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Contents
01
VoL oLTE TE Introd Introduction uction
02
VoL oLTE TE Basic Feature Verification
VoLTE VoL TE with intra-fr intra-frequency equency HO
SRVCC to Utran
03
VoL oLTE TE Advanced Feature Verifi erification cation
VoLTE VoL TE with inter-freq inter-frequency uency HO
ROHC
TTI Bundling
DRX
UL RLC Segmentati Segmentation on
VoLTE Introduction-Concept
4G Voice Evolution Three
Stage of 4G Voice Evolution：
CS is on 2G/3G, PS is On LTE
Advantage
On the early stage of LTE network deployment, the operators haven’t implemented IMS (IP Multimedia Subsystem), they usually take CSFB as transitional voice solution. After the IMS implementation, they will move to the final Voice Solution as VoLTE.
Both CS and PS are on LTE.
on VoLTE Solution SVLTE
CSFB
VoLTE
Voice Quality
2/3G Voice Quality
2/3G Voice Quality
HD Voice Quality
Access Time
Short (5~6S)
Long (8S)
Shorter (0.5~2S)
UE Power Consumption
High
High
Low
Spectrum Effieiency
Low
Low
High (4 Time)
What is VoLTE? VoLTE is the voice communication between UE and IMS, and the voice is carried on PS domain.
CS fall back to 2/3G, PS is on LTE as first priority.
VoLTE Introduction—Basic Structure Signaling
Description VoLTE is voice sessions set up over IP networks between the UE and the IMS. That is, the calling and the called parties can use voice services within an LTE network.
Terminal
Access
Bearer
CS
eMGW
(Called)
Media
IMS
eMSC
AS VOLTE AS
IM-MGW MGCF
BTS/NodeB BSC/RNC
EPC
Voice & PS service continuity
HLR/HSS SCP AS
SRVCC （ Single-Radio Voice Call Continuity） based on LTE coverage and inter-RAT mobility
CSCF
•
MME
PS se rvice handover to 2G/3G networks when DTM (Dual Transfer Mode) is supported
PCRF
SMSC
•
SBC
eNodeB
ENUM
(Caller) •
PS service suspended when DTM is not supported.
Note: SRVCC is triggered if and only if the LTE UE is going o ut of the LTE coverage
Core Network Support
EMSC
MME
Sv interface between MME and MSC enhanced for SRVCC.
S-GW
P-GW
CRBT Platform
MME: Mobility Management Entity
HSS：Home Subscriber Server
SCP：Service Control Point
SBC：Session Border Controller
CRBT：Color Ring Back Tone MGCF: Media Gateway Control Function
PCRF：Policy and Charging Rule Function HSS：Home Subscriber Server
CSCF：Proxy Call Session Control Function
SMSC：Short Message Service Centre
Benefits
Terminal Support •
3GPP SRVCC UE is needed to perform SRVCC
eSRVCC：ATCF(Access Transfer Control Function)/ATGW(Access Transfer Gateway)
VoLTE provides UEs in the E-UTRAN with voice services, without the need of falling back to GERAN or UTRAN .
VoLTE features the following characteristics: Higher spectral efficiency, Better user experience, such as lower access delay and better voice quality
IMS-based Voice Services PCRF
MME
EPC IMS Core
E-UTRAN
SBC
S-GW/P-GW
I/S-CSCF
/P-CSCF
UE
Default bearer: IMS signaling streams Dedicated bearer: Voice media streams
SIP signaling streams Voice media streams
A default bearer(QCI5) is set up for IMS signaling streams when the UE attaches to the network.
After the UE initiates a call , SIP signaling streams for call connection is transmitted over the default bearer through the PGW to the IMS Core.
A dedicated bearer for IMS(QCI1) voice media streams is set up during call connection.
Voice media streams of the calling and called parties are transmitted over the dedicated bearer.
VoLTE Bearing Data Bearing
UE setup default bearing QCI 9 for data service
Voice Bearing(QCI1&5)
Voice call Bearing(QCI1&5)
Dedicated Bearer(GBR)QCI=2
Video call Bearing(QCI1&2&5)
No VoLTE session
QCI9
QCI5+QCI9
VoLTE voice session QCI1 + QCI5 + QCI9
VoLTE video session QCI1 +QCI2+QCI5+QCI9
VOLTE use SIP protocol to create, update and terminate a VOTE call: IMS need to be deployed in LTE core network and 2/3G core network to be upgraded for SRVCC. The UE need registration in IMS APN for VOLTE service The voice code is negotiated between UE and IMS(independent with eNodeB), and carrier with QCI1
bearing. QCI1 is transparent to the eNodeB The VOLTE session negotiation(Signaling) is carrying with QCI5 which is control plane of LTE network. It is
transparent to the eNodeB.
QCI
Resource Type
1 2 5 9
GBR No-GBR Non-GBR
Priority
Packet Delay Budget
Packet Error Loss Rate
2
100 ms
10-2
4
150 ms
10-3
1 9
100 ms 300ms
10-6 10-6
Example Services Conversational Voice Conversational Video (Live Streaming) IMS Signalling Data
VoLTE voice Code ： AMR-NB：12.2K、10.2K、7.95K、7.4K、6.7K 、5.9K 、5.15K、4.75K AMR-WB： 23.85K、23.05K 、19.85K 、18.25K 、15.85K 、14.25K、12.65K、8.85K 、6.6K Silent Period one silent frame per 160ms Active period one voice frame per 20ms or 40ms
Contents
01
VoLTE Introduction
02
VoLTE Basic Feature Verification
VoLTE with intra-frequency HO
SRVCC to Utran
03
VoLTE Advanced Feature Verification
VoLTE with inter-frequency HO
ROHC
TTI Bundling
DRX
UL RLC Segmentation
Enable VoLTE Basic Function The system default setting has already open the VoIP basic function. It generally only need to check the configuration of the following parameters : 1.
Check the RLC PDCP parameter group ID of QCI=1/2/5
2.
Check the QCI=1/2/5 RlcMode transmission mode LST RLCPDCPPARAGROUP check the QCI=5 bearing mode to AM mode, RLC mode to UM mode carrying QCI=1/2; if a configuration error, use the MOD RLCPDCPPARAGROUP command to modify
3.
Check the eNodeB VoIP support switch LST ENODEBALGOSWITCH to check if VoIP support switch is open; otherwise, use the MOD ENODEBALGOSWITCH command to open the EtranVoipSupportSwith switch
Query QCI RLC PDCP parameter group ID:LST STANDARDQCI Query QCI RlcMode mode: LST RLCPDCPPARAGROUP Establishes the VoIP QCI=5 load bearing RLC mode is the AM mode, the QCI=1 load bearing RLC mode is the UM mode: MOD STANDARDQCI: Qci=QCI5, RlcPdcpParaGroupId=4; MOD STANDARDQCI: Qci=QCI1, RlcPdcpParaGroupId=0; MOD RLCPDCPPARAGROUP: RlcPdcpParaGroupId=4, RlcMode=RlcMode_AM; MOD RLCPDCPPARAGROUP: RlcPdcpParaGroupId=0, RlcMode=RlcMode_UM; Parameter name
Parameter ID
Suggestion Keep the default configuration. Different QCI corresponding to different RLC mode, according to the RLC mode QCI version has adaptive configuration of transmission （RLC-UM or RLC-AM RlcMode mode。 mode） QCI1： RlcMode_UM(UM mode) QCI2： RlcMode_UM(UM mode) QCI5： RlcMode_AM(AM mode) Keep the default configuration (support). If a eNodeB EUTRAN supports the not to support the VoIP service because of the EutranVoipSupport VoIP capability of the transmission and other reasons , it is suggested that the Switch switch operators after confirmation is set to OFF, otherwise the configuration for the ON.
VoLTE Intra-frequency handover policy S1 inerface handover process
X2 inerface handover process
S1
S1
MME
X2
6.Handover confirm
2.Handover request 1.Ueuse MR report RSRP measurement
3.Handover request ACK 4.RRC Reconfiguration service interruption duration3050ms
•
•
5.RRC Reconfiguration CMP
2.Handover require
1.Ue use MR report RSRP measurement
8.Handover confirm
3.Handover request 5.Handover command 4.Handover request ACK 6.RRC Reconfiguration service interruption duration50-80ms
7.RRC Reconfiguration CMP
LTE X2 handover duration30~50ms， S1 handover duration50~80ms （GSM handover duration120ms-140ms），x2 handover reduce impact of MOS； intra-frequency handover hysteresis 2dB（trigger handover if neighboring cells higher than serving cell），probability ping-pang handover，reduce MOS value，suggestion：
The erratic fluctuation of radio environment （e.g：crossroads），increased intra-frequnecy handover hysteresis according to radio environment ,reduce ping-pang handover one-way moving of high speed railway ， intra-frequency handover policy would not lead to ping-pang handover, suggested use existing parameters
VoLTE Intra-freq HO Verification Scenario 1: UE1 & UE2 both VoLTE, keep the VoLTE call during intra-freq HO VoLTE subscriber MS1 (MSISDN: 005521982137868) called VoLTE subscriber MS2 (MSISDN: 005521982137869)
At 11:22:50.080 MS1 started the call, and dedicated bearer QCI1 setup at 11:22:54. the call connected at 11:22:54 and terminated at 11:46:06.
During the call, MS2 finished the intra-freq HO from serving cell to neighbor cell PCI155 at 11:25:05. the handover succeeded.
the RTP sequence numbers were continuous during the handover, that’s, in scenario of UE1 & UE2 both VoLTE, VoLTE call will keep continuous during intra-freq HO.
VoLTE Intra-freq HO Verification Scenario 2: UE1 VoLTE, UE2 fallback 3G with intra-freq LTE HO VoLTE subscriber MS2 (Huawei MATE7, MSISDN: 005521982137869) called CSFB subscriber MS1 (Samsung Galaxy S4, MSISDN: 982135200).
MS1 (Samsung Galaxy S4) sent Extend Service Request message to eNodeB to start CSFB at 15:55:47.631. The connected at 15:55:55, and terminated at 15:57:56.
During the call, MS2 finished the intra-freq HO from serving cell to neighbor cell PCI315 at 15:56:52. the handover succeeded.
the RTP sequence numbers were continuous during the handover, that’s, in scenario of UE1 VoLTE, UE2 fallback 3G , VoLTE call will keep continuous during intra-freq HO.
SRVCC to Utran Open coverage-based eSRVCC need to adjust existing parameters. Analysis for A2： LTE RSRP
3G RSCP
high
high
Adjust parameter，active 3G measurement A2
•
B1_UTRAN
●
●
A2_blind
low
low
●
Time ①
②
③
user move to edge coverage of LTE
Time point Time point
•
Time point
3G signal not coincidence requirement of
LTE RSRP below A2，Ue report
UE MR indicate 3G level above
B1 or UE not support inter-frequency
A2 event -> eNB deliver B1
B1_UTRAN，report B1 event--》
measure，LTE RSRP below A2_blind，
measurement--》UE measure
eNB launch to 3G eSRVCC
trigger A2 blind event--》eNB lanuch to 3G
3G signal。
handover
blind redrirection， voice interrupt。
•
eSRVCC need to launch neighboring cell for 3G,handover to 3G On eSRVCC process, if UE not support inter-RAT measurement, eNB pending delivers the A4 measurement configuration, will wait until time point ③ launch to 3G redirection When voice and data concurrency ,support by terminal and network(MME/RNC/IMS)，use eSRVCC PS+CS handover to 3G
SRVCC to Utran To activate SRVCC to Utran, we need to configure the parameters as below. parameter UtranSrvc cSwitch UtranVoipCa pSwitch GeranVoipCa pSwitch QciPriorityForHo
Technology MML LTE MOD ENODEBALGOSWI TCH LTE MOD ENODEBALGOSWI TCH LTE MOD ENODEBALGOSWI TCH LTE MOD CELLSTANDARDQCI
recommend value 1 0 0 QCI1: 1/QCI2: 3/QCI3: 2/QCI4: 4/QCI5: 9/QCI6: 5/QCI7: 6/QCI8: 7/QCI9: 8
InterRatPolicyCfgGroupId
LTE
MOD STANDARDQCI
UtranHoC fg
LTE
MOD INTERRATPOLICYCFG GROUP
CsPsHOIn d INTERRATHOA1A2HYST
LTE LTE
MOD UTRANEXTERN ALCELL MOD INTERRATHOCOMMGROUP
INTERRATHOA1A2TI METOTRIG
LTE
MOD INTERRATHOCOMMGROUP
640ms
INTERRATHOA1THDRSR P
LTE
MOD INTERRATHOCOMMGROUP
-109dbm
INTERRATHOA1THDRSRQ
LTE
MOD INTERRATHOCOMMGROUP
-20db
QCI1: 0/QCI2: 2/QCI5: 1/QCI9: 3 GroupId0: PS_HO-0&SRVCC-1&REDIRECTION-0 GroupId1: PS_HO-0&SRVCC-1&REDIRECTION-1 GroupId2: PS_HO-0&SRVCC-0&REDIRECTION-1 GroupId3: PS_HO-0&SRVCC-0&REDIRECTION-1 BOOLEAN_FALSE 4 （2db）
INTERRATHOA2THDRSR P
LTE
MOD INTERRATHOCOMMGROUP
-113dBm
INTERRATHOA2THDRSRQ
LTE
MOD INTERRATHOCOMMGROUP
-24
INTERRATHOUTRANB1T HDECN0
LTE
ADD INTERRATHOUTRANGROUP
-20
INTERRATHOUTRANB1T HDRSCP
LTE
ADD INTERRATHOUTRANGROUP
-109
INTERRATHOUTRANB1H YST
LTE
ADD INTERRATHOUTRANGROUP
4
INTERRATHOUTRANB1T IMETOTRIG
LTE
ADD INTERRATHOUTRANGROUP
HoSignalingOptSwitch RsvdPara1 CmpSwitch=CMP_IU_IMS_PROC_AS_NOR MAL_PS_SWITCH
LTE UMTS
MOD ENODEBALGOSWITCH SET URRCTRLSWITCH
AddA2MeasIfQciAdjSwitch-1 SYSHO_CSIN_PERMIT_SWITCH-1
UMTS
SET UCORRMALGOSWITCH
ON
320ms
SRVCC to Utran Verification VoLTE call connected at 10:32:29.
Then eNodeB sent MobilityFromEUTRACommand message to UE at 10:33:19.661 to start the SRVCC handover.
At 10:33:19.307, UE reported the measurement result that serving 4G cell RSRP 122dBm, and 3G RSCP -106dBm.
UE replied HandoverToUtranComplete message to eNodeB at 10:33:19.837. SRVCC handover succeeded.
Contents
01
VoLTE Introduction
02
VoLTE Basic Feature Verification
VoLTE with intra-frequency HO
SRVCC to Utran
03
VoLTE Advanced Feature Verification
VoLTE with inter-frequency HO
ROHC
TTI Bundling
DRX
UL RLC Segmentation
VoLTE with Inter-Freq HO policy VoLTE interference increased by more service provided. Multi-carrier scene need to balance traffic for each carrier, to ensure voice quality, and to maximize resource usage.
1800 frequency band
2600 frequency band
2600 frequency band
1800 frequency band
1800 frequency band
load-based handover coverage-based handover 1800 frequency band
UE move to edge coverage will trigger coverage-based inter-frequency handover, existing network setting accord with VoLTE need. Open load-based inter-frequency function ：when load of serving cell attained to threshold ，MLB algorithm will choose some UEs to receive load-based inter-frequency measurement according to frequency of UE,APR and resource. When signal of interfrequency attained to threshold, handover to inter-frequency neighboring cell. It can balance load of carriers and increase usage. Traffic-based handover fit for service hierarchical scene(1800 as coverage layer to bear high priority service,2600 as data laye r to bear Non GBR data service),used for 1800/2600 hierarchical and continuouscoverage scene.
VoLTE with Inter-Freq HO Scenario 1: Inter-frequency Handover from 1549 to 3100 volte call started at 17:35:50, and connected at 17:36:00. This call lasted about 20 min, and terminated at 17:54:14.
During the volte call, the inter-frequency handover occurred at 17:44:51, handover succeeded from 1549 to 3100.
During the volte call, UE reported the measurement report. It showed that the serving cell RSRP result was 28, and there was a neighbor cell with PCI 441, RSRP result 45.
the RTP sequence numbers were continuous during the inter-frequency handover. The VoLTE call is continuous during the S1-based inter-freq HO.
VoLTE with Inter-Freq HO Scenario 1: Inter-frequency Handover from 3100 to 1549 volte call started at 15:54:40, and connected at 15:54:57. This call lasted about 4 min, and terminated at 15:58:38.
During the volte call, the inter-frequency handover occurred at 15:58:36, handover succeeded from 3100 to 1549.
During the volte call, UE reported the measurement report. It showed that the serving cell RSRP result was 26, and there was a neighbor cell with PCI 52, RSRP result 46.
the RTP sequence numbers were continuous during the inter-frequency handover. The VoLTE call is continuous during the S1-based inter-freq HO.
RoHC-Enhance coverage & capacity AMR-NB12.2K raw data block 93 bytes AMR-WB23.85k raw data block 123 bytes
downlink, IP header compression, sended by eNB on air interface
CN IP Header 60 Bytes
AMR frame 33 Bytes
3. Uplink, eNB decompress and restore IP header
1 ~ 6Bytes
2.Uplink, after IP header compression, sended by UE on air interface
AMR frame 33 Bytes
IP Header 60 Bytes
1. raw data RTP Header + 12 Bytes
RoHC key point： RoHC need support by eNB & UE, eNB negotiate with UE, if negotiation fails, not use compressed mode RoHC only used for data block header compression and decompress on user plane (QCI=1), VOIP DRB setup， RoHC parameter will be negotiated by eNB and UE; inter-eNB handover，ROHC need negotiate again； intra-eNB handover，ROHC need not negotiate again . •
UDP Header 8 Bytes
AMR frame 33 Bytes
+
IPv6 Header 40 Bytes
FDD: RoHC can be deployment in the existing network TDD: Not Suggesting Deployment
RoHC gain： •
increase capacity: AMR-NB12.2K speech data compression rate about 58%((60-6)/93), AMR-WB23.85K speech data compression rate about
•
•
downlink, UE decompress and restore IP header
44%((60-6)/123), decreased used RB, increase system capacity. •
Enhance coverage: RoHC reduces edge rate of VoIP, reduces the power requirement of UE, enhances the edge coverage area (increase 2dB)
RoHC-Enhance coverage & capacity
1. Check License 2. Activate header compression feature: open the ROHC switch, set the ROHC top model and compression protocol type
LOFD-001017
Header compression
Switch on ROHC, set ROHC highest mode, configure types of compression protocol : MOD PDCPROHCPARA: RohcSwitch=ON, HighestMode=O_MODE, Profiles=Profile0x00011&Profile0x0002-1&Profile0x0003-1&Profile0x0004-1; If deactivation of the ROHC feature, close the ROHC switch:: MOD PDCPROHCPARA: RohcSwitch=OFF;
ROHC switch
PdcpRohcPara.RohcSwitch
ROHC highest mode
PdcpRohcPara.HighestMode
Compression protocol type
RObust Header Compression (ROHC)
PdcpRohcPara.Profiles
When eNodeB cell RB utilization rate is high and the VoIP service proportion is high, suggest to open ROHC. According to the radio link quality to determine: When radio link quality is GOOD, choose "U_MODE (one- way mode)“ When radio link quality is FAIR, choose "O_MODE (model)“ When radio link quality is BAD, choose "R_MODE (safe mode)" This parameter is bit-map type, if one bit checked, it means eNodeB support that corresponding compression profile.
RoHC-Enhance coverage & capacity Huawei Mate7 can support ROHC. The UE capability information list relative information.
Volte call connected at 11:23:30.661. During the volte call, MS1 moved from PCI 54 to PCI 141. It reported the measurement result at 11:25:15, and received the RRC connection reconfiguration message.
In the RRC connection reconfiguration message ,the mobility control information: target cell PCI 141. And in the radio resource configure dedicated IE, we found that the RoHC feature was activated.
Check the KPIs after 1 hour test, we found that during the RoHC activated, the header compression radio was almost below 20%, the packet compression ratio was below 60%, and uplink decompression failure ratio usually was 0%.
TTI B-Enhance edge coverage 3GPP TS 36.213 stipulate TTI Bundling can use at most 3 RB , QPSK, highest rank of MCS is 10
Implementation scheme unbundled
bind4 TTIs
After transmits the data block in a bundle of TTIs, among which the last TTI is numbered N. The eNodeB sends an ACK or NACK
4 continuous subframes transfer 1 TB, no need to wait ACK/NACK of eNB
Based on the feedback, the UE determines whether a retransmission is required. If it is required, the UE retransmits the data block in the ( N + 13)th through (N + 16)th TTIs.
bundled
LTE stipulate TTI Bundling retransmission also Bundling •
Uplink Gain •
•
•
3dB •
FDD: TTIB can be deployment in the existing network TDD: Not Suggesting Deployment
TTI Bundling only used to enhance Uplink coverage at cell edge of voice When edge user on bad channel quality, UE transmit the same data block on4 continuous uplink sub frames, uplink combining gain is 3 dB TTI Bundling transmit the same TB on 4 continuous sub-frames (TTI_BUNDLE_SIZE =4), no need to wait ACK/NACK of eNB, the same TB will be transmitted 4 times, used different redundancy algorithm UE must support TTI Bundling : TTI Bundling can be active according to radio link status adaptively by network, the criterion for entering TTI Bundling is UE has VoLTE bearer(QCI1) only and UE has move to cell edge require improve uplink.
TTI B-Enhance edge coverage
1. Check License 2. Activate TTI Bundling feature switch
LOFD-001048
TTI Bundling
TTI bunding
Open TTI Bundling MOD CELLALGOSWITCH: LocalCellId=0, UlSchSwitch=TtiBundlingSwitch-1; Close TTI Bundling MOD CELLALGOSWITCH: LocalCellId=0, UlSchSwitch=TtiBundlingSwitch-0;
Uplink scheduling switch
CellAlgoSwitch.UlSchSwitch
This parameter has a sub switch “TTI Bundling switch” to switch on/off the TTI Bundling function. In the conventional operational scenario, it is suggested to uncheck the TTI Bundling switch. When the UE channel has poor quality and output power is limited, it is suggested to switch on TTI Bundling.
TTI B-Enhance edge coverage After QCI1 setup, when edge user’s radio environment became worse, TTI Bundling feature worked. The relative information was contained in RRC connection reconfiguration message. Queried the counter about TTI Bundling, we found that during the verification test, TTI Bundling enter number reached 112.
DRX-UE Power saving
DRX(Discontinuous Reception)
UE open receiver into activated state at necessary time,to receive downlink data and signaling, other time
close receiver into sleeping state, stop to receive downlink data and signaling i n order to save power .
Open DRX
Close DRX
Monitor PDCCH information
Receive voice frame(1ms)
Receive voice frame(1ms)
20ms
Monitor PDCCH information
Sleep state
20ms
in the open DRX function, UE transmission cycle of speech frames based on open receiving antenna, PDCCH information monitoring, and receives downlink data; in sleep state closed DRX receiving antenna, stop receiving downlink data and signaling
close DRX function,for LTE voice service,receive a 1ms frame in 20ms,UE has been monitoring the PDCCH information during the call.
DRX suggested parameter settings(Only for Reference) QCI Type
QCI1
Long Short DRX On DRX Retrans DRX period Whether to Duration Inactivity Timer period is enable Timer(psf) Timer(psf) (psf) （ms） enabled suggested 40 10 80 8 close open close -
QCI2、3、4 QCI5、6、7、8 open 、9
80
2
80
8 open
Short DRX period （ms）
DRX features of key points: (refer to the specific VoLTE solutions engineering instructions) QCI=1 configuration for a set of DRX parameters According to the QCI=5 recommendations and QCI9 configuration use a same set of parameters Keep other DRX parameters of QCI, DRX parameters of the VoLTE service and data service does not conflict DRX needs to support the terminal chip. Some terminal chip supporting DRX properties, but the RF module does not support. It is closed during the period of DRX. Therefore opened DRX feature, power saving effect is not obvious. The feature of DRX gain: The use of DRX, in the data connection state without service maximum save power 66% ；speech to be tested •
•
•
•
20
•
DRX-UE Power saving During the DT in 10th June, when UE entered cell 137277-1 (cell name: 18NLRJBT20A), DRX was triggered. At 11:37:03.920, eNodeB sent RRC connection reconfiguration message to UE to configure DRX. The details show that DRX for QCI1 worked.
After the volte call terminated, eNodeB sent RRC connection reconfiguration message to UE. The details showed that DRX for QCI9 worked.
Uplink RLC Segment 20ms Voice Frame (AMR 12.2k)
MAC
RLC
PDCP
RoHC
Voice Payload
2
1
1
6
33 Bytes
Far end User (6PRB MCS4)
←√
TBS = 51 Bytes
Edge User (3PRB MCS2)
←X
TBS = 18 Bytes
PDCP
Segment
cannot hold one voice frame
RoHC
10 Bytes
Voice Payload
+
10 Bytes
+
10 Bytes
+
10 Bytes
Segment one PDCP packet into
Edge User (3PRB MCS2)
MAC
RLC
Seg Payload
2
1
10
TBS = 18 Bytes
More UL segments for voice frame may cause increase of packet delay in
←√
several small packets and transmitted in different subframe, this will reduce TBS size per subframe which result in low MCS and improve the UL coverage TDD-LTE system, for the SA2(3:1), there are 4 U L frame in 20ms. The 4 UL frame could be used to transmitted the same voice frame and response with one HARQ, this will gain around 4dB for UL coverage and save the PDCCH resource in downlink .
the air, this may cause the increase of packet loss (Schedule issue) or voice quality Issue. RLC segments will increase the bits number of RLC head and MAC head or signaling cost. HARQ channel issue may influence the decode the PDCP layer packet and result in bad voice quality.
parameter
script
UlVoipRlcMaxSegNum MOD CELLULSCHALGO
Recommend value 20
Uplink RLC Segment For RLC Segmentation feature, there is no special i ndicator in the signaling. We can only check the uplink packet loss rate. On the U2000, the uplink packet loss rate counters for QCI of 1 are queried and the uplink packet loss rate is calculated. The uplink packet loss rate decreases significantly after the RLC segmentation feature is enabled. Test of and comparison between the uplink packet loss rates before and after the RLC segmentation feature is enabled.
•The uplink packet loss rate is about 3.77% when the RLC segmentation feature is disabled. And it decreases to about 3.44% whe n the RLC segmentation feature is enabled. •Conclusion RLC segmentation worked well during the volte call. It will reduce the uplink packet loss rate and improve subscribers’ exper ience.
Thank You!
