oeo106060 lte eran3.0 handover feature issue1.00
DESCRIPTION
HuaweiTRANSCRIPT
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3.0 (Update to eRAN3.0 feature)
( Add more message tracing )
(Add muti-band mobility deployment policy)
LTE eRAN3.0 Load Control Feature
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LTE eRAN3.0 Handover Feature
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LTE eRAN3.0 Handover Feature
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LTE eRAN3.0 Handover Feature
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Mobility management is classified into mobility management in idle mode and mobility
management in connected mode, based on RRC states. A UE with an RRC connection to
the radio network is considered to be in connected mode. In the case of mobility
management in connected mode, an eNodeB delivers the associated configuration through
signaling on the control plane, and UEs perform measurements accordingly and complete
the handover procedures under the control of the eNodeB, thus ensuring uninterrupted
service provision.
In the case of mobility management in connected mode, the mobile network ensures
continuity of physical channels and provides uninterrupted communications service for UEs
in connected mode through handovers when the UEs are moving in the network. A
handover is a procedure where the serving cell of a UE in connected mode is changed.
Handovers can be classified into intra-frequency handover, inter-frequency handover, and
inter-RAT handover.
LTE eRAN3.0 Handover Feature
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LTE eRAN3.0 Handover Feature
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All the handover involve 3 setups
Measurement step: UE strart intra-frequency or inter-frequency measurement
according to the different triggers
Decision step: eNodeB make handover decision according to the resource state and
related parameters
Execution step: eNodeB send execution command to UE to perform handover
The relative parameters can be automatically optimized by MRO
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Different types of handover measurement are triggered by different causes, as shown
above
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When a UE establishes a radio bearer, the eNodeB delivers the intra-frequency
measurement configuration to the UE through an RRC Connection Reconfiguration
message by default. Then, the UE performs intra-frequency measurements by default.
When measurement gaps need to be set up, the eNodeB delivers the inter-frequency
and/or inter-RAT measurement configuration to the UE. After that, the UE performs gap-
assisted inter-frequency and/or inter-RAT measurements. Inter-frequency and inter-RAT
measurements can use the same gap pattern, but the eNodeB is able to differentiate
between the gap configurations for inter-frequency and inter-RAT measurements.
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Related commands
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The concept of event-triggered reporting as specified in 3GPP is used by the measurement
and decision phases of handovers. Reporting configurations consist of the parameters
related to specific events. Currently, the eNodeB supports mechanisms as responses to the
above events.
In the report configuration IE, eNodeB should deliver all the relevant for event based
report. After eNodeB receive specific report, it will implement corresponding action
Each event has the individual report configuration with the unique report configuration ID.
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Before evaluating the reporting criteria and sending measurement reports, the UE performs
layer 1 (L1) filtering and L3 filtering on the measurement results. The L1 filtering is
performed by the UE at the physical layer to eliminate the impact of fast fading on the
measurement results. No user configuration is required for the L1 filtering. The L3 filtering
aims at eliminating the impact of shadow fading and certain fast fading. In this way, better
measurement data can be provided for the evaluation of the reporting criteria. Based on
the triggering quantity, two L3 filtering coefficients are applicable: one for RSRP
measurements and the other for RSRQ measurements.
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A measurement gap is a time period during which the UE performs measurements on a neighboring
frequency of the serving frequency. Measurement gaps are applicable to inter-frequency and inter-
RAT measurements. The UE performs inter-frequency or inter-RAT measurements only within the
measurement gaps. One UE normally has only one receiver, and consequently one UE can receive
the signals on only one frequency at a time.
When inter-frequency or inter-RAT measurements are triggered, the eNodeB delivers the
measurement gap configuration, and then the UE starts gap-assisted measurements accordingly. As
shown above, Tperiod denotes the repetition period of measurement gaps, and TGAP denotes the gap
width, within which the UE performs measurements.
Gap-assisted measurements for the following types of handover may co-exist: coverage-based, load-
based, and service-based handovers. When two or all of the preceding types of gap-assisted
measurement co-exist, the eNodeB records the measurements based on these types. These different
types of measurement are called member gap-assisted measurements. The member gap-assisted
measurements can share the measurement gap configuration. A UE releases measurement gaps
only when all member measurements are stopped.
There are two measurement gap patterns available: pattern 1 and pattern 2. In pattern 1, TGAP is 6
ms and Tperiod is 40 ms. In pattern 2, TGAP is 6 ms and Tperiod is 80 ms. The pattern to be used is
specified through the GapPatternType parameter.
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A neighboring relation is a relation between the serving cell and each candidate cell involved in a
handover. Neighboring relation management covers the following aspects:
Whether to allow automatic removal of a neighboring relation by ANR or not
Whether to allow handovers of UEs between two cells or not
Whether to allow handovers over an X2 interface or not
Neighboring relations are planned in the network design stage. They can be automatically adjusted
by ANR. The ANR function reduces the risk of missing neighboring cells and solves the problems of
inappropriate neighboring relations caused by collisions of physical cell IDs or by physical positions.
In this way, the call drop rate is reduced and the handover success rate is increased.
Intra-frequency neighboring cell
An intra-frequency neighboring cell is a neighboring cell whose DL E-UTRA Absolute Radio
Frequency Channel Number (EARFCN) is the same as the DL EARFCN of the serving cell. An
E-UTRAN cell can be configured with a maximum of 32 intra-frequency neighboring cells.
Inter-frequency neighboring cell
An inter-frequency neighboring cell is a neighboring cell whose DL EARFCN is different from
the DL EARFCN of the serving cell. An E-UTRAN cell can be configured with a maximum of
64 inter-frequency neighboring cells, which can be located on a maximum of 8 neighboring
E-UTRAN frequencies. TDD cells can also be configured as inter-frequency neighboring cells
of FDD cells. Huawei eNodeB supports interoperability between LTE FDD and LTE TDD.
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Inter-RAT neighboring cell
Inter-RAT neighboring cells are neighboring UTRAN cells, neighboring GERAN cells,
and neighboring CDMA2000 cells. The maximum configurations of neighboring
cells and frequencies for an E-UTRAN cell are as follows: 64 neighboring UTRAN
cells and 16 neighboring UTRAN frequencies; 64 neighboring GSM cells and 16
neighboring GSM frequency groups; 32 neighboring CDMA2000 EVDO cells and
32 neighboring CDMA2000 1x cells.
Black cell:
Blacklisted cells are not considered in event evaluation or measurement reporting.
This list should be configured manually and delivered to UE via SIB
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The handover switch can be modified by the following command:
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Each object has a unique ID, and the object is mapping with frequency number but not
cell. If some neighbors for this object is configured, then you can also find the neighbor
info to simplify UE measurement
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LTE eRAN3.0 Handover Feature
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Mn: The measurement result of the neighboring cell
Ofn: The frequency-specific offset for the frequency of the neighboring cell, it is not valid
during intra-frequency handover.
Ocn: The cell-specific offset (that is, CIO) for the neighboring cell, related command: MOD
EUTRANINTERFREQNCELL
Ms: The measurement result of the serving cell
Ofs: The frequency-specific offset for the serving frequency
Ocs: The cell-specific offset for the serving cell
Hys: The hysteresis for event A3. It is specified through the IntraFreqHoA3Hyst
parameter and contained in the delivered measurement configuration.
Off: The offset for event A3. It is specified through the IntraFreqHoA3Offset parameter.
If the entering condition of the event is continuously met during the time specified through
IntraFreqHoA3TimeToTrig, the UE reports event A3 and starts the event-triggered
periodical reporting. Then, if the leaving condition of the event is continuously met during
the time specified through IntraFreqHoA3TimeToTrig, the UE stops reporting event A3.
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Load based HO is controlled by MLB module which is enabled with MlbAlgoSwitch, once
it is triggered then CIO can be modified by MLB, to easily trigger A3 event report.
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LTE eRAN3.0 Handover Feature
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After receiving a measurement report from the UE, the eNodeB generates a list of
candidate cells, which meet the triggering condition of the specific event. As a second
step, the eNodeB filters the candidate cells. If the measurement result of an intra-eNodeB
cell is the same as that of an inter-eNodeB cell among the candidate cells, the eNodeB
prioritizes the intra-eNodeB cell to prevent signaling and data forwarding required in an
inter-eNodeB handover.
LTE eRAN3.0 Handover Feature
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In the handover execution phase, the UE and the eNodeB exchange signaling over the
radio interface according to 3GPP TS 36.331. During an inter-eNodeB handover, the
source eNodeB and the target eNodeB exchange signaling and data through X2/S1
adaptation. The LTE system uses hard handover, that is, only one radio link is connected to
a UE at a time. Therefore, to prevent user data loss at the eNodeB during the handover,
data forwarding is performed to ensure eNodeB data integrity. The loss of data may cause
a decrease in the data transfer ratio and an increase in the data transfer delay.
In the case of an intra-MME inter-eNodeB handover, the source eNodeB checks whether
the X2 interface is available between the source and target eNodeBs or not and then
automatically selects a path for the handover as follows:
If the X2 interface is available, the handover request is sent over the X2 interface.
Data forwarding is also performed over the X2 interface.
If the X2 interface is unavailable, the handover request is sent over the S1
interface. Data forwarding is also performed over the S1 interface.
In the case of an inter-MME inter-eNodeB handover, the handover request is sent over the
S1 interface. In addition, the source eNodeB checks whether the X2 interface is available
between the source and target eNodeBs or not and then automatically selects a path for
data forwarding as follows:
If the X2 interface is available, data forwarding is performed over the X2 interface.
If the X2 interface is unavailable, data forwarding is performed over the S1
interface.
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The data forwarding process is as follows: After the source eNodeB sends a handover
command to the UE, the UE detaches the connection from the source eNodeB. The source
eNodeB then forwards the uplink (UL) data that is received out of order and the DL data to
be transmitted, to the target eNodeB.
Data forwarding prevents a decrease in the data transfer ratio and an increase in the data
transfer delay that are caused by user data loss during the handover.
Intra-eNodeB handovers do not require data forwarding. In the case of inter-eNodeB
handover, the source eNodeB selects a data forwarding path by using the X2/S1
adaptation mechanism.
In the case of an inter-RAT handover to UTRAN or GERAN, the eNodeB checks whether the
core network supports direct forwarding or not and then selects a data forwarding path
accordingly. If the core network supports direct forwarding, the eNodeB directly forwards
the data to the target Radio Network Controller (RNC) in the case of UTRAN or to the
target Serving GPRS Support Node (SGSN) in the case of GERAN, so as to shorten the data
forwarding time. If the core network does not support direct forwarding, the eNodeB
sends the data to the Serving Gateway (S-GW).
In the case of an inter-RAT handover to CDMA2000, the eNodeB sends the data to the S-
GW.
LTE Handover Feature
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Specific Cell Individual Offset (CIO) values can be set for the serving cell and its neighboring
cells. (Ocs and Ocn described in the subsequent chapters denote the CIO for the serving
cell and the CIO for the neighboring cell respectively.) When the quality of signals
fluctuates, the probability of triggering handovers to or from a specific cell can be adjusted
by changing the value of CIO. This reduces the risk of call drops. The CIO values can be
adjusted automatically by the MRO function.
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Each parameters are described as below:
Max report cell number: Indicates the maximum number of cells to be included in
the measurement report after an event for the intra- or inter-frequency handover
within the E-UTRAN is triggered.
Measurement report amount: Indicates the number of periodic measurement
reports to be sent after an event for the intra- or inter-frequency handover within
the E-UTRAN is triggered. It is used to prevent the impact of measurement report
loss and internal processing failure on the handover.
A3 measurement trigger quantity: Indicates the quantity used to evaluate the
triggering condition for the intra-frequency handover event. The quantity can be
RSRP or RSRQ. Recommended value: RSRP
A3 measurement report quantity: Indicates the quantity to be included in the
measurement report for the intra-frequency handover event
Intrafreq measurement report interval: Indicates the interval between each periodic
report
Measurement A4 report quantity: The same meaning as A3 measurement
A1A2 Measurement trigger quantity: The same meaning as A3 measurement
Interfreq measurement report interval: The same as itrafreq measurement report
interval
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In LTE, 9 QCI are defined as QoS level. Each QCI is mapped with a series handover group.
The related command is : MOD CELLSTANDARDQCI
The main parameters for intra-handover decision algorithm are shown as following
Intrafreq handover hysteresis: Indicates the hysteresis to be used in the triggering
condition for the intra-frequency handover event. This parameter helps reduce the
number of times the event is triggered because of radio signal fluctuation. Thus,
the probability of ping-pong handovers or wrong handover decisions is reduced.
Intrafreq handover offset: Indicates the quality offset of the neighboring cell over
the serving cell to be used in the triggering condition of the intra-frequency
handover event.
Intrafreq handover time to trigger: Indicates the time-to-trigger for intra-frequency
handover event A3.When detecting that the signal quality in the serving cell and
that in at least one neighboring cell meet the entering condition, the UE does not
send a measurement report to the eNodeB immediately. Instead, the UE sends a
report only when the signal quality continuously meets the entering condition
during the time-to-trigger
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The signaling procedure shown in above figure is described as follows:
When the UE establishes a radio bearer, the source eNodeB sends the UE an RRC
Connection Reconfiguration message that contains the measurement
configuration. The measurement configuration is set by the source eNodeB to
control the measurements of the UE in connected mode.
The UE sends measurement reports to the source eNodeB based on the
measurement results.
The source eNodeB makes a handover decision based on the measurement reports.
After deciding that a handover is preferred, the source eNodeB sends a Handover
Request message to the target eNodeB, to request the target eNodeB to prepare
for the handover.
The target eNodeB makes admission decisions. If resources can be granted by the
target eNodeB, the target eNodeB performs admission control depending on the
QoS information about the Evolved Packet System (EPS) bearer.
The target eNodeB prepares L1/L2 resources for the handover and then sends a
Handover Request Acknowledge message to the source eNodeB.
The source eNodeB sends the UE an RRC Connection Reconfiguration message that
contains the mobilityControlInfo IE, indicating that the handover shall start.
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The UE performs a procedure of random access towards the target eNodeB, to
achieve the UL synchronization of the UE with the target eNodeB.
After successfully accessing the target cell, the UE sends the target eNodeB an RRC
Connection Reconfiguration Complete message, indicating that the handover
procedure is complete. At this time, the target eNodeB can start sending data to
the UE.
The DL data path switching is performed.
The target eNodeB sends the source eNodeB a UE Context Release message, to
inform the source eNodeB of the success of the handover and to trigger the release
of the resources at the source eNodeB.
After receiving the UE Context Release message, the source eNodeB releases the
radio and control-plane resources associated with the UE context.
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Blind HO switch:
Once blind HO is activated, eNodeB directly decide the HO target based on the priority
configuration of each neighbor
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The switch for each scenario
eNodeB level switch: coverage based, service based, UL quality based
Cell level switch: frequency priority based and distance based
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LTE Handover Feature
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This execution is mandatory to for inter-frequency measurement, must be done by manual
configuration.
If it is configured, then A1/A2 event parameters will be delivered by eNB by default, thus
to trigger inter-frequency measurement.
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In a coverage-based inter-frequency handover, event A2 triggers inter-frequency
measurements. The triggering of this event indicates that the signal quality in the serving
cell is lower than a specified threshold.
Ms: The measurement result of the serving cell
Hys: The hysteresis for event A2
Thresh: The threshold for event A2, it can be defined separately with RSRP or RSRQ
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The triggering and stopping of inter-frequency measurements for load-based handovers
are determined by the MLB algorithm. When the load of the serving cell reaches the
threshold for inter-frequency load balancing, the MLB algorithm selects a number of UEs
based on the frequency capabilities of the UEs, ARPs, and resource usage and then
instructs the UEs to perform gap-assisted inter-frequency measurements for load-based
handovers. The MLB algorithm also determines the cells on which the measurements need
to be performed.
After load-based inter-frequency measurements are triggered, the eNodeB does not
process the outputs from the MLB algorithm if the eNodeB detects that measurement gaps
have been set up among which there are measurement gaps for other types of handover.
Otherwise, the eNodeB sets up the measurement gaps for the load-based handovers.
When the measurement gaps for load-based handovers are released, the gap-assisted
measurements for other types of handover are not affected. The measurement gap
configuration stops only when all gap-assisted measurements are stopped.
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Event A1 triggers measurements for frequency-priority-based handover.
The FreqPriInterFreqHoA1TrigQuan parameter specifies the event A1 triggering
quantity for frequency-priority-based measurement, which can be either RSRP or RSRQ. If
the triggering quantity is RSRP, the threshold for this event is specified by the
FreqPriInterFreqHoA1ThdRsrp parameter. If the triggering quantity is RSRQ, the
threshold for this event is specified by the FreqPriInterFreqHoA1ThdRsrq parameter.
Other parameters related to event A1 for frequency-priority-based measurement are the
same as those for coverage-based inter-frequency measurement.
After receiving an event A1 report from a UE, the eNodeB proceeds as follows:
If frequency-priority-based blind handover is enabled,the eNodeB selects the
neighboring cell with the highest blind-handover priority to perform a handover.
However, if load balancing from that neighboring cell to the serving cell is in
progress, the eNodeB selects the neighboring cell with the second highest priority.
If the eNodeB traverses all candidate cells but fails to find a cell that fulfills the
criteria, the eNodeB will decide not to perform a handover.
If frequency-priority-based blind handover is disabled, the eNodeB delivers the
inter-frequency measurement configuration to the UE. If the triggering condition of
event A4 is fulfilled, the UE sends a frequency-priority-based event A4 report to the
eNodeB. (The triggering of event A4 for frequency-priority-based handover is
similar to that for coverage-based inter-frequency handover
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Service-based inter-frequency handovers are applicable to two neighboring E-UTRAN
frequencies that cover the same area. Based on the QCIs of the services that are running
on a UE, the eNodeB can divert the UE to an appropriate co-coverage E-UTRAN frequency
by means of a service-based inter-frequency handover.
To implement service-based inter-frequency handovers, operators need to configure
service-based inter-frequency handover policies. Each service-based inter-frequency
handover policy has an ID (ServiceIfHoCfgGroupId) and specifies the frequency
(DlEarfcn) that is preferentially used to carry the services of a specific operator
(CnOperatorId). Since the services of each operator are further classified by QCIs, each
QCI can be associated with a service-based inter-frequency handover policy so that the
frequency specified by the policy preferentially carries the services with this QCI.
Service-based inter-frequency handovers are controlled by the corresponding switch under
the HoAlgoSwitch parameter. If this switch is turned on, the eNodeB triggers a service-
based inter-frequency handover for a UE based on the highest-priority QCI of the services
running on the UE. If the highest-priority QCI is associated with a service-based inter-
frequency handover policy with the InterFreqHoState parameter set to PERMIT_HO,
and there is at least one neighboring cell working on the frequency, the eNodeB delivers
the measurement configuration related to event A4 to the UE. The triggering of event A4
in service-based inter-frequency handovers is the same as that in coverage-based inter-
frequency handovers.
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Related commands:
LTE Handover Feature
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As shown above, F1 and F2 indicate two frequencies: Cell 1 uses F1, and Cells 2, 3, and 4
all use F2. The gray area in the figure (Cell 1) is covered by F1, while Cells 2, 3, and 4 is
covered by F2. It is obvious that cell 1 exerts cross-cell coverage to the other three cells.
Assume that the UE moves along the direction indicated by the arrow. As the UE moves,
F1 provides sustained signal quality and therefore inter-frequency measurements are not
triggered for the UE even when the UE has been in the coverage of F2 for a long time.
Gradually, the UE enters the overlap coverage between Cell 1 and Cell 4. Considering the
long distance between the two cells, it is unlikely that Cell 4 is configured as a neighboring
cell of Cell 1. As a result, as soon as the UE leaves the coverage of Cell 1, it experiences a
call drop. To prevent such a call drop and ensure service continuity, the UE should have
been handed over to F2 earlier.
Related command:
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UL-quality-based inter-frequency handovers are triggered based on the UL quality. When
the UL quality is unsatisfactory, call drops may occur if handovers are not performed in
time. Therefore, UL-quality-based inter-frequency handovers are introduced to reduce call
drops caused by poor UL quality. The eNodeB uses the modulation and coding scheme
(MCS) and initial block error rate (IBLER) to determine the UL quality.
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In this message it contain inter-frequency measurement control parameters, almost the
same as intra-frequency measurement, just one more gap configuration, used to trigger or
stop the measurement
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Related command:
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Mn: The measurement result of the neighboring cell.
Ofn: The frequency-specific offset for the frequency of the neighboring cell.
Ocn: The cell-specific offset for the neighboring cell.
Hys: The hysteresis for event A4
Thresh: The threshold for event A4
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Each parameters are described as below:
Max report cell number: Indicates the maximum number of cells to be included in
the measurement report after an event for the intra- or inter-frequency handover
within the E-UTRAN is triggered.
Measurement report amount: Indicates the number of periodic measurement
reports to be sent after an event for the intra- or inter-frequency handover within
the E-UTRAN is triggered. It is used to prevent the impact of measurement report
loss and internal processing failure on the handover.
A3 measurement trigger quantity: Indicates the quantity used to evaluate the
triggering condition for the intra-frequency handover event. The quantity can be
RSRP or RSRQ. Recommended value: RSRP
A3 measurement report quantity: Indicates the quantity to be included in the
measurement report for the intra-frequency handover event
Intrafreq measurement report interval: Indicates the interval between each periodic
report
Measurement A4 report quantity: The same meaning as A3 measurement
A1A2 Measurement trigger quantity: The same meaning as A3 measurement
Interfreq measurement report interval: The same as itrafreq measurement report
interval
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The same commands are used for inter-frequency handover as intra-frequency handover,
the main related parameters are shown as following:
Measurement parameters
Measurement A4 trigger quantity: Indicates the quantity to be included in the
measurement report for the inter-frequency handover event. The quantity can be
RSRP, RSRQ, or both.
Interfreq measurement report interval: Indicates the interval at which periodical
measurement reports are sent after an inter-frequency handover event is triggered.
A1A2 Measurement trigger quantity: Indicates the quantity used to evaluate the
triggering condition for inter-frequency measurement event A1 or A2.
QCI based parameters
Interfreq A1A2 hysteresis: Indicates the hysteresis to be used in the triggering
condition of event A1 or A2 for the inter-frequency handover.
Interfreq A1A2 time to trigger: Indicates the time-to-trigger for inter-frequency
measurement event A1 or A2.
Interfreq handover hysteresis: Indicates the hysteresis to be used in the triggering
condition of the inter-frequency handover event.
Interfreq HandOver Time to Trigger: Indicates the time-to-trigger for inter-
frequency handover event A4.
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If the InterRatHoState parameter is set to MUST_HO for a QCI, the eNodeB delivers the
service-based handover measurement configuration to a UE when the UE initiates a service
with that QCI.
If the InterRatHoState parameter is set to NO_HO for a QCI, the eNodeB does not deliver
the service-based handover measurement configuration to a UE on which a service with
that QCI is running, even if the UE initiates a service for which InterRatHoState is set to
MUST_HO.
If the InterRatHoState parameter is set to PERMIT_HO for a QCI, the eNodeB does not
deliver the service-based handover measurement configuration to a UE when the UE
initiates a service with that QCI. When a service with that QCI is running on the UE, the
eNodeB delivers the service-based handover measurement configuration to the UE if the
UE initiates a service for which InterRatHoState is set to MUST_HO.
If a service-based inter-RAT handover is not initiated after the gap-assisted measurements
are performed for a relatively long time, the eNodeB instructs the UE to stop the service-
based inter-RAT measurements and release the measurement gaps.
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Mn: The measurement result of the neighboring cell
Ofn: The frequency-specific offset for the frequency of the neighboring cell
Hys: The hysteresis for event B1. The hysteresis values for inter-RAT handovers to UTRAN,
GERAN, and CDMA2000
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LTE eRAN3.0 Handover Feature
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LTE Handover Feature
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LTE Handover Feature
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The following inter-RAT handover policies are applicable:
PS handover: is applicable to PS services. In PS handover, services are handed over
from the PS domain of the source system to the PS domain of the target system to
ensure continuous service provision.
Single Radio Voice Call Continuity (SRVCC): is applicable to voice services. In the
case of SRVCC, the services are handed over from the LTE system to the CS domain
of the target system.
Cell Change Order with or without Network Assisted Cell Change (CCO/NACC): is
specific to the GSM cases. During the CCO/NACC, the UE is ordered to switch to
the GERAN idle mode, and consequently it can try to access the GSM network. The
procedure is simple but causes a long delay. In GSM, however, the CCO/NACC
mode is a substitute for PS handover. For the CCO with NACC, the eNodeB needs
to acquire the system information from the target system and then send the
information to the UE through a handover command, thereby accelerating the UE
access to the target GSM cell.
Redirection: It is the simplest method to transfer UEs to an inter-RAT system. The
3GPP protocols stipulate that UEs that can work in another RAT also support
redirections to the RAT.
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LTE eRAN3.0 Handover Feature
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For SRVCC from E-UTRAN to UTRAN/GERAN, MME first receives the handover request
from E-UTRAN with the indication that this is for SRVCC handling, and then triggers the
SRVCC procedure with the MSC Server enhanced with SRVCC via the Sv reference point if
MME has SRVCC STN-SR information for this UE. MSC Server enhanced for SRVCC then
initiates the session transfer procedure to IMS and coordinates it with the CS handover
procedure to the target cell. MSC Server enhanced for SRVCC then sends PS-CS handover
Response to MME, which includes the necessary CS HO command information for the UE
to access the UTRAN/GERAN.
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In the case of CCO/NACC to GERAN, the eNodeB directly orders the UE to switch to the
GERAN, instead of sending a handover request over the S1 interface. In the procedure
shown in the figure, steps 3 to 8 are used to request the system information of the
GERAN. They are applicable only to CCO with NACC.
LTE Handover Feature
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LTE eRAN3.0 Handover Feature
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LTE eRAN3.0 Handover Feature
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LTE eRAN3.0 Handover Feature
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LTE eRAN3.0 Handover Feature
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Intra-frequency key parameters
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Id Name Description Recommended
Value
IntraFreqHoA3
Hyst
Intrafreq
handover
hysteresis
Indicates the hysteresis for event A3. This
parameter is used to prevent frequent
triggering of event evaluation due to radio
signal fluctuation. In this way, the
probability of ping-pong handovers or
handover decision errors is reduced. A
larger value of this parameter results in a
lower probability
GUL value: 2
Actual value: 1dB
IntraFreqHoA3
Offset
Intrafreq
handover
offset
Indicates the offset for event A3. If the
parameter is set to a large value, an intra-
frequency handover is performed only
when the signal quality of the neighboring
cell is significantly better than that of the
serving cell and other triggering conditions
are met.
GUL value: 2
Actual value: 1dB
IntraFreqHoA3
TimeToTrig
Intrafreq
handover
time to
trigger
Indicates the time-to-trigger for event A3
for the intra-frequency handover.
When detecting that the signal quality in
the serving cell and that in at least one
neighboring cell meet the entering
condition, the UE does not send a
measurement report to the eNodeB
immediately. Instead, the UE sends a
report only when the signal quality
continuously meets the entering condition
during the time-to-trigger.
This parameter helps decrease the number
of occasionally triggered event reports, the
average number of handovers, and the
number of wrong handovers. In summary,
it helps prevent unnecessary handovers.
320ms
CellIndividualO
ffset
Cell
individual
offset
Indicates the cell-specific offset for the
intra-frequency neighboring cell. It affects
the probability of triggering intra-frequency
measurement reports. A larger value of
this parameter indicates a higher
probability.
dB0
-
Inter-frequency key parameters
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Id Name Description Recomm
ended
Value
InterFreqHoA
1A2Hyst
Interfreq
A1A2
hysteresis
Indicates the hysteresis for inter-frequency
measurement events A1 and A2. This parameter is
used to prevent frequent triggering of event
evaluation caused by radio signal fluctuation. In
this way, the probability of ping-pong handovers or
handover decision errors is reduced. A larger value
of this parameter results in a lower probability.
GUL
value: 2
Actual
value:
1dB
InterFreqHoA
1A2TimeToT
rig
Interfreq
A1A2 time
to trigger
Indicates the time-to-trigger for inter-frequency
measurement event A1 or A2.
When detecting that the signal quality in the
serving cell meets the triggering condition, the UE
does not send a measurement report to the
eNodeB immediately. Instead, the UE sends a
report only when the signal quality continuously
meets the entering condition during the time-to-
trigger. This parameter helps decrease the number
of occasionally triggered event reports, the average
number of handovers, and the number of wrong
handovers. In summary, it helps prevent
unnecessary handovers.
640ms
InterFreqHoA
1A2TrigQuan
InterFreq
A1A2
Measurem
ent trigger
quantity
The quantity can be RSRP, RSRQ, or both. The
measured RSRP values are stable, varying little
with the load, and therefore there is little signal
fluctuation. The measured RSRQ values vary with
the load and are likely to reflect the signal quality of
the cell in real time.
RSRP
CellIndividual
Offset
Cell
individual
offset
Indicates the cell-specific offset for the intra-
frequency neighboring cell. It affects the probability
of triggering intra-frequency measurement reports.
A larger value of this parameter indicates a higher
probability.
dB0
InterFreqHoA
1ThdRsrp
Interfreq
A1 RSRP
threshold
Indicates the RSRP threshold for inter-frequency
measurement event A1.
When the measured RSRP value exceeds this
threshold, a measurement report may be sent.
-105dBm
InterFreqHoA
2ThdRsrp
Interfreq
A2 RSRP
threshold
Indicates the RSRP threshold for inter-frequency
measurement event A2.
When the measured RSRP value is below the
threshold, a measurement report may be sent.
-109dBm
-
Inter-frequency key parameter
LTE eRAN3.0 Handover Feature
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Id Name Description Recomm
ended
Value
InterFreqHoA
4Hyst
Interfreq
handover
hysteresis
Indicates the hysteresis for event A4. This
parameter is used to prevent frequent triggering of
event evaluation caused by radio signal fluctuation.
In this way, the probability of ping-pong handovers
or handover decision errors is reduced. A larger
value of this parameter results in a lower
probability.
2dB
InterFreqHoA
4ThdRsrp
Coverage
Based
Interfreq
RSRP
threshold
Indicates the RSRP threshold for event A4 related
to coverage-based or distance-based inter-
frequency handover. When the measured RSRP
value exceeds this threshold, an inter-frequency
measurement report may be sent.
-105dBm
InterFreqHoA
4RprtQuan
Measurem
ent A4
report
quantity
The measured RSRP values are stable, varying
little with the load, and therefore there is little signal
fluctuation. The measured RSRQ values vary with
the load and are likely to reflect the signal quality of
the cell in real time.
After an inter-frequency handover event is
triggered, the reporting quantity is BOTH, that is,
both RSRP and RSRQ.
SAME_A
S_TRIG_
QUAN
InterFreqHoA
4TimeToTrig
Interfreq
HandOver
Time to
Trigger
Indicates the time-to-trigger for event A4 for the
inter-frequency handover. When detecting that the
signal quality in at least one neighboring cell meets
the entering condition, the UE does not send a
measurement report to the eNodeB immediately.
Instead, the UE sends a report only when the
signal quality continuously meets the entering
condition during the time-to-trigger.
This parameter helps decrease the number of
occasionally triggered event reports, the average
number of handovers, and the number of wrong
handovers. In summary, it helps prevent
unnecessary handovers.
640ms
InterFreqLoa
dBasedHoA4
ThdRsrp
Load
Based
Interfreq
RSRP
threshold
Indicates the RSRP threshold for event A4 related
to load- based, frequency-priority-based, UL quality
based or service based inter-frequency handover.
When the measured RSRP value exceeds this
threshold, an inter-frequency measurement report
may be sent.
-103dBm
-
Inter-frequency key parameter
LTE eRAN3.0 Handover Feature
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Id Name Description Recomm
ended
Value
FreqPriInt
erFreqHo
A1ThdRsr
p
Freq Priority
Based Interfreq
A1 RSRP
threshold
Indicates the RSRP threshold for frequency-
priority-based inter-frequency measurement event
A1. When the measured RSRP value exceeds this
threshold, an event A1 report may be sent.
-85dBm
IFreqPriInt
erFreqHo
A2ThdRsr
p
Freq Priority
Based Interfreq
A2 RSRP
threshold
Indicates the RSRP threshold for frequency-
priority-based inter-frequency measurement event
A2.When the measured RSRP value exceeds this
threshold, a measurement report may be sent.
-87dBm
FreqPriInt
erFreqHo
A1TrigQu
an
A1 Measurement
trigger quantity
of Freq Priority
Indicates the triggering quantity for frequency-
priority-based inter-frequency measurement event
A1. The quantity can be either RSRP or RSRQ.
The measured RSRP values are stable, varying
little with the load, and therefore there is little signal
fluctuation. The measured RSRQ values vary with
the load and are likely to reflect the signal quality of
the cell in real time.
RSRP
InterFreq
HoA4Trig
Quan
FreqPrior
loadBased A4
Measurement
trigger quantity
Indicates the triggering quantity for frequency
priority, load based, UL quality based, service
based or distance based inter-frequency handover
event A4.
RSRP
InterFreqL
oadBased
HoA4Thd
Rsrp
Load Based
Interfreq
RSRP
threshold
Indicates the RSRP threshold for event A4 related
to load- based, frequency-priority-based, UL quality
based or service based inter-frequency handover.
When the measured RSRP value exceeds this
threshold, an inter-frequency measurement report
may be sent.
-103dBm
InterFreq
HoA3Offs
et
Interfreq A3
offset
Indicates the offset for event A3 associated with
inter-frequency handover. This parameter
determines the border between the serving cell and
the neighboring cell. If the parameter is set to a
large value, an inter-frequency handover is
performed only when the signal quality of the
neighboring cell is significantly better than that of
the serving cell and other triggering conditions are
met.
1dB
-
Inter-frequency key parameter
LTE eRAN3.0 Handover Feature
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Id Name Description Recomm
ended
Value
A3InterFre
qHoA1Thd
Rsrp
A3 based
interfreq A1
RSRP
threshold
Indicates the RSRP threshold for event A1
associated with event-A3-triggered inter-frequency
handover.
When the measured RSRP value exceeds this
threshold, a measurement report may be sent.
-95dBm
A3InterFre
qHoA2Thd
Rsrp
A3 based
Interfreq A2
RSRP
threshold
Indicates the RSRP threshold for event A2
associated with event-A3-triggered inter-frequency
handover. When the measured RSRP value is
below the threshold, a measurement report may be
sent.
-99dBm
InterFreq
HoEventT
ype
Inter-Freq HO
trigger Event
Type
Indicates the event to trigger inter-frequency
handovers. If the neighboring E-UTRAN frequency
and the serving frequency are in the same
frequency band, either event A3 or event A4 can
be used to trigger an inter-frequency handover.
Note that the handover performance when event
A3 is used is better than that when event A2 is
used. If the neighboring E-UTRAN frequency and
the serving frequency are in different frequency
bands, only event A4 can be used to trigger an
inter-frequency handover
EventA4
-
Inter-RAT key parameter
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Id Name Description Recomm
ended
Value
InterRatH
oA1A2Hys
t
InterRAT A1A2
hysteresis
Indicates the hysteresis for inter-RAT
measurement events A1 and A2. This parameter is
used to prevent frequent triggering of event
evaluation caused by radio signal fluctuation. In
this way, the probability of ping-pong handovers or
handover decision errors is reduced. A larger value
of this parameter results in a lower probability.
2dB
InterRatH
oA1A2Tim
eToTrig
InterRAT A1A2
time to trigger
Indicates the time-to-trigger for inter-RAT
measurement event A1 or A2.
When detecting that the signal quality in the
serving cell meets the entering condition, the UE
does not send a measurement report to the
eNodeB immediately. Instead, the UE sends a
report only when the signal quality continuously
meets the entering condition during the time-to-
trigger.
640ms
InterRatH
oA1A2Trig
Quan
InterRat A1A2
measurement
trigger quantity
Indicates the RSRP threshold for inter-RAT
measurement event A1.
When the measured RSRP value of the serving
cell exceeds this threshold, an event A1 report may
be sent.
RSRP
InterRatH
oA1ThdRs
rp
InterRAT A1
RSRP trigger
threshold
Indicates the RSRP threshold for inter-RAT
measurement event A1.
When the measured RSRP value of the serving
cell exceeds this threshold, an event A1 report may
be sent.
-115dBm
InterRatH
oUtranB1
MeasQua
n
Utran
measurement
trigger
quantity
Indicates the measurement quantity required for
the inter-RAT handover to UTRAN.
The RSCP values are relatively stable, and Ec/No
fluctuates much with the network load.
UTRAN_
RSCP
InterRatH
oUtranB1
ThdRscp
CoverageBas
ed UTRAN
RSCP trigger
threshold
Indicates the RSCP threshold for event B1 related
to coverage-based inter-RAT handover to UTRAN.
This parameter specifies the requirement for RSCP
of the target UTRAN cell.
When the measurement value exceeds this
threshold, a measurement report may be sent.
-103dBm
-
Inter-RAT key parameter
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Id Name Description Recomm
ended
Value
InterRat
HoUtran
B1ThdEc
n0
CoverageBased
UTRAN ECN0
trigger threshold
This parameter specifies the requirement for Ec/No
of the target UTRAN cell. For a cell with large
signal fading variance, set this parameter to a large
value to prevent unnecessary handovers. For a cell
with small signal fading variance, set this
parameter to a small value to ensure timely
handovers. A larger value of this parameter results
in a lower probability of handover to the UTRAN
cell, and a smaller value leads to a higher
probability.
-20dB
InterRat
HoUtran
B1TimeT
oTrig
UTRAN time to
trigger
Indicates the time-to-trigger for event B1 related to
inter-RAT handover to UTRAN. When detecting
that the signal quality in at least one neighboring
cell meets the entering condition, the UE does not
send a measurement report to the eNodeB
immediately. Instead, the UE sends a report only
when the signal quality continuously meets the
entering condition during the time-to-trigger
640ms
LdSvBas
edHoUtr
anB1Thd
Rscp
Load Service
Based UTRAN
EventB1 RSCP
trigger threshold
Indicates the RSCP threshold for event B1 related
to load- or service-based inter-RAT handover to
UTRAN.
-101dBm
LdSvBas
edHoUtr
anB1Thd
Ecn0
Load Service
Based
UTRANB1
ECN0 threshold
Indicates the Ec/No threshold for event B1 related
to load- or service-based inter-RAT handover to
UTRAN.
-18dB
InterRat
HoGeran
B1Thd
Coverage
Based GERAN
trigger
threshold
Indicates the RSSI threshold for event B1 related
to coverage-based inter-RAT handover to GERAN.
A UE sends a measurement report related to event
B1 to the eNodeB when the RSSI in at least one
GERAN cell exceeds this threshold and other
triggering conditions are met.
-100dBm
LdSvBas
edHoGer
anB1Thd
Load Service
Based Geran
EventB1 trigger
threshold
Indicates the RSSI threshold for event B1 related
to load- based or service-based inter-RAT
handover to GERAN.
When the measured RSSI value exceeds this
threshold, a measurement report may be sent.
-98dBm
-
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