VoLTE Features Descriptions v1b

VoLTE Features Overview

TTI Bundling

TTI Bundling Overview TTI bundling enables a data block to be transmitted in four consecutive TTIs, which are bound together and  treated as the same resource.  TTI bundling improves HARQ combining gains and reduces the number of retransmissions and RTT. When the UE's channel quality is poor and transmit power is limited, TTI bundling increases the cell edge  coverage of the PUSCH.  The gains produced by this feature can be observed when voice quality is maintained at a cell edge with  poor RF quality.

TTI Bundling Activation The TtiBundlingSwitch option is enabled by CellAlgoSwitch.UlSchSwitch parameter  When this option is selected, the eNodeB determines whether to activate TTI bundling based on the channel  quality.  After activating TTI bundling, the eNodeB determines the number of PRBs and selects an MCS based on the  channel quality and the amount of data to be transmitted.

Entry into the TTI Bundling State When the TtiBundlingTriggerStrategy parameter is set to SERVICE_VOIP(SERVICE_VOIP), TTI bundling applies to  only VoLTE. Entering the TTI bundling state are as follows: • • • • •

The TtiBundlingSwitch of the eNodeB is turned on. The UE supports TTI bundling. The UE has only one QCI 1 dedicated bearer and stays in the talk spurts state. In addition, the UE does not have data to  transmit on the data bearer. The UL power of the UE is limited. The measured SINR is less than the target SINR for multiple consecutive times. 

When the TtiBundlingTriggerStrategy parameter is set to SERVICE_MULTIAPP(SERVICE_MULTIAPP), TTI bundling  can apply to VoLTE or a combination of VoLTE and data.  Entering the TTI bundling state are as follows: • • • • •

The TtiBundlingSwitch of the eNodeB is turned on. The UE supports TTI bundling. The UE has a QCI 1 dedicated bearer. The UL power of the UE is limited. The measured SINR is less than the target SINR for multiple consecutive times. 

The number of consecutive times to measure SINR is specified by CellUlschAlgo.StatisticNumThdForTtibTrig. If the UE meets all these conditions, the eNodeB sends the UE an RRC Connection Reconfiguration message,  instructing the UE to enter the TTI bundling state. The target SINR is controlled by CellTtiBundlingAlgo.SinrThdToTrigTtib.

UE in the TTI Bundling State • For the UE in the TTI bundling state, the eNodeB determines the number of PRBs and MCS based on channel  quality and the amount of data to transmit. Then, the eNodeB transmits data blocks. • When the UE is in the TTI bundling state, the maximum number of uplink HARQ retransmissions is specified by  the CellUlschAlgo.TtiBundlingHarqMaxTxNum parameter. • In the TTI bundling state, the number of RLC segments of a voice packet cannot be greater than the value  specified by the CellUlschAlgo.TtiBundlingRlcMaxSegNum.

Restrictions in TTI Bundling • TTI bundling uses a maximum of 3 PRBs and adopts QPSK with the highest MCS order of 10.  • With TTI bundling is enabled, the maximum number of TBS that can be transmitted is 504 bits. This restricts  the uplink throughput of TTI bundling.

Exit from TTI Bundling The eNodeB does not instruct the UE to exit the TTI bundling state even when  • the UE has data to transmit on the default bearer,  • needs to set up a new dedicated bearer, or  • stops the voice service QCI 1.  The eNodeB instructs the UE to exit the TTI bundling state when  • the UE meets the exit conditions,  • experiences handover or  • service drop, or  • needs to reestablish a new connection. If the voice service is not released the eNodeB instructs the UE to exit the TTI bundling state through 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 voice service is released the eNodeB instructs the UE to exit the TTI bundling state through an RRC Connection Reconfiguration message when  the measured SINR is greater than MIN{(target SINR + CellUlschAlgo.HystToExitTtiBundling), 6 dB} for multiple  consecutive times. The number of consecutive times is specified by the StatisticNumThdForTtibExit parameter.

Counters for TTI bundling Counters for observing whether TTI bundling is activated

VoLTE Rate Control

VoLTE Rate Control Overview VoLTE Rate Control adjusts the AMR‐NB/AMR‐WB rate for uplink voice services depending on the uplink  channel quality and voice quality. • When the uplink channel quality and voice quality are favorable: a high voice coding rate is used to  further improve voice quality. • When the uplink channel quality and voice quality are poor: a low voice coding rate is used to reduce  the uplink packet loss rate and improve uplink voice coverage. 

Voice Rate Adjustment The eNodeB determines whether to adjust the voice rate depending on  • the uplink channel quality and  • voice quality.  The eNodeB or SBC adjusts the voice rate of the UE.  Voice rate adjustment is controlled by the CellAlgoSwitch.UlAmrcMode parameter as follows: • If CellAlgoSwitch.UlAmrcMode = ULAMRC_ENB_CONTROL(ULAMRC_ENB_CONTROL), the eNodeB adjusts  the voice rate of the UE. • If CellAlgoSwitch.UlAmrcMode = ULAMRC_SBC_CONTROL(ULAMRC_SBC_CONTROL), the SBC adjusts the  voice rate of the UE.  •If IMS signaling is encrypted, the eNodeB cannot obtain the rate set supported by the UE. In this situation, SBC can be used to perform voice rate control

Supported AMR Codec Rates VoLTE Rate Control feature supports the following rates for AMR‐NB services: 12.2 kbit/s, 7.4 kbit/s, and 4.75 kbit/s  VoLTE Rate Control feature supports the following rates for AMR‐WB services: 23.85 kbit/s, 12.65 kbit/s, and 6.6 kbit/s  Both rates in each AMR group can be allocated to a UE. AMR groups are controlled by the following parameters: •VoiceAmrControl.VoiceAmrCtrlParaGroupId •VoiceAmrControl. HighAmrCodingMode •VoiceAmrControl. LowAmrCodingMode VoLTE Rate Control feature supports rate adjustment within AMR‐NB services or within AMR‐WB services,  not between AMR‐NB and AMR‐WB services.

VoLTE Rate Control feature Function After the VoLTE Rate Control feature is enabled: •The AMR coding rate increases if the following conditions are both met: • The TBS of the UE is greater than TbsUpTh. • The uplink packet loss rate for services with a QCI 1  VoiceAmrControl.PlrThdForDecreasingAmr for two  consecutive times. •If the UlAmrcExceedingInitialSw(UlAmrcExceedingInitialSw) option of the CellAlgoSwitch.AmrcAlgoSwitch parameter is selected, the increased coding rate can exceed the initial coding rate of this call.  •Otherwise, the increased coding rate cannot exceed the initial coding rate of this call.

Counters for VoLTE Rate Control Counters for observing whether VoLTE Rate Control is activated

DRX

Overview of DRX • With DRX the UE can switch between active and sleep states. DRX cycle consists: • active state and • sleep state. • In non-DRX mode, the UE always turns on its receiver and stays in the active state. • DRX enables the UE to turn on its receiver and enters active state only when it needs to receive DL data or signaling. • The UE turns off its receiver and enters sleep state in other situations to reduce power consumption.

Advantages of DRX Compared with continuous reception, DRX has the following advantages: In DRX mode, the UE does not need to continuously monitor the physical downlink control channel (PDCCH).  power consumption is reduced, and battery runtime is prolonged.



As an intermediate state between the RRC_CONNECTED and RRC_IDLE modes, DRX reduces the probability of transitions from RRC_CONNECTED to RRC_IDLE.  reduce signaling overhead of a network, especially a network with a large number of smart UEs. 



UEs can perform automatic neighbor relation (ANR) measurements during the sleep time in DRX.

DRX Mode Entering and Exiting Conditions DRX Mode Entering Conditions The DRX functionality is controlled by the general DRX switch DrxAlgSwitch and the EnterDrxSwitch. After the UE receives an RRC Connection Reconfiguration message it enters the DRX mode. This message is sent by the eNodeB if all the following conditions are met:  The DrxAlgSwitch parameter is set to ON.  All the bearers for the UE support DRX. The EnterDRXSwitch parameter of each bearer is set to ON.  The traffic volume of the UE is low.

For the traffic measurement, the traffic volume threshold is specified by the FddEnterDrxThd parameter, and the measurement period is specified by the DataAmountStatTimer parameter. DRX Mode Exiting Conditions A UE exits the DRX mode in any of the following scenarios:  after it receives an RRC Connection Reconfiguration message with release: This message is sent by the eNodeB if one of the following conditions is met: − The QCI of a new service does not allow the UE to enter the DRX mode. The EnterDRXSwitch parameter of the QCI is set to OFF. − The traffic volume of the UE is high. For the traffic measurement, the traffic volume threshold is specified by the FddExitDrxThd parameter, and the measurement period is specified by the DataAmountStatTimer parameter. However, if the FddExitDrxThd parameter is set to 100, the UE does not exit the DRX mode.

If the DrxAlgSwitch parameter is set to OFF, the eNodeB instructs the UE to exit the DRX mode upon DRX reconfiguration originated by the UE.  If the UE in RRC_CONNECTED mode experiences a radio link failure (RLF) when radio conditions deteriorate, the UE automatically exits the DRX mode. 

Concepts Related to the DRX Cycle On Duration In DRX mode, a UE continuously monitors the PDCCH for possible signaling for a certain period of time. This continuous period is called On Duration, and the related timer is OnDurationTimer. DRX Cycle A DRX cycle specifies the periodic repetition of the On Duration followed by a possible period of inactivity. Active Time In active time, the UE turns on its receiver and monitors the PDCCH. Active time may be an On Duration period during which the UE needs to turn on its receiver. DRX timers include the DRX Inactivity Timer, Contention Resolution Timer, and DRX Retransmission Timer. Sleep Time In sleep time, the UE turns off its receiver and does not monitor the PDCCH. Long DRX Cycle After the UE enters the DRX mode, it must apply a long DRX cycle at the beginning. The duration of a long DRX cycle is specified by the LongDrxCycle parameter. Short DRX Cycle It is not mandatory to apply a short DRX cycle. The ShortDRXCycle parameter specifies the duration of a short DRX cycle. If a short DRX cycle is configured for the UE, the UE determines when to apply the long or short DRX cycle.

Switching Between Active Time and Sleep Time DRX Cycle Switching between active time and sleep time is determined by DRX timers and service processes.

Conditions for starting active time Condition OD IA

Meaning A DRX cycle starts. A PDCCH indicating an initial UL or DL data transmission is received.

R SR UR

The HARQ RTT Timer expires. A UL scheduling request is sent. A UL negative acknowledgment (NACK) is received, and retransmission is required. A non-contention-based random access response is received. Msg3 is sent in a random access procedure.

RAR CR

Switching between active time and sleep time

DRX for VoIP Services For VoIP services, users can set DRX parameters corresponding to QCI 1. For VoIP services, a set of special DRX parameter settings is available for reducing UE power consumption while maintaining VoIP capacity. Long DRX Cycle The long DRX cycle is specified by the LongDrxCycle parameter. The value SF20(20 subframes) is recommended for QCI 1, because VoIP services have a scheduling period of 20 ms.  If the parameter value is too small, it results in a high proportion of time that the UE is in active state and therefore less power savings.  If the parameter value is too large, it leads to a possibility of a conflict between the VoIP scheduling occasion and the silent period. This delays packet transmission and has a negative impact on user experience.

Short DRX Cycle Short DRX cycles are not available for VoIP services. On Duration Timer An eNodeB counts the number of UEs with VoIP services in each cell and set a value for the On Duration Timer, which is specified by the OnDurationTimer parameter. If there are a large number of UEs with VoIP services, set a large value for this parameter to ensure scheduling of the VoIP services. The value PSF10(10 subframes) is recommended for QCI 1. DRX Inactivity Timer The DRX Inactivity Timer is specified by the DrxInactivityTimer parameter. The value PSF3(3subframes) is recommended for QCI 1.

DRX Counters Counters to verify when DRX take effect. L.Traffic.PktInterval.Num.Index0 L.Traffic.PktInterval.Num.Index1 L.Traffic.PktInterval.Num.Index2 L.Traffic.PktInterval.Num.Index3 L.Traffic.PktInterval.Num.Index4 L.Traffic.PktInterval.Num.Index5 L.Traffic.PktInterval.Num.Index6 L.Traffic.PktInterval.Num.Index7 L.Traffic.PktInterval.Num.Index8

Counters to obtain out‐of‐synchronization durations in DRX L.User.UL.Unsync.Dur.Index0 L.User.UL.Unsync.Dur.Index1 L.User.UL.Unsync.Dur.Index2 L.User.UL.Unsync.Dur.Index3 L.User.UL.Unsync.Dur.Index4 L.User.UL.Unsync.Dur.Index5 L.User.UL.Unsync.Dur.Index6 L.User.UL.Unsync.Dur.Index7 L.User.UL.Unsync.Dur.Index8

Semi-Persistent Scheduling

Semi-Persistent Scheduling Overview • Semi-persistent scheduling feature for small-packet services that are periodically transmitted such as VoLTE. • Before entering talk spurts, the eNodeB allocates fixed resources to UEs through the PDCCH message. • Before exiting talk spurts or releasing resources. • The UEs do not need to apply for resource allocation from the PDCCH again, thereby saving PDCCH resources.

PDCCH allocation compared between Dynamic and SPS Scheduling

dynamic scheduling

semi‐persistent scheduling

Comparison between Semi-Persistent Scheduling Dynamic Scheduling

Semi-Persistent Scheduling Selection During talk spurts, eNodeBs use semi-persistent scheduling in the following scenarios: •The parameters are selected: • The SpsSchSwitch option of the CELLALGOSWITCH.UlSchSwitch parameter in the UL • The SpsSchSwitch option of the CELLALGOSWITCH.DlSchSwitch parameter in the DL. •The UE supports semi-persistent scheduling. •The UE performing voice services is in UL or DL talk spurts. •The UL or DL for the UE has only one dedicated bearer for services with QCI 1. There is no data transmission on the UL data bearer. •RLC segmentation is not performed in the UL or DL for the UE. •When ROHC is enabled, the UL or DL ROHC is in the stable compression state, the size of the ROHC header is relatively stable. During talk spurts, eNodeBs use dynamic scheduling in the following scenarios: •Transmission of large packets, signaling or uncompressed packets generated •Downlink semi-persistent retransmission •Uplink semi-persistent adaptive retransmission

Semi-Persistent Scheduling Selection Uplink Semi‐Persistent Scheduling During semi‐persistent scheduling, the eNodeB determines  • the modulation and coding scheme (MCS) and  • the number of PRBs  based on: • Voice packet size  • SINR

Downlink Semi‐Persistent Scheduling During semi‐persistent scheduling, the eNodeB determines  • the modulation and coding scheme (MCS) and  • the number of PRBs  based on: • Voice packet size  • Wideband CQI

Load‐based scheduling Load‐based scheduling allows the eNodeB to adaptively select dynamic or semi‐persistent scheduling based on  service load in both UL and DL. HIGH LOAD: the eNodeB applies semi‐persistent scheduling to avoid PDCCH overload and the impact on voice quality  and capacity. LOW LOAD: the eNodeB applies dynamic scheduling to provide better experience on voice services and improve  spectral efficiency. Load‐based scheduling in the UL and DL is controlled by: The UlVoIPLoadBasedSchSwitch of the CellUlSchAlgo. UlEnhencedVoipSchSw parameter controls LB scheduling in UL. The DlVoIPLoadBasedSchSwitch of the CellDlSchAlgo. DlEnhancedVoipSchSw parameter controls LB scheduling in DL.

Power Control in Semi-Persistent Scheduling Semi‐persistent scheduling for VoLTE in the DL: Power Control is not performed.  Instead, the eNodeB transmit power is evenly shared by each PRB. Semi‐persistent scheduling for VoLTE in the UL: Closed‐loop Power Control for the PUSCH can be enabled or  disabled by setting the CloseLoopSpsSwitch option of the CellAlgoSwitch.UlPcAlgoSwitch parameter. •If the CloseLoopSpsSwitch option is selected, the eNodeB adjusts transmit power for the PUSCH  based on the measured IBLER of voice services. •If the CloseLoopSpsSwitch option is deselected, the eNodeB uses open‐loop (not closed‐loop)  power control for the PUSCH.

Counters for Semi-Persistent Scheduling To verify when adaptive dynamic scheduling and semi‐persistent scheduling take effect.

ROHC

ROHC Overview ROHC provides an efficient header compression mechanism for data packets transmitted on radio links to solve  the problems of high bit error rates (BERs) and long round trip time (RTT).  ROHC helps reduce header overheads, lower the packet loss rate, and shorten response time. In the current version of ROHC is used to compress the headers of only voice packets (QCI of 1 and PTT QCI  services). ROHC reduces the packet size and physical resource block (PRB) overheads. When PRBs are insufficient, ROHC  helps increase system capacity.

ROHC Profiles • ROHC is consisting of different profiles for packet flows compliant with different protocols.  • Profiles define the compression modes for packet flows with different types of protocol headers.  • Each profile is identified by a profile ID. Profile 0x0000 indicates that packet headers are not compressed. Profile ID 0x0001

Protocol RTP, User Datagram Protocol  (UDP), and IP

0x0002 0x0003

UDP and IP For details, see RFC3095 and RFC4815. Encapsulating Security Payload  For details, see RFC 3095 and RFC 4815. (ESP) and IP

0x0004

IP

UE Capability IE

Remarks For details, see RFC 3095 and RFC 4815.

For details, see RFC 3843 and RFC 4815.

RRC Reconfiguration

ROHC Operating Modes ROHC operates in  • Unidirectional Mode (U‐Mode),  • Bidirectional Optimistic Mode (O‐Mode), or  • Bidirectional Reliable Mode (R‐Mode) mode.  Operating Mode Transition The initial operating mode of the compressor is U‐Mode. After confirming packet reception by the decompressor, the  compressor switches to O‐Mode or R‐Mode.  The operating mode transition is determined by the decompressor. • When the eNodeB is the compressor, the UE works as the decompressor and triggers operating mode  transition for the eNodeB. • When the eNodeB is the decompressor, it determines the target operating mode based on the  PdcpRohcPara.HighestMode parameter and instructs the UE to change the operating mode. • If the PdcpRohcPara.HighestMode parameter is set to R_MODE(Bi‐Directional Reliable Mode), the UE  can switch to a higher mode (O‐Mode or R‐Mode) and stay in R‐Mode. • If the PdcpRohcPara.HighestMode parameter is set to O_MODE(Bi‐directional Optimistic Mode), the UE  can switch to and stay in O‐Mode.

ROHC Impacts on Features

Feature ID LOFD‐001016

Feature Name Semi‐Persistent Scheduling

LOFD‐110225

Uplink Data Compression

Description When ROHC is enabled, compressed packet sizes fluctuate, even during talk  spurts, due to changes in the quality of the radio channels, the ROHC  operating mode used, and variations in the dynamic fields of the packet  headers at the application layer. Therefore, ROHC impacts LOFD‐001016  VoIP Semi‐persistent Scheduling. If the packet size after compression is  greater than the maximum size allowable for semi‐persistent scheduling, the  eNodeB uses dynamic scheduling for the data beyond the size limit. When the UL normal or smart preallocation function is enabled, UL ROHC  will yield few gains in resource saving if the size of packets scheduled by the  eNodeB in preallocation is greater than the size of voice packets. When ROHC is enabled, compressed packet sizes fluctuate, even during talk  spurts, due to changes in the quality of the radio channels, the ROHC  operating mode used, and variations in the dynamic fields of the packet  headers at the application layer. Therefore, ROHC impacts LOFD‐001016  VoIP Semi‐persistent Scheduling. If the packet size after compression is  greater than the maximum size allowable for semi‐persistent scheduling, the  eNodeB uses dynamic scheduling for the data beyond the size limit. When the UL normal or smart preallocation function is enabled, UL ROHC  will yield few gains in resource saving if the size of packets scheduled by the  eNodeB in preallocation is greater than the size of voice packets.

ROHC Parameters Parameter Name

ROHC switch

Parameter ID

Setting Notes In later versions, the PdcpRohcPara.RohcSwitch parameter will be replaced  by the CellAlgoSwitch.RohcSwitch(N/A,LTE FDD eNodeB) parameter. The  current version supports configuration synchronization and delivery of eNodeB‐ level and cell‐level parameters. If the eNodeB‐level parameter is set to ON(On),  PdcpRohcPara.RohcS whether the function is provided in cells is determined by the eNodeB‐level  witch switch. If the eNodeB‐level parameter is set to OFF(Off), whether the function is  provided in cells is determined by the cell‐level switch. Therefore, you are  advised to switch to the cell‐level switch, then turn off the eNodeB‐level switch,  and avoid using the eNodeB‐level switch for ROHC afterwards. This parameter applies to the uplink only. The highest operating mode of ROHC  in the downlink is controlled by UEs. The recommended value is O_Mode.

ROHC Highest mode

Compression profiles

ROHC switch

PdcpRohcPara.Highe stMode

The reasons are as follows: When U_Mode is used, if the radio link quality is poor, the compression will be  inefficient. R_Mode introduces more feedback data than O_Mode although these two  modes have similar compression efficiency. In addition, frame loss may occur  on some VoLTE UEs working in R_Mode.

Commercial VoLTE UEs do not support profiles 0x0003 and 0x0004 at present.  As a result, set this parameter to Profile0x0001(Profile0x0001) or  PdcpRohcPara.Profile Profile0x0002(Profile0x0002). s If this parameter is adjusted while the eNodeB is running, the adjustment  affects only new services (not ongoing services). GLOBALPROCSWITCH It is recommended that this parameter is set to ON(On) when the operator  .ProtocolSupportSwit provides the IMS‐based VoIP services in the LTE network and the mainstream  ch commercial VoLTE UEs have passed the interconnection test.

ROHC Counters For downlink transmission, check the values of  L.PDCP.DL.RoHC.HdrCompRatio and L.PDCP.DL.RoHC.PktCompRatio.  Smaller values indicate higher compression efficiency. •For uplink transmission, check the values of the following counters: L.PDCP.UL.RoHC.FailDecompRatio A smaller value indicates a higher decompression success rate. If the value is 0, the decompression  success rate is 100%. L.PDCP.UL.RoHC.HdrCompRatio and  L.PDCP.UL.RoHC.PktCompRatio. Smaller values indicate higher compression efficiency.When ROHC is working under normal radio  conditions, the values of the two counters are less than 100%.