gsm-to-umts training series 11_wcdma handover fundamentals_v1.0
DESCRIPTION
CQTTRANSCRIPT
Slide 12009-01-07
1.1
Comments in pages 12, 16, 22, 34, 49, 69, 72, and 94 are added.
Cheng Fangyuan
2009-01-19
1.2
Comments on the GPRS state are added in page 5. Comments on the GSM handover purpose are added in page 9. Comments on the GSM handover types are added in page 10. Comments on the GSM handover procedure are added in page 14.
Kuang Jun
Preface: Why the Handover is Required?
A major characteristic in the mobile communications: Mobility of the UE
As a key component of the mobile communication system, the cell has a limited coverage area.
The primary function of the handover is to provide the continuous service for the moving UEs in the coverage of the network.
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Handover and directed retry
Cell selection and reselection
Camped cell change for the UE in IDLE, CELL_FACH, CELL_PCH, or URA_PCH state
Also referred to as the forward handover
A UE can operate in two basic modes, which are the idle mode and connected mode.
Idle mode: The UE is in standby state. There is no RRC connection or network service. The UTRAN has no own information about the individual idle mode UEs. In idle mode, the UE is identified by non-access layer identities such as IMSI, TMSI, or P-TMSI.
Connected mode: After the RRC connection is complete, the UE transits to the connected mode from the idle mode. In connected mode, the UE has four states, which are Cell_DCH, Cell_FACH, Cell_PCH, and URA_PCH.
Cell_DCH:
The UE is in activated state and communicates through its own dedicated channel. Dedicated channels are available on the uplink and downlink. The UTRAN knows exactly the cell the UE is camped on.
Cell_FACH:
The UE is in activated state but there is no dedicated channel for the UE because the traffic volume is low on the uplink and downlink. The downlink data is transmitted on the FACH and the uplink data on the RACH. The downlink monitors its information on the FACH. The UTRAN knows exactly the cell the UE is camped on. The resources and state of the UE are reserved.
Cell_PCH:
There is no data transmission on the uplink and downlink. The UE listens to the PICH to receive the paging information. In this case, the UE transits to the DRX mode and the battery lifetime can be prolonged.
The UTRAN knows exactly the cell the UE is camped on. In this case, the UTRAN needs to update the cell information after the cell the UE is camped on changes.
URA-PCH:
There is no data transmission on the uplink and downlink. The UE listens to the PICH and transits to the DRX mode. The UTRAN only knows the UTRAN Registration Area (URA) information about the UE. That is, the UTRAN performs the location updating for the UE only when the URA of the UE changes. Thus, the involved resources are reduced and the number of related signaling decreases.
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Preface: UE Mode and State
In a GPRS cell, the UE has two modes, which are stand-alone and ready.
CELL_FACH
CELL_DCH
CELL_PCH
URA_PCH
GPRS Packet Transfer Mode
Camping on a GSM / GPRS cell
1
GSM Connected Mode
Release RR Connection
Scope
Learn about the differences between the GSM handover and the WCDMA handover
Grasp the WCDMA handover decision algorithm
Grasp the WCDMA handover procedure
Grasp the WCDMA handover parameters
Grasp the WCDMA blind handover and directed retry
After this course, you are able to:
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Chapter 2 Handover Measurement
Chapter 3 Basic Handovers
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Handover Purpose
Handover Types
Handover Procedure
WCDMA HO Purpose
Main purpose: to provide the continuous service for the moving UEs in the coverage of the network
Load balancing: resource sharing
GSM HO Purpose
Main purpose: to maintain the continuity of the conversation for the moving mobile stations (MSs)
QoS improvement for the network
Call drop rate reduction
Congestion rate reduction
Load balancing: A feature related to the cell capacity limit, which puts forward the requirements of resource sharing in the network.
The GSM handover purposes also involve load balancing (load handover) and customer experience improvement (quality handover and interference handover).
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WCDMA HO Types
Intra-frequency handover
Inter-frequency handover
Coverage-based handover (primary function)
Load balancing-based handover (optional)
Service sharing-based handover (optional)
Speed estimation-based handover (optional)
Emergency handover
TA handover
Concentric cell handover
In terms of the time that the link configuration takes effect:
Synchronous handover
Asynchronous handover
The GSM handover is classified into the synchronous handover, asynchronous handover, pseudo-synchronization handover, and pre-synchronization handover.
In terms of triggering conditions, the handover can also be classified into the full/half rate handover and the AMR handover.
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Differences between the soft handover and the softer handover:
In the softer handover, the maximum ratio combination is performed on the uplink signals at the NodeB. In the soft handover, the selection combination is performed on the uplink signals at the RNC. As the gain of maximum ratio combination is larger than the gain of selection combination, the softer handover is better than the soft handover.
Because the combination of the softer handover is performed at the NodeB, the transmission resources on the Iub interface are saved.
Comparison
Number of radio links in the active set after handover
Multiple
One
No
Yes
Cells of the same frequency
Cells of the same frequency, different frequencies, or different systems.
Characteristics of the hard handover:
Disconnect the original link, and then set up a new link between the UE and the target cell.
The conversation has the “gap” during the handover.
Non-CDMA systems allow only the hard handover.
Characteristics of the soft handover:
Only the CDMA systems have soft handovers, which occur only between the cells of the same frequency.
Set up a new link between the UE and the target cell, and then disconnect the original link. Thus, the “gap” in the conversation can be avoided.
A soft handover consumes more network resources than a hard handover. In other words, a soft handover achieves the optimum network performance at the price of certain network resources.
In a soft handover, if the target cell and original cell are within a same NodeB, the maximum ratio combination can be achieved on the uplink. In this case, the handover is referred to as a softer handover.
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RNC
Overall procedure of the GSM handover algorithm
Execution
Handover
Measurement
Phase
Decision
Phase
MR
preprocessing
Penalty
processing
HO decision
The GSM handover procedure can also be summarized as measurement, decision, and execution. From this aspect, the difference between GSM and WCDMA is insignificant.
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Measurement
Measurement report
Decision
Resource application and assignment
Execution
Active set
Monitored set
Detected set
Event report
Soft handover gain
Pilot channel (CPICH)
Blind handover
Active set: RLs that keep connecting with the UE
Monitored set: RLs not included in the active set, but are included in the neighbouring cell list and detected by UE.
Detected set: RLs detected by the UE, which are neither in the neighbouring cell list nor in the active set.
Radio Link (RL): Each link between a UE and the NodeB is referred to as a Radio Link (RL).
Radio Link Set (RLS): RLs that belong to a same NodeB. The softer handover can be achieved between the cells in an RLS.
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Typical scenarios of the WCDMA handover
Basic concepts of the WCDMA handover
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Summary
This chapter describes the handover purpose and the common types of the WCDMA handover.
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Chapter 2 Handover Measurement
Chapter 3 Basic Handovers
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Basic Concepts of Measurement
UE-Internal Measurement
Measurement control:
Measurement report, normal case
The RNC informs the UE of measurement objects, neighboring cell list, reporting mode, and event parameters.
When the measurement conditions change, the RNC informs the UE of the new measurement conditions.
The UE sends the measurement report to the RNC when the triggering conditions are satisfied.
Measurement control uses AM RLC.
Measurement report uses UM RLC.
In GSM, the BSS controls the handover and does not receive the MRs from the network. The MS sends the MRs periodically and does not perform the handover decision.
UE
UTRAN
Intra-frequency and inter-frequency: CPICH RSCP, CPICH Ec/N0, Pathloss
Inter-frequency: CPICH RSCP, CPICH Ec/N0
Inter-RAT: GSM Carrier RSSI, BSIC Identification, BSIC Reconfirmation
Reporting mode of the MR
Periodical report (event-to-period report)
Intra-frequency events: 1A, 1B, 1C, 1D, 1F
Inter-frequency events: 2D, 2F, 2B, 2C
Inter-RAT events: 3A, 3C
6G, Rx-Tx Observed time difference less than the threshold To
6F, Rx-Tx Observed time difference larger than the threshold To
Observe the time difference:
SFN-SFN observed time difference, set in the intra-frequency and inter-frequency measurements
CFN-SFN observed time difference, set in the intra-frequency and inter-frequency measurements
The intra-frequency measurement event is identified by 1X and the inter-frequency measurement event is identified by 2X. The inter-RAT measurement event is identified by 3X.
Event 1A: A primary CPICH enters the reporting range, indicating that the quality of a cell reaches the quality of the best cell or active set quality.
Event 1B: A primary CPICH leaves the reporting range, indicating that the quality of a cell is far lower than the quality of the best cell or active set quality.
Event 1C: Replacement event. A non-active primary CPICH becomes better than an active primary CPICH.
Event 1D: Change of the best cell
Event 1F: A primary CPICH becomes worse than an absolute threshold.
Event 2B: The estimated quality of the currently used frequency is below a certain threshold and the estimated quality of a non-used frequency is above a certain threshold.
Event 2C: The estimated quality of a non-used frequency is above a certain threshold.
Event 2D: The estimated quality of the currently used frequency is below a certain threshold. Used to enable the compressed mode.
Event 2F: The estimated quality of the currently used frequency is above a certain threshold. Used to disable the compressed mode.
Event 3A: The estimated quality of the currently used UTRAN frequency is below a certain threshold and the estimated quality of the GSM cell is above a certain threshold.
Event 3C: The estimated quality of the GSM cell is above a certain threshold.
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Measurement Model
Point A is the direct measurement result on the physical layer. Point B is the filtered measurement result on the physical layer, which is provided for higher layers. Point C is the measurement result filtered by higher layers, used for event decision.
The filtering shall be performed according to the following formula.
The variables in the formula are defined as follows:
Fn is the updated filtered measurement result
Fn-1 is the old filtered measurement result
Mn is the latest received measurement result from physical layer measurements, the unit used for Mn is the same unit as the reported unit in the MEASUREMENT REPORT message or the unit used in the event evaluation.
a = 1/2(k/2), where k is the parameter received in the IE "Filter coefficient".
NOTE: If a is set to 1 (k set to 0) that will mean no layer 3 filtering.
By selecting the measurement coefficient, the network layer can maintain the balance between the number of reports of measurement events and the reaction time of the active set update, and performs fine adjustment accordingly. When the filtering coefficient is larger, the impact on the measurements after layer 3 filtering of the measurement results on the current physical layer is smaller, the variation of measurements after layer 3 filtering becomes smoother, and the sensitivity of the network layer to the variation of measurements on the physical layer becomes lower. In this case, the number of reports of measurement events may decrease and the reaction time of the active set update is prolonged.
Layer 3 filtering excludes the random impact as much as possible, making the filtered measurements reflect the basic variation trend of actual measurements. Layer 1 filtering is performed on the measurement value of point B to eliminate the fast fading. Therefore, the layer 3 filtering is performed to eliminate the shadow fading and few fast fading burrs, to provide an optimum measurement data for event decision.
2. Satisfy the reaction time requirements to enable the filtered values to have enough sensitivity to the measurements. The network layer filtering is an iteration process. The iteration frequency decides the tracing capability of the filter signals to the actual signals. A great filter coefficient indicates a small smooth factor. Thus, the number of iterations increases required for the measurements after layer 3 filtering to trace the changes reported by layer 1, leading to a longer tracing time. In emergencies, however, the handover speed has to be high. In normal cases, the handover accuracy is handled with priority. The measurement period of different measurement types and the minimum reaction speed of layer 3 determine the maximum number of iterations.
According to Plan R2-000809, we use the following method to evaluate the tracing capability of layer 3 filtering. View the layer 3 filter as a single-input and single-output port. At the input end, sample the layer 1 measurement results. Layer 3 filter performs the signal filtering. The processing period is equal to the sampling period at the input end. At the output end, the reporting operation is performed with the reporting period is equal to the sampling period. To the filter, the required samples when the step response reaches 85% of the final output value indicate the tracing capability of the filter. We use the obtained number of samples as the tracing capability indicator of measurement values after layer 3 filtering towards the measurement results of layer 1.
The following describes the relation between the filter coefficient and the number of iterations.
Filter coefficient 012345678911 and number of iterations 12357101521304285. The above table lists the required number of iterations for the step response to reach 85% of the final output value by using different filter coefficients.
According to the 3GPP TS 25.133, in CELL_DCH state, the period of layer 1 reporting to layer 3 the intra-frequency measurement results is 200 ms. Replace the number of iterations with the iteration time, and the above table is changed into:
According to the above table, filter coefficient 012345678911 and intra-frequency tracing time (s) 0.20.40.611.4234.268.417 can roughly determine the layer 3 filter coefficient on the basis of the practical cell environment.
807.unknown
Measurement event ID
Filtering coefficient
Report hysteresis
One measurement ID in the case of intra-frequency HO
One measurement ID in the case of inter-frequency HO
One measurement ID in the case of inter-RAT HO
Where, the former two items on the right of the inequation for Event 1A are the same as those for Event 1B
(1)
The above formula indicates the overall quality of the active set. Where, NA is the number of cells in the active set. The value range of W is from 0 to 2.
Deform the above formula:
Because NA contains the best cells, the above formula is the monotone increasing function of W. That is, a great value of W indicates a high threshold for Event 1A comparison, making it more difficult to join the active set. On the contrary, a small W indicates a low threshold for Event 1A comparison, making it easier to join the active set.
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Judge the inequation, in the case of Event 1F:
Reporting range
Intra-Frequency Measurement Events
The intra-frequency measurement event is identified by 1X where X is A, B, C….
Event 1A: Relative threshold addition event. A primary CPICH enters the reporting range (FDD only), indicating that the quality of a cell reaches the quality of the best cell or active set quality. When the active set of the UE is full, the event 1A reporting stops.
Event 1B: Relative threshold deletion event. A primary CPICH leaves the reporting range (FDD only), indicating that the quality of a cell is far lower than the quality of the best cell or active set quality.
Event 1C: Replacement event. A non-active primary CPICH becomes better than an active primary CPICH (FDD only).
Event 1D: Change of the best cell (FDD only).
Event 1F: A primary CPICH becomes worse than an absolute threshold (FDD only).
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The inter-frequency measurement event is identified by 2X.
Event 2B: The estimated quality of the currently used frequency is below a certain threshold and the estimated quality of a non-used frequency is above a certain threshold.
Event 2C: The estimated quality of a non-used frequency is above a certain threshold.
Event 2D: The estimated quality of the currently used frequency is below a certain threshold. Used to enable the compressed mode.
Event 2F: The estimated quality of the currently used frequency is above a certain threshold. Used to disable the compressed mode.
The inter-RAT measurement event is identified by 3X.
Event 3A: The estimated quality of the currently used UTRAN frequency is below a certain threshold and the estimated quality of the GSM cell is above a certain threshold.
Event 3C: The estimated quality of the GSM cell is above a certain threshold.
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UE-Internal Measurement
Event 6G: The UE DL Rx-UL Tx time difference for a RL included in the active set becomes less than an absolute threshold.
Event 6F: The UE DL Rx-UL Tx time difference for a RL included in the active set becomes larger than an absolute threshold.
According to the 3GPP TS 25.214, in order to maximize the cell radius distance within which one-slot control delay is achieved, the frame timing of an uplink DPCH is delayed by 1024 chips from that of the corresponding downlink DPCH measured at the UE antenna.
After the SRNC receives the Event 6F or 6G report from the UE, it re-configures the physical channels to achieve the downlink timing adjustment.
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Chapter 2 Handover Measurement
Chapter 3 Basic Handovers
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The soft handover procedure is as follows:
1) Based on the measurement control information sent by the RNC, the UE measures the signals of neighboring cells of the same frequency. The measurement results are processed and then reported to the RNC.
2) The RNC compares the reported measurement results with the preset thresholds, and determines which cells should be added or deleted for the UE.
3) If a cell or cells are to be added, the RNC notifies the corresponding NodeB that the cell(s) should be ready.
4) The RNC notifies the UE of adding or deleting the cell(s) through the update message of the active set.
5) After the UE updates the active set, the NodeB releases the corresponding resources if a cell is deleted.
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Overview
Characteristics
RLs between the UE and multiple cells in the UTRAN after the handover—Active set
Softer handover can be implemented between multiple cells in a RLS.
Soft handover. Selection combination on the uplink and maximum ratio combination on the downlink.
Softer handover. Maximum ratio combination on the uplink and downlink.
Advantages
Soft handover gain, which involves
Multi-cell gain: Multiple unrelated branches in the soft handover reduce the requirements on shadow fading margin.
Macro diversity combining gain: The improvement on the link demodulation performance brings the power gain against the fast fading.
Load sharing: On the uplink, multiple cells receive the UE signals, which reduces the transmit power of the UE. On the downlink, multiple cells transmit the RF signals, which reduces the transmit power of each cell.
Number of call drops due to…
1.1
Comments in pages 12, 16, 22, 34, 49, 69, 72, and 94 are added.
Cheng Fangyuan
2009-01-19
1.2
Comments on the GPRS state are added in page 5. Comments on the GSM handover purpose are added in page 9. Comments on the GSM handover types are added in page 10. Comments on the GSM handover procedure are added in page 14.
Kuang Jun
Preface: Why the Handover is Required?
A major characteristic in the mobile communications: Mobility of the UE
As a key component of the mobile communication system, the cell has a limited coverage area.
The primary function of the handover is to provide the continuous service for the moving UEs in the coverage of the network.
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Handover and directed retry
Cell selection and reselection
Camped cell change for the UE in IDLE, CELL_FACH, CELL_PCH, or URA_PCH state
Also referred to as the forward handover
A UE can operate in two basic modes, which are the idle mode and connected mode.
Idle mode: The UE is in standby state. There is no RRC connection or network service. The UTRAN has no own information about the individual idle mode UEs. In idle mode, the UE is identified by non-access layer identities such as IMSI, TMSI, or P-TMSI.
Connected mode: After the RRC connection is complete, the UE transits to the connected mode from the idle mode. In connected mode, the UE has four states, which are Cell_DCH, Cell_FACH, Cell_PCH, and URA_PCH.
Cell_DCH:
The UE is in activated state and communicates through its own dedicated channel. Dedicated channels are available on the uplink and downlink. The UTRAN knows exactly the cell the UE is camped on.
Cell_FACH:
The UE is in activated state but there is no dedicated channel for the UE because the traffic volume is low on the uplink and downlink. The downlink data is transmitted on the FACH and the uplink data on the RACH. The downlink monitors its information on the FACH. The UTRAN knows exactly the cell the UE is camped on. The resources and state of the UE are reserved.
Cell_PCH:
There is no data transmission on the uplink and downlink. The UE listens to the PICH to receive the paging information. In this case, the UE transits to the DRX mode and the battery lifetime can be prolonged.
The UTRAN knows exactly the cell the UE is camped on. In this case, the UTRAN needs to update the cell information after the cell the UE is camped on changes.
URA-PCH:
There is no data transmission on the uplink and downlink. The UE listens to the PICH and transits to the DRX mode. The UTRAN only knows the UTRAN Registration Area (URA) information about the UE. That is, the UTRAN performs the location updating for the UE only when the URA of the UE changes. Thus, the involved resources are reduced and the number of related signaling decreases.
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Preface: UE Mode and State
In a GPRS cell, the UE has two modes, which are stand-alone and ready.
CELL_FACH
CELL_DCH
CELL_PCH
URA_PCH
GPRS Packet Transfer Mode
Camping on a GSM / GPRS cell
1
GSM Connected Mode
Release RR Connection
Scope
Learn about the differences between the GSM handover and the WCDMA handover
Grasp the WCDMA handover decision algorithm
Grasp the WCDMA handover procedure
Grasp the WCDMA handover parameters
Grasp the WCDMA blind handover and directed retry
After this course, you are able to:
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Chapter 2 Handover Measurement
Chapter 3 Basic Handovers
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Handover Purpose
Handover Types
Handover Procedure
WCDMA HO Purpose
Main purpose: to provide the continuous service for the moving UEs in the coverage of the network
Load balancing: resource sharing
GSM HO Purpose
Main purpose: to maintain the continuity of the conversation for the moving mobile stations (MSs)
QoS improvement for the network
Call drop rate reduction
Congestion rate reduction
Load balancing: A feature related to the cell capacity limit, which puts forward the requirements of resource sharing in the network.
The GSM handover purposes also involve load balancing (load handover) and customer experience improvement (quality handover and interference handover).
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WCDMA HO Types
Intra-frequency handover
Inter-frequency handover
Coverage-based handover (primary function)
Load balancing-based handover (optional)
Service sharing-based handover (optional)
Speed estimation-based handover (optional)
Emergency handover
TA handover
Concentric cell handover
In terms of the time that the link configuration takes effect:
Synchronous handover
Asynchronous handover
The GSM handover is classified into the synchronous handover, asynchronous handover, pseudo-synchronization handover, and pre-synchronization handover.
In terms of triggering conditions, the handover can also be classified into the full/half rate handover and the AMR handover.
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Differences between the soft handover and the softer handover:
In the softer handover, the maximum ratio combination is performed on the uplink signals at the NodeB. In the soft handover, the selection combination is performed on the uplink signals at the RNC. As the gain of maximum ratio combination is larger than the gain of selection combination, the softer handover is better than the soft handover.
Because the combination of the softer handover is performed at the NodeB, the transmission resources on the Iub interface are saved.
Comparison
Number of radio links in the active set after handover
Multiple
One
No
Yes
Cells of the same frequency
Cells of the same frequency, different frequencies, or different systems.
Characteristics of the hard handover:
Disconnect the original link, and then set up a new link between the UE and the target cell.
The conversation has the “gap” during the handover.
Non-CDMA systems allow only the hard handover.
Characteristics of the soft handover:
Only the CDMA systems have soft handovers, which occur only between the cells of the same frequency.
Set up a new link between the UE and the target cell, and then disconnect the original link. Thus, the “gap” in the conversation can be avoided.
A soft handover consumes more network resources than a hard handover. In other words, a soft handover achieves the optimum network performance at the price of certain network resources.
In a soft handover, if the target cell and original cell are within a same NodeB, the maximum ratio combination can be achieved on the uplink. In this case, the handover is referred to as a softer handover.
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RNC
Overall procedure of the GSM handover algorithm
Execution
Handover
Measurement
Phase
Decision
Phase
MR
preprocessing
Penalty
processing
HO decision
The GSM handover procedure can also be summarized as measurement, decision, and execution. From this aspect, the difference between GSM and WCDMA is insignificant.
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Measurement
Measurement report
Decision
Resource application and assignment
Execution
Active set
Monitored set
Detected set
Event report
Soft handover gain
Pilot channel (CPICH)
Blind handover
Active set: RLs that keep connecting with the UE
Monitored set: RLs not included in the active set, but are included in the neighbouring cell list and detected by UE.
Detected set: RLs detected by the UE, which are neither in the neighbouring cell list nor in the active set.
Radio Link (RL): Each link between a UE and the NodeB is referred to as a Radio Link (RL).
Radio Link Set (RLS): RLs that belong to a same NodeB. The softer handover can be achieved between the cells in an RLS.
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Typical scenarios of the WCDMA handover
Basic concepts of the WCDMA handover
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Summary
This chapter describes the handover purpose and the common types of the WCDMA handover.
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Chapter 2 Handover Measurement
Chapter 3 Basic Handovers
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Basic Concepts of Measurement
UE-Internal Measurement
Measurement control:
Measurement report, normal case
The RNC informs the UE of measurement objects, neighboring cell list, reporting mode, and event parameters.
When the measurement conditions change, the RNC informs the UE of the new measurement conditions.
The UE sends the measurement report to the RNC when the triggering conditions are satisfied.
Measurement control uses AM RLC.
Measurement report uses UM RLC.
In GSM, the BSS controls the handover and does not receive the MRs from the network. The MS sends the MRs periodically and does not perform the handover decision.
UE
UTRAN
Intra-frequency and inter-frequency: CPICH RSCP, CPICH Ec/N0, Pathloss
Inter-frequency: CPICH RSCP, CPICH Ec/N0
Inter-RAT: GSM Carrier RSSI, BSIC Identification, BSIC Reconfirmation
Reporting mode of the MR
Periodical report (event-to-period report)
Intra-frequency events: 1A, 1B, 1C, 1D, 1F
Inter-frequency events: 2D, 2F, 2B, 2C
Inter-RAT events: 3A, 3C
6G, Rx-Tx Observed time difference less than the threshold To
6F, Rx-Tx Observed time difference larger than the threshold To
Observe the time difference:
SFN-SFN observed time difference, set in the intra-frequency and inter-frequency measurements
CFN-SFN observed time difference, set in the intra-frequency and inter-frequency measurements
The intra-frequency measurement event is identified by 1X and the inter-frequency measurement event is identified by 2X. The inter-RAT measurement event is identified by 3X.
Event 1A: A primary CPICH enters the reporting range, indicating that the quality of a cell reaches the quality of the best cell or active set quality.
Event 1B: A primary CPICH leaves the reporting range, indicating that the quality of a cell is far lower than the quality of the best cell or active set quality.
Event 1C: Replacement event. A non-active primary CPICH becomes better than an active primary CPICH.
Event 1D: Change of the best cell
Event 1F: A primary CPICH becomes worse than an absolute threshold.
Event 2B: The estimated quality of the currently used frequency is below a certain threshold and the estimated quality of a non-used frequency is above a certain threshold.
Event 2C: The estimated quality of a non-used frequency is above a certain threshold.
Event 2D: The estimated quality of the currently used frequency is below a certain threshold. Used to enable the compressed mode.
Event 2F: The estimated quality of the currently used frequency is above a certain threshold. Used to disable the compressed mode.
Event 3A: The estimated quality of the currently used UTRAN frequency is below a certain threshold and the estimated quality of the GSM cell is above a certain threshold.
Event 3C: The estimated quality of the GSM cell is above a certain threshold.
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Measurement Model
Point A is the direct measurement result on the physical layer. Point B is the filtered measurement result on the physical layer, which is provided for higher layers. Point C is the measurement result filtered by higher layers, used for event decision.
The filtering shall be performed according to the following formula.
The variables in the formula are defined as follows:
Fn is the updated filtered measurement result
Fn-1 is the old filtered measurement result
Mn is the latest received measurement result from physical layer measurements, the unit used for Mn is the same unit as the reported unit in the MEASUREMENT REPORT message or the unit used in the event evaluation.
a = 1/2(k/2), where k is the parameter received in the IE "Filter coefficient".
NOTE: If a is set to 1 (k set to 0) that will mean no layer 3 filtering.
By selecting the measurement coefficient, the network layer can maintain the balance between the number of reports of measurement events and the reaction time of the active set update, and performs fine adjustment accordingly. When the filtering coefficient is larger, the impact on the measurements after layer 3 filtering of the measurement results on the current physical layer is smaller, the variation of measurements after layer 3 filtering becomes smoother, and the sensitivity of the network layer to the variation of measurements on the physical layer becomes lower. In this case, the number of reports of measurement events may decrease and the reaction time of the active set update is prolonged.
Layer 3 filtering excludes the random impact as much as possible, making the filtered measurements reflect the basic variation trend of actual measurements. Layer 1 filtering is performed on the measurement value of point B to eliminate the fast fading. Therefore, the layer 3 filtering is performed to eliminate the shadow fading and few fast fading burrs, to provide an optimum measurement data for event decision.
2. Satisfy the reaction time requirements to enable the filtered values to have enough sensitivity to the measurements. The network layer filtering is an iteration process. The iteration frequency decides the tracing capability of the filter signals to the actual signals. A great filter coefficient indicates a small smooth factor. Thus, the number of iterations increases required for the measurements after layer 3 filtering to trace the changes reported by layer 1, leading to a longer tracing time. In emergencies, however, the handover speed has to be high. In normal cases, the handover accuracy is handled with priority. The measurement period of different measurement types and the minimum reaction speed of layer 3 determine the maximum number of iterations.
According to Plan R2-000809, we use the following method to evaluate the tracing capability of layer 3 filtering. View the layer 3 filter as a single-input and single-output port. At the input end, sample the layer 1 measurement results. Layer 3 filter performs the signal filtering. The processing period is equal to the sampling period at the input end. At the output end, the reporting operation is performed with the reporting period is equal to the sampling period. To the filter, the required samples when the step response reaches 85% of the final output value indicate the tracing capability of the filter. We use the obtained number of samples as the tracing capability indicator of measurement values after layer 3 filtering towards the measurement results of layer 1.
The following describes the relation between the filter coefficient and the number of iterations.
Filter coefficient 012345678911 and number of iterations 12357101521304285. The above table lists the required number of iterations for the step response to reach 85% of the final output value by using different filter coefficients.
According to the 3GPP TS 25.133, in CELL_DCH state, the period of layer 1 reporting to layer 3 the intra-frequency measurement results is 200 ms. Replace the number of iterations with the iteration time, and the above table is changed into:
According to the above table, filter coefficient 012345678911 and intra-frequency tracing time (s) 0.20.40.611.4234.268.417 can roughly determine the layer 3 filter coefficient on the basis of the practical cell environment.
807.unknown
Measurement event ID
Filtering coefficient
Report hysteresis
One measurement ID in the case of intra-frequency HO
One measurement ID in the case of inter-frequency HO
One measurement ID in the case of inter-RAT HO
Where, the former two items on the right of the inequation for Event 1A are the same as those for Event 1B
(1)
The above formula indicates the overall quality of the active set. Where, NA is the number of cells in the active set. The value range of W is from 0 to 2.
Deform the above formula:
Because NA contains the best cells, the above formula is the monotone increasing function of W. That is, a great value of W indicates a high threshold for Event 1A comparison, making it more difficult to join the active set. On the contrary, a small W indicates a low threshold for Event 1A comparison, making it easier to join the active set.
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Judge the inequation, in the case of Event 1F:
Reporting range
Intra-Frequency Measurement Events
The intra-frequency measurement event is identified by 1X where X is A, B, C….
Event 1A: Relative threshold addition event. A primary CPICH enters the reporting range (FDD only), indicating that the quality of a cell reaches the quality of the best cell or active set quality. When the active set of the UE is full, the event 1A reporting stops.
Event 1B: Relative threshold deletion event. A primary CPICH leaves the reporting range (FDD only), indicating that the quality of a cell is far lower than the quality of the best cell or active set quality.
Event 1C: Replacement event. A non-active primary CPICH becomes better than an active primary CPICH (FDD only).
Event 1D: Change of the best cell (FDD only).
Event 1F: A primary CPICH becomes worse than an absolute threshold (FDD only).
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The inter-frequency measurement event is identified by 2X.
Event 2B: The estimated quality of the currently used frequency is below a certain threshold and the estimated quality of a non-used frequency is above a certain threshold.
Event 2C: The estimated quality of a non-used frequency is above a certain threshold.
Event 2D: The estimated quality of the currently used frequency is below a certain threshold. Used to enable the compressed mode.
Event 2F: The estimated quality of the currently used frequency is above a certain threshold. Used to disable the compressed mode.
The inter-RAT measurement event is identified by 3X.
Event 3A: The estimated quality of the currently used UTRAN frequency is below a certain threshold and the estimated quality of the GSM cell is above a certain threshold.
Event 3C: The estimated quality of the GSM cell is above a certain threshold.
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UE-Internal Measurement
Event 6G: The UE DL Rx-UL Tx time difference for a RL included in the active set becomes less than an absolute threshold.
Event 6F: The UE DL Rx-UL Tx time difference for a RL included in the active set becomes larger than an absolute threshold.
According to the 3GPP TS 25.214, in order to maximize the cell radius distance within which one-slot control delay is achieved, the frame timing of an uplink DPCH is delayed by 1024 chips from that of the corresponding downlink DPCH measured at the UE antenna.
After the SRNC receives the Event 6F or 6G report from the UE, it re-configures the physical channels to achieve the downlink timing adjustment.
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Chapter 2 Handover Measurement
Chapter 3 Basic Handovers
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The soft handover procedure is as follows:
1) Based on the measurement control information sent by the RNC, the UE measures the signals of neighboring cells of the same frequency. The measurement results are processed and then reported to the RNC.
2) The RNC compares the reported measurement results with the preset thresholds, and determines which cells should be added or deleted for the UE.
3) If a cell or cells are to be added, the RNC notifies the corresponding NodeB that the cell(s) should be ready.
4) The RNC notifies the UE of adding or deleting the cell(s) through the update message of the active set.
5) After the UE updates the active set, the NodeB releases the corresponding resources if a cell is deleted.
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Overview
Characteristics
RLs between the UE and multiple cells in the UTRAN after the handover—Active set
Softer handover can be implemented between multiple cells in a RLS.
Soft handover. Selection combination on the uplink and maximum ratio combination on the downlink.
Softer handover. Maximum ratio combination on the uplink and downlink.
Advantages
Soft handover gain, which involves
Multi-cell gain: Multiple unrelated branches in the soft handover reduce the requirements on shadow fading margin.
Macro diversity combining gain: The improvement on the link demodulation performance brings the power gain against the fast fading.
Load sharing: On the uplink, multiple cells receive the UE signals, which reduces the transmit power of the UE. On the downlink, multiple cells transmit the RF signals, which reduces the transmit power of each cell.
Number of call drops due to…