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Handover is a basic function of the cellular mobile network. The purpose of
handover is to ensure that a UE in CELL_DCH state is served continuously
when it moves.
With the development of WCDMA network, more and more users join in the
system. Using Handover can achieve load balance between carriers and fully
utilizes system resources.
HCS: Hierarchical Cell Structure.
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Handover types supported by UMTS:
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Active set: A set of cells simultaneously involved in a specific communication
service between the UE and the UTRAN.
Monitored set: A set of cells included in the CELL_INFO_LIST, but do not
belong to the active set.
Detected set: A set of cells detected by the UE, and do not included in the
CELL_INFO_LIST.
RL: Radio link between NodeB and UE.
RLS: All radio links from the same NodeB consist of a radio link set.
Combination way: For soft handover, the uplink signals are combined in RNC.
The RNC will select one best signal to process. We call this selective
combination. For softer handover, the uplink signals are combined in the RAKE
receiver of NodeB. It is maximum ratio combination.
Soft handover gain: Please refer to the WCDMA Coverage Planning course.
PCPICH: Primary Common Pilot Channel. UE measures the signal strength of
PCPICH for handover decision.
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Intra-frequency handover is of the following two types:
Intra-frequency soft handover: means that multiple radio links are
connected to the UE at the same time.
Intra-frequency hard handover: means that only one radio link is
connected to the UE at the same time.
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The maximum number of RL in the active set is 3 by default. And This
parameter can be changed in the RNC. But this function need the UE to support.
Normally, the active set supported by UE is fixed 3 and can not be changed.
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Intra-frequency soft handover is characterized by the function that the UE can
be connected to multiple Universal Terrestrial Radio Access Network (UTRAN)
access points at the same time. Addition and/or release of radio links are
controlled by the ACTIVE SET UPDATE procedure.
The HO_INTRA_FREQ_SOFT_HO_SWITCH parameter in the SET
CORRMALGOSWITCH command is used to determine whether to enable both
soft handover and softer handover. By default, this switch is set to ON,
indicating that both soft handover and softer handover are enabled.
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During softer handover, the uplink signaling are combined in NodeB by
maximum ratio combination, but during soft handover they are combined in
RNC by selective combination.
Compare to later one, the maximum ratio combination can get more gain. So
the performance of maximum ratio combination is better.
Since softer handover is completed in NodeB, it do not consume more transport
resource of Iub.
In telecommunications, maximal-ratio combining is a method of diversity
combining in which:
(a) the signals from each channel are added together,
(b) the gain of each channel is made proportional to the rms signal level and
inversely proportional to the mean square noise level in that channel.
(c) different proportionality constants are used for each channel. It is also known
as ratio-squared combining and combining. Maximal-ratio-combining is the
optimum combiner for independent AWGN channels.
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Compared with soft handover, intra-frequency hard handover uses fewer
resources. The scenarios of intra-frequency hard handover are as follows:
No Iur interface is present between RNCs. In this scenario, intra-
frequency hard handover instead of soft handover can be performed
between two RNCs.
The Iur interface is congested between RNCs. In this scenario, also
intra-frequency hard handover instead of soft handover can be
performed between two RNCs.
There is a high-speed Best Effort (BE) service. Compared with soft
handover, intra-frequency hard handover is used to save downlink
bandwidth for a high-speed BE service.
The intra-frequency soft handover fails and intra-frequency hard
handover is allowed. When intra-frequency soft handover fails because
of a congestion problem of the target cell, the RNC tries an intra-
frequency hard handover with a lower service bit rate.
The HO_INTRA_FREQ_HARD_HO_SWITCH parameter in the SET
CORRMALGOSWITCH command is used to determine whether to enable intra-
frequency hard handover. By default, this switch is set to ON.
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The intra-frequency handover procedure is divided into three phases: handover
measurement, handover decision, and handover execution.
After the UE transits to the CELL_DCH state in connected mode during a call,
the RNC sends a MEASUREMENT CONTROL message to instruct the UE to
take measurements and report the measurement event results. Upon the
reception of an event report from the UE, the RNC makes a handover decision
and performs the corresponding handover.
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The MEASUREMENT CONTROL message carries the following information:
Event trigger threshold
Hysteresis value
Event trigger delay time
Neighboring cell list
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MNew is the measurement value of the cell in the reporting range.
CIONew is equal to the sum of CIO and CIOOffset, which adjusts the cell
boundary in the handover algorithms. To facilitate handover in neighboring cell
configuration, the parameter is set as a positive value; otherwise, the parameter
is set as a negative value.
W represents Weighted factor, which is determined by the parameter Weight.
The total quality of the best cell and the active set is specified by W.
Mi is the measurement value of a cell in the active set.
NA is the number of cells not forbidden to affect the reporting range in the active
set. The parameter CellsForbidden1A indicates whether adding the cell to the
active set affects the relative threshold of event 1A.
MBest is the measurement value of the best cell in the active set.
R1a is the reporting range or the relative threshold of soft handover. The
threshold parameters of the CS non-VP service, VP service, and PS service are
as follows:
IntraRelThdFor1ACSVP
IntraRelThdFor1ACSNVP
IntraRelThdFor1APS
H1a represents 1A hysteresis, the hysteresis value of event 1A.
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The above figure shows the triggering of event 1A. In this procedure, the default
parameter values are used.
If the signal quality of a cell that is not in the active set is higher than Th1A for a
period of time specified by TrigTime1A (that is, Time to trigger in the figure), the
UE reports event 1A.
Th1A = (CPICH Ec/No of the best cell in the active set) - (reporting range for
event 1A)
If Weighted factor > 0, then Th1A = (general signal quality of all the cells in the
active set) - (reporting range for event 1A).
Reporting range for event 1A is equal to the value of IntraRelThdFor1ACSVP,
IntraRelThdFor1ACSNVP, or IntraRelThdFor1APS.
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CIO
Content: This parameter works with the Neighboring cell oriented CIO. It
is used for intra- or inter-frequency handover decisions. The larger the
sum, the higher the handover priority of the neighboring cell. The smaller
the sum, the lower the handover priority of the neighboring cell. Usually it
is configured to 0.
Value range: -20~20
Physical value range: -10~10; step: 0.5
Physical unit: dB
Set this parameter through ADD CELLSETUP/MOD CELLSETUP.
CIOOffset
Content: This parameter defines the neighboring cell oriented cell
individual offset. The set value functions in combination of the cell
oriented CIO. Their sum is added to the measurement quantity before
the UE evaluates whether an event has occurred. In handover
algorithms, this parameter is used for moving the border of a cell.
Value range: -20~20
Physical value range: -20~20; step: 1
Physical unit: dB
Set this parameter through ADD INTRAFREQNCELL/MOD
INTRAFREQNCELL.
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IntraRelThdFor1ACSNVP/IntraRelThdFor1ACSVP/IntraRelThdFor1APS
Content: These parameters specify the CS non-VP/VP and PS services
relative threshold of event 1A. The higher the threshold is, the more
easily the target cell joins the active set, the harder the call drops, the
larger the ratio of the UE involved in soft handover is, but the more the
use of forward resources is. The lower the threshold is, the more difficult
the target cell joins the active set. Thus the communication quality and
the smooth handover cannot be guaranteed.
Value range: 0~29
Physical value range: 0~14.5; step: 0.5
Physical unit: dB
Set these parameters through SET INTRAFREQHO/ADD
CELLINTRAFREQHO/MOD CELLINTRAFREQHO.
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Hystfor1A
Content: This parameter specifies the hysteresis value for event 1A. The value of this
parameter correlates with slow fading. The larger the value of this parameter, the less
possibility of ping-pong effect or wrong decision. But the event might not be triggered in
time.
Value range: 0~15
Physical value range: 0~7.5; step: 0.5
Physical unit: dB
TrigTime1A
Content: This parameter specifies the time delay to trigger event 1A. The value of this
parameter correlates with slow fading. The larger the value of this parameter, the lower
the incorrect decision probability, but the slower the response of the event to
measurement signal change.
Value range: D0, D10, D20, D40, D60, D80, D100, D120, D160, D200, D240, D320,
D640, D1280, D2560, D5000
Physical value range: 0, 10, 20, 40, 60, 80, 100, 120, 160, 200, 240, 320, 640, 1280,
2560, 5000
Physical unit: ms
Weight
Content: This parameter is used to define the soft handover relative threshold based on
the measured value of each cell in the active set. The greater the parameter value, the
higher the soft handover relative threshold. When this value is set to 0, the soft handover
relative threshold is determined only by the best cell in the active set.
Value range: 0~20
Physical value range: 0~2; step: 0.1
Set these parameters through SET INTRAFREQHO/ADD CELLINTRAFREQHO/MOD
CELLINTRAFREQHO.
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The report mode of 1A is event trigger report.
Generally the event 1A is reported only once. However, to avoid measurement
report loss, the event 1A reporting can be turned to periodical reporting.
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ReportIntervalfor1A
Content: This parameter specifies the reporting period of event 1A. That
is, event 1A is reported at each reporting interval. Usually, event 1A is
reported only once. Nevertheless, if the cell, where event 1A is reported,
does not join the active set in a specified period of time, the UE can
change the reporting of event 1A into periodical mode to avoid missing
of measurement reports. The event 1A of this cell is reported for
PeriodMRReportNumfor1A times with the reporting interval as the set
value.
Value range: NON_PERIODIC_REPORT, D250, D500, D1000, D2000,
D4000, D8000, D16000
Physical value range: NON_PERIODIC_REPORT, 250, 500, 1000, 2000,
4000, 8000, 16000
Physical unit: ms
PeriodMRReportNumfor1A
Content: This parameter specifies the number of reporting times of event
1A for periodical reporting. When the actual reporting times exceeds the
set value, the periodical reporting ends.
Value range: D1, D2, D4, D8, D16, D32, D64, INFINITY
Physical value range: 1, 2, 4, 8, 16, 32, 64, INFINITY
Set these parameters through SET INTRAFREQHO/ADD
CELLINTRAFREQHO/MOD CELLINTRAFREQHO.
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MOld is the measurement value of the cell that becomes worse.
CIOOld is equal to the sum of CIO and CIOOffset, which is the offset between
the cell in the reporting range and the best cell in the active set.
W represents Weighted factor, used to weight the quality of the active set. The
total quality of the best cell and the active set is specified by the parameter
Weight.
Mi is the measurement value of a cell in the active set.
NB is the number of cells not forbidden to affect the reporting range in the active
set. The parameter CellsForbidden1B indicates whether adding the cell to the
active set affects the relative threshold of event 1B.
MBest is the measurement value of the best cell in the active set.
R1b is the reporting range or the relative threshold of soft handover. The
threshold parameters of the CS non-VP service, VP service, and PS services
are as follows:
IntraRelThdFor1BCSVP
IntraRelThdFor1BCSNVP
IntraRelThdFor1BPS
H1b is the hysteresis value of event 1B, which is determined by the parameter
Hystfor1B.
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The above figure shows the triggering of event 1B. In this procedure, the default
parameter values are used.
If the signal quality of a cell in the active set is lower than Th1B for a period of
time specified by TrigTime1B (Time to trigger in the figure), the UE reports
event 1B.
Th1B = (CPICH Ec/No of the best cell in the active set) - (reporting range for
event 1B)
If Weight > 0, then Th1B = (general signal quality of all the cells in the active set)
- (reporting range for event 1B).
Reporting range for event 1B is equal to the value of IntraRelThdFor1BCSVP,
IntraRelThdFor1BCSNVP, or IntraRelThdFor1BPS.
Configuration rule and restriction:
The value of IntraRelThdFor1BCSNVP has to be larger than that of
IntraRelThdFor1ACSNVP.
The value of IntraRelThdFor1BCSVP has to be larger than that of
IntraRelThdFor1ACSVP.
The value of IntraRelThdFor1BPS has to be larger than that of
IntraRelThdFor1APS.
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IntraRelThdFor1BCSNVP/IntraRelThdFor1BCSVP/IntraRelThdFor1BPS
Content: These parameters specify the CS non-VP/VP and PS services
relative threshold of event 1B. The lower the threshold is, the more
easily the event 1B is triggered. The higher the threshold is, the harder
the event 1B is triggered.
Value range: 0~29
Physical value range: 0~14.5; step: 0.5
Physical unit: dB
Set these parameters through SET INTRAFREQHO/ADD
CELLINTRAFREQHO/MOD CELLINTRAFREQHO.
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Hystfor1B
Content: This parameter specifies the hysteresis value for event 1B. The
value of this parameter correlates with slow fading. The larger the value
of this parameter, the less possibility of ping-pong effect or wrong
decision. But the event might not be triggered in time.
Value range: 0~15
Physical value range: 0~7.5; step: 0.5
Physical unit: dB
TrigTime1B
Content: This parameter specifies the time delay to trigger event 1B. The
value of this parameter correlates with slow fading. The larger the value
of this parameter, the lower the incorrect decision probability, but the
slower the response of the event to measurement signal change.
Value range: D0, D10, D20, D40, D60, D80, D100, D120, D160, D200,
D240, D320, D640, D1280, D2560, D5000
Physical value range: 0, 10, 20, 40, 60, 80, 100, 120, 160, 200, 240, 320,
640, 1280, 2560, 5000
Physical unit: ms
Set these parameters through SET INTRAFREQHO/ADD
CELLINTRAFREQHO/MOD CELLINTRAFREQHO.
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MNew is the measurement value of the cell in the reporting range.
CIONew is the cell individual offset value of the cell in the reporting range. It is
equal to the sum of CIO and CIOOffset, which is the offset between the cell in
the reporting range and the best cell in the active set.
MInAS is the measurement value of the worst cell in the active set.
H1c is the hysteresis value of event 1C, which is determined by the parameter
Hystfor1C.
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The above figure shows the triggering of event 1C. In this procedure, the default
parameter values are used.
If the signal quality of a cell not in the active set is higher than Th1C for a period
of time specified by TrigTime1C (Time to trigger in the figure), the UE reports
event 1C, as shown in the figure.
Th1C = (CPICH Ec/No of the worst cell in the active set) + (Hystfor1C/2)
The UE reports event 1C for qualified cells after the number of cells in the active
set reaches the maximum value. The maximum number of cells in the active set
can be set by the MaxCellInActiveSet parameter.
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Hystfor1C
Content: This parameter specifies the hysteresis value for event 1C. The
value of this parameter correlates with slow fading. The larger the value
of this parameter, the less possibility of ping-pong effect or wrong
decision. But the event might not be triggered in time.
Value range: 0~15
Physical value range: 0~7.5; step: 0.5
Physical unit: dB
TrigTime1C
Content: This parameter specifies the time delay to trigger event 1C. The
value of this parameter correlates with slow fading. The larger the value
of this parameter, the lower the incorrect decision probability, but the
slower the response of the event to measurement signal change.
Value range: D0, D10, D20, D40, D60, D80, D100, D120, D160, D200,
D240, D320, D640, D1280, D2560, D5000
Physical value range: 0, 10, 20, 40, 60, 80, 100, 120, 160, 200, 240, 320,
640, 1280, 2560, 5000
Physical unit: ms
Set these parameters through SET INTRAFREQHO/ADD
CELLINTRAFREQHO/MOD CELLINTRAFREQHO.
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The report mode of 1C is event trigger report.
Generally the event 1C is reported only once. However, to avoid measurement
report loss, the event 1C reporting can be turned to periodical reporting.
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ReportIntervalfor1C
Content: This parameter specifies the number of reporting times of event
1C for periodical reporting. That is, event 1C is reported at each
reporting interval. Usually, event 1C is reported only once. Nevertheless,
if the cell, where event 1C is reported, does not join the active set in a
specified period of time, the UE can change the reporting of event 1C
into periodical mode to avoid missing of measurement reports. The
event 1C of this cell is reported for PeriodMRReportNumfor1C times with
the reporting interval as the set value.
Value range: NON_PERIODIC_REPORT, D250, D500, D1000, D2000,
D4000, D8000, D16000
Physical value range: NON_PERIODIC_REPORT, 250, 500, 1000, 2000,
4000, 8000, 16000
Physical unit: ms
PeriodMRReportNumfor1C
Content: This parameter specifies the number of reporting times of event
1C for periodical reporting. When the actual reporting times exceeds the
set value, the periodical reporting ends.
Value range: D1, D2, D4, D8, D16, D32, D64, INFINITY
Physical value range: 1, 2, 4, 8, 16, 32, 64, INFINITY
Set these parameters through SET INTRAFREQHO/ADD
CELLINTRAFREQHO/MOD CELLINTRAFREQHO.
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MNotBest is the measurement value of a cell that is not the best cell.
CIONotBest is equal to the sum of CIO and CIOOffset, which is the offset
between the cell in the reporting range and the best cell in the active set.
MBest is the measurement value of the best cell in the active set.
CIOBest is the cell individual offset value of the best cell. This parameter is not
used for event 1D.
H1d is the hysteresis value of event 1D, which is determined by the parameter
Hystfor1D.
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The above figure shows the triggering of event 1D. In this procedure, the default
parameter values are used.
If the signal quality of a cell not in the active set is higher than Th1D for a period
of time specified by TrigTime1D (Time to trigger in the figure), the UE reports
event 1D.
Th1D = (CPICH Ec/No of the best cell in the active set) + (Hystfor1D/2)
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Hystfor1D
Content: This parameter specifies the hysteresis value for event 1D. The
value of this parameter correlates with slow fading. The larger the value
of this parameter, the less possibility of ping-pong effect or wrong
decision. But the event might not be triggered in time.
Value range: 0~15
Physical value range: 0~7.5; step: 0.5
Physical unit: dB
TrigTime1D
Content: This parameter specifies the time delay to trigger event 1D. The
value of this parameter correlates with slow fading. The larger the value
of this parameter, the lower the incorrect decision probability, but the
slower the response of the event to measurement signal change.
Value range: D0, D10, D20, D40, D60, D80, D100, D120, D160, D200,
D240, D320, D640, D1280, D2560, D5000
Physical value range: 0, 10, 20, 40, 60, 80, 100, 120, 160, 200, 240, 320,
640, 1280, 2560, 5000
Physical unit: ms
Set these parameters through SET INTRAFREQHO/ADD
CELLINTRAFREQHO/MOD CELLINTRAFREQHO.
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MNew is the measurement result of the cell not in the E-DCH active set but in
the DCH active set.
CIONew and CIOInAS refer to the offset of each cell.
MInAS is the measurement result of the cell in the E-DCH active set with the
lowest measurement result.
H1J is the hysteresis parameter for event 1J and is determined by Hystfor1J.
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The above figure shows the triggering of event 1J. In this procedure, the
hysteresis and the cell individual offsets for all cells equal 0.
If the signal quality of a cell not in the E-DCH active set is higher than Th1J for a
period of time specified by TrigTime1J (Time to trigger in the figure), the UE
reports event 1J.
Th1J = (CPICH Ec/No of the worst cell in the active set) + (Hystfor1J/2)
The first measurement report is sent when primary CPICH D becomes better than
primary CPICH B. The "cell measurement event result" of the measurement report
contains the information of primary CPICH D and CPICH B.
On the assumption that the E-DCH active set has been updated after the first
measurement report (E-DCH active set is now primary CPICH A and primary CPICH D),
the second report is sent when primary CPICH C becomes better than primary CPICH A.
The "cell measurement event result" of the second measurement report contains the
information of primary CPICH C and primary CPICH A.
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The characteristics of 1J event:
3GPP define the maximum DCH active set size is 6 and the maximum E-DCH
active set size is 4.
The DCH active set covers the E-DCH active set or they are the same.
The best cell in E-DCH active set should be the same as that in DCH active set.
Uplink channel type of UE is decided by the best cell in DCH active set:
Uplink channel is E-DCH if the best cell in DCH active set supports
HSUPA.
Uplink channel is DCH if the best cell in DCH active set can NOT
support HSUPA.
Processing procedure of 1J event:
The UE reports 1J event if it find a non-active E-DCH but active DCH cell
PCICH becomes better than an active E-DCH PCIPCH.
RNC will add the target cell into E-DCH active set if the E-DCH active set is
NOT full.
RNC will perform replace procedure if the E-DCH active set is full.
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Hystfor1J
Content: This parameter specifies the hysteresis value for event 1J. The value of this
parameter correlates with slow fading. The larger the value of this parameter, the less
possibility of ping-pong effect or wrong decision. But the event might not be triggered in
time.
Value range: 0~15
Physical value range: 0~7.5; step: 0.5
Physical unit: dB
Set this parameter through SET INTRAFREQHO/ADD CELLINTRAFREQHO/MOD
CELLINTRAFREQHO.
TrigTime1J
Content: This parameter specifies the time delay to trigger event 1J. The value of this
parameter correlates with slow fading. The larger the value of this parameter, the lower
probability of incorrect decision, but the slower the response of event to the change of
measured signals.
Value range: D0, D10, D20, D40, D60, D80, D100, D120, D160, D200, D240, D320,
D640, D1280, D2560, D5000
Physical value range: 0, 10, 20, 40, 60, 80, 100, 120, 160, 200, 240, 320, 640, 1280,
2560, 5000
Physical unit: ms
Set this parameter through SET INTRAFREQHO/ADD CELLINTRAFREQHO/MOD
CELLINTRAFREQHO.
MaxEdchCellInActiveSet
Content: This parameter determines the maximum number of links in the EDCH active
set. When the RNC acts as the SRNC, the number of links in the EDCH active set for all
the UEs under the RNC cannot exceed the parameter value. If the parameter value is
too large, a lot of resources on the RAN side will be occupied as the same data is
transferred over multiple EDCH links in macro diversity, thus affecting the system
performance. If this parameter value is too small, insufficient combination gain can be
achieved in macro diversity by the EDCH, which causes excessive retransmissions and
affects the UE speed.
Value range: 1~4
Physical value range: 1~4; step: 1
Set this parameter through SET HOCOMM.
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The report mode of 1J is event trigger report.
Generally the event 1J is reported only once. However, to avoid measurement report
loss, the event 1J reporting can be turned to periodical reporting.
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ReportIntervalfor1J
Content: This parameter specifies the number of reporting times of event
1J for periodical reporting. That is, event 1J is reported at each reporting
interval. Usually, event 1J is reported only once. Nevertheless, if the cell,
where event 1J is reported, does not join the EDCH active set in a
specified period of time, the UE can change the reporting of event 1J
into periodical mode to avoid missing of measurement reports. The
event 1J of this cell is reported for PeriodMRReportNumfor1J times with
the reporting period as the set value.
Value range: NON_PERIODIC_REPORT, D250, D500, D1000, D2000,
D4000, D8000, D16000
Physical value range: NON_PERIODIC_REPORT, 250, 500, 1000, 2000,
4000, 8000, 16000
Physical unit: ms
PeriodMRReportNumfor1J
Content: This parameter specifies the number of reporting times of event
1J for periodical reporting. When the actual reporting times exceeds the
set value, the periodical reporting ends.
Value range: D1, D2, D4, D8, D16, D32, D64, INFINITY
Physical value range: 1, 2, 4, 8, 16, 32, 64, INFINITY
Set these parameters through SET INTRAFREQHO/ADD
CELLINTRAFREQHO/MOD CELLINTRAFREQHO.
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Event Decision and Execution
1A
When receiving an event 1A report, the RNC decides whether to add a
cell.
For event 1A, the UE can report more than one cell in the event list in
one measurement report. These cells are in the list of the
MEASUREMENT CONTROL message, and they are sequenced in
descending order of measurement quantity. For the cells in the list, the
RNC adds the radio link to the active set only if the number of cells in
the active set does not reach the maximum value. This operation is not
required if the number of cells in the active set reaches a specified value.
1B
When receiving an event 1B report, the RNC decides whether to delete
a cell. For event 1B, if there is more than one radio link in the active set,
the RNC decides whether to delete a radio link. This operation is not
required if there is only one radio link in the active set.
1C
When receiving an event 1C report, the RNC decides whether to
change the worst cell. For event 1C, the UE reports a list that contains
good cells and the cells to be replaced, and sequences the cells in
descending order by measurement quantity. After receiving the list from
the UE, the RNC replaces the bad cells in the active set with the good
cells in the list.
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MaxCellInActiveSet
Content: This parameter specifies the maximum number of cells in the
active set. This parameter can achieve the balance between the signal
quality in the SHO area and the performance of the system. The more
cells the active set contains, the larger macro diversity gain the user
obtains in the SHO area, and the smaller the intra-frequency interference
is. But in this case, the user occupies resources of several cells, which
increases the amount of data to be processed by the system and lowers
the system performance.
Value range: 1~6
Physical value range: 1~6; step: 1
SHOQualmin
Content: When the RNC receives events 1A, 1C and 1D, the target cell
can be added to the active set only when CPICH Ec/No of the target cell
is higher than this absolute threshold.
Value range: -24~0
Physical value range: -24~0; step: 1
Physical unit: dB
Set these parameters through SET INTRAFREQHO/ADD
CELLINTRAFREQHO/MOD CELLINTRAFREQHO.
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After the active set is updated, the RNC updates the neighboring cell list by
using the neighboring cell combination algorithm according to the status of the
active set. This list includes the new intra-frequency, inter-frequency, and inter-
RAT neighboring cells. The combination methods of intra-frequency handover,
inter-frequency handover, and inter-RAT handover are the same.
The neighboring cell combination result is contained in the MEASUREMENT
CONTROL message and sent to the UE, which instructs the UE to perform
intra-frequency, inter-frequency, and inter-RAT measurement and handover
procedures.
The number of inter-frequency neighboring cells is configured as follows:
A maximum of 32 intra-frequency neighboring cells are configured.
A maximum of 32 single-carrier inter-frequency neighboring cells are
configured.
A maximum of 64 multi-carrier inter-frequency neighboring cells are
configured.
A maximum of 32 inter-RAT neighboring cells are configured.
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Neighboring cell combination switch:
HO_MC_NCELL_COMBINE_SWITCH is the neighboring cell combination
switch.
If the switch is set to ON, measurement objects are chosen from the
neighboring cells of all the cells in the active set.
If the switch is set to OFF, measurement objects are chosen from the
neighboring cells of the best cell.
Neighboring cell combination procedure:
After obtaining the intra-frequency neighboring cells of each cell in the active set,
the RNC calculates the union neighboring cell set of the intra-frequency cells,
which is referred as Sall, by using the following method. This method can also
be used to generate the Sall of inter-frequency or inter-RAT cells.
The intra-frequency, inter-frequency, and inter-RAT neighboring cells of
each cell in the current active set are obtained.
The RNC sequences the cells in the active set in descending order of
CPICH Ec/No according to the latest measurement report (event 1A, 1B,
1C, or 1D) from the UE. The best cell is based on event 1D, whereas
other cells are based on the latest measurement report.
The cells in the active set are added to Sall.
The neighboring cells of the best cell in the active set are added to Sall.
NprioFlag (the flag of the priority) and Nprio (the priority of the
neighboring cell), which are set for each neighboring cell, are used to
change the order of adding the neighboring cells to Sall.
The neighboring cells of other cells in the active set are added to Sall in
descending order by CPICH Ec/No values of these cells in the active set.
The neighboring cells of the same cell in the active set are added
according to Nprio and the number of repeated neighboring cell is
recorded.
If there are more than 32 intra-frequency neighboring cells in Sall, delete
the repeated neighboring cells whose number in Sall is less. The top 32
neighboring cells are grouped into the final Sall.
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HO_MC_NCELL_COMBINE_SWITCH
Content: When the switch is on, the neighboring cell combined algorithm
is used during the delivery of the objects to be measured. When the
switch is off, the best cell algorithm is used.
Value range: ON, OFF
Physical value range: 1, 0
Set this parameter through SET CORRMALGOSWITCH.
NprioFlag
Content: Priority identifier of neighboring cells. TRUE indicates that the
neighboring cell priority is valid in the algorithm of neighboring cell
combination. FALSE indicates that the neighboring cell priority is invalid,
and, in the algorithm of neighboring cell combination, the cell with invalid
priority is the last one to be considered as the measurement object.
Value range: FALSE, TRUE
Physical value range: FALSE, TRUE
Nprio
Content: Priority of neighboring cells. The lower the priority, the easier it
is for the neighboring cell to be delivered as the measurement object.
For example, it is more possible for a neighboring cell of priority 1 than a
cell of priority 2 to be delivered as the measurement object.
Value range: 0~30
Physical value range: 0~30; step: 1
Set the upper two parameters through ADD INTRAFREQNCELL/MOD
INTRAFREQNCELL / ADD INTERFREQNCELL/MOD INTERFREQNCELL /
ADD GSMNCELL/MOD GSMNCELL.
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Coverage-based inter-frequency handover:
If a moving UE leaves the coverage of the current frequency, the RNC
needs to trigger the coverage-based inter-frequency handover to avoid
call drops.
QoS-based inter-frequency handover:
According to the Link Stability Control Algorithm, the RNC needs to
trigger the QoS-based inter-frequency handover to avoid call drops.
Load-based inter-frequency blind handover:
To balance the load between inter-frequency con-coverage cells, the
RNC chooses some UEs and performs the inter-frequency blind
handover according to user priorities and service priorities.
Speed-based inter-frequency handover:
When the Hierarchical Cell Structure (HCS) applies, the cells are divided
into different layers according to coverage. The macro cell has a larger
coverage and a lower priority, whereas the micro cell has a smaller
coverage and a higher priority.
Inter-frequency handover can be triggered by the UE speed estimation
algorithm of the HCS. To reduce frequent handovers, the UE at a higher
speed is handed over to a cell under a larger coverage, whereas the UE
at a lower speed is handed over to a cell under a smaller coverage.
The InterFreqHOSwitch parameter in the ADD CELLHOCOMM command is
used to chooses the inter-frequency measurement control parameters to
implement handover measurement based on coverage, QoS and speed.
The HO_INTER_FREQ_HARD_HO_SWITCH parameter in the SET
CORRMALGOSWITCH command is used to determine whether to allow load-
based inter-frequency handover.
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In the triggering phase:
The RNC requests the UE to measure through an inter-frequency
measurement control message. If the CPICH Ec/No or CPICH RSCP of
the current cell is lower than the corresponding threshold, the UE reports
event 2D.
In the measurement phase:
The RNC sends an inter-frequency measurement control message to the
UE, requesting the NodeB and UE to start the compressed mode. The
RNC also requests the UE to perform the inter-frequency measurement.
In this phase, the method of either periodical measurement report or
event-triggered measurement report can be used.
In the decision phase:
After the UE reports event 2B, the RNC performs the handover.
Otherwise, the UE periodically generates measurement reports, and the
RNC makes a decision after evaluation.
In the execution phase:
The RNC executes the handover procedure.
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When the estimated quality or strength of the currently used frequency is below
a certain threshold, 2D event will be triggered. Then RNC will initiate the
compressed mode to start inter-frequency measurement.
During compressed mode, if the estimated quality of the currently used
frequency is above a certain threshold, 2F event will be triggered. Then RNC
will stop the compressed mode.
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Compressed mode control is a mechanism whereby certain idle periods are
created in radio frames during which the UE can perform measurements on
other frequencies. The UE can carry out measurements in the neighboring cell,
such as GSM cell and FDD cell on other frequency. If the UE needs to measure
the pilot signal strength of an inter-frequency WCDMA or GSM cell and has one
frequency receiver only, the UE must use the compressed mode.
Each physical frame can provide 3 to 7 timeslots for the inter-frequency or inter-
RAT cell measurement, which enhances the transmit capability of physical
channels but reduces the volume of data traffic.
In DL, during compressed mode, UE receiver can test signal from other
frequency. In order to avoid the effect cause by UE transmitter, compressed
mode is also used in UL.
The compressed mode includes two types, spreading factor reduction (SF/2)
and high layer approaches. The usage of type of compressed mode is decided
by the RNC, according to spreading factor used in uplink or downlink.
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QUsed is the measured quality of the used frequency.
TUsed2d is the absolute quality threshold of the cell that uses the current
frequency. Based on the service type and measurement quantity, this threshold
can be configured through one of the following parameters:
InterFreqCSThd2DEcN0
InterFreqR99PsThd2DEcN0
InterFreqHThd2DEcN0
InterFreqCSThd2DRSCP
InterFreqR99PsThd2DRSCP
InterFreqHThd2DRSCP
H2d is the event 2D hysteresis value set through the parameter HystFor2D.
After the conditions of event 2D are fulfilled and maintained until the
TimeToTrig2D is reached, the UE sends the event 2D measurement report
message.
Any of the Ec/No and RSCP measurement result can trigger the 2D
event.
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InterFreqCSThd2DEcN0
Content: Threshold to trigger inter-frequency measurement with
measurement quantity of Ec/No for CS domain services.
Value range: -24~0
Physical value range: -24~0; step: 1
Physical unit: dB
InterFreqR99PsThd2DEcN0 Content: Threshold to trigger inter-frequency measurement with
measurement quantity of Ec/No for PS domain non-HSPA services.
Value range: -24~0
Physical value range: -24~0; step: 1
Physical unit: dB
InterFreqHThd2DEcN0 Content: Threshold to trigger inter-frequency measurement with
measurement quantity of Ec/No for PS domain HSPA services.
Value range: -24~0
Physical value range: -24~0; step : 1
Physical unit: dB
Set these parameters through ADD CELLINTERFREQHOCOV/MOD
CELLINTERFREQHOCOV/SET INTERFREQHOCOV.
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InterFreqCSThd2DRSCP
Content: Threshold to trigger inter-frequency measurement with measurement quantity of RSCP for CS domain services.
Value range: -115~-25
Physical value range: -115~-25; step: 1
Physical unit: dBm
InterFreqR99PsThd2DRSCP
Content: Threshold to trigger inter-frequency measurement with measurement quantity of RSCP for PS domain non-HSPA services.
Value range: -115~-25
Physical value range: -115~-25; step: 1
Physical unit: dBm
InterFreqHThd2DRSCP
Content: Threshold to trigger inter-frequency measurement with measurement quantity of RSCP for PS domain HSPA services.
Value range: -115~-25
Physical value range: -115~-25; step: 1
Physical unit: dBm
Set these parameters through ADD CELLINTERFREQHOCOV/MOD
CELLINTERFREQHOCOV/SET INTERFREQHOCOV.
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HystFor2D
Content: Hysteresis value for the event 2D. The value of this parameter
correlates with slow fading. The larger the value of this parameter, the
smaller probability of ping-pong effect or wrong decision, but event 2D
might not be triggered in time.
Value range: 0~29
Physical value range: 0~14.5; step: 0.5
Physical unit: dB
TimeToTrig2D Content: Time delay to trigger event 2D. The value of this parameter
correlates with slow fading. The larger the value of this parameter, the
lower probability of incorrect decision, but the slower the response of
event 2D to the change of measured signals.
Value range: D0, D10, D20, D40, D60, D80, D100, D120, D160, D200,
D240, D320, D640, D1280, D2560, D5000
Physical value range: 0, 10, 20, 40, 60, 80, 100, 120, 160, 200, 240, 320,
640, 1280, 2560, 5000
Physical unit: ms
Set these parameters through ADD CELLINTERFREQHOCOV/MOD
CELLINTERFREQHOCOV/SET INTERFREQHOCOV.
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QUsed is the measured quality of the used frequency.
TUsed2f is the absolute quality threshold of the cell that uses the current
frequency. Based on the service type and measurement quantity, this threshold
can be configured through one of the following parameters:
InterFreqCSThd2FEcN0
InterFreqR99PsThd2FEcN0
InterFreqHThd2FEcN0
InterFreqCSThd2FRSCP
InterFreqR99PsThd2FRSCP
InterFreqHThd2FRSCP
H2f is the event 2F hysteresis value set through the parameter HystFor2F.
After the conditions of event 2F are fulfilled and maintained until the parameter
TimeToTrig2F is reached, the UE reports the event 2F measurement report
message.
Any of Ec/No and RSCP measurement result can trigger the 2F event.
Conditions of event 2F are as follows: TUsed2d - H2d/2 < TUsed2f + H2f/2, for
example, (InterFreqCSThd2DEcN0–HystFor2D/2) < (InterFreqCSThd2FEcN0+
HystFor2F/2).
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InterFreqCSThd2FEcN0
Content: Threshold to stop inter-frequency measurement with
measurement quantity of Ec/No for CS domain services.
Value range: -24~0
Physical value range: -24~0; step: 1
Physical unit: dB
InterFreqR99PsThd2FEcN0 Content: Threshold to stop inter-frequency measurement with
measurement quantity of Ec/No for PS domain non-HSPA services.
Value range: -24~0
Physical value range: -24~0; step: 1
Physical unit: dB
InterFreqHThd2FEcN0 Content: Threshold to stop inter-frequency measurement with
measurement quantity of Ec/No for PS domain HSPA services.
Value range: -24~0
Physical value range: -24~0; step: 1
Physical unit: dB
Set these parameters through ADD CELLINTERFREQHOCOV/MOD
CELLINTERFREQHOCOV/SET INTERFREQHOCOV.
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InterFreqCSThd2FRSCP
Content: Threshold to stop inter-frequency measurement with measurement quantity of RSCP for CS domain services.
Value range: -115~-25
Physical value range: -115~-25; step: 1
Physical unit: dBm
InterFreqR99PsThd2FRSCP
Content: Threshold to stop inter-frequency measurement with measurement quantity of RSCP for PS domain non-HSPA services.
Value range: -115~-25
Physical value range: -115~-25; step: 1
Physical unit: dBm
InterFreqHThd2FRSCP
Content: Threshold to stop inter-frequency measurement with measurement quantity of RSCP for PS domain HSPA services.
Value range: -115~-25
Physical value range: -115~-25; step: 1
Physical unit: dBm
Set these parameters through ADD CELLINTERFREQHOCOV/MOD
CELLINTERFREQHOCOV/SET INTERFREQHOCOV.
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HystFor2F
Content: Hysteresis value for the event 2F. The value of this parameter
correlates with slow fading. The larger the value of this parameter, the
smaller probability of ping-pong effect or wrong decision, but event 2F
might not be triggered in time.
Value range: 0~29
Physical value range: 0~14.5; step: 0.5
Physical unit: dB
TimeToTrig2F Content: Time delay to trigger the event 2F. The value of this parameter
correlates with slow fading. The larger the value of this parameter, the
lower probability of incorrect decision, but the slower the response of
event 2F to the change of measured signals.
Value range: D0, D10, D20, D40, D60, D80, D100, D120, D160, D200,
D240, D320, D640, D1280, D2560, D5000
Physical value range: 0, 10, 20, 40, 60, 80, 100, 120, 160, 200, 240, 320,
640, 1280, 2560, 5000
Physical unit: ms
Set these parameters through ADD CELLINTERFREQHOCOV/MOD
CELLINTERFREQHOCOV/SET INTERFREQHOCOV.
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When the UE enters the compress mode, RNC will trigger the inter-frequency
handover measurement by two additional measurement control signaling, so as
to request UE test inter-frequency neighbor cell.
In this Measurement control message, RNC should inform the UE inter-
frequency measurement parameter, including neighbor list and reporting mode
as well.
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The measurement report mode of inter-frequency handover is configured
through the parameter InterFreqReportMode. By default, periodically reporting
is recommended.
The advantage of periodical measurement report is that if the handover fails, the
RNC reattempts the handover to the same cell after receiving the periodical
measurement report from the UE. This increases the probability of the success
of inter-frequency handover.
Based on the measurement control message received from the RNC, the UE
periodically reports the measurement quality of the target cell. Then, based on
the measurement report, the RNC makes the handover decision and performs
handover.
If the reporting mode is periodically reporting: UE test the Inter-frequency
neighbor RSCP and Ec/No.
If the reporting mode is event trigger reporting: UE test the Inter-frequency
neighbor RSCP and Ec/No, and current cell Ec/No or RSCP.
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InterFreqReportMode
Content: This parameter specifies the inter-frequency measurement report mode.
Value range: PERIODICAL_REPORTING(Periodical reporting), EVENT_TRIGGER(Event trigger)
Physical value range: Periodical reporting, Event trigger
PrdReportInterval
Content: This parameter specifies the interval of the inter-frequency measurement report.
Value range: NON_PERIODIC_REPORT(Non periodical reporting), D250, D500, D1000, D2000, D3000, D4000, D6000, D8000, D12000, D16000, D20000, D24000, D28000, D32000, D64000
Physical value range: NON_PERIODIC_REPORT, 250, 500, 1000, 2000, 3000, 4000, 6000, 8000, 12000, 16000, 20000, 24000, 28000, 32000, 64000
Physical unit: ms
InterFreqMeasTime
Content: Timer length for inter-frequency measurement. After inter-frequency measurement starts, if no inter-frequency handover is performed when this timer expires, the inter-frequency measurement and the compressed mode (if started) are stopped. The value 0 indicates the timer is not to be enabled.
Value range: 0~512
Physical value range: 0~512; step: 1
Physical unit: s
Set these parameters through ADD CELLINTERFREQHOCOV/MOD
CELLINTERFREQHOCOV/SET INTERFREQHOCOV.
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Mother_Freq is the CPICH Ec/No or CPICH RSCP measurement value of the
target cell reported by the UE. Both of the two measurement values of the inter-
frequency cell must satisfy the formula.
CIOother_Freq is the cell individual offset value of the target cell. It is equal to
the sum of CIO and CIOOffset.
Tother_Freq is the decision threshold of inter-frequency hard handover. Based
on the service type and measurement quantity, this threshold can be configured
through one of the following parameters:
TargetFreqCsThdEcN0
TargetFreqR99PsThdEcN0
TargetFreqHThdEcN0
TargetFreqCsThdRscp
TargetFreqR99PsThdRscp
TargetFreqHThdRscp
These thresholds are the same as the quality threshold of event 2B.
H is the inter-frequency hard handover hysteresis value set through the
parameter HystForPrdInterFreq.
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Each cell in the measurement report shall be evaluated as mentioned
previously. When the hard handover time-to-trigger timers of more than one cell
expire at the same time, the latest measurement report is used for selecting the
best inter-frequency neighboring cell for handover. For example, the cell with
the highest CPICH RSCP in the latest measurement report is selected, as
shown in the above figure.
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CIO
Content: This parameter works with the Neighboring cell oriented CIO. It
is used for intra- or inter-frequency handover decisions. The larger the
sum, the higher the handover priority of the neighboring cell. The smaller
the sum, the lower the handover priority of the neighboring cell. Usually it
is configured to 0.
Value range: -20~20
Physical value range: -10~10; step: 0.5
Physical unit: dB
Set this parameter through ADD CELLSETUP/MOD CELLSETUP.
CIOOffset
Content: This parameter defines the neighboring cell oriented cell
individual offset. The set value functions in combination of the cell
oriented CIO. Their sum is added to the measurement quantity before
the UE evaluates whether an event has occurred. In handover
algorithms, this parameter is used for moving the border of a cell.
Value range: -20~20
Physical value range: -20~20; step: 1
Physical unit: dB
Set this parameter through ADD INTERFREQNCELL/MOD
INTERFREQNCELL.
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HystForPrdInterFreq
Content: Hysteresis for inter-frequency hard handover in periodical
report mode. This parameter is used to estimate the inter-frequency
handover at the RNC. The larger the value of this parameter, the
stronger the capability of resisting signal fluctuation. Thus, the ping-pong
effect can be resisted, but the speed of the handover algorithm to
respond to signal change becomes lower, and therefore event 2B might
not be triggered in time.
Value range: 0~29
Physical value range: 0~14.5; step: 0.5
Physical unit: dB
TimeToTrigForPrdInterFreq
Content: Hysteresis for inter-frequency hard handover in periodical
report mode. This parameter is used to estimate the inter-frequency
handover at the RNC. The larger the value of this parameter, the
stronger the capability of resisting signal fluctuation. Thus, the ping-pong
effect can be resisted, but the speed of the handover algorithm to
respond to signal change becomes lower, and therefore event 2B might
not be triggered in time.
Value range: 0~64000
Physical value range: 0~64000; step: 1
Physical unit: ms
Set these parameters through ADD CELLINTERFREQHOCOV/MOD
CELLINTERFREQHOCOV/SET INTERFREQHOCOV.
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QNoused is the measured quality of the cell that uses the other frequencies.
QUsed is the measured quality of the used frequency.
H2b is the event 2B hysteresis value set through the parameter HystFor2B.
TNoused2b is the absolute quality threshold of the cell that uses the other
frequencies. Based on the service type and measurement quantity, this
threshold can be configured through one of the following parameters:
TargetFreqCsThdEcN0
TargetFreqR99PsThdEcN0
TargetFreqHThdEcN0
TargetFreqCsThdRscp
TargetFreqR99PsThdRscp
TargetFreqHThdRscp
TUsed2b is the absolute quality threshold of the cell that uses the current
frequency.
After the conditions of event 2B are fulfilled and maintained until the parameter
TimeToTrig2B is reached, the UE reports the event 2B measurement report
message.
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TUsed2b is set in the following way:
Based on the service type and measurement quantity, this threshold can be
configured through one of the following parameters:
If event 2D with the CPICH RSCP value is received by the RNC:
TUsed2b of event 2B with the CPICH RSCP value can be:
UsedFreqCSThdRSCP
UsedFreqR99PsThdRSCP
UsedFreqHThdRSCP
TUsed2b of event 2B with the CPICH Ec/No value is configured
as the maximum value 0dB.
According to 3GPP specifications, TUsed2b of event 2B with the
CPICH Ec/No value should be configured as the maximum value
0dB. If the event 2F with the CPICH Ec/No value is received by
the RNC and TUsed2b of event 2B with the CPICH Ec/No value
is modified, TUsed2b is reset to 0dB.
If event 2D with the CPICH Ec/No value is received by the RNC:
TUsed2b of event 2B with the CPICH Ec/No value can be:
UsedFreqCSThdEcN0
UsedFreqR99PsThdEcN0
UsedFreqHThdEcN0
TUsed2b of event 2B with the CPICH RSCP value is configured
as the maximum value –25 dBm.
According to 3GPP specification, TUsed2b of event 2B with the
CPICH RSCP value should be configured as the maximum value
-25dBm. If event 2F with the CPICH RSCP value is received by
the RNC and TUsed2b of event 2B with the CPICH RSCP value
is modified, TUsed2b is reset to -25 dBm.
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TargetFreqCsThdEcN0
Content: Threshold of the target frequency for triggering inter-frequency
measurement with measurement quantity of Ec/No for CS domain
services. For CS domain services, if the value of inter-frequency
measure report mode is set to EVENT_TRIGGER, this parameter is
used to set the measurement control of event 2B. One of the necessary
conditions for triggering event 2B can be met only when the quality of the
target frequency is higher than this threshold. If the value of inter-
frequency measure report mode is set to PERIODICAL_REPORTING,
this parameter is used to evaluate inter-frequency handovers at the
RNC. .
Value range: -24~0
Physical value range: -24~0; step: 1
Physical unit: dB
UsedFreqCSThdEcN0
Content: Threshold of used frequency quality for triggering inter-
frequency measurement with measurement quantity of Ec/No for CS
domain services. For CS domain services, if the value of inter-frequency
measure report mode is set to EVENT_TRIGGER, this parameter is
used to set the measurement control of event 2B. One of the necessary
conditions can be met only when the quality of the used frequency is
lower than this threshold.
Value range: -24~0
Physical value range: -24~0; step: 1
Physical unit: dB
Set these parameters through ADD CELLINTERFREQHOCOV/MOD
CELLINTERFREQHOCOV/SET INTERFREQHOCOV.
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Set these parameters through ADD CELLINTERFREQHOCOV/MOD
CELLINTERFREQHOCOV/SET INTERFREQHOCOV.
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HystFor2B
Content: Hysteresis value for the event 2B. The value of this parameter
correlates with slow fading. The larger the value of this parameter, the
stronger the capability of resisting signal fluctuation. Thus, the ping-pong
effect can be resisted, but the speed of the handover algorithm to
respond to signal change becomes lower, and therefore event 2B might
not be triggered in time.
Value range: 0~29
Physical value range: 0~14.5; step: 0.5
Physical unit: dB
TimeToTrig2B Content: Time delay to trigger event 2B. The value of this parameter
correlates with slow fading. The larger the value of this parameter, the
lower probability of incorrect decision, but the slower the response of
event 2B to the change of measured signals.
Value range: D0, D10, D20, D40, D60, D80, D100, D120, D160, D200,
D240, D320, D640, D1280, D2560, D5000
Physical value range: 0, 10, 20, 40, 60, 80, 100, 120, 160, 200, 240, 320,
640, 1280, 2560, 5000
Physical unit: ms
Set these parameters through ADD CELLINTERFREQHOCOV/MOD
CELLINTERFREQHOCOV/SET INTERFREQHOCOV.
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InterFreqNCovHOThdEcN0
Content: Threshold of signal quality of the target frequency for triggering inter-frequency
measurement. This parameter is used to set measurement control on the event 2C. The
event 2C is triggered when the signal quality of the target frequency is above this
threshold.
Value range: -24~0
Physical value range: -24~0; step: 1
Physical unit: dB
2C hysteresis
Content: Hysteresis value for the event 2C. The value of this parameter correlates with
slow fading. The larger the value of this parameter, the stronger the capability of resisting
signal fluctuation. Thus, the ping-pong effect can be resisted, but the speed of the
handover algorithm to respond to signal change becomes lower, and therefore event 2C
might not be triggered in time.
Value range: 0~29
Physical value range: 0~14.5; step: 0.5
Physical unit: dB
TrigTime2C
Content: Time delay to trigger the event 2C. The value of this parameter correlates with
slow fading. The larger the value of this parameter, the lower probability of incorrect
decision, but the slower the response of event 2C to the change of measured signals. .
Value range D0, D10, D20, D40, D60, D80, D100, D120, D160, D200, D240, D320,
D640, D1280, D2560, D5000
Physical value range: 0, 10, 20, 40, 60, 80, 100, 120, 160, 200, 240, 320, 640, 1280,
2560, 5000
Physical unit: ms
Set these parameters through ADD CELLINTERFREQHONCOV/MOD
CELLINTERFREQHONCOV/SET INTERFREQHONCOV.
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N-90
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Inter-RAT handover refers to the handover performed between 3G network and
2G network. Inter-RAT handover provides continuous coverage, load sharing,
and HCS services, which fully utilizes the existing 2G network resources and
thus reduces operator's cost.
In this handover, however, GSM and UMTS dual-mode UEs (MSs) are required,
and both the GSM MSC and the GSM BSS must be upgraded.
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Coverage-based 3G to 2G handover:
The coverage of the 3G network is incontinuous at the initial stage. On the border of the coverage, the poor signal quality of the 3G network triggers the 3G-to-2G measurement. If the signal quality of the 2G network is good enough and all the services of the UE are supported by the 2G network, the coverage-based 3G to 2G handover is triggered.
QoS-based 3G to 2G handover:
According to the Link Stability Control Algorithm, the RNC needs to trigger the QoS-based 3G to 2G handover to avoid call drops.
Load-based 3G to 2G handover:
If the load of the 3G network is heavy and all the RABs of the UE are supported by the 2G network, the load-based 3G to 2G handover is triggered.
Service-based 3G to 2G handover:
Based on layered services, the traffic of different classes is handed over to different systems. For example, when an Adaptive Multi Rate (AMR) speech service is requested, this service can be handed over to the 2G network.
Speed-based 3G to 2G handover:
The principles of the 3G-to-2G handover based on HCS speed estimation are similar to those of inter-frequency handover.
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2G cell capability:
2G cell capability is configured through the parameter RATCELLTYPE.
This parameter indicates whether the cell supports the GSM, GPRS, or
EDGE.
For more detailed information, please refer to the ADD GSMCELL
command.
Service capability:
The required 2G capability (Req2GCap) specifies the capability of 2G
cells required by inter-RAT handover. This indicates whether the service
is supported by the GSM, GPRS, or EDGE.
For more detailed information, please refer to the ADD TYPRABBASIC
command.
UE capability:
Upon the reception of the UE capability information message, the RNC
decides whether to start the inter-RAT measurement. The information
indicates whether the UE supports the GSM, GPRS, or EDGE.
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Service handover indicator:
The IE service handover indicator indicates the CN policy for the service
handover to the 2G network. This IE is indicated in the Radio Access Bearer
(RAB) assignment signaling assigned by the CN, or in the following table
configured in the RNC by default.
The algorithm switch HoSwitch:
HO_INTER_RAT_RNC_SERVICE_HO_SWITCH decides whether the service
attribute of inter-RAT handover is based on the RNC or the CN.
If the switch is set to on, the service attribute of inter-RAT handover is
based on the parameter configured on the RNC side.
If the switch is set to off, the service attribute of inter-RAT handover is
first based on the CN when the indicator is contained in the RAB
assignment signaling assigned by the CN. If the CN does not allocate a
service indicator, the service attribute of inter-RAT handover is based on
the RNC side.
For more detailed information, please refer to the SET
CORRMALGOSWITCH command.
Through the SHIND parameter, the service handover indicators are set as
follows:
HO_TO_GSM_SHOULD_BE_PERFORM: means that the handover to
the 2G network is performed when 2G signals are available.
HO_TO_GSM_SHOULD_NOT_BE_PERFORM: means that the
handover to the 2G network is performed when 3G signals are weak but
2G signals are strong.
HO_TO_GSM_SHALL_NOT_BE_PERFORM: means that the handover
to the 2G network is not performed even when 3G signals are weak but
2G signals are strong.
For more detailed information, please refer to the ADD TYPRABBASIC
command.
CN
DomainTraffic Class Max Rate
Service Handover
Indicator
Required 2G
Capability
CS CONVERSATIONAL 12.2kHO_TO_GSM_SHOULD_
NOT_BE_PERFORMGSM
CS CONVERSATIONAL 64kHO_TO_GSM_SHALL_N
OT_BE_PERFORMGSM
PS INTERACTIVE 64kHO_TO_GSM_SHOULD_
NOT_BE_PERFORMGPRS
PS INTERACTIVE 384kHO_TO_GSM_SHOULD_
NOT_BE_PERFORMEDGE
PS BACKGROUND 64kHO_TO_GSM_SHOULD_
NOT_BE_PERFORMGPRS
PS BACKGROUND 384kHO_TO_GSM_SHOULD_
NOT_BE_PERFORMEDGE
PS BACKGROUND >384kHO_TO_GSM_SHALL_N
OT_BE_PERFORMEDGE
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Cell
Capability
UE Capability Service Capability (Required by 2G)
EDGE GPRS GSM
EDGE EDGE Allowed Allowed Allowed
GPRS Allowed Allowed Allowed
GSM Not allowed Not allowed Allowed
Not supported
by 2G
Not allowed Not allowed Not allowed
GPRS EDGE Allowed Allowed Allowed
GPRS Allowed Allowed Allowed
GSM Not allowed Not allowed Allowed
Not supported
by 2G
Not allowed Not allowed Not allowed
GSM EDGE Not allowed Not allowed Allowed
GPRS Not allowed Not allowed Allowed
GSM Not allowed Not allowed Allowed
Not supported
by 2G
Not allowed Not allowed Not allowed
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Cell
Capability
UE Capability Service Capability (Required by 2G)
EDGE GPRS GSM
EDGE EDGE Allowed Allowed Allowed
GPRS Not allowed Allowed Allowed
GSM Not allowed Not allowed Allowed
Not supported by 2G Not allowed Not allowed Not
allowed
GPRS EDGE Not allowed Allowed Allowed
GPRS Not allowed Allowed Allowed
GSM Not allowed Not allowed Allowed
Not supported by 2G Not allowed Not allowed Not
allowed
GSM EDGE Not allowed Not allowed Allowed
GPRS Not allowed Not allowed Allowed
GSM Not allowed Not allowed Allowed
Not supported by 2G Not allowed Not allowed Not
allowed
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To perform the service-based 3G to 2G handover, the RNC must turn on the
related switches for services in the CS and PS domains.
When a single CS service is initially set up by the UE, the RNC allows
the 3G to 2G service-based handover if CSServiceHOSwitch is set to on.
When a single PS service is initially set up by the UE, the RNC allows
the service-based 3G-to-2G handover if PSServiceHOSwitch is set to on.
For the CS and PS combined services, no service-based handover is
triggered.
For more detailed information, please refer to the ADD CELLHOCOMM
command.
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In the triggering phase:
The RNC requests the UE to measure through an inter-RAT
measurement control message. If the CPICH Ec/No or CPICH RSCP of
the current cell is lower than the corresponding threshold, the UE reports
event 2D.
In the measurement phase:
The RNC sends an inter-RAT measurement control message to the UE,
requesting the NodeB and UE to start the compressed mode. The RNC
also requests the UE to perform the inter-RAT measurement.
In this phase, the method of either periodical measurement report or
event-triggered measurement report can be used.
In the decision phase:
After the UE reports event 3A, the RNC performs the handover.
Otherwise, the UE periodically generates measurement reports, and the
RNC makes a decision after evaluation.
In the execution phase:
The RNC executes the handover procedure.
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When the estimated quality or strength of the currently used frequency is below
a certain threshold,2D event will be triggered. Then RNC will initiate the
compressed mode to start inter-RAT handover measurement.
During compressed mode, if the estimated quality or strength of the currently
used frequency is above a certain threshold, 2F event will be triggered. Then
RNC will stop the compressed mode.
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QUsed is the measurement value of the cell at the currently used frequency.
TUsed2d is the absolute quality threshold of the cell at the currently used
frequency. Based on the service type and measurement quantity, this threshold
can be configured through the following parameters:
InterRATCSThd2DEcN0
InterRATR99PsThd2DEcN0
InterRATHThd2DEcN0
InterRATCSThd2DRSCP
InterRATR99PsThd2DRSCP
InterRATHThd2DRSCP
H2d is the event 2D hysteresis value set through the parameter HystFor2D.
When the conditions for event 2D are met and maintained in time-to-trigger
specified by the parameter TimeToTrig2D, the UE sends the measurement
report of event 2D.
Any of the Ec/No and RSCP measurement result can trigger the 2D
event.
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The parameters for inter-RAT handover 2D are similar with inter-frequency
handover.
Set above parameters through ADD CELLINTERRATHOCOV/MOD
CELLINTERRATHOCOV/SET INTERRATHOCOV.
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QUsed is the measurement value of the cell at the currently used frequency.
TUsed2f is the absolute quality threshold of the cell at the currently used
frequency. Based on the service type and measurement quantity, this threshold
can be configured through the following parameters:
InterRATCSThd2FEcN0
InterRATR99PsThd2FEcN0
InterRATHThd2FEcN0
InterRATCSThd2FRSCP
InterRATR99PsThd2FRSCP
InterRATHThd2FRSCP
H2f is the event 2F hysteresis value set through the parameter HystFor2F.
When the conditions for event 2F are met and maintained in time-to-trigger
specified by TrigTime2F, the UE sends the measurement report of event 2F.
Any of Ec/No and RSCP measurement result can trigger the 2F event.
Conditions of event 2F are as follows: TUsed2d - H2d/2 < TUsed2f + H2f/2, for
example, (InterRATCSThd2DEcN0–HystFor2D/2) < (InterRATCSThd2FEcN0+
HystFor2F/2).
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The parameters for inter-RAT handover 2F are similar with inter-frequency
handover.
Set above parameters through ADD CELLINTERRATHOCOV/MOD
CELLINTERRATHOCOV/SET INTERRATHOCOV.
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During the coverage-based and QoS-based 3G to 2G handover, the
measurements on both inter-frequency and inter-RAT neighboring cells can be
made, which enables the cells to provide continuous coverage and high quality.
The preconditions for the measurements are as follows:
Both inter-frequency and inter-RAT neighboring cells are available.
InterFreqRATSwitch is set to SIMINTERFREQRAT.
If InterFreqRATSwitch is set to:
Inter-frequency measurement (INTERFREQ), the RNC allows the UE to
perform only this type of measurement.
Inter-RAT measurement (INTERRAT), the RNC allows the UE to
perform only this type of measurement.
Concurrent inter-frequency and inter-RAT measurement
(SIMINTERFREQRAT), the RNC allows the UE to perform both types of
measurement at the same time.
During the concurrent inter-frequency and inter-RAT measurement, the values
of the parameter CoexistMeasThdChoice for event 2D are chosen as follows:
When the value COEXIST_MEAS_THD_CHOICE_INTERFREQ is
chosen, the inter-frequency measurement threshold for event 2D is used.
When the value COEXIST_MEAS_THD_CHOICE_INTERRAT is chosen,
the inter-RAT measurement threshold for event 2D is used.
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InterFreqRATSwitch
Content: Cell-level switch for inter-frequency and inter-RAT handover.
INTERFREQ: only measuring inter-frequency cells and performing inter-
frequency handover.
INTERRAT: only measuring GSM cells and performing inter-RAT handover .
SIMINTERFREQRAT: measuring both inter-frequency and inter-RAT cells,
performing inter-frequency or inter-RAT handover according to the type of the
cell that first meets the handover decision condition.
Value range: INTERFREQ, INTERRAT, SIMINTERFREQRAT
Physical value range: Inter-frequency handover only, Inter-RAT handover only,
Inter-frequency and Inter-RAT handover
CoexistMeasThdChoice
Content: Type of event 2D/2F measurement thresholds when inter-frequency
and inter-RAT measurements coexist.
COEXIST_MEAS_THD_CHOICE_INTERFREQ: choosing the inter-frequency
oriented parameters as event 2D/2F measurement thresholds for inter-
frequency measurement.
COEXIST_MEAS_THD_CHOICE_INTERRAT: choosing the inter-RAT oriented
parameters as event 2D/2F measurement thresholds for inter-RAT
measurement.
Value range: COEXIST_MEAS_THD_CHOICE_INTERFREQ,
COEXIST_MEAS_THD_CHOICE_INTERRAT
Physical value range: Choosing the inter-frequency oriented parameters,
Choosing the inter-RAT oriented parameters
Set these parameters through SET HOCOMM/ADD CELLHOCOMM/MOD
CELLHOCOMM.
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When the UE enters the compressed mode, RNC will trigger the inter-RAT
handover measurement by one measurement control signaling, so as to request
UE test inter-RAT neighbor cell.
In this Measurement control message, RNC should inform the UE inter-RAT
measurement parameters, including neighbor list and reporting mode as well.
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The measurement report mode of inter-RAT handover is configured through the
parameter InterRatReportMode. By default, periodically reporting is
recommended.
Based on the measurement control message received from the RNC, the UE
periodically reports the measurement quality of the target cell. Then, based on
the measurement report, the RNC makes the handover decision and performs
handover.
If the reporting mode is periodically reporting: UE only test the Inter-RAT
neighbor RSSI only.
If the reporting mode is event trigger reporting: UE test the Inter-RAT neighbor
RSSI and current cell Ec/No or RSCP:
In coverage-based 3G to 2G handover, the event 3A measurement
quantity is set through the parameter MeasQuantityOf3A.
In QoS-based 3G to 2G handover, the event 3A measurement quantity is
set through the parameter UsedFreqMeasQuantityForQos3A.
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InterRatReportMode
Content: Inter-RAT measurement report mode.
When PERIODICAL_REPORTING is selected, you can infer that
periodical inter-RAT measurement report is adopted; when
EVENT_TRIGGER is selected, you can infer that event-triggered inter-
RAT measurement report is adopted.
Value range: PERIODICAL_REPORTING, EVENT_TRIGGER
Physical value range: Periodical reporting, Event trigger
InterRATPeriodReportInterval
Content: Interval that the UE reports inter-RAT measurement results to
the RNC. In periodical report mode, the interval between two reports is
the configured value. That is, the UE submits reports at intervals of the
configured time.
Value range: NON_PERIODIC_REPORT, D250, D500, D1000, D2000,
D3000, D4000, D6000, D8000, D12000, D16000, D20000, D24000,
D28000, D32000, D64000
Physical value range: Non periodical reporting, 250, 500, 1000, 2000,
3000, 4000, 6000, 8000, 12000, 16000, 20000, 24000, 28000, 32000,
64000
Physical unit: ms
Set these parameters through ADD CELLINTERRATHOCOV/MOD
CELLINTERRATHOCOV/SET INTERRATHOCOV.
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InterRATMeasTime
Content: Timer length for inter-RAT measurement. After inter-RAT
measurement starts, if no inter-RAT handover is performed when this timer
times out, the inter-RAT measurement is stopped. In addition, the compressed
mode is deactivated, if any; If the value is 0, you can infer that the inter-RAT
measurement timer is not started.
Value range: 0~512
Physical value range: 0~512; step: 1
Physical unit: s
MeasQuantityOf3A
Content: Measurement quantity used in coverage-based inter-RAT
measurement in event 3A-triggered reporting mode.
CPICH_Ec/No indicates that the Ec/No measurement quantity is used for event
3A measurement. The physical unit is dB.
CPICH_RSCP indicates that the RSCP measurement quantity is used for event
3A measurement. The physical unit is dBm.
AUTO indicates that the Ec/N0 measurement quantity is used for event 3A
measurement if RNC receives the Ec/No 2D firstly; the RSCP measurement
quantity is used for event 3A measurement if RNC receives the RSCP 2D firstly.
This parameter can be configured only when InterRatReportMode is set to
EVENT_TRIGGER.
Value range: CPICH_EC/NO, CPICH_RSCP, AUTO
Physical value range: CPICH_EC/NO, CPICH_RSCP, AUTO
Set these parameters through ADD CELLINTERRATHOCOV/MOD
CELLINTERRATHOCOV/SET INTERRATHOCOV.
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Mother_RAT is the measurement result of inter-RAT handover (RSSI) received
by the RNC.
CIOother_RAT is the cell individual offset value of the target cell. It is equal to
the sum of CIO and CIOOffset.
Tother_RAT is the decision threshold of inter-RAT hard handover.Based on the
service type and measurement quantity, this threshold can be configured
through the following parameters:
TargetRatCsThd
TargetRatR99PsThd
TargetRatHThd
These thresholds are the same as the quality threshold of event 3A.
H is the inter-RAT handover hysteresis value set through HystforInterRAT.
The length of the time-to-trigger timer is configured through the parameter
TimeToTrigForVerify (with BSIC acknowledged, and it is the default setting) or
the parameter TimeToTrigForNonVerify (with BSIC unacknowledged).
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CIO
Content: This parameter is used for the inter-RAT handover decision in
combination with the neighboring cell oriented CIO. The larger the sum,
the higher the handover priority of the GSM cell. The smaller the sum,
the lower the handover priority of the GSM cell. The parameter is
generally set to 0.
Value range: -50~50
Physical value range: -50~50; step: 1
Physical unit: dB
Set this parameter through ADD GSMCELL/MOD GSMCELL.
CIOOffset
Content: This parameter is used for decision making for the inter-RAT
handover. The larger the value of the parameter, the higher the
handover priority of the GSM cell. The smaller the value of the parameter,
the lower the handover priority of the GSM cell.
Value range: -50~50
Physical value range: -50~50; step: 1
Physical unit: dB
Set this parameter through ADD GSMNCELL/MOD GSMNCELL.
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HystforInterRAT
Content: Hysteresis value for inter-RAT measurement periodical reports. This parameter
aims to prevent the mis-decision caused by unexpected jitters of signals during inter-
RAT handover decisions. The HystforInterRAT and the inter-RAT handover decision
threshold determine whether to trigger inter-RAT handovers.
Value range: 0~15
Physical value range: 0~15; step: 0.5
Physical unit: dB
TimeToTrigForVerify
Content: Time delay for triggering handovers to GSM cells with verified BSIC. During the
period of time specified by this parameter, if the signal quality in a neighboring GSM cell
satisfies inter-RAT handover conditions and the neighboring GSM cell is verified, an
inter-RAT handover is triggered.
Value range: 0~64000
Physical value range: 0~64000; step: 1
Physical unit: ms
TimeToTrigForNonVerify
Content: Time delay for triggering handovers to GSM cells with non-verified BSIC.
During the period of time specified by this parameter, if the signal quality in a neighboring
GSM cell satisfies inter-RAT handover conditions and the neighboring GSM cell is not
verified, an inter-RAT handover is triggered. When the value of this parameter is 65535,
the RNC does not perform inter-RAT handovers to non-verified GSM cells.
Value range: 0~64000, 65535
Physical value range: 0~64000, 65535; step: 1
Physical unit: ms
Set this parameter through ADD CELLINTERRATHOCOV/MOD CELLINTERRATHOCOV/SET
INTERRATHOCOV.
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QUsed is the measurement value of the cell at the currently used frequency.
TUsed is the absolute quality threshold of the cell that uses the current
frequency.
MOtherRAT is the measurement value of the cell (in another RAT) in the
reporting range.
CIOOtherRAT is the cell individual offset value of the cell (in another RAT) in
the reporting range which is equal to the sum of CIO and CIOOffset.
TOtherRAT is the absolute inter-RAT handover threshold. Based on different
service types (CS , PS domain R99 service, or PS domain HSPA service), this
threshold can be configured through the following parameters:
TargetRatCsThd
TargetRatR99PsThd
TargetRatHThd
H3a is 3A hysteresis, the hysteresis value of event 3A.
When the conditions for event 3A are met and maintained in time-to-trigger
specified by TrigTime3A the UE sends the measurement report of event 3A.
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UsedFreqCSThdEcN0
Content: Threshold of used frequency quality for triggering inter-RAT measurement with measurement quantity of Ec/No for CS domain services. For CS domain services, when Ec/No is used as the measurement quantity for inter-RAT measurement, this parameter is used to set measurement control on the event 3A. The event 3A is triggered, when the quality of the currently used UTRAN frequency is below this threshold and the TargetRatCsThd is reached.
Value range: -24~0
Physical value range: -24~0; step: 1
Physical unit: dB
TargetRatCsThd
Content: Quality requirement for the inter-RAT cell during an inter-RAT handover with CS domain services. For CS domain services, if the value of InterRatReportMode is set to EVENT_TRIGGER, this parameter is used to set the measurement control of event 3A. One of the necessary conditions for triggering event 3A can be met only when the quality of the target frequency is higher than this threshold; if the value of InterRatReportMode is set to PERIODICAL_REPORTING, this parameter is used to evaluate inter-RAT coverage handovers at the RNC. Note that the value 0 means the physical value is smaller than -110 dBm.
Value range: 0~63
Physical value range: Lower than -110, -110~-48 (1: -110; 2: -109; ...; 63: -48 )
Physical unit: dBm
Set these parameters through ADD CELLINTERRATHOCOV/MOD
CELLINTERRATHOCOV/SET INTERRATHOCOV.
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Set these parameters through ADD CELLINTERRATHOCOV/MOD
CELLINTERRATHOCOV/SET INTERRATHOCOV.
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Hystfor3A
Content: Hysteresis value for the event 3A. The value of this parameter
correlates with slow fading. The larger the value of this parameter, the stronger
the capability of resisting signal fluctuation. Thus, the ping-pong effect can be
avoided, but the speed of the handover algorithm to respond to signal change
becomes lower. If the inter-RAT handover hysteresis is set to an excessively
high value, the GSM cell to which the UE is handed over must be of good quality.
Therefore, the conditions for triggering the inter-RAT handover decision are hard
to be satisfied, and the call drop rate increases.
Value range: 0~15
Physical value range: 0~7.5; step: 0.5
Physical unit: dB
TrigTime3A
Content: Time delay to trigger the event 3A. The value of this parameter
correlates with slow fading. The larger the value of this parameter, the lower the
incorrect decision probability, but the slower the response of the event 3A to
measurement signal change.
Value range: D0, D10, D20, D40, D60, D80, D100, D120, D160, D200, D240,
D320, D640, D1280, D2560, D5000
Physical value range: 0, 10, 20, 40, 60, 80, 100, 120, 160, 200, 240, 320, 640,
1280, 2560, 5000
Physical unit: s
Set these parameters through ADD CELLINTERRATHOCOV/MOD
CELLINTERRATHOCOV/SET INTERRATHOCOV.
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N-123
PeriodFor3A
Content: Retry period for the event 3A. This parameter defines the length
of the event 3A retry period. The smaller the value of this parameter, the
more frequent the handover retry due to inter-RAT handover failure, and
the faster the UE to be successfully handed over to the target cell whose
load is restored, thus lowering the probability of call drops. In this case,
however, frequent handover retry brings more load to the RNC system.
Value range: 1~64
Physical value range: 500~32000; step: 500
Physical unit: ms
AmntOfRpt3A
Content: Maximum retry times of the event 3A. This parameter defines
the number of times for event 3A retry when the measurement control is
valid. The larger the value of this parameter, the larger the number of
times for inter-RAT handover retry, and the higher probability the UE is
successfully handed over to the target cell whose load is restored. When
the retry times reaches the maximum value, the RNC stops the retry
process. Or if the measurement control message is released, the retry
will be immediately stopped.
Value range: 0~63
Physical value range: 0~62, 63: Infinity; step: 1
Set these parameters through ADD CELLINTERRATHOCOV / MOD
CELLINTERRATHOCOV / SET INTERRATHOCOV.
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PeriodFor3C
Content: Retry period for the event 3C. This parameter defines the
length of the event 3C retry period. The smaller the value of this
parameter, the more frequent the handover retry due to inter-RAT
handover failure, and the faster the UE to be successfully handed over
to the target cell whose load is restored, thus lowering the probability of
call drops. In this case, however, frequent handover retry brings more
load to the RNC system.
Value range: 1~64
Physical value range: 500~32000; step: 500
Physical unit: ms
AmntOfRpt3C
Content: Maximum retry times of the event 3C. This parameter defines
the number of times for event 3C retry when the measurement control is
valid. The larger the value of this parameter, the larger the number of
times for inter-RAT handover retry, and the higher probability the UE is
successfully handed over to the target cell whose load is restored. When
the retry times reaches the maximum value, the RNC stops the retry
process. Or if the measurement control message is released, the retry
will be immediately stopped.
Value range: 0~63
Physical value range: 0~62, 63: Infinity; step: 1
Set these parameters through ADD CELLINTERRATHOCOV / MOD
CELLINTERRATHOCOV / SET INTERRATHOCOV.
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N-125
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N-126
The above figure shows the signaling procedures for the 3G-to-2G handover in
the CS domain. The 2G messages shown in the figure are for your reference
only.
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Signaling procedures for CS inter-RAT handover:
1. The SRNC sends the 3G MSC a RANAP message RELOCATION
REQUIRED if the condition of Inter-RAT outgoing handover is met.
2. As indicated in the received message, the 3G MSC forwards this request to
the 2G MSC on the MAP/E interface through a MAP message PREPARE
HANDOVER.
3. The 2G MSC forwards the request to the BSC. The message shown in the
figure is for reference only and is subject to the actual condition of the GSM.
4. The BSC responds to this request. The message shown in the figure is for
reference only and is subject to the actual condition of the GSM.
5. Once the initial procedures are completed in the 2G MSC/BSS, the 2G MSC
returns a MAP/E message PREPARE HANDOVER RESPONSE.
6. The 3G MSC sends the SRNC a RANAP message RELOCATION
COMMAND.
7. The SRNC sends the UE an RRC message HANDOVER FROM UTRAN
through the existing RRC connection. This message may include information
from one or several other systems.
8. The BSC performs handover detection. The figure does not show such
procedures as GSM BSS synchronization. The message shown in the figure is
for reference only and is subject to the actual condition of the GSM.
9. The UE sends the BSC a HANDOVER COMPLETE message.
10. The BSC sends the MSC a HANDOVER COMPLETE message. The
message shown in the figure is for reference only and is subject to the actual
condition of the GSM.
11. After detecting the UE in the coverage area of the GSM, the MSC sends the
CN a MAP/E message SEND END SIGNAL REQUEST.
12. The CN sends the former SRNC an IU RELEASE COMMAND message,
requesting the former SRNC to release the allocated resource.
13. After the bearer resource is released in the UMTS, the former SRNC sends
the CN an IU RELEASE COMPLETE message.
14. After the call ends, the CN sends the MSC a MAP/E message SEND END
SIGNAL RESPONSE.
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For a UE in idle mode or connected mode, if the SGSN changes with the shift of
the system that the UE accesses from 3G network to 2G network, the inter-
SGSN handover will be performed.
The handover procedures are different in the following two cases:
When the UE is in CELL_DCH state:
The 3G to 2G handover in the PS domain is triggered after the UTRAN
sends a CELL CHANGE ORDER FROM UTRAN message.
When the UE is in CELL_FACH, CELL_PCH, or URA_PCH state:
The 3G to 2G handover in the PS domain is triggered through the cell
reselection.
The above figure shows an example of handover for the UE in CELL_FACH,
CELL_PCH, or URA_PCH state. When the UE is in idle mode, the cell
reselection procedure does not include the elementary procedures marked "UE
CONNECTED" in figure.
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Signaling procedures for PS inter-RAT handover:
1. The UE in CELL_DCH state or the UTRAN (when the UE is in CELL_FACH
state) decides to initiate an Inter-RAT handover in the PS domain to hand over
the UE to a new GSM cell and stop the data transmission between the UE and
the network.
2. The UE sends a ROUTING AREA UPDATE REQUEST message to the 2G
SGSN. The Update Type in the message indicates RA update, combined
RA/LA update, or combined RA/LA update with IMSI attach. The BSS adds the
CGI including the RAC and LAC of the cell to the received message before
forwarding the message to a new 2G SGSN.
3. The new 2G SGSN sends an SGSN CONTEXT REQUEST message to the
old 3G SGSN to obtain the MM and PDP contexts. The old 3G SGSN validates
the old P-TMSI Signature. If the old P-TMSI Signature is valid, the old 3G
SGSN starts a timer. Otherwise, the old 3G SGSN responds with an error
cause.
4. If the UE stays in connected mode before handover, the old 3G SGSN sends
an SRNS CONTEXT REQUEST message. After receiving this message, the
SRNS buffers the DPUs, stops sending the PDUs to the UE, and sends an
SRNS CONTEXT RESPONSE message to the old 3G SGSN.
5. The old 3G SGSN sends an SGSN CONTEXT RESPONSE message to the
2G SGSN, including the MM and PDP contexts.
6. The security functions can be executed.
7. The new 2G SGSN sends an SGSN CONTEXT ACKNOWLEDGE message
to the old 3G SGSN. This informs the old 3G SGSN that the new 2G SGSN is
ready to receive the PDUs belonging to the activated PDP contexts.
8. The old 3G SGSN sends a DATA FORWARD COMMAND message to the
SRNS. The SRNS starts a data-forwarding timer and sends the buffered PDUs
to the old 3G SGSN.
9. The old 3G SGSN tunnels the GTP PDUs to the new 2G SGSN. In the PDUs,
the sequence numbers in the GTP header remain unchanged.
10. The new 2G SGSN sends an UPDATE PDP CONTEXT REQUEST
message to each related GGSN. Each GGSN sends an UPDATE PDP
CONTEXT RESPONSE message after updating its PDP context fields.
11. The new 2G SGSN sends an UPDATE GPRS LOCATION message,
requesting the HLR to modify the SGSN number.
12. The HLR sends a CANCEL LOCATION message to the old 3G SGSN. The
old 3G SGSN responds with a CANCEL LOCATION ACK message. After the
timer expires, the old 3G SGSN removes the MM and PDP contexts.
13. The old 3G SGSN sends an IU RELEASE COMMAND message to the
SRNS. After the data-forwarding timer expires, the SRNS responds with an IU
RELEASE COMPLETE message.
14. The HLR sends an INSERT SUBSCRIBER DATA message to the new 2G
SGSN. The 2G SGSN constructs an MM context and PDP contexts for the UE
and returns an INSERT SUBSCRIBER DATA ACK message to the HLR.
15. The HLR sends an UPDATE GPRS LOCATION ACK message to the new
2G SGSN.
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16. If the association has to be established, the new 2G SGSN sends a
LOCATION UPDATE REQUEST message to the VLR. The VLR stores the
SGSN number for creating or updating the association.
17. If the subscriber data in the VLR is marked as not confirmed by the HLR,
the new VLR informs the HLR. The HLR cancels the old VLR and inserts
subscriber data in the new VLR.
1. The new VLR sends an UPDATE LOCATION message to the HLR.
2. The HLR cancels the data in the old VLR by sending a CANCEL
LOCATION message to the old VLR.
3. The old VLR acknowledges the message by responding with a
CANCEL LOCATION ACK message.
4. The HLR sends an INSERT SUBSCRIBER DATA message to the
new VLR.
5. The new VLR acknowledges the message by responding with an
INSERT SUBSCRIBER DATA ACK message.
6. The HLR responds with a UPDATE LOCATION ACK message to the
new VLR.
17. The new VLR allocates a new TMSI and responds with a LOCATION
UPDATE ACCEPT message to the 2G SGSN.
18. The new 2G SGSN checks the presence of the MS in the new RA. If all
checks are successful, the new 2G SGSN constructs the MM and PDP contexts
for the MS. A logical link is established between the new 2G SGSN and the UE.
The 2G SGSN responds to the UE with a ROUTING AREA UPDATE ACCEPT
message.
19. The UE acknowledges the new P-TMSI by returning a ROUTING AREA
UPDATE COMPLETE message, including all PDUs successfully sent to the UE
before the routing area update procedure.
20. The new 2G SGSN sends a TMSI REALLOCATION COMPLETE message
to the new VLR if the UE confirms the VLR TMSI.
21. The 2G SGSN and the BSS perform the BSS PACKET FLOW CONTEXT
procedure.
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N-131
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