SPD LTE IRAT Troubleshooting Guide 20120718 a 1.0

1LTE IRAT Troubleshooting Guide
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IRAT Fault Diagnosis
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GSM, UMTS and, LTE will coexist for a long time.
Voice service keeps creating huge revenue for operators.
Main revenue growth will come from data services.
Revenues (US$bn)
Source: Informa Telecoms & Media
HUAWEI TECHNOLOGIES CO., LTD.
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1. An example of LTE & GSM interoperation is TMO of Germany.
2. Examples of LTE & UMTS interoperation are Bell of Canada, eMobile of Japan, and Genius of Hong Kong.
3. An example of LTE, GSM, and UMTS interoperation is N4M of Sweden.
Function requirements
UEs preferentially receive services from the LTE network for better user experience.
The continuity of the LTE services is guaranteed.
The services and load are appropriately shared among the LTE, GSM, and UMTS.
The network upgrade causes minimum impact on the network and users.
Performance requirements
The KPIs must be guaranteed, for example, IRAT handover success rate and IRAT handover delay.
Users of high-speed data services receive services from preferably the LTE for better user experience. Where the LTE is unavailable, the UMTS or GSM is used.
Parameters are correctly set to improve the IRAT handover success rate, lower the impact of a handover on the service, and prevent ping-pong handovers.
Minimum LTE to UMTS/GSM handover delay is guaranteed. Users are unaware of the service degradation caused by handovers.
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LTE/EPC
GSM/UMTS
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LTE
UTRAN/GERAN
UE moving out of LTE coverage
Camping priority:
UE moving out of LTE coverage
Connected Mode
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Target
UEs preferentially reside in LTE except when the LTE cell has poor signal quality.
UE resides in the LTE cell even when the G/U cell has good signal quality.
Cell reselection from LTE to GSM/UMTS :
The eNodeB is so configured that the priority of LTE cell reselection is greater than that of GSM/UMTS cell reselection. If the signal strength of the serving LTE cell is lower than the inter-RAT measurement threshold, the GSM/UMTS measurement is triggered. If the signal strength of the LTE cell is lower than the serving-frequency low-priority reselection threshold and the signal strength of the inter-RAT frequency is greater than the inter-RAT frequency low-priority reselection threshold, the GSM/UMTS cell reselection is triggered.
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Target
UEs preferentially reside in LTE except when the LTE cell has poor signal quality.
UEs reside in LTE cell even when the G/U cell has good signal quality.
L to G/U:
Cell reselection from GSM/UMTS to LTE:
All LTE frequencies are configured on the BSC/RNC and the priority of LTE cell reselection is greater than that of GSM/UMTS cell reselection. After the UE returns to the idle or PCH mode upon completion of a service in the GSM/UMTS network, the UE periodically measures the LTE signal strength. If the signal strength of the LTE cell is greater than the high-priority reselection threshold configured on the BSC/RNC, the LTE cell reselection is triggered.
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Events and meaning related to the LTE system
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A2
A3
A4
A5
Serving becomes worse than threshold and neighbor becomes better than threshold2
B1
B2
Serving becomes worse than threshold and inter RAT neighbor becomes better than threshold2
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Delivery Policies of IRAT – Connected Status
Coverage-based: When a UE moves out of the LTE coverage, the LTE signal worsens. After the UE reports event A2, the eNodeB determines whether the UE supports inter-RAT measurement.
If the UE supports inter-RAT measurement, the eNodeB delivers the inter-RAT measurement control. After the UE reports inter-RAT measurement event B1, the inter-RAT PS handover or redirection is triggered. If both the UE and network support PS handover, PS handover is preferred to obtain shorter service interruption. If the operator does not want to upgrade the GERAN/UTRAN to support PS handover or the UE does not support PS handover, redirection is performed. In this case, the PS handover switch must be turned off.
If the UE does not support inter-RAT measurement, the eNodeB performs the UMTS blind redirection triggered by event A2.
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Delivery Policies of IRAT – Voice Service
Before the IMS becomes mature, CSFB is a solution for providing voice service over the LTE system. When the UE performs a mobile-originated or mobile-terminated voice service over the LTE, the CSFB works as follows:
If the UE supports inter-RAT measurement, the eNodeB delivers the inter-RAT measurement control. After the UE reports inter-RAT measurement event B1, CSFB based on inter-RAT PS handover or redirection is triggered. If both the UE and network support PS handover, PS handover is preferred to obtain shorter service interruption. If the operator does not want to upgrade the GERAN/UTRAN to support PS handover or the UE does not support PS handover, redirection is performed. In this case, the PS handover switch must be turned off.
If the UE does not support inter-RAT measurement, the CSFB is based on inter-RAT blind redirection.
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3. RRC CONNECTION RELEASE
4. UE reselect the target UTRAN cell and launch RAU procedure
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A1/A2 measurement control
A2 measurement report
B1 measurement control
B1 measurement report
Handover command, instructing the UE to hand over to the inter-RAT
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KPI
Meaning
L2U redirection control-plane delay
From reception of RRC CONN REL on the LTE to transmission of RRC CONN REQ on the UMTS
L2G redirection control-plane delay
From reception of RRC CONN REL on the LTE to transmission of Channel Request on the GERAN.
PSHO control-plane delay
From reception of Handover Command to reply of Handover Complete
CSFB voice service setup delay
From transmission of Extend Service Request to reception or transmission of the Alerting message on the UMTS/GERAN
User-plane interruption delay (uplink)
Average E2E IP-layer interruption delay. Observed on the FTP server. From reception of the last data packet on the LTE to reception of the first data packet on the UMTS/GERAN
User-plane interruption delay (downlink)
Average E2E IP-layer interruption delay. Observed on the UE. From reception of the last data packet on the LTE to reception of the first data packet on the UMTS/GERAN
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Definitions and Observation of IRAT KPIs - Probe
The CSFB KPIs, including CS setup delay and success rate, can be observed on the Probe/Assistant.
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Type
IRAT not supported by GSM or UMTS BTS version
IRAT not supported by core network version
Parameter Configuration
Inter-RAT neighboring cell not configured or incorrectly configured
Core network interface not configured or incorrectly configured
Interference Coverage
Large interference
Known Problem
Known bugs of the UE
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IRAT Troubleshooting Flowchart
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Discover a Problem
Check each signaling procedure to determine where the problem occurs.
eRAN 2.1 provides performance statistics for only L2U, L2G, and L2C outgoing handovers for calculating the handover success rate. eRAN3.0 provides additional performance statistics for redirection and CSFB. For details, see the performance indexes of eRAN3.0.
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Determining the UE Capability
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IRAT Parameter Configuration – Reselection
The following command configures the LTE cell reselection priority and parameters:
MOD CELLRESEL: LocalCellId=0, SNonIntraSearchCfgInd=CFG, SNonIntraSearch=8, ThrshServLow=7, CellReselPriority=6;
where CellReselPriority indicates the LTE cell reselection priority and SnonInterSearch indicates the time that the UE starts the inter-RAT measurement. CellReselPriority ranges from 0 to 7. To let the UE preferentially reside in the LTE system, this parameter is set to a high value.
The following command configures the UMTS frequency and reselection priority:
ADD UTRANNFREQ: LocalCellId=0, UtranDlArfcn=2825, UtranFddTddType=UTRAN_FDD, UtranUlArfcnCfgInd=NOT_CFG, CellReselPriorityCfgInd=CFG, CellReselPriority=3, ThreshXLow=6;
where UTRANDLARFCN indicates the UMTS downlink frequency and CELLRESELPRIORITY indicates the UMTS cell reselection priority ranging from 0 to 7. If the LTE signal quality is less than ThrshServLow and the UMTS signal quality is greater than ThreshXLow, the UE reselects the UMTS.
The following command adds the UMTS cell reselection information:
ADD CELLRESELUTRAN: LocalCellId=0, SpeedStateSfCfgInd=NOT_CFG;
After this command is configured, the SIB6 can be delivered.
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IRAT Parameter Configuration – Redirection and Handover
The following command adds the UMTS frequency:
ADD UTRANNFREQ:LOCALCELLID=0,UTRANDLARFCN=2825,UTRANFDDTDDTYPE=UTRAN_FDD,UTRANULARFCNCFGIND=NOT_CFG,CELLRESELPRIORITYCFGIND=CFG,CELLRESELPRIORITY=3;
The following command adds the UMTS external cell:
ADD UTRANEXTERNALCELL:MCC="460",MNC="00",UTRANCELLID=18,UTRANDLARFCN=2825,UTRANULARFCNCFGIND=NOT_CFG,RNCID=20,RACCFGIND=CFG,RAC=5,PSCRAMBCODE=18,LAC=3;
where RACCFGIND and RAC are mandatory for PS handovers.
The following command adds the UMTS neighboring relationship:
ADD UTRANNCELL:LOCALCELLID=0,MCC="460",MNC="00",UTRANCELLID=18,BLINDHOPRIORITY=5;
where BLINDHOPRIORITY indicates the priority of the blind handover and blind redirection and has 32 values. The value has a positive correlation with the priority. Value 0 indicates that blind handover is prohibited. A non-zero value must not be duplicate with the value of existing neighboring cell of the same type in the local cell.
The following command configures the handover and redirection switches:
ADD MOD ENODEBALGOSWITCH: HoModeSwitch=UtranPsHoSwitch-1&UtranRedirectSwitch-1;
If both the UtranPsHoSwitch and UtranRedirectSwitch are turned on, the former has a higher priority.
The following commands configure the handover and redirection thresholds:
MOD INTERRATHOCOMMGROUP:LOCALCELLID=0,INTERRATHOCOMMGROUPID=0,INTERRATHOA1THDRSRP=-111,INTERRATHOA2THDRSRP=-115;
MOD INTERRATHOUTRANGROUP: LocalCellId=0, InterRatHoUtranGroupId=0, InterRatHoUtranB1ThdRscp=-103;
where the INTERRATHOCOMMGROUPID and InterRatHoUtranGroupId of a QCI are queried by running the LST CELLSTANDARDQCI. These two parameters are used to set the coverage-based inter-RAT…

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SPD LTE IRAT Troubleshooting Guide 20120718 a 1.0