04_u-lii 302 principles of handover in wcdma-20080917-a-1.0_level 2
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8/12/2019 04_U-LII 302 Principles of Handover in WCDMA-20080917-A-1.0_level 2
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HUAWEI TECHNOLOGIES CO., LTD.
Internal
www.huawei.com
Huawei Confidential
WCDMA HandoverPrinciple
8/12/2019 04_U-LII 302 Principles of Handover in WCDMA-20080917-A-1.0_level 2
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Why mobile systems need handover?
Mobile systems are composed by cellswhich the coverage is limited.
The mobility of the UE.
Providing the continuous service - thebasic element in QoS.
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TS25.331 Flow of Handover andRelated Parameters
TS25.133 Measurement Process
TS25.215 Definitions of MeasurementIndexes
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After studying this course, you will:
Understand basic concepts abouthandover
Understand the flow of soft handover
Master basic parameters about softhandover
Master soft handover decision algorithms
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Chapter 1 Overview of Handover
Chapter 2 Handover MeasurementChapter 3 Soft Handover
Chapter 4 Hard Handover
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Chapter 1 Overview of Handover
1.1 Purposes of Handover
1.2 Modes and Status of the UE
1.3 Methods and Types ofHandover
1.4 Comparison between SoftHandover and Hard Handover
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Purposes of Handover
Providing the continuous service in mobile system is the basicelement in QoS
Providing continuous communication service is the main purposeof handover.
The load balance: sharing the resourceThe hierarchy divided by speed and service: high efficiency ofusing resource
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Chapter 1 Overview of Handover
1.1 Purposes of Handover
1.2 Modes and Status of the UE
1.3 Methods and Types ofHandover
1.4 Comparison between SoftHandover and Hard Handover
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CELL_DCH CELL_FACH
CELL_PCHURA_PCH
IDLEDEAD R RC c o n n e c t io n
UE Modes and Status
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CELL_DCH CELL_FACH
CELL_PCHURA_PCH
IDLE
DEAD
- Searching a PLMN- Find a cell to camps on
- Monitering the paging channel- Cell reselecting
- Dedicated channel - Common channel,low speed service
- Triggered by theCN
- Reducing activities, DRX, saving power and resource
R RC c o n n e c t io n
These statuses are only appliedin the UTRAN and UE. Theyare transparent to the CN.
UE Modes and Status (Status migration)
SMSVP/Voice/PS
Low speed PS
Cell Update No trafficAfter several CellUpdates
URA Update
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Chapter 1 Overview of Handover
1.1 Purposes of Handover
1.2 Modes and Status of the UE
1.3 Methods and Types of Handover
1.4 Comparison between Soft
Handover and Hard Handover
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Handover Methods
Changing cells in the status of CELL_DCHHandover
Direct retry
Changing residing cells in the statuses of IDLE, CELL_FACH,CELL_PCH, and URA_PCH
Cell reselection (forward handover)
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Handover Types in CELL_DCH
Classify bySystem Change
Classify bySignaling Flow
Classify byFrequency
ChangeDescription
Intra- system
Soft handover
Intra-frequency
Low-rate services (such as AMR
Hard handover
High-rate services (such asPS384K)
Without the Iur interface
Inter-frequency
For the purpose of coverage orload balancing (e.g. handoverbetween carriers with differentload, handover to the carrier thatsupports the HSDPA service.
WCDMA-to-GSM handover)
Inter-system(Inter-RAT)
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Chapter 1 Overview of Handover
1.1 Purposes of Handover
1.2 Modes and Status of the UE
1.3 Methods and Types of Handover
1.4 Comparison between SoftHandover and Hard Handover
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Features Comparison between Soft Handoverand Hard Handover
Item Soft Handover (Softer Handover) Hard HandoverNumber of radio links in
the activate set Several One
Interruption duringhandover No Yes
Frequencies in the cellsbefore and after
handoverIntra-frequency
Intra-frequency
Inter-frequency orInter-RAT
Handover gainMaximum-ratio combining or selectivecombining which can reduce the impact offading and transmission power of the UE.
None
Disadvantage
Occupies more resources.
Problems occur when the power of softhandover cells is unbalanced.
Call drop ratio isrelatively higher
In a word, some resources are wasted to obtain optimal system performance in soft handover.
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Soft Handover – (Connection before Disconnection)
RNCNodeB1 NodeB2
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Softer Handover – (A Special Case of Soft Handover)
RNCNode B
Cell A Cell B
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Hard Handover- (Disconnection before Connection)
RNCNodeB1 NodeB2
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Questions
What are the differences between softhandover, softer handover, and hardhandover?
Why intra-frequency handover is notalways soft handover?
How does handover gain arise? Howmuch are various handover gains?
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Summary
This chapter describes the purposes ofhandover, working modes of the UE andcommon handover types in the WCDMAsystem, compares soft handover and hardhandover and describes respectiveadvantages and disadvantages.
In addition, this chapter describes a briefflow of each type of handover.
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Chapter 1 Overview of Handover
Chapter 2 Handover Measurement
Chapter 3 Soft Handover
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Chapter 2 Handover Measurement
2.1 Basic Concepts aboutHandover
2.2 Three Steps of Handover
2.3 Measurement Control
2.4 Measurement Report
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Basic Concepts about Handover
Active set
monitor set
Detection set
Event report
Event to periodic report
Periodic report
Radio link (RL)
Radio link set (RLS)
Maximum-ratio combining
Selective combining
Soft handover gain
Pilot channel (CPICH)
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Chapter 2 Handover Measurement
2.1 Basic Concepts about Handover
2.2 Three Steps of Handover
2.3 Measurement Control
2.4 Measurement Report
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Three Steps of Handover
Decision
Execution
Measurement
The following figure shows handoverprocedure (measurement quality setto PCPICH Ec/No)
UE measures the CPICH Ec/Noof its serving cell(s) andneighbor cells. And sends themeasurement report to RNC.
Are handover criteria meet?
Perform a handoverand update relativeparameters
Measure
Decision
Execution
Y
N
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Chapter 2 Handover Measurement
2.1 Basic Concepts about Handover
2.2 Three Steps of Handover
2.3 Measurement Control
2.4 Measurement Report
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Measurement Control
Measurement control is used to notify the UE of the object to bemeasured, neighbor cell list, report method, and event parameters.
When measurement conditions are changed, the RNC notifies theUE of new conditions.
Measurement Control, normal case
UE UTRAN
Measurement Control
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Measurement ControlMeasurement 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
− Criteria of measurement report
− Measurement report mode
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Measurement Objects
Measurement objects
Intra-frequency measurement
− CPICH RSCP, CPICH Ec/Io, or Pathloss (normally Ec/Io)
Inter-frequency measurement
− CPICH RSCP, CPICH Ec/Io
Inter-RAT measurement
− GSM Carrier RSSI, BSIC Identification, and BSIC Reconfirmation
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Measurement Model
Measurement time of layer 1 is 200 ms. The vendorcan decide the filtering method.
Filtering parameters of layer 3 can be configured.Measurement results are reported when the reportingcriteria are met.
Layer 1filtering
Layer 3filtering Evaluation
of reportingcriteria
A DB C
C'
parameters parameters
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Measurement Model - Layer 3 Filtering
Filtering of measurement results by the UE is calculated according to
the following formula:
Fn (1- α)F n-1 +αM n
Fn: new measurement result after filtering
Fn-1 : the last measurement result after filtering
Mn: the latest measurement result from the physical layer of the UE
α 0.5 k/2 , K is the parameter in filter coefficient in the measurementcontrol message (default=3 ). If it is set to 0 , layer 3 filtering isunavailable.
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Chapter 2 Handover Measurement
2.1 Basic Concepts aboutHandover
2.2 Three Steps in Handover
2.3 Measurement Control
2.4 Measurement Report
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Measurement Report
When the measurement reporting criteria are met, the UEreports the results to the RNC as an event.
Measurement Report
UE UTRAN
Measurement Report
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Measurement Report Methods
Event reportThe 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, theUE switches to periodic report.
The interval between report and total report times are controlledthrough parameters.
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Intra-frequency Measurement Events
Intra-frequency measurement events are identified
through 1X. They include:1A: A primary pilot channel enters the reporting range. Means a monitoredcell is good enough that the UE can add it into active set .
1B A primary pilot channel leaves the reporting range. Means a cell in the
active set is not good enough according to the best cell .1C: Substitution event. A primary pilot channel in an monitor set is better thanthat 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 lowerthan the absolute threshold.
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Inter-frequency Measurement Events
Inter-frequency measurement events are identified by 2X.
2B event: The quality of the serving cell is lower than an absolutethreshold value and the quality of another inter-frequency neighbor cell ishigher than another threshold value.
2C event: The quality of the inter-frequency neighbor cell is higher thanan absolute threshold value.
2D event: The quality of the serving cell is lower than a certain absolutethreshold value. It is used to start the compress mode.
2F event: The quality of the serving cell is higher than a certain absolutethreshold value. It is used to stop the compress mode.
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Inter-RAT Measurement Events
Inter-RAT Measurement events are identified through 3X.
3A event: The quality of the currently used frequency is lower than anabsolute threshold value, but the quality in a GSM cell is higher thananother absolute threshold value.
3C event: The quality in a GSM cell is higher than an absolute threshold
value.2D event: The quality of the currently used frequency is lower than acertain absolute threshold value. It is used to start the compressed mode.
2F event: The quality of the currently used frequency is higher than acertain absolute threshold value. It is used to stop the compressed mode.
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Some Event Report Control Parameters
Relative threshold (reporting range)
Unidirectional difference between two measurement results, for example,relative threshold value between 1A event and 1B event
Absolute threshold (threshold)
Measurement results reach an absolute value, for example, absolute
threshold values of 1E event and 1F eventHysteresis
Bi-directional difference between two measurement results
Time to trigger
Time that lasts until the previous threshold value is met
Weight factor (W)
Control calculation of comparative benchmark values
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Event Report Decision
Deciding according to the judgment inequation
Example: decision inequation of 1A event
If W = 0, for RSCP and Ec/Io,
10LogM(New)≥10LogM(Best) - (R1a-H1a/2)
M: measurement results
R: relative threshold values
H: hysteresis
W: weight factor. It is zero generally .
),2/(10)1(1010 11
a Best
N
ii New H R LogM W M Log W LogM
A
2. Other measurement variables (e.g. RSCP, Ec/Io)
),2/(10)1(1010 11
a Best
N
ii New H R LogM W M Log W LogM
A
1. Path loss
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Event Report Decision- Example of 1A Event Measurement Report
Measurement results in the primary cell
1A event occurs
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Event Report Decision (Continued)
Trigger criteria of 1B event:
)2/(10)1(1010 111
bb Best
N
iinew H R LogM W M Log W LogM
A
,2/11 f f New H T M Trigger criteria of 1F event:
,2/1d Best NotBest H M M Trigger criteria of 1D event:
,2/1c InAS New H M M Trigger criteria of 1C event:
E R D i i
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Event Report Decision- Example of 1B Event Measurement Report
1B event is reported
Delete the cell in which the interference code is 23
Event Report
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Event Report
Event Report
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Event Report
E ent Report
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Event Report
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Questions
In which cases does the RNC triggermeasurement control?
Is the start time of intra-frequency,inter-frequency, and Inter-RATmeasurement the same?
When is an event reported?How to report an event?
What events does intra-frequencymeasurement contain?
What events does inter-frequencymeasurement contain?
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Summary
This chapter describes concepts related tohandover, explains measurement control, which
covers measurement objects, event report.
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Chapter 1 Overview of Handover
Chapter 2 Handover Measurement
Chapter 3 Soft Handover
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Chapter 3 Soft Handover
3.1 Flow of Soft Handover
3.2 Common Parameters and IntraFrequency Neighbor Cell
Fl f S ft H d Addi R di Li k
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Flow of Soft Handover - Adding Radio Link
(Reporting 1A event )
( Add new radio link )
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Flow of Soft Handover - Adding Radio Link
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Flow of Soft Handover - Deleting Radio Link
(Reporting 1B event )
(Del old radio link )
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Chapter 3 Flow of Soft Handover
3.1 Flow of Soft Handover
3.2 Common Parameters and IntraFrequency Neighbor Cell
Setting Common Parameters of Soft Handover
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Setting Common Parameters of Soft HandoverRelative threshold
1A and 1B event have their individual values.
The value of 1B should be larger than that of 1A, to avoid ping-ponghandover. ( 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 thoseof 1C, 1D, 1F are 4 dB.
This value affects the soft handover area of the UE.
MML command for adding cell-class intra-frequency handoverparameters: ADD CELL INTRA FREQ HOMML Command for setting RNC-class intra-frequency handoverparameters: SET INTRA FREQ HO
C P f S f H d (C i d)
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Common Parameters of Soft Handover (Continued)
Time to trigger
Configured it for each event separately.
The value of 1B should be larger than that of 1A, to avoid ping-ponghandover. ( 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.
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Intra Frequency Neighbor Cell
The Handover can only happened among the neighbor cells
MML: Add Intra Freq NCell:
Configure neighbor cells with the same frequency
The maxim number of IntraFreqNCell for each cell is 31
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Questions
Draw the signaling flow chart of softhandover.
What is the impact of parameters in softhandover on system performance?
What parameters can affectperformance of soft handover besidesthe parameters described in thischapter?
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Summary
This chapter describes the signalingflow and common parameters of softhandover in WCDMA.
O h H d
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Other Handovers
The WCDMA system supports many handover technologies.
Besides soft (softer) handover described previously, there areintra-frequency hard handover, inter-frequency hard handover,and Inter-RAT handover.
If the system supports HSDPA, the WCDMA system alsosupports handover between carrier frequency of HSDPA andordinary carrier frequency to balance load and to utilize networkresources efficiently.
Refer to supplementary contents for description of intra-frequency hard handover, inter-frequency hard handover, andInter-RAT handover. This part is provided for self-study.
C S
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CourseSummary
Course Summary
This course describers the principles,
algorithm, related parameters andgeneral flow of soft handover in theWCDMA system.
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Thank youwww.huawei.com
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Chapter 4 Hard Handover
4.1 Intra-frequency Hard Handover
4.2 Inter-frequency Hard Handover
4.3 Inter-RAT Hard Handover
Intra-frequency Hard Handover
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Intra-frequency Hard Handover- Measurement and Event
Measurement
It is similar to that in soft handover
Related events
1D event
Intra frequency Hard Handover
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Intra-frequency Hard Handover- Handover Flow
TARGET NODEB SOARCE NODEB
3. ALCAP ESTABLISHMENT
9. ALCAP RELEASE
Intra-frequency Hard Handover
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q y- Common Parameters
BeBitrateThd: BE service handover rate decision threshold.
If the maximum rate of transmission channel of the BE service is not morethan this threshold, the system performs soft handover for the users usingthis service.
If the maximum rate of transmission channel of the BE service is greaterthan 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 trackchanges of the signal to perform handover, but also avoid ping-ponghandover.
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Chapter 4 Hard Handover
4.1 Intra-frequency Hard Handover
4.2 Inter-frequency Hard Handover
4.3 Inter-RAT Hard Handover
Inter frequency Hard Handover Overview
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Inter-frequency Hard Handover Overview
Features
The frequency is different after handover.
For the UE with only one transceiver, the compressed mode should bestarted to assist measurement.
Advantages
The handover success rate is higher than that of intra-frequency hardhandover.
The load on carrier frequencies are balanced.
Inter-frequency Hard Handover Overview
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Inter frequency Hard Handover Overview(Continued)
DisadvantagesThe compressed mode causes extra radio resource
Application scenarios
Uncontinuous coverage of carrier
Load caused handover
Hierarchical cell
Inter-frequency Hard Handover
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Inter frequency Hard Handover- Measurement and Event
Measurement in inter-frequency hard handoverMeasurement variables:
− CPICH RSCP, CPICH Ec/N0
Different measurement types are used for different handover purposes:
− Edge of carrier coverage area: CPICH RSCP
− Center of carrier coverage area: CPICH Ec/No
Inter-frequency Hard Handover
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- Measurement and Event (Continued)
Measurement Report Methods
Event report− 2D event: The quality of current frequency is lower than a certain absolute
threshold value. It is used to start the compressed mode.
− 2F event: The quality of current frequency is higher than a certain absolutethreshold value. It is used to stop the compressed mode.
− 2B event: The quality of current frequency is lower than the absolutethreshold value, and the quality of the neighbor frequency is higher thananother 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
Inter-frequency Hard Handover
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- Starting and Stopping of the Compression ModeStarting conditions of measurement
2D event: If the quality of the currently frequency is lower than a certainabsolute threshold value, the compressed mode is started.
Use the velocity estimation algorithm to decide starting of inter-frequencyhandover measurement.
Stopping conditions of measurement2F 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-frequencyhandover measurement is disabled according to the hierarchical cell algorithm
In hard handover, if the coverage reason is triggered, handover is stoppedsimultaneously.
Inter frequency Hard Handover Flow
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Inter-frequency Hard Handover Flow
Signaling flow
9. ALCAP RELEASE
3. ALCAP ESTABLISHMENT
SOARCE NODEBTARGET NODEB
Inter-frequency Hard Handover
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- Common ParametersInter-frequency coverage handover parameters:
Methods for report inter-frequency measurement: periodic or eventInter-frequency measurement variables: CPICH Ec/No or CPICH RSCP.
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/No, CPICH RSCP, and configure2D, 2F event for CS and PS.
Inter-frequency coverage handover threshold value: quality threshold valueof the target cell
Quality threshold value of used frequency in inter-frequency hard handoverLowest access threshold value in inter-frequency handover
Inter-frequency Hard Handover - Questions
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q yWhy the compressed mode threshold for the CS and PS areconfigured different?
The Eb/No required by these two services are different, so theRSCPs 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 decidestarting the compressed mode?
If the parameters of any service meet the threshold, thecompressed mode is started.
Is the compressed mode started immediately after the UE sendsthe 2D parameter?
The compressed mode is started after the RNC reconfigure the RB.
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Chapter 4 Hard Handover
4.1 Intra-frequency Hard Handover
4.2 Inter-frequency Hard Handover
4.3 Inter-RAT Hard Handover
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Inter-RAT Hard Handover
Overview
Measurement and Event
Handover Decision Algorithm
Handover Flow
Common Parameters
Inter-RAT Hard Handover - Overview
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CategoryWCDMA FDD < >GSMWCDMA FDD < >WCDMA TDDWCDMA FDD < >CDMA2000
FeaturesThe radio access technology (RAT) adopted in the system after handoveris different.
Need compressed 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)
DisadvantagesThe flow is complicated, and the requirement for compatibility ofequipment is high.The UE is complicated.
Inter-RAT Hard Handover
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- Measurement and Event
Measurement in Inter-RAT hard handover (GSM measurement)Measurement types:
− GSM Carrier RSSI
− BSIC Identification
− BSIC Reconfirmation
Measurement processing: layer-1 filtering, layer-3 filtering
Inter-RAT Hard Handover
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- Measurement and Event (Continued)
Measurement Report− Event report
▪ 2D event: starting GSM measurement
▪ 2F event: stopping GSM measurement
▪ 3A event: The quality of WCDMA is lower than an absolute threshold butquality of a GSM neighbor cell is higher than another absolute threshold.
▪ 3C event: The quality of a GSM neighbor cell is higher than an absolutethreshold.
Inter-RAT Hard Handover - Decision Algorithm
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Inter RAT Hard Handover Decision Algorithm
Decision of Inter-RAT handover
Inter-RAT handover based on coverage
− Event
▪ 3A event: The quality of the currently used frequency is lowerthan 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 RSSImeasurement value and the BSIC of the target cell in GSM andevaluate the cell of which the GSM RSSI exceeds the absolutethreshold value. If both conditions are met, consider the cell ofwhich the BSIC is confirmed.
Inter-RAT Hard Handover
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- Decision Algorithm (Continued)
Inter-RAT handover based on non-coverage
− Event
▪ The 3C event means that the quality of the GSM cell is
higher than an absolute threshold value .
Inter-RAT Handover Flow
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1. RelocationRequired 2. Prepare
Handover 3. HandoverRequest
4. HandoverRequest Ack
12. Iu ReleaseCommand
13. Iu ReleaseComplete 14. Send End
Signal Response
5. PrepareHandover6. Relocation
Command7. DCCH : Handover
from UTRAN Command
8. HandoverDetect
9. Handover Complete
10. HandoverComplete11. Send
End
UE Node B SRNC CN MSC BSC
Inter-RAT Handover - Common Parameters
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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 CPICHEc/No, CPICH RSCP for the CS service and PS service respectively.
Measurement variables for the 2D event and 2F event in Inter-RAThandover: Select CPICH Ec/No or PICH RSCP.
BSIC selection confirmation switch
Inter-RAT coverage handover threshold: GSM RSSI threshold in Inter-RATcoverage handover. Configure it for the CS service and PS servicerespectively.
Quality threshold of used frequency in Inter-RAT handover
Configure time to trigger and hysteresis for each event respectivelyPenalty duration
f
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Summary - Categories of Handover
According to the signaling characters
− Soft handover (softer handover)
− Hard handover
According to the properties of source cell and target cell:
− Intra-frequency handover
− Inter-frequency handover
− Inter- RAT handover (UMTS ↔ GSM/GPRS)
According to the purpose of handover:
− Based on Coverage
− Based on Noncoverage