wcdma handover principle
TRANSCRIPT
www.huawei.com
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
WCDMA Handover Principle
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page2
Foreword
Why mobile systems need handover?
It is decided by the characters of mobile system:
The mobility of UE
The mobile system is composed by cells which the
coverage ability is limited.
Providing the continuous service in mobile system
is the basic element in QoS.
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page3
Objectives
Upon completion of this course, you will be able to:
The basic definitions of Handover
The algorithms of handover decision
The handover flow
The parameters of handover
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page4
Contents
1. Introduction of Handover
2. Measurement of Handover
3. The Basic Handovers
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page5
The Purpose of Handover
Providing the continuous service in mobile system is the
basic element in QoS.
The load balance: sharing the resource
The hierarchy divided by speed and service: high
efficiency of using resource
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page6
The Basic Concepts of Handover Active Set Monitored Set Detected set Event reporting
Event reporting to Periodic reporting Periodic reporting Radio Link (RL) Radio Link Set (RLS) Combination way:
maximum ratio combination selection combination
The soft handover gain CPICH Soft handover, softer handover, hard handover
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page7
The 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-system handover (UMTS <-> GSM)
According to the purpose of handover Based on Coverage Based on Load (Optional) Based on mobility of UE (Optional) Based on Service (Optional)
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page8
The Characters of Different Handovers
Item Soft Handover Hard Handover
The numbers of RL in
active set after
handover
Several One
Interruption during
handover
No Yes
The frequencies of
cells
Only happened in
Intra-frequency
cells
Can be happened in Intra-
frequency cells or Inter-
frequency cells
Comparison between soft handover and hard
handover:
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page9
The Characters of Different Handovers Comparison between soft handover and softer
handover
During softer handover, the uplink signaling are combined
in NodeB by maximum ratio combination, but during soft
handover they are combined in RNC by selection
combination
Compare to later one, the maximum ration combination can
get more gain. So the performance of maximum ration
combination is better
Since softer handover is completed in NodeB, it do not
consume transport resource of Iub
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page10
RNC
NodeB 2NodeB 1
Soft Handover
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page11
RNC (WFMR)
NodeB
Softer Handover
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page12
Hard Handover
RNC
NodeB 2NodeB 1
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page13
Three Steps of Handover
Decision
Execute
Measurement
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page14
Questions
The differences among Soft handover, softer
handover and hard handover
Typical application scenarios
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page15
Summary
This chapter focus on the purpose of handovers and
the categories of handover in WCDMA.
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page16
Contents
1. Introduction of Handover
2. Measurement of Handover
3. The Basic Handovers
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page17
Contents
2. Measurement of Handover
2.1 Measurement control and measurement report
2.2 The basic definitions of measurement
2.3 Measurement event
2.4 Compressed mode
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page18
Measurement Control, normal case
UE UTRAN
MEASUREMENT CONTROL
Measurement Control
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page19
Measurement Control
Measurement Control, normal case
UE UTRAN
MEASUREMENT CONTROL
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page20
Measurement Control, normal case
UE UTRAN
MEASUREMENT REPORT
Measurement Report
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page21
Contents
2. Measurement of Handover
2.1 Measurement control and measurement report
2.2 The basic definitions of measurement
2.3 Measurement event
2.4 Compressed mode
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page22
The Basic Concepts of Measurement The measurement values of Handover
Soft handover and Intra-frequency hard handover : CPICH RSCP, CPICH Ec/N0, Path loss
Inter-frequency : CPICH RSCP, CPICH Ec/N0 Inter-system : GSM Carrier RSSI, BSIC Identification, BSIC
Reconfirmation
The reporting methods of measurement Periodic reporting Event reporting
The events of reporting Intra-frequency events : 1A,1B,1C,1D,1F Inter-frequency events : 2D,2F,2B,2C Inter-system events : 3A,3C
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page23
Measurement Model
Layer 1filtering
Layer 3filtering
Evaluationof reporting
criteria
A DB C
C'
parameters parameters
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page24
Reporting Criterion
),2/(10)1(1010 11
aBest
N
iiNew HRLogMWMLogWLogM
A
),2/(10)1(1010 11
aBest
N
iiNew HRLogMWMLogWLogM
A
Reporting Criterion
Decision formula: for example, 1A event :
Path Loss
Other measurement:
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page25
Key Parameters
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page26
Contents
2. Measurement of Handover
2.1 Measurement control and measurement report
2.2 The basic definitions of measurement
2.3 Measurement event
2.4 Compressed mode
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page27
Intra-frequency Measurement Events Intra-frequency measurement report events are identified
with 1X
1A : A primary pilot channel enters the reporting range. When
the active set of UE is full, UE stops reporting 1A event;
1B : A primary pilot channel leaves the reporting range;
1C : The primary pilot channel
l in a non active set is better than the primary pilot channel in
an active set;
1D : The best cell changes;
1E : The measurement value of a primary pilot channel
exceeds the absolute threshold
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page28
Inter-frequency Measurement Events Inter-frequency measurement events are identified
with 2X 2B : The estimated quality value of the used frequency
is lower than a certain threshold, and that of the non-used frequency is higher than a certain threshold;
2C : The estimated quality value of the non-used frequency is higher than a certain threshold;
2D : The estimated quality value of the used frequency is lower than a certain threshold
2F : The estimated quality value of the used frequency is higher than a certain threshold
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page29
Inter-system Measurement Events Inter-system measurement events are identified with
3X
3A : The estimated quality value of the used UTRAN
frequency is lower than a certain threshold, and that of
the other system is higher than a certain threshold
3C : The estimated quality value of the other system is
higher than a certain threshold
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page30
Contents
2. Measurement of Handover
2.1 Measurement control and measurement report
2.2 The basic definitions of measurement
2.3 Measurement event
2.4 Compressed mode
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page31
The Purpose of Compressed mode Purpose
Measure the inter-frequency cell or inter-system cell
under FDD mode
Categories
Downlink compressed
Uplink compressed
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page32
Compressed Mode Sketch Map
One frame(10 ms) Transmission gap available for
inter-frequency measurements
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page33
The realization Methods of Compressed mode Realization Methods
SF/2
Rate matching/puncturing
Higher layer scheduling
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page34
Questions
How many events are there in intra-frequency
measurement? What are they?
How many events are there in UE internal
measurement?
How many events are there in inter-frequency
measurement? What are they?
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page35
Summary
This chapter covers intra-frequency measurement,
inter-frequency measurement, inter-system
measurement and UE internal measurement from
their definitions and application scenarios
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page36
Contents
1. Introduction of Handover
2. Measurement of Handover
3. The Basic Handovers
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page37
Contents
3. The Basic Handovers
3.1 Soft Handover
3.2 Intra-frequency Hard Handover
3.3 Inter-frequency Hard Handover
3.4 Inter-system Hard Handover
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page38
Brief Introduction of Soft Handover Characters of Soft Handover
During handover, UE has several RLs with different
cells - active set
The handover among different cells which are in same
RLS can be softer handover
Soft handover:
– Selection combination in uplink
– Maximum combination in downlink
Softer handover
– Maximum combination in uplink and downlink
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page39
Brief Introduction of Soft Handover Advantages
Soft handover gain
Load balance
Decrease the possibility of call drop caused by ping-pong
handover
Disadvantages
More resource needed in downlink, especially for the code
resource of BE service
Usually, the gain of downlink power is negative
When the downlink power from different cells is not
balanced, it will bring side-effect
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page40
Measurement of Soft Handover
The measurement of soft handover/softer handover Measurement value : CPICH RSCP 、 CPICH
Ec/No 、 Pathloss
Process of Measurement : Layer 1 filter, Layer 3 filter
Reporting way
Periodic reporting
Event reporting
– Event type : 1A 、 1B 、 1C 、 1D 、 1F
– UE measures the time difference between CFN and SFN
– Reporting rules: trigger condition, Relative threshold, Absolute
threshold, Hysteresis, Time to trigger
Event reporting to periodic reporting
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page41
The Decision Algorithm of Soft Handover Soft/softer handover decision
1A : Radio Link Addition
1B : Radio Link Removal
1C : Combined Radio Link Addition and Removal
1D : change best cell
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page42
The Execution of Soft Handover Soft handover execution
The update principal of measurement control Configure the neighbor cells and the parameters
according to best cell
RLC mode AM mode is used for measurement control UM mode is used for measurement report
The compensation and restriction of soft handover From event reporting to periodic reporting
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page43
Soft Handover Flow (add RL)
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page44
Soft Handover Flow (del RL)
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page45
Key Parameters
Relative threshold
Time to trigger
Layer 3 filter coefficient
Absolute threshold of soft handover
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page46
Contents
3. The Basic Handovers
3.1 Soft Handover
3.2 Intra-frequency Hard Handover
3.3 Inter-frequency Hard Handover
3.4 Inter-system Hard Handover
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page47
Brief Introduction of Intra-frequency Hard Handover Characters
UE only has one RL with one cell in the process of handover Disconnect UE with the original cell, then hand it over to target
cell The working frequency of source cell and target cell are same
Advantages Enhance the using efficiency of the OVSF code and hardware
resource Disadvantages
High call drop possibility because of the intra-frequency interference
Application scenarios Without Iur interface between two RNCs or the Iur interface jam
(only happened in inter-RNC handover) The different strategies can be used for different conditions, such
as code resource condition, the QoS condition and so no
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page48
The Measurement, Decision and Execution of Intra-frequency Hard Handover Measurement
Similar to soft handover Decision
1D event Execution
UE reports CFN-SFN information Synchronization hard handover Use the original DOFF value Continuous CFN
UE does not report CFN-SFN information The hard handover based on timing Re-configure DOFF Calculate CFN according to DOFF
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page49
The Measurement, Decision and Execution of Intra-frequency Hard Handover Measurement
Similar to soft handover Decision
1D event Execution
UE reports CFN-SFN information Synchronization hard handover Use the original DOFF value Continuous CFN
UE does not report CFN-SFN information The hard handover based on timing Re-configure DOFF Calculate CFN according to DOFF
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page50
Intra-frequency Hard Handover Flow
UE
1.RADIO LINK SETUP REQUEST
Target NODEB
Source NODEB SRNC
2. RADIO LINK SETUP RESPONSE
3.ALCAP establish
4. PHYSICAL CHANNEL RECONFIGURATION
5. RADIO LINK FAILURE INDICATION
6. PHYSICAL CHANNEL RECONFIGURATION COMPLETE
7. RADIO LINK DELETION REQUEST
8. RADIO LINK DELETION RESPONSE
9.ALCAP release
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page51
Key Parameters
Handover decision threshold based on BE speed
UE should do soft handover when the speed of BE
service is less than the threshold.
UE should do intra-frequency hard handover when the
speed of BE service is greater than the threshold.
The parameters about 1D event
Time to trigger, hysteresis
The parameters should be set accord with the Qos
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page52
Contents
3. The Basic Handovers
3.1 Soft Handover
3.2 Intra-frequency Hard Handover
3.3 Inter-frequency Hard Handover
3.4 Inter-system Hard Handover
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page53
The Brief Introduction of Inter-frequency Hard Handover
Characters The working frequency is different after handover The compressed mode needed if the UE only has one
receiver Usually, the timing re-initiation hard handover is used
for hard handover
Application scenarios Disconnected coverage Handover based on load Hierarchy cells
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page54
Measurement Values and Events The Inter-frequency hard handover measurement
values
Measurement values
CPICH RSCP 、 CPICH Ec/N0
Different handover purpose for different measurement
type
In the edge of carrier coverage: CPICH RSCP
In the center of carrier coverage: CPICH Ec/No
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page55
Compressed Mode Initiation
Conditions for measurement initiated
2D event : The estimated quality value of the used
frequency is lower than a certain threshold
Conditions for Measurement stopping
2F event : The estimated quality value of the used
frequency is higher than a certain threshold
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page56
Cells Hierarchy Algorithm Based on UE Moving Speed
When UE is in one of the hierarchy cells, the moving
speed estimation algorithm is initiated
Handover events in a while decides whether the speed
of UE satisfies the current cell hierarchy condition
UE’s moving speed decided the result
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page57
Decision Algorithm
The inter-frequency hard handover decision
The coverage triggers the handover
2B event:– the quality in the used frequency is lower than absolute
threshold, but the quality in another non-used frequency is
higher than another absolute threshold.
The load triggers handover
2C event:– the quality in another frequency is higher than an absolute
threshold
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page58
Inter-frequency Hard Handover Signaling Flow
UE
1.RADIO LINK SETUP REQUEST
Target NODEB
Source NODEB SRNC
2. RADIO LINK SETUP RESPONSE
3.ALCAP established
4. PHYSICAL CHANNEL RECONFIGURATION
5. RADIO LINK FAILURE INDICATION
6. PHYSICAL CHANNEL RECONFIGURATION COMPLETE
7. RADIO LINK DELETION REQUEST
8. RADIO LINK DELETION RESPONSE
9.ALCAP released
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page59
Key Parameters (I) Inter-frequency coverage handover parameters
Inter-frequency measurement reporting: periodic reporting or event reporting
Inter-frequency measurement values: CPICH Ec/No or CPICH RSCP Inter-frequency measurement layer 3 filter coefficient, delay
trigger time and hysteresis Inter-frequency initiated and stopped threshold: Considering the
different demands of CPICH Ec/No and CPICH RSCP for PS domain and CS domain, the different 2D and 2F parameters are configured.
Inter-frequency handover based on coverage: the quality threshold of target cell
Using frequency quality threshold in inter-frequency hard handover
The minimum access threshold for inter-frequency handover
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page60
Key Parameters (II)
Inter-frequency handover parameters caused by
non-coverage ability
Inter-frequency measurement layer 3 filter coefficient,
delay trigger time and hysteresis
Inter-frequency handover based on non-coverage
ability
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page61
Contents
3. The Basic Handovers
3.1 Soft Handover
3.2 Intra-frequency Hard Handover
3.3 Inter-frequency Hard Handover
3.4 Inter-system Hard Handover
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page62
The Brief Introduction of Inter-system Hard Handover
Application scenarios WCDMA FDD < - >GSM
Characters Different radio access technology is used after handover Usually, compressed mode should be used to help the
measurement Advantages
For coverage, it can solve the problems from one system to another system
For capacity, it can enhance the utilizing efficiency of old equipments(2G->3G)
Disadvantages The flow is complicated, and it demands higher
compatibility for equipments Demands more complicated UE
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page63
Compressed Mode Initiated The inter-system measurement (GSM measurement)
Measurement type:
GSM Carrier RSSI
BSIC Identification
BSIC Reconfirmation
The process of measurement: layer 1 filter, layer 3
filter
Measurement reporting
Event reporting
– 2D Event: initiate GSM measurement
– 2F Event: stop GSM measurement
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page64
Decision Algorithm Inter-system handover caused by coverage
Event reporting:
3A event : The estimated quality value of the used UTRAN
frequency is lower than a certain threshold, and that of the
other system is higher than a certain threshold
Periodic reporting:
Evaluation : According to the periodic reported GSM RSSI
measurement value and the BSIC confirming state of target
cell of GSM system, and meanwhile the UE evaluates the
GSM RSSI of target cell is greater than the absolute
threshold, then consider the cell confirmed by BSIC
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page65
Decision Algorithm Inter-system handover caused by non-coverage
Event reporting
3C event: The estimated quality value of the other
system is higher than a absolute threshold
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page66
1. Relocation Required 2. Prepare
Handover 3. Handover
Request
4. Handover Request Ack
12. Iu Release Command
13. Iu Release Complete 14. Send End
Signal Response
5. Prepare Handover Response
6. Relocation Command
7. DCCH : Handover from UTRAN Command
8. Handover
Detect
9. Handover Complete
10. Handover Complete
11. Send End
Signal Request
UE Node B SRNC CN MSC BSC
Inter-system Handover Flow
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page67
Key Parameters (I) Inter-system handover caused by coverage parameters
Inter-system measurement initiated and stopped threshold: Considering the different demands of CPICH Ec/No and CPICH RSCP for PS domain and CS domain, the different 2D and 2F parameters are configured
Inter-system measurement values (2D, 2F) CPICH Ec/No CPICH RSCP
BSIC confirmed (Optional) Inter-system handover caused by coverage parameters
configure the GSM RSSI threshold of CS domain and PS domain separately
Using inter-system frequency quality handover threshold Configure the delay trigger time, hysteresis for each event
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page68
Key Parameters (II)
Inter-system handover caused by non-coverage
parameters
The period of inter-system measurement report
The decision threshold for inter-system handover:
configure the CS, PS, signaling separately
Time delay trigger : configure BSIC with
acknowledged and unacknowledged mode
Inter-frequency measurement layer 3 filter
coefficient and hysteresis
Penalty time
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page69
Questions
What are the differences between soft handover and
softer handover?
What is compressed mode?
Draw out the hard handover signaling flow.
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page70
Summary This chapter focus on the basic handovers in WCDMA:
soft handover, softer handover, intra-frequency hard
handover, inter-frequency hard handover and inter-
system hard handover. It also introduced the
application scenarios for these different handovers
Meanwhile, compressed mode is introduced in this
chapter
Thank youwww.huawei.com