‘silent’ period.
• The interruption time of SRVCC should not be higher than 300ms as required in
TS 22.278 from EUTRAN to UTRAN.
27
© Nokia Solutions and Networks 2014
SRVCC to WCDMA/GSM
Challenge
• SRVCC causes always a short audio interruption (<300ms) and therefore, number of
SRVCC attempts should be reduced by lowering triggering threshold as much as possible
→ VoLTE service area is increased.
-
SRVCC threshold and redirection thresholds should be enough far apart to avoid call drop during SRVCC.
• On the other hand, SRVCC should be triggered early enough to avoid degradation of voice
quality → VoLTE service area is reduced.
-
28
SRVCC during the alerting stage without aSRVCC support (terminal/IMS) may cause the increased number of call
setup failures
© Nokia Solutions and Networks 2014
References
KPI definitions
•
Report Set RSLTE052 (accessible from JUMP) in Report Manager collects OSS KPIs and counters to
monitor the traffic load and VoLTE Service Quality.
•
Performance monitoring for VoLTE by NetEng. Based on references from JUMP and RAN LTE KPIs
document is a collection of LTE KPIs and counters used when monitoring the VoLTE service.
KPI values
•
The MBB and NPO KPI commitment targets guideline . Its contents are aligned with the more detailed
document KPI Targets document below. Note: Always download the latest one from the link above.
•
MBB Performance Benchmarker
VoLTE KPI List for Acceptance
•
29
A list covering all domains (not only radio) with OSS and drive test KPIs to be used as part of
customer discussions: VoLTE KPI List for Acceptance
© Nokia Solutions and Networks 2014
VoLTE Voice Quality
30
© Nokia Solutions and Networks 2014
Voice Quality Analysis
Measurement methods
•
Perceptual methods (POLQA) try to model the human perception.
-
Transforms the original and degraded speech signals into a psychophysical representation that approximates
human perception and maps this into an objective MOS score.
-
E2E delay (mouth-to-ear) is not taken into account by POLQA as a degradation of the speech signal but only delay
variations that happen during active speech, i.e. Listening Quality.
Specified by ITU-T
recommendation P.800
•
Non-perceptual methods (E-Model with R-Factor) are general physical or technical measures.
-
31
Combines a number of values measuring the effect of various network impairments such as codec bitrate, jitter,
packet loss as well as mouth-to-ear delay which contributes to Conversational Quality.
© Nokia Solutions and Networks 2014
Voice Quality Analysis
Measurement considerations for drive testing
• Used voice codec will have a big impact on the achieved MOS score
• Also the used voice samples (even languages) will have an effect on the MOS score.
-
Results from different network cannot be compared unless the same sample used for all cases.
• Different handsets have different audio properties (frequency response, distortion, etc.)
-
Changing the handset might give different results
-
In the worst case handset audio module needs to be also calibrated and adjusted as there might
be differences in different units
• Drive test tool hardware (UEs, laptops, audio modules, power supplies, etc.) can have
effect on the MOS score if setup varies (cable routing)
• Other factors, e.g. there has been a case where a faulty switching power supply has
caused interference that has degraded the achieved MOS score
32
© Nokia Solutions and Networks 2014
VoLTE Voice Quality
Voice codecs
• New EVS codec brings substantially
enhanced voice quality, improved error
resilience and increased coding
efficiency for narrowband (NB) and
wideband (WB) audio bandwidths.
33
-
Introduction of super wideband (SWB)
and fullband (FB) audio.
-
Backward compatibility with the Adaptive
Multi-Rate Wideband (AMR-WB) Codec
-
Improved network capacity and coverage
while maintaining the same quality as in
HD Voice
© Nokia Solutions and Networks 2014
9.6 kbps
24.4 kbps
Voice Quality Optimization
PDCP discard timer
t Di scar d
Med ian PO LQA
300ms
2.9
500ms
2.86
1500ms
3.30
• The testing for the cell edge user showed significant MOS i mprovement when tDiscard
(for QCI1) was increased.
34
© Nokia Solutions and Networks 2014
Voice Quality Optimization
PDCP discard timer
• Case #1 (high loaded cells in DL)
-
During high load the HARQ
retransmissions can be delayed in DL
and thus, the total delay can easily
exceed the tDiscard default value:
100ms.
• Case #2 (cell edge user)
-
35
the tDiscard starts running @ PDCP layer
when the PDCP SDU is sent to lower
layer and timer runs despite the lower
layer problems for e.g. SR transmissions
-> some VoLTE packets never
transmitted causing problems for MOS
and causing OWA (One Way Audio)
© Nokia Solutions and Networks 2014
Voice Quality Optimization
PDCP sequence number size
• The UE might experience long lasting UL (or DL)
coverage problems (RTP time out) and eNB might
not hear the SRs at all (sent by PUCCH or RACH)
-
This can cause several PDCP packets to be discarded and
eventually the PDCP HFN in the Tx and Rx (cipher and decipher
respectively) can have a mismatch causing ciphering
(deciphering) problems and RTP time out.
-
Recommendation is to set 12bit to enable 2^12*20=81.92s
duration for better recovery and reduced probability of sequence
number ambiguity.
-
Similarly the RLC header size should be 10bit to enable better
recovery
-
Negative impact of the PDCP SN and RLC SN increase is that
the total TB size due to larger PDCP and RLC overhead.
36
© Nokia Solutions and Networks 2014
Voice Quality Optimization
Field Results
1. From the test resut, disable DRX can improve the RTP Jitter
2. increasing pdcp-SN-Size can further improve RTP jitter and MOS and RTP packet loss
Date
37
Test Case
RSRP
SINR
Packet Loss
Ratio
RTP
Jitter
(ms)
MOS
Duration
Comments
20151215 Default
-83.172
14.767
0.83%
3.83
14.37
286.31
20151215 Test case1
-83.166
15.129
0.58%
3.8
9.57
309.46
Disable QCI1 DRX
20151215 Test case2
-82.765
14.942
0.03%
3.98
7.99
281.86
Disable QCI1 DRX, AND
pdcp
© Nokia Solutions and Networks 2014
Voice Quality Optimization
PDCP Parameters
Parameter
pdcpProf101 - rohcMaxCid
pdcpProf101 - snSize
pdcpProf101 - tDiscard
38
Value
Description
Remarks
This parameter configures
the maximum number of
ROHC contexts used for a
data radio bearer in one
direction.
Intel chipset based iPhone7 models (A1778, A1784) are
suffering from a UE device SW bug that can lead to VoLTE
call drops and to a temporary loss of service under certain
circumstances. Therefore, Nokia recommends to all
customers that have a substantial amount of Intel based
iPhone7 in their network to implement the parameter
mitigation action (LNBTS:rohcMaxCid = 2).
12bit
This parameter configures
the size of the SN field in t he
PDCP header
It may be beneficial to increase to 12 bits (s equence number
range corresponds to 81.92 secs) to improve PDCP
recovery in case of lost packets and avoid RTP timeout. This
increases the PDCP overhead but reduces the probability of
sequence number ambiguity.
300ms
This parameter indicates the
delay before a PDCP PDU
along with the corresponding
PDCP SDU is discarded
from the buffer.
The cell edge user might experience MOS improvement and
reduction of discard packets when tDiscard (for QCI1) is
increased, e.g. 300ms
2
© Nokia Solutions and Networks 2014
Voice Quality Optimization
RLC Parameters
Parameter
rlcProf101 - snFieldLengthDL
rlcProf101 - snFieldLengthUL
rlcProf101 - tReord
39
Value
Description
10bit
This parameter configures
the length of the SN field for
RLC UM procedures in
downlink direction.
10bit
This parameter configures
the length of the SN field for
RLC UM procedures in
uplink direction
50ms
This timer is used by the
receiving side of an UM RLC
entity for reordering and PDU
loss detection.
© Nokia Solutions and Networks 2014
Remarks
It may be beneficial to increase to 10 bits (s equence number
range corresponds to 20.48 secs) to improve RLC recovery
in case of lost packets and avoid RTP tim eout. This
increases the RLC overhead but reduces the probability of
sequence number ambiguity.
This timer depends on HARQ RTT and number of HARQ
retransmissions.
VoLTE Mobility
40
© Nokia Solutions and Networks 2014
VoLTE Layering Strategy
• The layering strategy for the initial VoLTE deployments globally is depending on
country regulations, network topology and available spectrum.


41
LTEnetworkmay
nothavenothave
contiguous
coverage
VoLTEisenabled
acrossallthe
carrierstoprovide
thebestpossible
service
accessibility
© Nokia Solutions and Networks 2014



Trafficsteeringis
handledbyidleor
connectedmode
loadbalancing
features
VoLTEtrafficmay
nothavea
dedicatedlayer
TD-LTEmaynot
beallowedtobe
usedforVoLTE
serviceaccording
togovernment
regulationsin
somecountries
VoLTE Layering Strategy
Introduction
• However, VoLTE traffic steering with proper layering management could be beneficial in
order to improve network efficiency and end user experience for both VoLTE and data
services.
-
Steering VoLTE traffic to dedicated layer free up control and data channel resources for non-VoLTE
users and thus, average throughput of data user s might increase.
-
Target VoLTE layer may have a better continuous coverage and therefore, VoLTE speech quality is
improved due to less frequent IFHO/SRVCC handovers, i.e. less voice interruptions during HO
measurement and execution phase.
• VoLTE calls can be steered to the preferred frequency layer using either service based
handover upon QCI1 bearer establishment or coverage/load based handovers.
-
42
On the other hand, traffic steering is also increasing inter-frequency handovers in the network
which might lead drop calls unless mobility parameters are properly optimized.
© Nokia Solutions and Networks 2014
Idle Mode Mobility
General strategy
Priority Scheme
• The general strategy is to use idle mode reselection
based on absolute priorities, i.e. UEs are pushed to
the highest priority LTE layer (e.g. carrier with largest
bandwidth) and UEs only move away from the highest
priority layer when coverage becomes poor.
-
Higher Priority Reselection: UE always searches for
higher priority layers
-
Lower Priority Reselection: UE only searches for lower
priority when source layer falls below a certain threshold
• Note that VoLTE users cannot be steered differently
from data users in idle mode, i.e. existing strategy
applies also after VoLTE deployment.
43
© Nokia Solutions and Networks 2014
e
l
b
a
li
a
v
a
n
e
h
w
r
e
y
a
l
q
e
rf
t
s
e
h
g
i
h
o
t
e
v
o
m
s
E
U
LTE 2600 (F4)
7
LTE 2100 (F3)
6
LTE 1800 (F2)
5
LTE 900 (F1)
4
UMTS2100
3
GSM900
2
Idle Mode Mobility
Considerations for SBHO parameterization
• Service based handover is recommended to offload VoLTE users to preferred frequency
layers from non-VoLTE layers.
• However, the target VoLTE layer should be set as a lower priority layer for idle mode cell
reselection otherwise non-VoLTE users can camp VoLTE preferred layer and establish PS
data call.
VoLTE user (Service Based HO)
Priority 6
Priority 5
44
© Nokia Solutions and Networks 2014
F2 Data layer
VoLTE and Non-VoLTE user
(Cell Reselection)
F1 VoLTE layer
LTE Idle Mode Measurements and Cell Reselection Thresholds
Parameter alignment
Intra-frequency measurements will be started at
qrxlevmin + sIntrasearch. Relatively high threshold is
recommended in order to allow UE always to camp on the
best cell (drawback is higher UE batt ery consumption).
Inter-frequency and inter-RAT measurements will be
started at qrxlevmin + s NonIntrs earch. The lower exit
threshold can be applied in case of the strategy is to
sustain more traffic in LTE.
UE is allowed to camp on LTE cell when RSRP level
exceeds qrxlevmin (must be aligned with
qrxlevminintraF , qRxLevMinInterF and
A djL Qr xlevmi nE UTR A )
Intra-frequency cell reselection to other LTE
cell will happen when neighbor is qHyst dB
better than serving cell.
interFrqThrH
RSRP decreases
s Intras earch
s NonI ntrs earch
Inter-frequency cell reselection towards a higher priority
LTE layer will be always triggered while a neighboring cell
coverage is better than qRx LevMinInterF + interFrqThrH
The inter-RAT cell releselection from WCDMA towards a higher
priority LTE will be always triggered while a LTE neighboring cell
coverage is better than A djL Qr xlevmi nE UTR A + AdjL Thr es hig h.
The lower threshold can be applied in case of the strategy is
capture more traffic to LTE.
45
© Nokia Solutions and Networks 2014
threshSrvLow
qrxlevmin
Inter-frequency cell reselection towards a lower priority LTE
layer will be triggered once a own serving cell coverage falls
below qrxlevmin + threshSrvLow and a neighboring cell is
better than qRxL evMinInterF + interFrqThrL
If no suitable LTE cell found, then reselection to WCDMA will
happen when a neighbouring UMTS cell RSCP is better than
qRxLevMinUtr + UtraFrqThrL
The target UMTS cell must also have a CPICH Ec/Io >
qQualMinUtra.
Sufficient (e.g. 6dB) hysteresis required to avoid ping-pong effect because
Tracking Area Updates (TAU) might be drastically increased due to too small
hysteresis. MT calls may be directed to voice mail because UEs might not
receive paging messages during TAU procedure.
Connected Mode Mobility
General strategy for VoLTE
• The general strategy for VoLTE deployment is to initially enable voice service on all
carriers in the network in order to ensure maximum coverage and accessibility.
• Once VoLTE traffic is increasing the strategy should be reviewed and possible layering
options studied to gain understanding of the impact of network capacity and coverage on
both VoLTE and data services.
• VoLTE preferred frequencies can be chosen based on the following factors:
46
-
Coverage: Contiguous coverage to avoid risk of dropped calls due to IFHO or SRVCC handovers.
Alternatively, low frequency band operation for higher cell range is beneficial to minimize the
number of handovers as well as to provide a good indoor coverage.
-
Capacity: Frequency band with highest capacity (i.e. large bandwidth) can serve more VoLTE
users and on the other hand, data users might have improved throughputs on non-VoLTE layers
due to more scheduling occasions without VoLTE traffic.
© Nokia Solutions and Networks 2014
LTE Connected Mode Measurements and Handover Thresholds - Data
Parameter alignment
Inter-frequency measurements will be started at
threshold2InterFreq and A3 event is triggered once neighbouring
cell becomes a3OffsetRsrpInterFreq better than serving cell. The
recommendation is to activate LTE inter-frequency measurements
2-3 dB earlier than I-RAT measurements to favor handover to other
LTE frequency before moving to WCDMA.
Intra-frequency neighbouring
cell measurements will be
started at Threshold1
RRC connection release with
redirect will be started at
threshold4
Thresholds are relative to -140 dBm
Inter-RAT WCDMA
measurements will be
started at
threshold2Wcdma.
Threshold2a
RSRP decreases
Threshold1
b2Threshold1Utra
threshold2InterFreq
threshold2Wcdma
Inter-RAT and interfrequency measurements
are stopped at Threshold2a
threshold4
-140
Inter-RAT handover will be triggered once a serving cell
coverage falls below b2Threshold1Utra and a
neighboring cell RSCP and/or EcNo is better than
b2Threshold2UtraRscp and/or b2Threshold2UtraEcn0
Cell reselection hysteresis from WCDMA to LTE should be
large enough to avoid UE immediately handover back to
WCDMA once entering the RRC connected mode (e.g. to
perform Tracking Area Update) in LTE.
47
© Nokia Solutions and Networks 2014
LTE Connected Mode Measurements and Handover Thresholds - VoLTE
Parameter alignment
Inter-frequency measurements will be started at threshold2InterFreqQci1
and A3 event is triggered once neighbouring cell becomes
a3OffsetRsrpInterFreqQci1 better than serving cell. The recommendation
is to activate LTE inter-frequency measurements 2-3 dB earlier than
SRVCC measurements to favor handover to other LTE frequency before
moving to WCDMA.
Intra-frequency neighbouring
cell measurements will be
started at Threshold1
SRVCC measurements
will be started at
threshold2WcdmaQci1.
Threshold2aQci1
RSRP decreases
Threshold1
threshold2InterFreqQci1
threshold2WcdmaQci1
Inter-RAT and inter-frequency
measurements are stopped at
Threshold2aQci1
48
b2Threshold1UtraQci1
© Nokia Solutions and Networks 2014
Thresholds are relative to -140 dBm
RRC connection release with
redirect will be started at
threshold4. Parameter
a2RedirectQci1 (= disabled)
can be configured not to
trigger redirection for VoLTE
users
threshold4
-140
SRVCC handover will be triggered once a serving cell coverage falls
below b2Threshold1UtraQci1 and a neighboring cell RSCP and/or
EcNo is better than b2Threshold2UtraRscpQci1 and/or
b2Threshold2UtraEcn0 Qci1
VoLTE Layering Strategy
Considerations for IFHO parameterization
• LTE inter-frequency measurement can be triggered at the same conditions
(threshold2InterFreqQci1 = threshold2InterFreq) for both VoLTE and non-VoLTE users
but measurements should not be configured too early before better cell (A3) criteria can
be met because there is no data transmission during measurement gaps which may lead
to user throughput and speech quality deterioration.
-
The better cell (A3) inter-frequency handover from co-sited low frequency band to high frequency
band layer is advisable to be disabled for both VoLTE and data service and use idle mode selection
instead to avoid frequent IFHOs.
-
Note also that frequent IFHO attempts might increase the propability of VoLTE call drops in case
IFHO handover is in progress while EPC requests to modify/release QCI1 bearer and t herefore,
eNB may reject ‘parallel’ EPC request (36.413 - chapter 8.2) causing failure from MME/PGW
perspective.
•
49
GBR E-RAB modification can occur when core network supports services which may require a change in the
GBR bitrate, e.g. answering machine and conference call.
© Nokia Solutions and Networks 2014
VoLTE Layering Strategy
Considerations for SRVCC parameterization
• VoLTE users are recommended to start measuring WCDMA layer earlier than nonVoLTE users (threshold2WcdmaQci1 > threshold2Wcdma)
• SRVCC to trigger 2-3dB earlier than PS handover to maintain voice service quality
perceived by end users (b2threshold1UtraQci1 > b2Threshold1Utra).
50
© Nokia Solutions and Networks 2014
SRVCC Performance
SRVCC I-RAT measurements
Modus
avg time
Blind redirection w/o SRVCC and no 3G MEAS
110 ms
3G MEAS 1 neighbour 3G cell @ 1 UTRAN carrier
556 ms
3G MEAS 6 neighbour 3G cells @ 1 UTRAN carrier
707 ms
3G MEAS 12 neighbour 3G cells @ 1 UTRAN carrier
760 ms
3G MEAS 6+6 neighbour 3G cells @ 2 UTRAN carriers
853 ms
•
If the measurements are started too late (low A2 threshold) and too large amount of 3G neighbors the
UE does not have enough time to send measurement reports (B2) hence the call drops.
•
If A2 is set very close to B2 threshold this will reduce the time during which the measurement gaps
are scheduled to the mobile which may lead to non -optimal choice of target RAN cell if UE does not
have time to measure the best target cell (e.g. long neighboring list).
•
However, if the SRVCC is triggered too early there might be too many SRVCC attempts and aSRVCC
attempts causing further challenges in case not supported by IMS.
51
© Nokia Solutions and Networks 2014
SRVCC Performance
Setting B2 threshold
• If RRC release with redirect is
triggered before SRVCC the
VoLTE call drops. Especially,
high speed users can
experience this problem.
VoLTE call drop case by redirect (from field measurement)
No SRVCC
RSRP suddenly
degraded
• Sufficient margin between
SRVCC and RRC release with
redirect threshold need to be
assigned.
• In FL15A new parameter
a2RedirectQci1 = disabled
allows to disable redirection for
VoLTE users
52
© Nokia Solutions and Networks 2014
VoLTE call
dropped
SRVCC Performance
Disabling redirection for QCI1
• After disabling the redirection for QCI1:
-
Volte drop call rate (LTE_771 + LTE_5572) reduce significantly
-
This indirectly cause higher SRVCC attempts, though SRVCC FR still remain at similar level
2.5
120
2
100
40
35
30
80
1.5
25
60
1
15
40
10
0.5
20
0
5
0
0
LTE_771b Rel R, QCI1 ENB rel, RNL Redir
LTE_5562a Inter RAT HO Att, UTRAN, SRVCC
LTE_5572b E-RAB QCI1 DR, RAN view
LTE_5563a Inter RAT HO FR, UTRAN, SRVCC
Parameter Name
a2RedirectQci1
53
20
MOC
LNCEL
Full Name
<Change information classification in footer>
© Nokia Solutions and Networks 2014
A2 based redirect for VoLTE calls
Current value (Internal) Proposed value (Internal)
enabled (1)
disabled (0)
SRVCC
RSRQ based SRVCC HO
• If SRVCC triggering threshold is set to very low value the user might experience bad RF
quality before RSRP threshold is reached.
• However, SRVCC trigger (B2) is typically based on RSRP and thus, SRVCC is not
triggered once RSRQ degrades.
• LTE2572 RSRQ based B2 feature is available from FL17 onwards.
Do we need RSRQ based SRVCC
triggering?
VoLTE
(QCI1)
LTE
WCDMA
SRVCC threshold
(current:-113dBm)
54
© Nokia Solutions and Networks 2014
SRVCC threshold(after)
SRVCC
RSRQ based SRVCC HO
• Relation between RSRQ and UL BLER shows that VoLTE voice quality deteriorates when
RSRQ becomes lower than -14dB @ UL BLER = 20%
RSRQ
Call
drop
Clear voice quality
BLER
20%
55
© Nokia Solutions and Networks 2014
Partially
missing
Almost
missing
-5
○
-6
○
-7
○
-8
○
-9
○
-10
○
-11
○
-12
○
-13
○
-14
△
-15
△
-16
△
-17
▲
-18
▲
-19
×
Relation
between voice
quality and
RSRQ
Legend
○
Clear voice
Partially missing
voice
▲ Almost Missing
voice
×
Call drop
△
VoLTE Mobility Handling Features




56
ServicebasedMobilityTrigger
Servicebasedmobilitythresholds
DedicatedVoLTEinter-frequencytarget
frequencylist
QCI1EstablishmentTriggeredProtection
Timer
© Nokia Solutions and Networks 2014





DedicatedMobilityThresholdsforSRVCC
SRVCCTriggerEnhancements
SRVCCduetoAdmissionControlRejection
RSRQbasedB2
VoLTEqualitytriggeredSRVCCtoGSM
VoLTE Radio Optimization
Periodical CQI Reporting
57
© Nokia Solutions and Networks 2014
VoLTE Drop Call Optimization
CQI report failure detected on PUCCH
•
*Only 1 days data
58
© Nokia Solutions and Networks 2014
From Traffica news, more
than 50% call failures are
cause by CQI report failure
detection on PUCCH
VoLTE Drop Call Optimization
eNB Detected Radio Link Failures (RLF) – CQI DTX Detection
• Nokia eNB can use periodic CQI reports for radio link failure detection on PUCCH and
PUSCH
-
If MAC layer receives nCqiDtx consecutive reports from UL PHY, the MAC declares CqiRlf_ON
(this can be seen in BTS log and Emil)
-
If the MAC has set CqiRLF_ON for a specific UE and nCqiRec consecutive CQI reports are
again detected successfully for that UE, the MAC sets CqiRlf_OFF.
-
When a radio link problem is detected, an eNB-internal timer (T_RLF = T310 + T311 + 2200ms) is
started and stopped in case of radio link recovery or otherwise RRC+S1 release is triggered by
eNB
• In case the periodical CQI reporting periodicity is increased (or detection is disabled)
the dropped call rate decreases as some of the unnecessary call releases can be
avoided.
• NOTE: CQI_RLF detection does not apply to aperiodic CQI report in PUSCH
59
© Nokia Solutions and Networks 2014
VoLTE Drop Call Optimization
eNB Detected Radio Link Failures (RLF) – CQI DTX Detection
RLF timer running
T_RLF = t310 + t311
I
Q
C
ic
d
io
r
e
P
d
te
c
te
e
d
I X
Q T
C D
d
te
c
te
e
d
I
Q
C
ic
d
io
r
e
P
I X
Q T
C D
I X
Q T
C D
I X
Q T
C D
I X
Q T
C D
I X
Q T
C D
I X
Q T
C D
I X
Q T
C D
I X
Q T
C D
I X
Q T
C D
d
te
c
te
e
d
I
Q
C
ic
d
io
r
e
P
d
te
c
te
e
d
I
Q
C
ic
d
io
r
e
P
time
LNCEL/cqiPerNp=10ms
Example Vendor Parameter Values:
nCqiDtx=4
nCqiRec=2
60
© Nokia Solutions and Networks 2014
CQI_RLF ON
CQI_RLF
OFF
VoLTE Drop Call Optimization
•
E-RAB drop call rate has increased
from mid-March and it goes up to
0.2%, i.e. 2x higher than before.
•
However VoLTE drop looks no
difference.
•
Samsung Galaxy Note 3 was
launched at mid of March
ERAB Drop increased
suddenly
From mid of March
No Changes in VoLTE
Drop Ratio
61
© Nokia Solutions and Networks 2014
VoLTE Drop Call Optimization
Samsung Mobile Issue
•
Due to Missing CQI report from Galaxy Note3 (NB3, NBD, NC3 version), eNB detect CqiRLF_ON and send
UEcontextReleaseRequest to MME with “radio connection with ue lost” Cause
Nomal case – CQI report
Abnormal case – no CQI report
62
© Nokia Solutions and Networks 2014
VoLTE Drop Call Optimization
nCqiDtx from 100 to 0
•
Both E-RAB DR(LTE_5025D) and E-RAB DR,
QCI1(LTE_5572A) is decreased
•
•
63
© Nokia Solutions and Networks 2014
eNB RLF detection
based on periodic CQI
reporting was disabled
(nCqiDtx=0):
E-RAB DR
(LTE_5025D) is
dropped from 0.068%
to 0.055% in average
(19% improvement)
E-RAB DR,
QCI1(LTE_5572A) is
decreased from 0.116%
to 0.094% in average
(19% improvement)
LTE2206: Extended RLF handling
Feature in the Nutshell
• FL16 feature allows tuning RLF detection sensitivity at eNB in order to keep UEs longer
in RRC connection state.
• It applies to cases the eNB indicates RLF due to CQI DTX
- The tuning is possible by setting LNBTS:nCqiDtx and LNBTS:nCqiRec parameters
• LTE2206 does not change RLF detection functionality, sensitivity RLF indication is
issued
Before introduction LTE2206 feature:
With LTE2206 feature:
Range and step
LNBTS:nCqiDtx==100
LNBTS:nCqiRec==2
64
© Nokia Solutions and Networks 2014
Hardcoded
values
LNBTS:nCqiDtx
LNBTS:nCqiRec
0…250 step 1
1…8 step 1
VoLTE Radio Optimization
QCI1 Specific T310 and T311 Timers
65
© Nokia Solutions and Networks 2014
VoLTE Drop Call Optimization
Physical Layer Failure & Recovery
• Timer T310 supervises the recovery from physical layer problems and Timer T311
supervises the RRC connection re-establishment.
1. UE detects 1st out of
synchronization
3. T310 expires -> detection of radio link
failure : all RBs are suspended except
SRB0, the UE tx turned off in 40ms, the UE
initiates RRC re-establishment process and
searches for the best cell. T311 is started
6. UE acquires UL grant via random access
procedure and physical layer sends RRC
connection re-establishment request message
4. UE finds suitable cell
T310 running
2. UE detects n310 amount
of out of synchronization ->
The UE starts timer T310
66
© Nokia Solutions and Networks 2014
Time
T311 running
5. UE acquired System Information of
the target cell. The UE layer 3 sends
RRC connection re-establishment
message to the lower layers. T311 is
stopped and T301 started.
7. UE receives RRC connection reestablishment message and timer
T301 is stopped. SRB1 is resumed
and layer 3 sends RRC connection
re-establishment complete message
to physical layer and procedure ends.
LTE1569: QCI1 Specific RLF and Re-establishment Control
QCI1 specific T310 and N310
Only UEs Rel. 9 and higher are benefiting from LTE1569
LTE1569 allows to configure QCI1 specific settings of N310 (LNCEL:n310qci1) and T310 (LNCEL:t310qci1) which are provided to the
UE during QCI1 bearer establishment by RRC Connection Reconfiguration message (overwriting SIB2 broadcasted values).
When UE is ending the VoLTE call, eNB sends RRC Connection Re-configuration message to release QCI1 DRB, this message
includes also RLF-TimersAndConstants-r9 IE with legacy values of T310 and N310 (LNCEL:t310 and LNCEL:n310).
System Information Block Type 2
Information Element
Parameter
RRC Connection Reconfiguration
Information Element
Parameter
RLF-TimersAndConstants-r9
Ue-TimersAndConstans
> t300
LNCEL:t300
> t300-r9
LNCEL:t300
> t301
LNCEL:t301
> t301-r9
LNCEL:t301
> t310
LNCEL:t310
> t310-r9
LNCEL:t310qci1
> n310
LNCEL:n310
> n310-r9
LNCEL:n310qci1
> t311
LNCEL:t311
> t311-r9
LNCEL:t311
> n311
LNCEL:n311
> n311-r9
LNCEL:n311
Ue-TimersAndConstans from broadcasted SIB2 are replaced
in the UE by parameters from RLF-TimersAndConstants-r9 in
RRC Connection Reconfiguration
The rest of the parameters needed for
rlf-TimersAndConstants IE are taken from legacy
parameters used for SIB2.
Note: If configured QCI1 specific T310 and N310 are equal to legacy values, eNB will not include rlf-TimersAndConstants IE.
67
© Nokia Solutions and Networks 2014
VoLTE Drop Call Optimization
Field Trial Settings
• Tests were performed with 3 different parameter settings:
Abbreviate
d Name
68
Full Name
MO
Modification
Class
Range and step
Set 1:
Feature
OFF
n310Qci1
N310 for QCI1
LNCEL
On-line
1:n1;2:n2;3:n3;4:n4;6:n6;8:n8;10:n10;20:n20
-
t310Qci1
T310 for QCI1
LNCEL
On-line
0:0ms;50:50ms;100:100ms;200:200ms;500:500ms;1
000:1000ms;2000:2000ms
-
n310
Maximumnumberof
out-of-sync
LNCEL
indications
On-line
0:n1;1:n2;2:n3;3:n4;4:n6;5:n8;6:n10;7:n20
t310
Timer T310
LNCEL
On-line
0:0ms;1:50ms;2:100ms;3:200ms;4:500ms;5:1000ms
;6:2000ms
N311
Maximumnumberof
LNCEL
in-syncindications
On-line
0:n1;1:n2;2:n3;3:n4;4:n5;5:n6;6:n8;7:n10
T311
Timer T311
LNCEL
On-line
t301
Timer T301
LNCEL
On-line
© Nokia Solutions and Networks 2014
0:1000ms;1:3000ms;2:5000ms;3:10000ms;4:15000
ms;5:20000ms;6:30000ms
0:100ms;1:200ms;2:300ms;3:400ms;4:600ms;5:100
0ms;6:1500ms;7:2000ms
-
n6
1000ms
1000ms
n1
n1
n1
3000ms
3000ms
3000ms
400ms
400ms
400ms
VoLTE Drop Call Optimization
Field Trial Results
• Set 1: initial ERAB drop rate for QCI1 with feature not activated: 0.14%
• Set 2: reduction of T310qci1 to 500ms improvement of ERAB DR QCI1 to 0.10%
• Set 3: reduction of N310qci1 from n6->n4
n6 ->n4 did not lead to further
furt her reduction, result:0.13%
result: 0.13%
VoLTE capable Rel. 9 UEs during test: >95% => Higher penetration would even improve result
69
© Nokia Solutions and Networks 2014
VoLTE Drop Call Optimization
Field Trial Results
• Target is to start early re-establishment
re -establishment procedure by UE before call drop
drop,, but not to trigger too
early re-establishements and therefore, increase the risk to drop the call by a failed re-estabishment
re -estabishment
procedure itself
• Set 1:
1: Default parameters are T310=2000ms and N310=n10 -> Network was already adapted to
T310=1000ms, N310=n6 which leads to an improved ERAB DR.
tr iggering of re-establishment procedure
• Set 2: QCI1 specific T310qci1 reduction leads to earlier triggering
by UE and therewith to a further improvement of ERAB QCI1 DR from 0.14% -> 0.10%
• Set 3:
3: Further parameter adaptions to trigger re-establishment procedure by UE even earlier lead
to an increase of DR compared to previous setting (Set 2) -> increased amount of reestablishement procedures finally lead to an increased DR as re-establishement
re -establishement procedure might
fail as well
-
70
It is recommend
recommended
ed to activate
activate feature LTE161
TE1617
7 RLF trigger
triggered
ed handove
handoverr to improve
improve reestabliment success in overall.
© Nokia Solutions and Networks 2014
VoLTE Radio Optimization
DRX – Optimized Algorithm
71
© Nokia Solutions and Networks 2014
VoLTE Handset Power Consumption
Battery consumption:
E
G 
N
E
L
L
A
H 
C
E
H
T
VoLTE users have a high battery
consumption due to a long call session
time compared to data users
Voice application running in the handset
application processor requires a lot of
power
40 ms
Sleep mode
1 ms
VoLTE packets

Handset power consumption is generally minimized by integrating a VoLTE client into the modem
processor (chipset)

DRX (Discontinuous Reception) functionality uses sleep mode in the handset between VoLTE
packet receptions – eVTT profile further enhances battery savings
72
© Nokia Solutions and Networks 2014
VoLTE Handset Power Consumption
VoLTE
VoL
TE optimized
op timized DRX
• Different voice services tested on same
smartphone
-
3G CS AM
AMRR-WB
WB an
and
d AM
AMRR-NB
NB
-
Native VoLTE
-
VoIP (Viber)
• Without VoLTE optimized DRX
-
VoL
oLTE
TE cons
consume
umes
s up to 88%
88% highe
higherr power
power tha
than
n
3G CS call
-
Viber con
Viber
consum
sumed
ed up to
to two
two times
times mor
more
e powe
powerr
than 3G CS call
• With VoLTE optimized DRX
-
73
VoL
oLTE
TE has
has simil
similar
ar power
power con
consum
sumpti
ption
on as
as 3G CS
CS
call
© Nokia Solutions and Networks 2014
300
VoLTE
248
250
) 200
A
m
(
t
n150
e
rr
u
C
235
154
129
131
125
121
100
50
0
3G CS 3G CS noDRX
AMR-NB AMR-WB
DRX
20ms
6ms
OnDur
DRX
40ms
6ms
OnDur
DRX
40ms
4ms
OnDur
Viber
VoLTE Drop Call Optimization
DRX Impact on Poor RF
• The current analysis of DRX problems indicate that in case of poor RF the DRX causes
additional dropped calls:
-
These
The
se dro
droppe
pped
d call
calls
s coul
could
d be
be cause
caused
d by
by additional delays caused by DRX
-
Meas
Me
asur
urem
emen
entt de
dela
lay
ys for handovers
-
Measur
Meas
urem
emen
entt in
inac
accu
cura
raci
cies
es of CQI (reported CQI in DRX active state might not correctly reflect the
RF quality due to the DRX sleep state)
-
Due to th
thiis th
the
e LA might not work accurately and fast enough to be able to react on changing CQI in
poor RF and UE might never hear the HO command
• The DRX feature can be improved so that it could be turned off in poor RF (based on
CQI) and turned on in case of improved
i mproved RF (improving absolute CQI value)
74
© Nokia Solutions and Networks 2014
VoLTE Drop Call Optimization
DRX Optimized Algorithm for VoLTE
• If UE has QCI-1 DRB and DRX is currently enabled, and C-plane receives RL Status
Indication for this UE indicating “ BadChannelQuality
BadChannelQuality”” then C-plane
C-plane sends RRC
Reconfiguration message to UE to disable DRX:
rrcConnectionReconfiguration-r8 :
rrcConnectionReconfiguration-r8
{
radioResourceConfigDedicated
{
mac-MainConfig explicitValue :
{
drx-Config release : NULL,
…
}
• If UE has QCI-1 DRB and DRX was previously disabled due to Poor RF
RF,, and C-plane
receives new RL Status Indication for this UE indicating “ GoodChannelQuality
GoodChannelQuality”,
”, then CCplane sends RRC Reconfiguration message to UE to re-install the DRX profile (i.e. reenable DRX) provided that other DRX feature add conditions (feature flag, configuration,
etc.) are satisfied
75
© Nokia Solutions and Networks 2014
VoLTE Optimized DRX
Thresholds
• The parameters should be set according
to the network statistics i.e.
- qci1DrxOnThreshold (default=9) should be
set according to the average reported CQI
across the whole network i.e. if average
reported CQI = 9 then CDrxOnThreshold
should be set to 9.
- qci1DrxOffThreshold (default=7) should be
set 2 steps below the above parameter
value
• Above parameters will be tunable
parameters in release 16 (defaults used
as above)
76
© Nokia Solutions and Networks 2014
VoLTE Optimized DRX
DRX Optimized Algorithm for VoLTE – Field Test
• CQI threshold for deactivation and activation need to be set according to network
performance
DRX OFF
77
© Nokia Solutions and Networks 2014
CQI
7-9
DRX OFF
CQI
9-11
Average CQI is 11 or
higher in the cluster and
therefore, CQI thresholds
needs to be set higher
High Speed Users
Optimization
78
© Nokia Solutions and Networks 2014
High Speed Users Optimization
Doppler shift
• When a user is moving relative
to an eNodeB, the transmit
frequency of the eNodeB is
different from the receive
frequency of the user due to the
Doppler shift.
Access Point
• In an LTE system, this Doppler
shift causes interference in or
between OFDM symbols.
• The faster the speed the greater
the shift and thus, the
interference.
79
© Nokia Solutions and Networks 2014
The highest Doppler shift is experienced by the UE that is in the
middle of the two cells that are pointing towards each other
High Speed Users Optimization
High speed UE definition
•
UE should be considered as high speed UE in case Doppler shift at eNB is higher than 400Hz
•
LTE48 Support of High Speed Users feature improves the eNB UL reception performance for the high
speed users but does not bring any gain for the low speed user (Doppler shift less than 400 Hz)
•
Because of the frequency offset estimation and the signal correction, the computation complexity and
the processing latency are increased at eNB - Therefore the feature activation should be a subject for
consideration during the network planning by the customer
•
Table below shows exemplary calculations for different frequency bands:
80
Frequency Band [MHz]
High speed UE in case UE speed is
higher than app.[km/h]
1900
>110
2300
>90
2600
>80
© Nokia Solutions and Networks 2014
v[km/ h]
F _ o[ H z]

2 F _ c[G H z] 0.926


High Speed Users Optimization
LTE48 Support of High Speed Users
• LTE48 Support of High Speed Users feature can be activated by setting the parameter
prachHsFlag = ‘true’ (requires object locking)
- The range of allowed rootSeqIndex values becomes limited (restricted set) and the
number of PRACH sequences which can be generated from each root sequence is no
longer fixed -> RSI re-planning is required.
- hsScenario must be configured to ‘ scenario1’ or ‘scenario 3’ dependently on the
deployment scenario - Scenario 1 (open space scenario) and scenario 3 (tunnel
scenario) defined by 3GPP
- ulCombinationMode must be set to ‘MRC’, i.e. LTE1402 Intra eNB UL CoMP cannot
be used.
81
© Nokia Solutions and Networks 2014
High Speed Train Optimization
KPI Improvement after prachHsFlag=true
RRC Performance
DRB Performance
Total Att LTE_753A
CSSR LTE_5218C
100.00
20,000
98.00
15,000
96.00
10,000
94.00
92.00
5,000
90.00
0
0
0
.
8
2
.
4
0
6
0
.
8
2
.
4
0
2
1
.
8
2
.
4
0
8
1
.
8
2
.
4
0
before
6
2
0
0
.
9
2
.
4
0
0
.
9
2
.
4
0
1
.
9
2
.
4
0
8
1
.
9
2
.
4
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© Nokia Solutions and Networks 2014
98.00
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eRAB Performance
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High Speed Train Optimization
KPI Improvement after prachHsFlag=true
Intra ENB HO Att LTE_5124A
Inter ENB HO Att LTE_5125A
Intra ENB HO Prep att LTE_5123A
Inter ENB HO Prep att LTE_5126A
Intra ENB HO SR total LTE_5043A
Inter ENB HO SR total LTE_5058B
Intra ENB HO SR LTE_5035A
Inter ENB HO SR LTE_5048B
Intra ENB HO Prep SR LTE_5036A
Inter ENB HO Prep SR LTE_5049B
100.00
45,000
40,000
35,000
30,000
25,000
20,000
15,000
10,000
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after
before
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High Speed Train Optimization
LTE2445: Combined Supercell
• High speed users handovers occur very frequently causing a large amount of signaling.
Moreover, the train is running between cell centers and cell edges, which significantly
impacts data rates even causing service drops.
• LTE2445 Combined Supercell feature
reduces drastically the handover
frequency in high speed scenarios.
84
-
The UE can move seamlessly between
subcells, without interruption by a RACH
procedure due to cell change as with
normal cells
-
6 RRH support allows for extended
supercell coverage
© Nokia Solutions and Networks 2014
High Speed Train Optimization
VoLTE tunnel performance
• There are many RRC re-establishments of VoLTE call due to RLFs when train goes
through a tunnel and thus, RRC re-establishment causes missing voice packets and end
user experience is degraded.
RSRP
RSRQ
RRC
Re-establishment
VoLTE Packet
85
Re-esta
© Nokia Solutions and Networks 2014
Re-esta
Re-esta
Re-esta
High Speed Train Optimization
VoLTE tunnel performance
• LTE drop rate is around 38% but WCDMA’s drop rate is lower than LTE in tunnel sites.
Drop Rate (ADR) [%]
LTE
60
WCDMA
50
WCDMA Voice
should be used
when train goes
through a tunnel
40
30
Lower
drop rate
20
10
0
86
© Nokia Solutions and Networks 2014
.
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High Speed Train Optimization
Possible design concept
• To make UEs enter tunnels continuously without drop, our new design forces VoLTE UEs
to move to WCDMA by SRVCC in tunnel adjacent sites and tunnel si tes.
Forced SRVCC to WCDMA AMR
Tunnel
VoLTE
LTE
WCDMA
87
AMR
© Nokia Solutions and Networks 2014
AMR
High Speed Train Optimization
TAC design
• In case VoLTE is launched for certain areas only the design of TAC and eNB QCI1
support needs to be as below
SRVCC to WCDMA AMR
VoLTE area
Non VoLTE area
LTE
WCDMA
TAC
Configuration
eNB
Configuration
88
VoLTE ON site
VoLTE OFF site
VoLTE OFF site
VoLTE ON TAC
VoLTE OFF TAC
VoLTE OFF TAC
VoLTE ON
VoLTE ON
VoLTE ON
© Nokia Solutions and Networks 2014
High Speed Train Optimization
Considerations
• If VoLTE is supported by the target eNB but the TAC of the target eNB does not support
VoLTE then the HO for QCI1 should go through and path switch should be possible.
However there might be differences in different vendor’s MMEs.
• Also whether the UE SIP client drops the call or not (UE sending SIP : BYE message)
when TAC without VoLTE support is detected depends on the UE implementation.
• Therefore SRVCC to WCDMA is recommended to be triggered.
89
© Nokia Solutions and Networks 2014
VoLTE Call Flow Analysis
90
© Nokia Solutions and Networks 2014
xxx
VoLTE Call Flows:
Registration Procedure
91
08/08/2018
© Nokia 2015 - File Name - Version - Creator - DocID
VoLTE Call Flows: Registration Procedure (1/3)
92
© Nokia Solutions and Networks 2014
VoLTE Call Flows: Registration Procedure (2/3)
93
© Nokia Solutions and Networks 2014
VoLTE Call Flows: Registration Procedure (3/3)
94
© Nokia Solutions and Networks 2014
xxx
VoLTE Call Flows:
Mobile Originated VoLTE Call
95
08/08/2018
© Nokia 2015 - File Name - Version - Creator - DocID
VoLTE Call Flows: Mobile Originated VoLTE Call (1/2)
user’s perspective, Accessibility is
typically considered from 180
RINGING or ACK (200 OK)
Call Setup time : SIP INVITE – SIP 180 Ringing
= 4910 ms = 4.9 s
96
© Nokia Solutions and Networks 2014
VoLTE Call Flows: Mobile Originated VoLTE Call (1/2)
97
© Nokia Solutions and Networks 2014
VoLTE Call Flows: Mobile Originated VoLTE Call (2/2)
98
© Nokia Solutions and Networks 2014
xxx
VoLTE Signaling Flows:
Mobile Terminated VoLTE Call
99
08/08/2018
© Nokia 2015 - File Name - Version - Creator - DocID
VoLTE Signaling Flows
•
10
Mobile Terminated VoLTE Call (1/2)
© Nokia Solutions and Networks 2014
VoLTE Signaling Flows
•
10
Mobile Terminated VoLTE Call (2/2)
© Nokia Solutions and Networks 2014
Back to list of call flows
xxx
VoLTE Call Flows
SRVCC to 3G
10
08/08/2018
© Nokia 2015 - File Name - Version - Creator - DocID
VoLTE Signaling Flows
•
SRVCC to 3G
Measurement event B2 (UTRA) reported
SRVCC/HO command
10
© Nokia Solutions and Networks 2014