This document provides information about VoLTE training topics including: - TTI bundling which bundles transmission time intervals to improve coverage for VoLTE services in weak signal areas. - VoLTE and EVS rate control which adjusts voice coding rates to balance voice quality and resource usage based on channel conditions. - Parameters and counters related to these features to monitor performance such as voice coding rates and packet loss rates. The features aim to enhance VoLTE coverage and quality under different conditions but can impact network performance through increased signaling or resource usage. Careful configuration of parameters is recommended based on network scenarios.

1. VoLTE Training

2.  LOFD-001048 TTI Bundling
 Uplink RLC Segmentation Enhancement
 LOFD-111207 VoLTE Rate Control/LEOFD-121202 EVS Rate Control
 LOFD-081219 Inter-eNodeB VoLTE CoMP
 Coverage-based VoLTE Experience Optimization
 LOFD-121214 VoLTE Coverage-based CSFB
 Voice-Quality-based Inter-Frequency Handover
 LOFD-120204 VoLTE Coverage Enhancement Based on Extended Delay Budget

3. LOFD-001048 TTI Bundling
 TTI Bundling is controlled by the TtiBundlingSwitch(TtiBundlingSwitch) option of
the CellAlgoSwitch.UlSchSwitch parameter. When this option is selected, the eNodeB
determines whether a UE enters the TTI bundling state based on the channel quality.
 The functions supported by TTI Bundling vary with the release version and depend on
the CellTtiBundlingAlgo.R12TtiBundlingSwitch parameter setting as follows:
 When this parameter is set to OFF:
– According to section 8.6.1 "Modulation order and redundancy version determination" in 3GPP TS
36.213 of Release 10, when TTI Bundling is enabled, the modulation scheme must be QPSK and the
resource allocation size is restricted to a maximum of three PRBs.
– The selected MCS index cannot be greater than 10, and the transport block size (TBS) is at most 504
bits. VoLTE services are delay-sensitive. If higher-layer data is not transmitted within the specified
delay budget, voice quality deteriorates. This can be prevented by disabling TTI Bundling when a
G.711-defined high speech codec rate is used.

4. LOFD-001048 TTI Bundling
 The functions supported by TTI Bundling vary with the release version and depend on
the CellTtiBundlingAlgo.R12TtiBundlingSwitch parameter setting as follows:
 When this parameter is set to ON:
– According to 3GPP TS 36.213 CR0463 of Release 12, when TTI Bundling is enabled, the modulation
scheme must be QPSK but the resource allocation size is no longer limited to three PRBs.
– According to 3GPP TS 36.213 CR0463 of Release 12, the new HARQ feedback time sequence
shown in Figure is supported and the number of simultaneous uplink HARQ processes changes from
four to three.
– The restriction that MCS index 10 must be used is canceled.

5. Entry Conditions
 The conditions for UEs to enter the TTI bundling state are as follows:
– TTI Bundling is enabled.
– The UE supports TTI Bundling.
– The UE stays in the talk spurts state and has only one QCI 1 dedicated bearer which carries no data
transmission when the CellUlschAlgo.TtiBundlingTriggerStrategyparameter is set
to SERVICE_VOIP.
– The UE has a QCI 1 dedicated bearer when
the CellUlschAlgo.TtiBundlingTriggerStrategy parameter is set to SERVICE_MULTIAPP.
– The uplink UE power is limited.
– The measured SINR is less than the target SINR in multiple consecutive measurements. The number
of consecutive measurements is specified by CellUlschAlgo.StatisticNumThdForTtibTrig.
 If all the conditions are met, the eNodeB sends the UE an RRC Connection Reconfiguration
message, instructing the UE to enter the TTI bundling state.
– If CellTtiBundlingAlgo.R12TtiBundlingSwitch is set to ON, the target SINR value is controlled
by CellTtiBundlingAlgo.SinrThdToTrigR12TtiB.
– If CellTtiBundlingAlgo.R12TtiBundlingSwitch is set to OFF, the target SINR value is controlled
by CellTtiBundlingAlgo.SinrThdToTrigTtib.

6. Exiting Conditions
 If the VoLTE service is ongoing, the eNodeB instructs the UE to exit the TTI bundling state by
sending an RRC Connection Reconfiguration message when the measured SINR is greater
than the sum of the target SINR and the CellUlschAlgo.HystToExitTtiBundling parameter
value for multiple consecutive times. The number of consecutive times is specified by
the StatisticNumThdForTtibExit parameter.
– If the VoLTE service is released, the eNodeB instructs the UE to exit the TTI bundling state by
sending an RRC Connection Reconfiguration message when the measured SINR is greater than
Min{(target SINR + CellUlschAlgo.HystToExitTtiBundling parameter value), 6 dB} for multiple
consecutive times. The number of consecutive times is specified by
the StatisticNumThdForTtibExit parameter.
 The TTIB_EXIT_BASED_ON_QCI_SW option of
the CellTtiBundlingAlgo.TtiBundlingAlgoSw parameter determines whether to enable the
function of exiting the TTI bundling state based on the QCI. If this option is selected and a UE
performs both VoLTE services and data services, the UE exits the TTI bundling state after
releasing the VoLTE services and does not use TTI Bundling for the data service. Selecting
this option in weak-coverage scenarios may decrease the RRC connection reestablishment
success rate and increase call drop rate.

7. Enhanced TTI Bundling Algorithm
 In weak-coverage scenarios, after the UE exits the TTI bundling state due to a handover or
RRC connection reestablishment, the UE triggers another TTI bundling determination and
then returns to the TTI bundling state.
 Therefore, the TTIBUNDLING_ALGO_ENHANCE_SW option of
the CellTtiBundlingAlgo.TtiBundlingAlgoSw parameter is introduced. If this option is
selected:
 During a handover or RRC connection reestablishment, the UE inherits the TTI bundling state
from the source cell. Essentially, if a UE is in the TTI bundling state before a handover or
RRC connection reestablishment, the UE enters the TTI bundling state after the handover or
RRC connection reestablishment without another TTI bundling determination. In this way,
reconfiguration signaling reduces and voice quality improves. NOTE:This function requires
that TTI Bundling be enabled in the target cell of handover or RRC connection
reestablishment.
 The restriction that MCS index 10 must be used is canceled.

8. Network Performance - Impact
 TTI Bundling has the following impact on network performance:
– TTI Bundling increases the cell edge coverage of the PUSCH, improves the MCS index in uplink
weak-coverage areas, and reduces the packet loss rate. However, this feature increases signaling
overheads because the entry and exit of the TTI bundling state requires the exchange of RRC
messages. When the number of TTI bundling mode reconfiguration messages (indicated by the
counters L.Signal.Num.TtiBundling.Enter and L.Signal.Num.TtiBundling.Exit) increases, the
average board CPU usage (indicated by the counter VS.BBUBoard.CPULoad.Mean (%)) slightly
increases.
– A UE in the TTI bundling state uses an excessive high MCS index, which raises the probability of
DTX for HARQ feedback on the PUSCH and increases the downlink packet loss rate. The problem of
a high downlink packet loss rate is mitigated
when CellUciOnPuschPara.DeltaOffsetAckIndexForTtiB is set to 11 compared with when it is set
to the default value 9.
– TTI bundling uses a maximum of three PRBs and adopts QPSK with the highest MCS index 10. That
is, after TTI Bundling is enabled, the maximum number of TBS that can be transmitted is 504 bits.
This restricts the uplink throughput of TTI Bundling. The logical channel priority of signaling and
VoLTE services is higher than that of data services, which means that UEs preferentially send
signaling and VoLTE services. As a result, the uplink throughput of data services is further restricted.

9. Network Performance - Impact
 TTI Bundling has the following impact on network performance:
– The uplink packet loss rate
(L.Traffic.UL.FarUE.PktLoss.Loss.QCI.1/L.Traffic.UL.FarUE.PktLoss.Tot.QCI.1) of UEs in weak-
coverage areas decreases by 5% to 20% if the proportion of voice-service users exceeds 5%, the
proportion of uplink low-index MCSs on the PUSCH exceeds 20%, and users are evenly distributed.
 In addition to the network performance described above, TTI Bundling has the following
impact on network performance when
the CellTtiBundlingAlgo.R12TtiBundlingSwitchparameter is set to ON(On).
– The resource allocation size is no longer limited to three PRBs, and the restriction that MCS index 10
must be used is canceled. This enables flexible resource allocation and reduces the possibility of
limited uplink throughput for UEs in the TTI bundling state.
– The uplink packet loss rate
(L.Traffic.UL.FarUE.PktLoss.Loss.QCI.1/L.Traffic.UL.FarUE.PktLoss.Tot.QCI.1) of UEs in weak-
coverage areas decreases by 1% to 10% if the proportion of voice-service users exceeds 5%, the
proportion of uplink low-index MCSs on the PUSCH exceeds 20%, and users are evenly distributed.

10. Data Preparation and Feature Activation
 Parameters that must be set in a CellAlgoSwitch MO
 Parameters that must be set in a CellUlschAlgo MO
Parameter Name Parameter ID Setting Notes
Uplink schedule switch CellAlgoSwitch.UlSchSwitch The TtiBundlingSwitch option of this
parameter specifies whether to enable
TTI Bundling.
•In common scenarios, deselect this
option.
•When the UE's channel quality is poor
and transmit power is limited, select this
option.

11. Counters
Counter ID Counter Name Counter Description
1526728496 L.Traffic.User.TtiBundling.Avg Average number of UEs on which TTI
Bundling takes effect in a cell
1526728911 L.Signal.Num.TtiBundling.Ente
r
Number of messages sent for instructing
UEs to enter the TTI bundling state
1526728912 L.Signal.Num.TtiBundling.Exit Number of messages sent for instructing
UEs to exit the TTI bundling state
1526746002 L.Traffic.User.R12TtiBundling.
Avg
Average number of UEs on which TTI
bundling complying with 3GPP Release
12 takes effect in a cell

12. LOFD-111207 VoLTE Rate Control/LEOFD-121202 EVS Rate
Control
 When to Use
 VoLTE Rate Control and EVS Rate Control are recommended when the following conditions
are met:
– The number of voice-service UEs exceeds a threshold.L.Traffic.User.VoIP.Avg/L.Traffic.User.Avg >
5%
– The percentage of voice packets from the cell edge exceeds a threshold in the
uplink.L.Traffic.UL.FarUE.PktLoss.Tot.QCI.1/L.Traffic.UL.PktLoss.Tot.QCI.1 > 5%
– The uplink loss rate of voice packets from the cell edge exceeds a
threshold.L.Traffic.UL.FarUE.PktLoss.Loss.QCI.1/L.Traffic.UL.FarUE.PktLoss.Tot.QCI.1 > Voice
AmrControl.PlrThdForDecreasingAmr
 It is recommended that VoLTE rate control be disabled in the following scenarios:
– High-speed cells
– Ultra-high-speed cells
Feature ID Feature Name Model License
Control Item
NE Sales Unit
LOFD-111207 VoLTE Rate
Control
LT1SVLTERC
00
VoLTE Rate
Control(FDD)
eNodeB per Cell
LEOFD-121202 EVS Rate Control LT1S000EVS0
0
EVS Rate
Control(FDD)
eNodeB per Cell

13. Data Preparation
 Parameters that must be set in a CellAlgoSwitch MO

14. Data Preparation
 Parameters that must be set in a CellUlschAlgo MO
Parameter Name Parameter ID Setting Notes
AMRC Decreasing
Period
CellUlSchAlgo.AmrcDecre
asingPeriod
This parameter specifies the AMRC rate decrease determination period. The
default value is recommended.
•If this parameter is set to a smaller value, the rate decrease determination period
is shorter and it is easier to trigger an uplink voice rate decrease. That is, the
decrease in PDCCH resources and PRBs consumed by uplink VoLTE services is
more significant and the decrease in the uplink packet loss rate for QCI 1 services
is more significant. However, when the channel conditions change rapidly, ping-
pong rate adjustment is likely to occur.
•If this parameter is set to a larger value, the rate decrease determination period
is longer and it is more difficult to trigger an uplink voice rate decrease. That is,
the decrease in PDCCH resources and PRBs consumed by uplink VoLTE
services is slighter and the decrease in the uplink packet loss rate for QCI 1
services is slighter.

15. Data Preparation
 Parameters that must be set in a VoiceAmrControl MO

16. Counters
 AMR rate control is enabled if any value is greater than 0.
 EVS rate control is enabled if any value is not 0.
Counter ID Counter Name Counter Description
1526741685 L.Voice.UL.AMRNB.Increase.Times Number of times the uplink AMR-NB
speech coding rate increases
1526741686 L.Voice.UL.AMRWB.Increase.Times Number of times the uplink AMR-WB
speech coding rate increases
1526741687 L.Voice.UL.AMRNB.Decrease.Times Number of times the uplink AMR-NB
speech coding rate decreases
1526741688 L.Voice.UL.AMRWB.Decrease.Times Number of times the uplink AMR-WB
speech coding rate decreases
Counter ID Counter Name Counter Description
1526745691 L.Voice.UL.EVSSWB.Increase.Times Number of times the uplink EVS-
SWB speech coding rate
increases
1526745692 L.Voice.UL.EVSSWB.Decrease.Times Number of times the uplink EVS-
SWB speech coding rate
decreases

17. Network Performance - Impact
 VoLTE rate control has the following impacts on network performance:When the uplink
channel quality is favorable, using a high AMR coding rate increases the MOS by 0.01 to 0.2
and using a high EVS coding rate increases the MOS by 0.2 to 0.5.
 When the uplink channel quality is unfavorable and far-point UEs use low voice coding rates,
their uplink packet loss rate decreases by 5% to 20% and uplink voice coverage improves by
0.5 dB to 1 dB.Uplink packet loss rate of far-point UEs
= L.Traffic.UL.FarUE.PktLoss.Loss.QCI.1.Index0/L.Traffic.UL.FarUE.PktLoss.Tot.QCI.1.I
ndex0
 The impact on the traffic volume, throughput, and transmission delay varies depending on
scenarios:
– If the voice coding rates of most VoLTE services are increased, more PDCCH CCE and PRB
resources will be consumed, slightly decreasing the throughput and data rate of data services. This
increases the transmission delay.
– If the voice coding rates of most VoLTE services are reduced, less PDCCH CCE and PRB resources
will be consumed, slightly increasing the throughput and data rate of data services. This decreases
the transmission delay.

18.  Honey Charnalia
 Honey.charnalia@gmail.com
 +91 8586972332
 Skype: honey_charnalia

19. THANK YOU
THANK YOU