Principles of Handover in Wcdma

Why mobile systems need handover?
Mobile systems are composed by cells which the coverage is limited.
The mobility of the UE.
Providing the continuous service - the basic element in QoS.
HUAWEI TECHNOLOGIES CO., LTD.
TS25.133 Measurement Process
Understand basic concepts about handover
Understand the flow of soft handover
Master basic parameters about soft handover
Master soft handover decision algorithms
Chapter 2 Handover Measurement
Chapter 3 Soft Handover
Chapter 4 Hard Handover
1.1 Purposes of Handover
1.3 Methods and Types of Handover
1.4 Comparison between Soft Handover and Hard Handover
Purposes of Handover
Providing the continuous service in mobile system is the basic element in QoS
Providing continuous communication service is the main purpose of handover.
The load balance: sharing the resource
The hierarchy divided by speed and service: high efficiency of using resource
Handover is a basic function of a cellular mobile network. The purpose of handover is to ensure that a UE in CELL_DCH state is served continuously when it moves.
Handover refers to the process of transferring connection of the user from one radio link to another. Its purpose is to process transfer of radio links required by crossing cells due to movement of the UE, load balancing, and other reasons.
- Monitering the paging channel
RRC connection
These statuses are only applied in the UTRAN and UE. They are transparent to the CN.
UE Modes and Status (Status migration)
SMS
VP/Voice/PS
Status migration mainly involves the BE (Best Effort) service.
When we talk about handover, we consider the UE is in the CELL_DCH status.
The two kinds of status migration marked with lines of dashed CELL_DCH -> URA_PCH, CELL_DCH -> CELL_PCH are not practical now and are not adopted in any service.
Handover
Directly retry
Changing residing cells in the statuses of IDLE, CELL_FACH, CELL_PCH, and URA_PCH
Cell reselection (forward handover)
This course discusses changing the cell (handover) in the status of CELL_DCH.
Hard handover
High-rate services (e.g. PS384K) No Iur interface between to RNCs
Inter-frequency
For the purpose of coverage or load balancing (e.g. handover between carriers with different load, handover to the carrier that supports the HSDPA service. WCDMA-to-GSM handover)
Inter-system (Inter-RAT)
Handover is classified by the cell change after handover, signaling flow, or frequency change after handover.
If the same frequency is used in the two cells where handover occurs:
If the two cells belong to the same RNC, usually soft handover or softer handover is performed for low-rate services to obtain the best service quality.
Soft handover cannot be performed between different RNCs if no lur interface is configured. Only hard handover can be performed in this situation.
Because high rate data communication services, such as the PS348K service, occupy many resources, normally soft handover is not allowed. We can configure the RNC parameters so that soft handover is not performed if the service rate exceeds a certain threshold, even if these two cells belong to the same RNC.
The unique signaling of soft handover is Active Set Update, and the unique signaling of hard handover is Physical Channel Reconfiguration.
If the frequencies used in two cells are different, only hard handover can be performed.
Features Comparison between Soft Handover and Hard Handover
In a word, some resources are wasted to obtain optimal system performance in soft handover.
Item
Several
One
Intra-frequency
Handover gain
Maximum-ratio combining or selective combining which can reduce the impact of fading and transmission power of the UE.
None
Disadvantage
Occupies more resources. Problems occur when the power of soft handover cells is unbalanced.
Call drop ratio is relatively higher
Soft handover gain comprises:
Multi-cell gain: Multiple irrelevant branches in soft handover reduce the requirement of shadow fading margin.
Irrelevance between signal quick fading of different NodeB signals improves the communication quality of the UE on the edge of cells and reduces the call drop probability.
Macro diversity combining gain: gain brought about by improving link demodulation performance to counteract fading in soft handover.
The maximum number of radio link (RL) is 3. This value can be changed. But this function need the UE to support. Normally, the active set supported by UE is fixed 3 and can not be changed.
RNC
NodeB1
NodeB2
Soft handover refers to the process of transferring the radio link and radio link diversity when the UE crosses the handover area.
In the handover area, the UE keeps connection with two cells that belong to different NodeBs.
Question: If these two NodeBs belong to different RNCs, does soft handover occur?
The existence of the lur interface determines whether soft handover occurs between cells that belong to different RNCs.
Note: When connecting to the cell of NodeB2, the system first establishes the link between the RNC and NodeB2 and then the link between the cell of NodeB2 and the UE.
RNC
Node B
Cell A
Cell B
In the softer handover area, the two cells that connect with the UE belong to the same NodeB.
RNC
NodeB1
NodeB2
During hard handover, the UE in the hard handover area disconnects with the original service cell and then establishes connection with a new cell.
During handover, the system first establish the link between the RNC and NodeB2, then releases the connection between the UE and NodeB1 (the link between NodeB1 and the RNC remains), and then establishes the connection between NodeB2 and the UE. After that, the link between NodeB1 and RNC is disconnected.
During hard handover, there is only one connection between the UE and cell at one time.
What type of handover occurs between the two NodeBs that belong to different RNCs?
Questions
What are the differences between soft handover, softer handover, and hard handover?
Why intra-frequency handover is not always soft handover?
How does handover gain arise? How much are various handover gains?
Answers to these questions lie in previous slide pages.
Summary
This chapter describes the purposes of handover, working modes of the UE and common handover types in the WCDMA system, compares soft handover and hard handover and describes respective advantages and disadvantages.
In addition, this chapter describes a brief flow of each type of handover.
What does the system rely on to decide, when and what type of handover will occur?
- The measured information.
2.3 Measurement Control
2.4 Measurement Report
Soft handover gain
Pilot channel (CPICH)
Active set: the set of radio links that keep connections with the UE
monitor set: the set of signals that are from neighbor cells and are not in the active set, but can be detected by the UE
Detection set: the set of signals that are from other cells and can be detected by the UE. It is not the neighbor cell of the current active set (neighbor cell missing or over-coverage).
Radio link (RL): Each connection between the UE and NodeB is called a radio link (RL).
Radio link set (RLS): the set of RLs that belong to the same NodeB. Softer handover occurs between cells that belong to the same RLS.
Combination: 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.
CPICH: Common Pilot Channel. UE measure the signal strength of CPICH for handover decision.
Three Steps of Handover
The following figure shows handover procedure (measurement quality set to PCPICH Ec/Io)
Decision
Execution
Measurement
UE measures the CPICH Ec/Io of its serving cell(s) and neighbor cells. And sends the measurement report to RNC.
Are handover criteria meet?
Measure
Decision
Execution
Y
N
In the measurement phase, the UE takes measurement according to the MEASUREMENT CONTROL message received from the RNC. The UE sends related measurement reports to the RNC according to the rules defined in the MEASUREMENT CONTROL message when the event triggering conditions are met.
After receiving the measurement report from the UE, the RNC decides whether to go to the execution phase, depending on the information in the report.
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Measurement Control
Measurement control is used to notify the UE of the object to be measured, neighbor cell list, report method, and event parameters.
When measurement conditions are changed, the RNC notifies the UE of new conditions.
Measurement Control, normal case
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Measurement Control
Measurement Control
The RNC sends a measurement control message according to the best cell in the active set.
Measurement identity
Measurement command
Measurement type
Measurement object
Measurement report mode
Neighbor Combine algorithm:
In Huawei Neighbor Cell Combine Algorithm, RNC will combine all the active set cells‘ neighbor cells.
Measurement commands fall into three types: Setup, Modify, and Release.
Measurement identity: A reference number that should be used by the UTRAN when setting up, modifying or releasing the measurement and by the UE in the measurement report.
Principle of assigning the measurement identity:
Different IDs should be used for different types of measurement.
Multiple IDs can be used for the measurement of the same type.
One measurement ID can protect multiple measurement events that belong to the same measurement type.
One measurement can be applied in different situations by setting of different IDs.
Currently, the IDs used by the RNC are as follows:
ID=1: intra-frequency measurement control ID, which is used in decision of intra-frequency measurement and soft handover and includes 1A - 1F events.
ID=2: active set quality measurement control ID, which is used to start or stop the compress mode and includes 2D event and 2F event.
ID=3: Inter-RAT measurement control ID
ID=9: inter-frequency measurement control ID, which is used in inter-frequency cyclic measurement.
Other common measurement ID:
ID=4: measurement control ID of DCCC module dynamic channel configuration
Inter-frequency measurement
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Measurement Model
Measurement time of layer 1 is 200 ms. The vendor can decide the filtering method.
Filtering parameters of layer 3 can be configured.
Measurement results are reported when the reporting criteria are met.
This is the measurement model for the UE but not the one for the network side. Lay 1 and layer 3 refer to corresponding layers of the UE.
The measurement time is for intra-frequency measurement, and report cycle of inter-frequency measurement is 480 ms.
3.unknown
Measurement Model - Layer 3 Filtering
Filtering of measurement results by the UE is calculated according to the following formula:
Fn(1-α)Fn-1+αMn
Fn: new measurement result after L3 filtering
Fn-1: the last measurement result after filtering
Mn: the latest measurement result from the physical layer of the UE
α0.5k/2, K is the parameter in filter coefficient in the measurement control message (default=3 ). If it is set to 0 , layer 3 filtering is unavailable.
Accuracy of measurement results on the UE and handover delay should be considered in setting the value of K.
Usually, at a low speed, K should be larger so that more inaccurate measurement results caused by quick fading can be filtered; at a high speed, K should be smaller to reduce handover delay and to improve handover success rate.
In Huawei RNC parameters, the K is named FILTERCOEF. It can be set separately for intra frequency, inter frequency or inter-RAT. Also it can be set on RNC level and Cell level (Cell level has the higher priority).
Below are the MML commands for RNC level:
SET INTRAFREQHO: set the Intra Frequency FILTERCOEF
SET INTERFREQHO: set the Inter Frequency FILTERCOEF
SET INTERRATHOCOV: set the Inter RAT FILTERCOEF for handover based on coverage
SET INTERRATHONCOV: set the Inter RAT FILTERCOEF for handover based on non-coverage (e.g. load)
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Measurement Report
When the measurement reporting criteria are met, the UE reports the results to the RNC as an event.
Measurement Report
Event report
The measurement report is sent when the reporting criteria are met.
Periodic report (event to periodic report)
If the RNC does not respond after several events are reported, the UE switches to periodic report.
The interval between report and total report times are controlled through parameters.
What are the reporting criteria?
Example of event to Periodic report:
Generally, if 1A event is triggered, the UE sends a measurement report to the UTRAN, then the UTRAN will send an ACTIVE SET UPDATE message to order the UE to update the active set. However, if the UTRAN does not respond (for example, capacity is inadequate), the UE will switch to periodic report. The contents in the measurement report contain information of cells in the active set and cells in the monitor set in the reporting range. The UE stops sending periodic measurement report only when the new cell is added to the active set or leaves the reporting range.
Intra-frequency measurement events are identified through 1X:
1A: A CPICH signal from monitor set enters the reporting range. Means a monitor cell is good enough that the UE can add it into active set.
1BA CPICH signal in active set leaves the reporting range. Means a cell in the active set is not good enough according to the best cell.
1C: Replace event. A CPICH signal from a monitor set is better than one in the active set.
1D: Event of changing the best serving cell.
1F: Event that measurement results of the cells in the active set are lower than an absolute threshold.
Understand intra-frequency measurement events according to the following event report slides.
1A: A primary pilot channel enters the reporting range, which means that quality in a cell is close to quality in the best cell or active set. When the active set is full, the UE stops reporting 1A event.
1BA primary pilot channel leaves the reporting range, which means that quality in a cell is much worse than that in the best cell or active set.
1C: Substitution event. A primary pilot channel in an inactive set is better than that in the active set.
1D: Event of changing the best cell. A signal is better than the Best cell in the active cell. This event is also used for Intra-Frequency Hard handover
1E event: It refers to the event that measurement results are higher than the absolute threshold values. Currently Huawei does not use this event.
1F: Event that measurement results of the cells in the active set are lower than the absolute threshold values
The beginner should firstly master 1X events and just need know 2X and 3X events.
Inter-frequency measurement events are identified by 2X:
2B event: The quality of the serving cell is lower than an absolute threshold value and the quality of another inter-frequency neighbor cell is higher than another threshold value. - Handover based on Coverage
2C event: The quality of the inter-frequency neighbor cell is higher than an absolute threshold value. - Handover based on Non-Coverage (e.g. Load)
2D event: The quality of the serving cell is lower than an absolute threshold value. It is used to start the compress mode.
2F event: The quality of the serving cell is higher than an absolute threshold value. It is used to stop the compress mode.
The beginner should firstly master 1X events and just need know 2X events and 3X events.
Inter-RAT Measurement events are identified through 3X:
3A event: The quality of the currently used frequency is lower than an absolute threshold value, but the quality in a GSM cell is higher than another absolute threshold value. - Handover based on Coverage
3C event: The quality in a GSM cell is higher than an absolute threshold value. - Handover based on Non-Coverage (e.g. Load)
2D event: The quality of the currently used frequency is lower than an absolute threshold value. It is used to start the compress mode.
2F event: The quality of the currently used frequency is higher than another absolute threshold value. It is used to stop the compress mode.
The beginner should firstly master 1X events and just need know 2X events and 3X events.
Relative threshold (reporting range)
Absolute threshold (threshold)
Measurement results reach an absolute value, for example, absolute threshold values of 1E event and 1F event
Hysteresis
Time to trigger
Time that lasts until the previous threshold value is met
Weight factor (W)
If W = 0, for RSCP and Ec/Io,
10LogM(New)≥10LogM(Best) - (R1a-H1a/2)
1. Path loss
M: measurement results
W: weight factor. It is 0 generally.
Currently, Ec/Io or RSCP is usually used in the decision criteria. If W is set to 0, the decision inequation of 1A event can be simplified into:
10LogM(New)≥10LogM(Best) - (R1a-H1a/2)
1A event occurs
Trigger criteria of 1B event:
Trigger criteria of 1F event:
Trigger criteria of 1D event:
Trigger criteria of 1C event:
If W is 0, the triggering condition of 1B event is simplified into:
10LogM(New)≤10LogM(Best) – (R1b+H1b/2)
The following slides show the trigger criteria of the following events: 1A, 1B, 1C, and 1D (in the precondition that W equals 0).
1B event is reported
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Event Report
Time to trigger is set for 1A event, 1B event, and 1D event respectively.
Replace cell 1 by the cell 2
Note: The contents of this page is the same as those on the previous one. It just facilitates the trainees to print the training materials.
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Event Report
In the figure above, the cell where P-CPICH 1, P-CPICH 2 and P-CPICH 3 reside belongs to the active set and the cell where P-CPICH 4 resides does not belong to the active set.
This event is used in the case that the active set is full and the quality of signal in a cell is higher than substituting threshold of the active set. In this situation, the poor cell in the active set is substituted.
In the figure above, hysteresis of 1C event is assumed to be 0.
Is the start time of intra-frequency, inter-frequency, and Inter-RAT measurement the same?
When is an event reported?
How to report an event?
What events does intra-frequency measurement contain?
What events does inter-frequency measurement contain?
Currently, Huawei products adopt relative threshold algorithm as the algorithm for soft handover and softer handover:
When the RNC receives 1A events, it adds the links from the best quality (CPICH Ec/Io) to the worst quality (1A events are reported from several cells) if the active set is not full. If the active set is full, the RNC does not perform any operation.
When the RNC receives 1B events, it deletes the links from the worst quality to the best quality (CPICH Ec/Io) if there is more than one link in the active set. The RNC does not perform any operation if there is only one link in the active set.
When a 1C event is triggered, the UE reports the substitution cell and substituted cell in the list of triggered events and the RNC adds the link of the substitution cell and deletes the link of the substituted cell.
When a 1D event is triggered, if the triggering cell belongs to the active set, the RNC marks it as the best cell and updates measurement control; if the triggering cell does not belong to the active set, the RNC adds the link of this cell (if the active set is full, the RNC deletes one cell that is not the best before adding another), marks it as the best cell and updates measurement control.
3.2 Common Parameters and Intra Frequency Neighbor Cell
The trainee who learns this course for the first time only needs to know the flow of soft handover. Flows of other types of handover are not required.
(Reporting 1A event)
(Add new radio link)
On the air interface, only three signaling messages related to the UE can be seen.
Flow of Soft Handover - Adding Radio Link
From the figure above, we can see that soft handover has occurred for four times.
(Reporting 1B event)
(Del old radio link)
The signaling flow on the air interface is similar to the flow of adding radio link in soft handover. Note that the contents and sequence of messages are different.
3.1 Flow of Soft Handover
3.2 Common Parameters and Intra Frequency Neighbor Cell
Relative threshold
1A and 1B event have their individual values.
The value of 1B should be larger than that of 1A, to avoid ping-pong handover. (1A < 1B)
Default setting: 1A: 3 dB; 1B: 6 dB
Hysteresis
Configure it for each event separately.
Usually the threshold values of 1A event and 1B event are 0 dB and those of 1C, 1D, 1F are 4 dB.
This value affects the soft handover area of the UE.
MML command for adding cell-class intra-frequency handover parameters: ADD CELLINTRAFREQHO
MML Command for setting RNC-class intra-frequency handover parameters: SET INTRAFREQHO
A large hysteresis value can reduce ping-pong handover and wrong decision, but it also causes events not to be triggered in time.
To reduce radio links being added or deleted frequently, the following condition must be met:
(Relative threshold of 1A event - 1A hysteresis / 2) < (relative threshold of 1B event + 1B hysteresis / 2)
Time to trigger
Configured it for each event separately.
The value of 1B should be larger than that of 1A, to avoid ping-pong handover. (1A < 1B)
Default setting: 1A: 320 ms; 1B: 640 ms; 1C, 1D: 640 ms
Lay 3 filtering coefficient
It is shared by all types of intra-frequency measurement.
This parameter is sensitive to the delay of event triggering and ping-pong handover.
It is usually set to 3.
MML: Add IntraFreqNCell:
The maxim number of IntraFreqNCell for each cell is 31
Draw the signaling flow chart of soft handover.
What is the impact of parameters in soft handover on system performance?
What parameters can affect performance of soft handover besides the parameters described in this chapter?
Summary
This chapter describes the signaling flow and common parameters of soft handover in WCDMA.
The WCDMA system supports many handover technologies. Besides soft (softer) handover described previously, there are intra-frequency hard handover, inter-frequency hard handover, and Inter-RAT handover.
If the system supports HSDPA, the WCDMA system also supports handover between carrier frequency of HSDPA and ordinary carrier frequency to balance load and to utilize network resources efficiently.
Refer to supplementary contents for description of intra-frequency hard handover, inter-frequency hard handover, and Inter-RAT handover. This part is provided for self-study.
This course describers the principles, algorithm, related parameters and general flow of soft handover in the WCDMA system.
Course
Summary
Trainees may self-study the flow and parameters of hard handover. The beginners are not required to master the contents.
Thank you
Chapter 4 Hard Handover
4.1 Intra-frequency Hard Handover
4.2 Inter-frequency Hard Handover
4.3 Inter-RAT Hard Handover
Note: The beginners are not required to master supplementary contents. They may study the contents by themselves.
Related events
1D event
Questions:
Is 1D event the same in soft handover and in intra-frequency hard handover?
How does the RNC decide the type of handover?
What are the differences in the execution process? (Introduce the following flow)
Questions:
What parameters are involved in the signaling flow on the air interface?
What symbolizes completion of hard handover?
What must the system do after handover?
BeBitrateThd: BE service handover rate decision threshold.
If the maximum rate of transmission channel of the BE service is not more than this threshold, the system performs soft handover for the users using this service.
If the maximum rate of transmission channel of the BE service is greater than this threshold, the system performs intra-frequency hard handover for the users using this service.
MML: SET HOCOMM
Parameters related to the 1D event
Time to trigger (640ms), hysteresis (4dB)
The parameters should be appropriate so the system can not only track changes of the signal to perform handover, but also avoid ping-pong handover.
The frequency is different after handover.
For the UE with only one transceiver, the compress mode should be started to assist measurement.
Advantages
The handover success rate is higher than that of intra-frequency hard handover.
The load on carrier frequencies are balanced.
Purpose of starting the compress mode: perform inter-frequency measurement or Inter-RAT measurement in FDD.
Reasons:
Downlink compression: One transceiver can work only in one group of frequencies. If measurement for other frequencies is required, the transceiver has to stop working in the current frequency and switch to the target frequency for measurement. To guarantee the original downlink signal being received, it should be transmitted in other time.
Uplink compression: If the measurement frequency is close to the current uplink frequency (the frequency used in GSM 1800/1900 is close to uplink frequency in WCDMA FDD), transmission of uplink signal should also be stopped to guarantee measurement results.
Currently, the methods for realizing the compress mode are: half reduction of spread spectrum factor and high-layer scheduling.
Disadvantages
Application scenarios
Measurement variables:
Edge of carrier coverage area: CPICH RSCP
Center of carrier coverage area: CPICH Ec/Io
Questions:
What are the differences between inter-frequency hard handover and intra-frequency hard handover?
Why are different measurement variables adopted for the edge and center of carrier frequency coverage?
Event report
2D event: The quality of current frequency is lower than a certain absolute threshold value. It is used to start the compress mode.
2F event: The quality of current frequency is higher than a certain absolute threshold value. It is used to stop the compress mode.
2B event: The quality of current frequency is lower than the absolute threshold value, and the quality of the neighbor frequency is higher than another absolute threshold value. It is used in coverage handover trigger.
2C event: The quality of the neighbor frequency is higher than a certain absolute threshold value. It is used in load handover trigger.
Periodic report
Which measurement variable is suitable for triggering the quality threshold of the 2C event?
Ec/Io
In inter-frequency co-coverage, if cell parameter setting is the same, the Ec/Io depends on the load.
Starting conditions of measurement
2D event: If the quality of the currently frequency is lower than a certain absolute threshold value, the compress mode is started.
Use the velocity estimation algorithm to decide starting of inter-frequency handover measurement.
Stopping conditions of measurement
2F event
After the best cell is changed, the new best cell does not have any inter-frequency neighbor cell.
The timer of inter-frequency measurement expires.
The speed estimate status of the UE changes, and related inter-frequency handover measurement is disabled according to the hierarchical cell algorithm
In hard handover, if the coverage reason is triggered, handover is stopped simultaneously.
Signaling flow
What are the differences between this flow and that of intra-frequency hard handover?
The frequencies in the signaling messages are different and the process of starting the compress mode is involved in inter-frequency hard handover (before this slide page).
Inter-frequency measurement layer 3 filtering coefficient, time to trigger, and hysteresis
Starting and stopping threshold values of inter-frequency measurement: Configure it respectively for CPICH Ec/Io, CPICH RSCP, and configure 2D, 2F event for CS and PS.
Inter-frequency coverage handover threshold value: quality threshold value of the target cell
Quality threshold value of used frequency in inter-frequency hard handover
Lowest access threshold value in inter-frequency handover
Refer to MML for inter-frequency handover parameters:
ADD CELLINTERFREQHOCOV-based on coverage
Inter-frequency Hard Handover - Questions
Why the compress mode threshold for the CS and PS are configured different?
The Eb/No required by these two services are different, so the RSCPs are also different.
If the UE uses the CS service and PS service at the same time, the 2D and 2F parameters of which service are used to decide starting the compress mode?
If the parameters of any service meet the threshold, the compress mode will started.
Is the compress mode started immediately after the UE sends the 2D parameter?
The compress mode is started after the RNC reconfigure the RB.
Features
The radio access technology (RAT) adopted in the system after handover is different.
Need compress mode to assist measurement.
Advantages
Coverage: Solve the problem of transition between different systems.
Capacity: Improve the utilization of old equipments to the greatest extent (2G->3G)
Disadvantages
The flow is complicated, and the requirement for compatibility of equipment is high.
The UE is complicated.
Measurement types:
Questions:
Are the 2D event and 2F event the same in inter-frequency hard handover and Inter-RAT hard handover?
How does the UE decide to perform inter-frequency measurement or Inter-RAT measurement?
It is decided by measurement control information of the RNC, and the UE only executes corresponding commands.
2D event: starting GSM measurement
2F event: stopping GSM measurement
3A event: The quality of WCDMA is lower than an absolute threshold but quality of a GSM neighbor cell is higher than another absolute threshold. - Handover based on Coverage
3C event: The quality of a GSM neighbor cell is higher than an absolute threshold. - Handover based on Non-Coverage (e.g. Load)
Decision of Inter-RAT handover
Event
3A event: The quality of the currently used frequency is lower than an absolute threshold value, but quality of a GSM cell is higher than another absolute threshold value.
Periodic
Evaluation: Confirm the status according to the GSM RSSI measurement value and the BSIC of the target cell in GSM and evaluate the cell of which the GSM RSSI exceeds the absolute threshold value. If both conditions are met, consider the cell of which the BSIC is confirmed.
Event
The 3C event means that the quality of the GSM cell is higher than an absolute threshold value.
1. Relocation Required
5. Prepare Handover
3. Handover
Inter-RAT Handover - Common Parameters
Inter-RAT coverage handover parameters
Starting and stopping thresholds of Inter-RAT measurement: They determine the thresholds of the 2D event and 2F event. Configure CPICH Ec/Io, CPICH RSCP for the CS service and PS service respectively.
Measurement variables for the 2D event and 2F event in Inter-RAT handover: Select CPICH Ec/Io or PICH RSCP.
BSIC selection confirmation switch
Inter-RAT coverage handover threshold: GSM RSSI threshold in Inter-RAT coverage handover. Configure it for the CS service and PS service respectively.
Quality threshold of used frequency in Inter-RAT handover
Configure time to trigger and hysteresis for each event respectively
Penalty duration
ADD CELLINTERRATHOCOV – based on coverage
ADD CELLINTERRATHONCOV – based on non-coverage
Soft handover (softer handover)
According to the properties of source cell and target cell:
Intra-frequency handover
Inter-frequency handover
Based on Coverage
Based on Noncoverage
The unique signaling of soft handover is Active Set Update, and the unique signaling of hard handover is Physical Channel Reconfiguration.
Soft handover include soft handover and softer handover. It is depended on if the two (or three) RLs belong to one NodeB.
The handover based on load is load control algorithm.
The handover based on mobility of UE is for HCS handover.
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Principles of Handover in Wcdma

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