WCDMA RNO Handover Principal_20051214

Course code Course name*
The basic definitions of Handover
The algorithms of handover decision
The handover flow
Direct Retry Algorithm
It is decided by the characters of mobile system:
The mobility of UE
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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 (Inter-Freq.) because 3G provide multi services with different speeds so HO from one freq to other is more efficient.

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 Service (Optional)

Comparison between soft handover and hard handover:
Item
Several max for the UE is 3.
One
Can be happened in Intra-frequency cells or Inter-frequency cells
WCDMA Services:
Conversation Service.
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The Characters of Different Handovers
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.
Comparison between soft handover and softer handover:
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The measurement report
Execution
Measurement control refresh
The differences among Soft handover, softer handover and hard handover
Typical application scenarios
Summary
This chapter focus on the purpose of handovers and the categories of handover in WCDMA.

measurement report
Section 3 Intra-frequency measurement event
Section 4 Inter-frequency and
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Measurement Control
6GRx-Tx Observed time difference To
6FRx-Tx Observed time difference To

UE
UTRAN
Measurement report

UE
UTRAN
measurement report
Section 3 Intra-frequency measurement event
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Intra-frequency and inter-frequency:CPICH-RSCP,CPICH-Ec/N0,Path loss
Inter-systemGSM Carrier RSSI BSIC Identification BSIC Reconfirmation (Hard HO)
Inter-Mode: between FDD,TDD.
Periodic reporting
Event reporting
Others6G,6F
RSCP: Received Signal Code Power. After spreading indicates the signal strength on the Air-Interface.
Ec: Energy of the Chip.
No: Noise
UE Rx-Tx observed time difference, 6G,6F

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1.Path Loss
2.Other measurement
Mnew: Measurement
Key Parameters
For Adding a Cell to the Active Set , 1A event we choose the upper Hystersis.
For Removing a Cell to the Active Set , 1B event we choose the Lower Hystersis.
Delta T: time to trigger or to report the event.
1C is done to replace because we have pilot pollution.
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measurement report
Section 3 Intra-frequency measurement events
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All intra-frequency measurement report events are identified with 1X :
1AA primary pilot channel enters the reporting range. When the active set of UE is full, UE stops reporting 1A event;
1BA primary pilot channel leaves the reporting range;
1CThe primary pilot channel in a non active set is better than the primary pilot channel in an active set;
1DThe best cell changes;
1EThe measurement value of a primary pilot channel exceeds the absolute threshold
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measurement report
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2A: The best frequency changes;
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;
2DThe estimated quality value of the used frequency is lower than a certain threshold
2E:The estimated quality value of the non-used frequency is lower than a certain threshold
2F:The estimated quality value of the used frequency is higher than a certain threshold
Used Frequency: The serving freq.
Non-Used Frequency: The freq are going to be used.
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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;
3B: The estimated quality value of the other system is lower than a certain threshold ;
3C: The estimated quality value of the other system is higher than a certain threshold ;
3D: The best cell in the other system changes
UTRAN and Other System.
measurement report
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UE Internal measurement events are identified with 6X
6G: The time difference between downlink receiving and uplink transmission of the UE is shorter than an absolute threshold;
6F: The time difference between downlink receiving and uplink transmission of the UE is bigger than an absolute threshold;
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Questions
How many events are there in intra-frequency measurement? What are they?
How many events are there in UE internal measurement?
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Summary
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Section 1 Soft Handover
Section 5 HSDPA Handover
Section 6 Compressed Mode
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:

Advantages
Multi-Cell gain: Multiple irrelated soft handover branches low the required margin for fading
Macro Diversity Combining gain: Gain for the link demodulation of the soft handover:
Load balance: Different cells receive the signals from UE in uplink, which can decrease the transmission power of UE. And UE receive signal from different cells, which also can decrease the transmission power of base station.
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.

Measurement valueCPICH RSCPCPICH Ec/NoPathloss
Process of MeasurementLayer 1 filter, Layer 2 filter
Reporting way
Periodic reporting
Event reporting
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
UE Rx-Tx observed time difference, 6G,6F

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Soft/softer handover measurement events
Intra-frequency events reporting:
1AA primary pilot channel enters the reporting range. When the active set of UE is full, UE stops reporting 1A event;
1BA primary pilot channel leaves the reporting range;
1CThe primary pilot channel in a non active set is better than the primary pilot channel in an active set;
1DThe best cell changes;
1EThe measurement value of a primary pilot channel exceeds the absolute threshold
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Soft/softer handover decision
1Creplace cell
Soft handover execution
The update principal of measurement control
Configure the neighbor cells and the parameters according to best cell
RLC mode
From event reporting to periodic reporting
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The execution of soft handover (add RL)
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The execution of soft handover (del RL)
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Set 1A, 1B value separately
1A < 1Bwhich makes deleting RL is more difficult, and it can avoid ping-pong handover
Usually 1A: 3dB; 1B: 6dB (Reporting Range)
Time to trigger
Each event can be set separately
Usually, 1B>1Awhich makes deleting RL is more difficult, and it can avoid ping-pong handover
Usually, 1A: 320ms, 1B: 640ms
Layer 3 filter coefficient
Sensitive to the delay of event trigger and ping-pong handover
Usually3
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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
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.

Measurement
Continuous CFN
Re-configure DOFF
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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
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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
Advantages
Compare to intra-frequency hard handover, the success possibility is higher
The load balance among cells with different frequencies
Can realize the reasonable configuration for hierarchy cells
Disadvantages
Compressed mode results in extra radio resource occupied
The timing re-initiation hard handover increase the time of handover and the risk of call drop
Disconnected coverage
The Inter-frequency hard handover measurement values
Measurement values:
In the edge of carrier coverage: CPICH RSCP
In the center of carrier coverage: CPICH Ec/No
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Measurement reporting
Periodic reporting
Event reporting
2A: The best frequency changes;
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Conditions for measurement initiated
2D event can be used to enable the compressed mode to perform inter-frequency measurement.
Enable inter-frequency measurement by moving speed estimation algorithm
Conditions for Measurement stopping
2F event
After the best cell is changed, the cell does not contain inter-frequency neighbor cells.
Inter-frequency measurement timer expired
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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 is remained in the current cell if the speed is medium.
If the speed is very high, it will be handed over to higher hierarchy cell. And if not, hand it over to lower hierarchy cell.
UE’s moving speed decided the result.
If the hierarchy is configured by different frequencies, the inter-frequency blind handover or inter-frequency measurement handover can be initiated.
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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
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UE report the timing information
UE with two receivers does not need compressed mode.
Synchronization hard handover
UE with a single receiver has to initiate compressed mode
If the NodeB of target cell is not the same one which the cells in active set belong to
the timing re-initiation hard handover
Re-configure DOFF
Calculate the CFN according to DOFF
If the NodeB of target cell is the same one which the cells in active set belong to
Calculate the target cell timing relationship
Synchronization hard handover
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
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Inter-frequency measurement layer 3 filter coefficient, delay trigger time and hysteresis
Inter-frequency handover based on non-coverage ability
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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
The inter-system measurement (GSM measurement)
Measurement type:
The process of measurement: layer 1 filter, layer 3 filter
Event reporting
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The inter-system hard handover decision
Inter-system handover caused by coverage
Event reporting:
3A eventThe 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:
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The inter-system hard handover decision
Inter-system handover caused by non-coverage
Event reporting
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10. Handover
1. Relocation Required
5. Prepare Handover
3. Handover
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
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
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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
Application Scope
Related to the handover between the HS-DSCH channel of HSDPA
The service cell update of HSDPA
HSDPA<>DCH
Purpose
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Measurement type: CPICH RSCPCPICH Ec/N0Path loss
The process of measurement: layer 1 filter coefficient and layer 3 filter coefficient
Periodic reporting
Event reporting
The event reporting converted to periodic reporting
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Change the service cell for HS-PDSCH in active set
According to 1D event to decide the best cell, and hand it over to the cell.
After handover, initiate the timer to forbid the ping-pong handover
Change the service cell for HS-PDSCH after hard handover
Establish the HSDPA channel in target cell with hard handover
Establish DCH channel if the target cell can not support HSDPA
Change the service cell for HS-PDSCH during soft handover
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Conditions
UE in cell 1 requests to establish an BE/streaming RAB, or
UE of Cell-FACH state has much BE/streaming data volume to transfer (Switch channel type from FACH to HS-DSCH)
Existing cells: support HSDPA, with same coverage area
Advantage: To make full use of HSDPA resource
R5
HSDPA handover protecting timer
Configure the T-HSDPA to avoid the influence for the data service caused by the ping-pong handover. During this period, the service cell for HSDPA can not be changed.
The value scope ( 0… 1024) seconds
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Purpose
Measure the inter-frequency cell or inter-system cell under FDD mode
Cause:
Downlink compressed:
Since one receiver only can work in one frequency, the UE has to stop working if it is going to measure the signal from another frequency cell. To ensure the downlink service unaffected, the remained data should be sent in the limited time.
Uplink compressed
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Realization Methods
Should use the replace scrambling code
Advantage: easy to handle for RNC
Disadvantage: occupied the resource of NodeB, decrease the utilizing efficiency of OVSF, influenced the coverage and increased interference caused by the replace scrambling code.
rate matching/puncturing
Decrease the coding redundancy
Advantage: easy to handle for RNC; the SF 4 can be used; no influence to utilizing efficiency of OVSF
Disadvantage: limited to the property of channel coding; decreased the coding gain
higher layer scheduling
MAC can restrict TFCS to change the downlink data rate.
Advantage: the interference is lower
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What are the differences between soft handover and softer handover?
What is compressed mode?
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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
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RRC direct retry
During the initial signaling establishment, the RRC connection is refused.
RRC redirection
The initial signaling is already established, but the requested cell refused and RRC direct retry is failed.
RAB direct retry
The signaling is established successfully, but the service establishment is failed.
Blind handover
RRC direct retry
RAB direct retry
cell1
cell2
1
2
3
Signaling process:
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DRMaxNumber
The maximum allowed retry times for the direct retry module after the initial failure
CsThreshold.
When the signal quality of a cell is higher than this threshold, this cell will be included in the direct retry candidate set.
MinSignalRequired
The basic access threshold described in Section 2.2.8, namely the minimum requirement of the UE form the receiving CPICH Ec/No density during normal demodulation.
MaxRelatingTime
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RRC Redirection
The signaling connection is failed, and RRC retry is also failed.
Inter-freq cell
1’ UE initial the access process after cell re-selection
1’’ UE initial the access process in GSM cell after inter-system cell reselection
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The trigger condition should be the signaling permitting failure
if congestion happed, the RRC connection signaling is refused.
Advantages and disadvantages:
RRC direct retry can ensure the time delay.
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3 Handover from UTRAN ( Inform UE access to GSM system)
4 Handover Complete (GSM message)
2
CN
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Questions
What is the difference of RRC direct retry and RRC redirection?
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Summary
This chapter focus on RRC direct retry, RRC redirection, the application scenarios of RAB direct retry and blind handover.
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3.ALCAP establish
7. RADIO LINK
3.ALCAP established
7. RADIO LINK

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WCDMA RNO Handover Principal_20051214