Wcdma Rno Handover Algorithm Analysis And Parameter Configurtaion Guidance 20050316 A 1.0

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Wcdma Rno Handover Algorithm Analysis And Parameter Configurtaion Guidance 20050316 A 1.0

  1. 1. Product Version Confidentiality level Huawei Technologies V100R001 For Internal Use Co. Ltd. Product Name: WCDMA RNP Total pages: 52 WCDMA RNO Handover Algorithm Analysis and Parameter Configuration Guidance For internal use only Prepared by: URNP-SANA Date: 2003-12-15 Reviewed by: Date: Reviewed by: Date: Approved by: Date: Huawei Technologies Co., Ltd. All rights reserved
  2. 2. WCDMA RNO Handover Algorithm Analysis and Parameter Configuration Guidance For Intanal Use Revision Record Date Rev. Description Author Version 2003/12/15 Initial transmittal Znag Liang 2005/03/16 1.0 Change the date, no content updated. Qinyan 10-1-26 Confidential Page 2 of 52
  3. 3. WCDMA RNO Handover Algorithm Analysis and Parameter Configuration Guidance For Intanal Use Table of Contents 1 Introduction..................................................................................................................................................7 2 Handover Algorithm Analysis.....................................................................................................................7 2.1 Handover Measurement ..........................................................................................................................7 2.1.1 Intra-Frequency Measurement .........................................................................................................8 2.1.2 Inter-Frequency Measurement .......................................................................................................13 2.1.3 Inter-System Measurement ............................................................................................................14 2.1.4 UE Internal Measurement ..............................................................................................................15 2.2 Handover Algorithms ...........................................................................................................................16 2.2.1 Softer Handover and Soft Handover Algorithms ...........................................................................16 2.2.2 Intra-Frequency Hard Handover Algorithm ..................................................................................17 2.2.3 Inter-Frequency Hard Handover Algorithm ..................................................................................17 2.2.4 Inter-System Handover Algorithm .................................................................................................19 2.2.5 Handover Caused by Load Balancing ............................................................................................19 2.2.6 Cell Penalty.....................................................................................................................................20 2.2.7 Active Set Synchronization Maintenance.......................................................................................21 2.2.8 Direct Retry Algorithm ..................................................................................................................22 2.2.9 Principle for Generating Adjacent Cell List...................................................................................23 3 Handover Parameter Setting ......................................................................................................................24 3.1 Description.............................................................................................................................................25 3.2 Handover Common Parameters ............................................................................................................26 3.2.1 Maximum Number of Cells in Active Set......................................................................................26 3.2.2 Penalty Time....................................................................................................................................26 3.2.3 Event 6F Trigger Threshold ...........................................................................................................27 3.2.4 Event 6G Trigger Threshold...........................................................................................................27 3.2.5 Time-to-Trigger Parameters for Events 6F and 6G........................................................................28 3.2.6 BE Service Handover Rate Decision Threshold ............................................................................28 3.2.7 Soft Handover Method Select Switch ............................................................................................29 3.2.8 Handover Algorithm Switches........................................................................................................30 3.3 Intra-Frequency Handover Measurement Algorithm Parameters ........................................................31 3.3.1 Soft Handover Relative Thresholds ...............................................................................................31 3.3.2 Soft Handover Absolute Thresholds ..............................................................................................32 3.3.3 Intra-Frequency Measurement Filter Coefficient (FilterCoef).......................................................33 3.3.4 Hysteresis Related to Soft Handover .............................................................................................35 3.3.5 Time-to-Trigger Parameters Related to Soft Handover..................................................................36 3.3.6 WEIGHT.........................................................................................................................................37 3.3.7 Detected Set Statistics Switch.........................................................................................................38 3.4 Inter-Frequency Handover Algorithm Parameters ...............................................................................38 3.4.1 Inter-Frequency Measurement Filter Coefficient (FilterCoef).......................................................38 3.4.2 Cell Location Property....................................................................................................................39 3.4.3 Hysteresis Related to Inter-Frequency Handover...........................................................................40 3.4.4 Time-to-Trigger Parameters Related to Inter-Frequency Hard Handover.....................................41 3.4.5 Compressed Mode Enable/Disable Threshold Denoted by RSCP.................................................42 3.4.6 Compressed Mode Enable/Disable Threshold Denoted by Ec/No.................................................42 3.4.7 Inter-Frequency Hard Handover RSCP Threshold ........................................................................43 3.4.8 Inter-Frequency Hard Handover Ec/No Threshold ........................................................................44 3.5 inter-system handover measurement algorithm parameter ..................................................................44 3.5.1 inter-system measurement filter coefficient FilterCoef..................................................................44 3.5.2 Inter-System Hard Handover Decision Threshold .........................................................................45 3.5.3 Inter-system Hard Handover Hysteresis .......................................................................................45 3.5.4 Time-to-Trigger Parameter for Inter-System Hard Handover........................................................46 3.5.5 Inter-System Measurement Periodic Report Interval.....................................................................47 3.6 Compressed Mode Algorithm Parameter .............................................................................................47 3.6.1 CFN Offset to Enable Compressed Mode.......................................................................................47 10-1-26 Confidential Page 3 of 52
  4. 4. WCDMA RNO Handover Algorithm Analysis and Parameter Configuration Guidance For Intanal Use 3.6.2 Spreading Factor Threshold ...........................................................................................................48 3.7 Direct Retry Algorithm Parameter .......................................................................................................49 3.7.1 Maximum Direct Retry Times........................................................................................................49 3.7.2 Candidate Set Absolute Threshold .................................................................................................49 3.7.3 Minimum Ec/No Value...................................................................................................................50 3.7.4 Linear Factor of Relative Threshold and Time Interval.................................................................50 3.7.5 Maximum Relating Time for Direct Retry Decision......................................................................51 10-1-26 Confidential Page 4 of 52
  5. 5. WCDMA RNO Handover Algorithm Analysis and Parameter Configuration Guidance For Intanal Use List of Tables table 1Recommended Soft Handover Hysteresis Settings for Different Movement Speeds.......................35 table 2Recommended Time-to-Trigger Settings for Different Movement Speeds......................................36 table 3Recommended Inter-Frequency Hard Handover Hysteresis Settings for Different Movement Speeds..........................................................................................................................................................40 table 4Recommended Inter-Frequency Hard Handover Time-to-Trigger Settings for Different Movement Speeds..........................................................................................................................................................41 List of Figures Figure 1 Measurement Model.........................................................................................................................8 Figure 2 Example of Event 1A and Trigger Delay.........................................................................................9 Figure 3 Periodic Reporting Triggered by Event 1A....................................................................................10 Figure 4 Example of Event 1C......................................................................................................................11 Figure 5 Example of Event 1D......................................................................................................................11 Figure 6 Restriction of measurement reporting by means of hysteresis.......................................................12 Figure 7 Example of Event 1E......................................................................................................................12 Figure 8 Example of Event 1D1F.................................................................................................................13 Figure 9 Power Control Timing....................................................................................................................21 Figure 10 MML Client .................................................................................................................................25 10-1-26 Confidential Page 5 of 52
  6. 6. WCDMA RNO Handover Algorithm Analysis and Parameter Configuration Guidance For Intanal Use WCDMA RNO Handover Algorithm Analysis and Parameter Configuration Guidance Key words: handover algorithm, soft handover, hard handover, inter-system handover, parameter setting Abstract: This document first describes the measurements involved in the handover algorithms, and then analyzes the measurement control and decision rules in the implementation of the algorithm of each type of handover. Finally, it provides a detailed guidance for the setting of various types of handover parameters, so that correct and effective handover parameter adjustments can be carried out based on the actual requirements during network optimization. List of abbreviations: (Omitted) 10-1-26 Confidential Page 6 of 52
  7. 7. WCDMA RNO Handover Algorithm Analysis and Parameter Configuration Guidance For Intanal Use 1 Introduction Handover types include softer handover, soft handover, intra-frequency hard handover, inter-frequency hard handover and inter-system hard handover. A typical handover process is: measurement control → measurement report → handover decision → handover execution → new measurement control. Based on the measurement value, handover control method and handover type selection required for the handover decision, the handover algorithm determines how the UE carry out handover measurements and report the measurement result, and then makes handover decision and guides the handover execution according to the reported measurement result. Handover algorithms largely present themselves in the configuration of measurement control parameters. In Chapter 2, this document discusses the measurement control, reporting rules and related handover decision algorithms involved in various types of handover. In Chapter 3, based on the knowledge of the handover algorithms, this document provides detailed descriptions of the specific parameter setting methods value assignment recommendations and ranges of effect of the related algorithms of various types of handover, so as to provide a clear and practical guidance for parameter adjustments in network optimization. 2 Handover Algorithm Analysis Mobility management is an important part of radio resource management, while handover algorithms are the most important part of mobility management. A handover algorithm involves such contents as measurement control and handover decision. Therefore, to analyze a handover algorithm, we should first analyze handover measurement. 2.1Handover Measurement The radio resource management module (RRM) initiated measurements include dedicated measurement and common measurement. All the measurements in the UE are dedicated measurement. Handover measurement is specific to the physical layer, which provides measurement of various items for the higher layers, so as to trigger various functions, including handover. The measurement result will go twice through smoothening processing. The first processing is in the physical layer, and the purpose is to filter off the influence of fast fading before the physical layer reports the measurement result to the higher layer. The second processing is implemented by the higher layer on the measurement result reported by the physical layer before event evaluation. This processing is to determine the filter coefficient according to the time 10-1-26 Confidential Page 7 of 52
  8. 8. WCDMA RNO Handover Algorithm Analysis and Parameter Configuration Guidance For Intanal Use relation and implemented weighted averaging processing of the measurement result. The latest measurement result after L3 filtering is used for evaluation of the reporting rule, and as the reported result. The process is as follows: Parameter Parameter A L1 B L3 C Evaluation D filtering filtering of reporting rule C' Figure 1 Measurement Model The reporting types include “on-demand reporting”, “periodic reporting” and “event triggered reporting” (Event A to Event F). Generally, the last two types of measurement reporting are involved in handover. In the UE, measured cells are divided into the following three types:  Active set cells: Cells in an active set communicate with the UE simultaneously. Active set cells refer to those that are demodulated and correlatively combined at the UE and communicate with the UE in the FDD mode, namely in soft handover and softer handover. Cells in an active set are surely intra-frequency cells.  Monitored set cells: Among the cells included in the adjacent cell list delivered by the RNC, some adjacent cells may have already entered the active set at the time of soft handover, and the remaining cells are in monitored sets. Monitored sets include intra-frequency monitored sets, inter-frequency monitored sets and inter-system monitored sets.  Detected set cell: Detected set cells refer to those cells detected by the UE itself, rather than the cells in the active sets and monitored set. The types of measurement involved in handover include intra-frequency measurement, inter-frequency measurement and inter-system measurement, which will be discussed in the following paragraphs. 2.1.1Intra-Frequency Measurement UTRAN uses the measurement control message to inform the UE what events need to trigger measurement reporting. All intra-frequency measurement report events are identified with 1X. Event 1A: A primary pilot channel enters the reporting range If the network, in the measurement report mechanism field, requires the UE to report event 10-1-26 Confidential Page 8 of 52
  9. 9. WCDMA RNO Handover Algorithm Analysis and Parameter Configuration Guidance For Intanal Use 1A while the UE has entered the Cell_DCH state, then when a primary pilot channel enters the reporting range, the UE will send a measurement report. When the measurement values satisfy the following formulas, the UE deems that a primary pilot channel has entered the reporting range: 1. Path loss:  NA  10 ⋅ LogM New ≤ W ⋅10 ⋅ Log  ∑ M i  + (1 − W ) ⋅10 ⋅ LogM Best + ( R − H 1a / 2),    i =1  2. Other measurement values:  NA  10 ⋅ LogM New ≥ W ⋅10 ⋅ Log  ∑ M i  + (1 − W ) ⋅10 ⋅ LogM Best − ( R − H 1a / 2),    i =1  Where, MNew is the measurement result of the cell that has entered the reporting range Mi is the measurement result of the cells in the active set NA is the number of cells in the current active set MBest is the measurement result of the best cell in the current active set W is the weight factor R is the reporting range. With the signal strength as an example, R equals to the signal strength of the best cell in the current active set minus a value H1a is the hysteresis value of event 1A In order to reduce the signaling traffic flow of the measurement report, the TIME-TO- TRIGGER parameter is used so that the UE will not trigger measurement reporting before the primary pilot enters the reporting range and is maintained for a certain period of time. This parameter is also used in other events. An example of measurement reporting triggered by event 1A is given below: Measurement quantity P CPICH 1 Reporting range P CPICH 2 P CPICH 3 Time-to-trigger Reporting Time event 1A Figure 2 Example of Event 1A and Trigger Delay Generally, if event 1A is triggered, the UE will send a measurement report to UTRAN, and UTRAN will deliver an ACTIVE SET UPDATE signaling message to update the active set. 10-1-26 Confidential Page 9 of 52
  10. 10. WCDMA RNO Handover Algorithm Analysis and Parameter Configuration Guidance For Intanal Use However, UTRAN may give no response after the UE sends the measurement report (for example, due to insufficient capacity). In this case, the UE will shift from event reporting to periodic reporting mechanism, and the content of the measurement report includes the information of the cells in the active set and the cells in the monitored set that has entered the reporting range. The UE will not stop sending periodically the measurement report until this cell is successfully added into the active set or leaves the reporting range, as shown below: PCPICH 1 PCPICH 2 Reporting range Reporting terminated Periodic Periodic report report Event-triggered PCPICH 3 report Figure 3 Periodic Reporting Triggered by Event 1A Event 1B: A primary pilot channel leaves the reporting range When the following formulas are satisfied, the UE deems that a primary pilot channel has left the reporting range 1, Path loss:  NA  10 ⋅ LogM Old ≥ W ⋅ 10 ⋅ Log  ∑ M i  + (1 − W ) ⋅ 10 ⋅ LogM Best + ( R + H 1a / 2),    i =1  2, Other measurement values:  NA  10 ⋅ LogM Old ≤ W ⋅ 10 ⋅ Log  ∑ M i  + (1 − W ) ⋅ 10 ⋅ LogM Best − ( R + H 1b / 2),    i =1  Where, MOld is the measurement result of the cell that has left the reporting range Mi is the measurement result of the cell in the active set NA is the number of cells in the current active set MBest is the measurement result of the best cell in the current active set W is the weighted factor R is the reporting range H1a is the hysteresis value of event 1A If several cells satisfy the reporting condition simultaneously after the trigger delay, the UE 10-1-26 Confidential Page 10 of 52
  11. 11. WCDMA RNO Handover Algorithm Analysis and Parameter Configuration Guidance For Intanal Use will sort the cells according to the measurement values and report all the measurement results. Event 1C: The primary pilot channel in a non active set is better than the primary pilot channel in an active set This event can be described through the following example: Measurement quantity P CPICH 1 P CPICH 2 P CPICH 3 P CPICH 4 Reporting Reporting Time event 1C event 1C Figure 4 Example of Event 1C In this example, the cells where P CPICH 1, P CPICH 2 and P CPICH 3 are belong to an active set, while that of P CPICH 4 does not. This event is used to replace the poor cells in the active set, if the number of cells in the active set reaches or exceeds active set replacement threshold. Event 1D: The best cell changes Measurement quantity P CPICH 1 P CPICH 2 P CPICH3 Reporting Time event 1D Figure 5 Example of Event 1D 10-1-26 Confidential Page 11 of 52
  12. 12. WCDMA RNO Handover Algorithm Analysis and Parameter Configuration Guidance For Intanal Use In order to prevent frequent triggering of event 1D due to signal fluctuations when the channel difference is small, which results in unnecessary increase of the air interface signaling traffic flow, we can use the hysteresis parameter, as shown below: Measurement quantity P CCPCH 1 Hysteresis P CCPCH 2 Hysteresis Reporting Time event 1D Figure 6 Restriction of measurement reporting by means of hysteresis As we can see, as the hysteresis condition is not met at the second time, event 1D reporting is not triggered. This parameter can also be used in other events. Event 1E: The measurement value of a primary pilot channel exceeds the absolute threshold Measurement quantity P CPICH 1 P CPICH 2 Absolute threshold P CPICH 3 Reporting Time event 1E Figure 7 Example of Event 1E Event 1E can be used to trigger the measurement reports of cells including those detected by the UE before it receives the adjacent cell list. 10-1-26 Confidential Page 12 of 52
  13. 13. WCDMA RNO Handover Algorithm Analysis and Parameter Configuration Guidance For Intanal Use Event 1F: The measurement value of a primary pilot channel is lower than the absolute threshold Measurement quantity P CPICH 1 P CPICH 2 Absolute threshold P CPICH 3 Reporting Time event 1F Figure 8 Example of Event 1D1F 2.1.2Inter-Frequency Measurement Inter-frequency measurement events are identified with 2X. The frequency quality estimation involved in events 2A, 2B, 2C, 2D and 2E is defined as follows:  NA j  Qcarrier j = 10 ⋅ LogM carrier j = W j ⋅ 10 ⋅ Log  ∑ M i  i =1 j  + (1 − W j ) ⋅ 10 ⋅ LogM Best j − H ,    Where, Qcarrierj is the logarithmic form of the estimated quality value of frequency j Mcarrier j is the estimated quality value of frequency j Mi j is the measurement result of cell i with the frequency of j in the virtual active set NA j is the number of cells with the frequency of j in the virtual active set MBest j is the measurement result of the best cell with the frequency of j in the virtual active set Wj is the weight factor H is the hysteresis value Before we describe events 2x, we should make the following two concepts understood: “non-used frequency” refer to the frequency that the UE needs to measure but that is not in the active set, and “used frequency” refers to the frequency that the UE needs to measure and that is in the active set. 10-1-26 Confidential Page 13 of 52
  14. 14. WCDMA RNO Handover Algorithm Analysis and Parameter Configuration Guidance For Intanal Use Event 2A: The best frequency changes If the estimated quality value of the non-used frequency is better than that of the best cell in the used frequency, and the hysteresis value and the “time to trigger” conditions are satisfied, event 2A will be triggered. Event 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 If the estimated quality value of the used frequency is lower than the threshold defined by IE “Threshold used frequency” delivered in the measurement control message, while that of the non-used frequency is higher than the threshold defined by IE “Threshold non-used frequency” delivered in the measurement control message, and the hysteresis value and the “time to trigger” condition are satisfied, event 2B will be triggered. Event 2C: The estimated quality value of the non-used frequency is higher than a certain threshold This threshold is specified by IE “Threshold non-used frequency” in the measurement control message delivered by UTRAN. Event 2D: The estimated quality value of the used frequency is lower than a certain threshold Event 2D can be used to enable the compressed mode to perform inter-frequency measurement. This threshold is specified by IE “Threshold used frequency” in the measurement control message delivered by UTRAN. This type of parameters can be modified through MML commands. Event 2E: The estimated quality value of the non-used frequency is lower than a certain threshold This threshold is specified by IE “Threshold non-used frequency” in the measurement control message delivered by UTRAN. Event 2F: The estimated quality value of the used frequency is higher than a certain threshold Event 2F can be used to disable the compressed mode to stop inter-frequency measurement. This threshold is specified by IE “Threshold used frequency” in the measurement control message delivered by UTRAN. 2.1.3Inter-System Measurement 10-1-26 Confidential Page 14 of 52
  15. 15. WCDMA RNO Handover Algorithm Analysis and Parameter Configuration Guidance For Intanal Use Inter-system measurement events are identified with 3X. The quality estimation of a UTRAN active set involved in events 3A, 3B, 3C and 3D is defined as follows:  NA  QUTRAN = 10 ⋅ LogM UTRAN = W ⋅ 10 ⋅ Log  ∑ M i  + (1 − W ) ⋅ 10 ⋅ LogM Best ,    i =1  Where, QUTRAN is the logarithmic form of the estimated quality value of the UTRAN frequency currently in use MUTRAN is the estimated quality value of the UTRAN frequency currently in use Mi is the measurement result of cell i in the active set NA is the number of cells in the active set MBest result is the measurement result of the best cell in the active set W is the weight factor Event 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 If the estimated quality value of the used UTRAN frequency is lower than the threshold defined by IE “Threshold own system” delivered in the measurement control message, while that of the other system is higher than the threshold defined by IE “Threshold other system” delivered in the measurement control message, and the hysteresis value and the “time to trigger” condition are satisfied, event 3A will be triggered. Event 3B: The estimated quality value of the other system is lower than a certain threshold This threshold is specified by IE “Threshold other system” in the measurement control message. Event 3C: The estimated quality value of the other system is higher than a certain threshold This threshold is specified by IE “Threshold other system” in the measurement control message. Event 3D: The best cell in the other system changes 2.1.4UE Internal Measurement Two UE internal measurement events are involved in the handover algorithms: 6F and 6G. Event 6F: The time difference between downlink receiving and uplink transmission of the UE is bigger than an absolute threshold This threshold is specified in IE “UE Rx-Tx time difference threshold” delivered by UTRAN. 10-1-26 Confidential Page 15 of 52
  16. 16. WCDMA RNO Handover Algorithm Analysis and Parameter Configuration Guidance For Intanal Use Event 6G: The time difference between downlink receiving and uplink transmission of the UE is smaller than an absolute threshold This threshold is specified in IE “UE Rx-Tx time difference threshold” delivered by UTRAN. 2.2Handover Algorithms This section will describer the handover-related algorithms already supported by RNC V1.2, so as to provide algorithm guidance for network optimization and parameter adjustments. The contents of this section include softer handover and soft handover algorithms, intra-frequency hard handover algorithm, inter-frequency hard handover algorithm, inter-system hard handover algorithm, load balancing handover algorithm, cell penalty, direct retry algorithm and active set synchronization maintenance and adjacent cell list maintenance method. 2.2.1Softer Handover and Soft Handover Algorithms Presently, RNC V1.2 uses two soft handover algorithms: loose-mode algorithm and relative threshold algorithm. The user can make selection between these two algorithms through the algorithm switch. By default, algorithm 2, namely, relative threshold algorithm is enabled. 1. Loose-mode algorithm 1) When either event 1A or event 1E (referred to as “1A or 1E”) is satisfied, it will be deemed as the trigger condition for adding a soft handover branch; 2) After event 1A or 1E is received, if the number of cells in the active set is 3, no processing will be implemented. 3) When neither the relative threshold nor the absolute threshold (event 1B and 1F) is satisfied, it is deemed as the trigger condition for removing a soft handover branch. 4) If handover is triggered when either event 1B or event 1F is received, but the triggered cell is the best cell, then no processing will be made. 5) When the UE active set is full, event 1A and event 1E reporting is stopped, and event 1C reporting starts 6) Event 1C is the trigger condition for cell replacement in the active set. 7) Event 1D occurs in the active set cell, and measurement control changes, based on the best cell operation algorithm. 8) Event 1D occurs in the monitored set cell, and this cell is added into the active set. If the active set is full, remove any cell among non-best cells and then add the reported best cell, and mark it as the best cell. After successful operation, the measurement control change process is started. 10-1-26 Confidential Page 16 of 52
  17. 17. WCDMA RNO Handover Algorithm Analysis and Parameter Configuration Guidance For Intanal Use 2. Relative threshold algorithm 1) When event 1A report is received, if the active set is not full, then links are sequenced and added in the order of good quality to poor quality (CPICH Ec/No) (in case that multiple cells report event 1A), until the active set is full; if the active set is already full, no processing will be made. 2) When event 1B is received, if there are more than one links in the active set, then the braches are sequenced and removed in the order of poor quality to good quality (CPICH Ec/No) (in case that multiple cells report event 1B), until only one link is left; if there is only one in the active set, no processing will be made. 3) In case of event 1C, the UE will report the replacing and replaced cells in the event trigger list. If the active set is not full, then the triggered cell link will be added; if the active set is already full at this moment and the replaced cell is not the best cell in the active set, then this cell link will be removed. 4) In case of event 1D, if the triggered cell is an active set cell, then it will be marked as the best cell and measurement control is updated; if the triggered cell doe not belong to the active set, then this cell link will be added (if the active set is full, one of the non-best cell will be removed before this link is added) and marked as the best cell, with measurement control updated. 2.2.2Intra-Frequency Hard Handover Algorithm Intra-frequency hard handover will occur in two cases: 1, handover between intra-frequency adjacent cells that belong to different RNCs, between which no Iur interface is available; 2, handover of high-rate PS Best Effort services that exceeds the rate threshold, because too much forward capacity will be occupied if soft handover is adopted in this case. Event 1D is used as the judgment criterion for event intra-frequency hard handover. Namely, the event 1D triggered cell acts as the target cell of the handover. 2.2.3Inter-Frequency Hard Handover Algorithm 1. Basic concepts Carrier coverage verge cell: a cell located at the outmost verge of a carrier coverage area. The characteristic is that the cell does have an intra-frequency adjacent cell in a certain direction. 10-1-26 Confidential Page 17 of 52
  18. 18. WCDMA RNO Handover Algorithm Analysis and Parameter Configuration Guidance For Intanal Use Carrier coverage center cell: a cell other than carrier coverage verge cells. The characteristic is that the cell has intra-frequency adjacent cells in all directions. In a carrier coverage verge cell, when the UE moves towards the direction in which the cell has no intra-frequency adjacent cell, the CPICH Ec/No changes slowly because CPICH RSCP has the same speed with the fading of interference. Simulation shows that CPICH Ec/No can still reach -12dB or so when CPICH RSCP is already lower than the demodulation threshold (about -110dBm). At this moment, the inter-frequency handover algorithm based on CPICH Ec/No measurement has actually failed. Therefore, for a carrier coverage verge cell, it is more suitable and more efficient to use CPICH RSCP as the inter-frequency measurement quantity. For a carrier coverage center cell, CPICH RSCP can also be used as the inter-frequency measurement quantity, but CPICH Ec/No can better reflect the actual link communication quality and the load situation of the cell. 2. Enabling/disabling inter-frequency measurement Because inter-frequency measurement may use the compressed mode, which usually affects the link quality and system capacity, we generally hope that inter-frequency measurement is not enabled unless necessary. Currently, RNC V1.2 decides to enable or disable inter- frequency measurement through the reporting of event 2D and event 2F. When the UE enters the CELL_DCH state or when the best cell is updated, if the inter- frequency handover algorithm is enabled and an inter-frequency adjacent cell list is available for the best cell, then the measurement of event 2D and 2F is configured. The absolute thresholds of events 2D and 2F are the enabling/disabling thresholds of inter-frequency measurement. CPICH Ec/No or RSCP measurement quantity and thresholds will be adopted respectively according to the location property of the best cell in the active set (carrier coverage center or carrier coverage verge as previously described). If the measurement quantity is lower than the enabling threshold , event 2D will be reported, and inter-frequency measurement will be enabled through decision; if the active set quality rises and becomes higher than the disabling threshold, then event 2F reporting will be triggered and inter-frequency measurement will be stopped. 3. Inter-frequency hard handover decision Presently, the periodic measurement reporting mode is used for inter-frequency measurement. In RNC V1.2, the absolute threshold decision method based on cell properties is used for inter-frequency handover decision. According to different cell properties (carrier coverage verge cell and carrier coverage center cell), different physical measurement quantities (CPICH RSCP and CPICH Ec/No) and handover thresholds are used for handover decision. Based on the inter-frequency measurement result periodically reported by the UE, if the measurement values exceed the absolute threshold and the hysteresis values and the “time to 10-1-26 Confidential Page 18 of 52
  19. 19. WCDMA RNO Handover Algorithm Analysis and Parameter Configuration Guidance For Intanal Use trigger” condition is met, then the RNC will implement inter-frequency hard handover with the reported cell as the handover target cell. Note: Due to lack of a special compressed mode control policy, it is recommended that inter-frequency handover be used only for necessary handover caused by discontinuous carrier coverage. In this case, we can consider to enable the compressed mode only at the carrier coverage verge, while disable the compressed mode at the carrier coverage center by means of parameter configuration (by setting the absolute threshold of event 2D to the minimum) to disable inter-frequency hard handover. 2.2.4Inter-System Handover Algorithm RNC V1.2 supports 3G->GSM/GPRS handover. Presently, inter-system handover is used only for inter-system handover caused by discontinuous coverage of 3G networks, and other types of inter-system handover, such as load balancing, are not supported. 1) Inter-system handover is enabled only in cells located at the verge of WCDMA FDD system coverage. 2) Inter-system handover algorithms and inter-frequency handover algorithms are mutually exclusive. That is, when the compressed-mode measurement of inter-system handover is enabled, the compressed-mode measurement of inter-frequency handover must be disabled. 3) Cells at the verge of WCDMA FDD system coverage are identified through the configuration of GSM/GPRS adjacent cell list for them. 4) For inter-system handover, CPICH RSCP is used as the physical measurement quantity and events 2D and 2F are used to decide enabling or disabling the compressed mode. 5) For inter-system handover, three compressed mode style sequences are used for concurrent measurement of GSM RSSI, BASIC identification and BASIC reconfirm, and the configuration of parameters is oriented to the cell type, namely, the parameters can be selected and configured based on the cell characteristics and user mobility statistics characteristics. 6) Periodic measurement reports are used for inter-system handover, and the RNC decides whether to implement hard handover according to the measurement reports. 2.2.5Handover Caused by Load Balancing When the loads of the adjacent cells become unbalanced, the load control algorithm will balance the loads between the adjacent cells through handover. Generally, the algorithm implements load balancing by changing the power of the common pilot channel between adjacent cells. Since handover algorithms obtain the Ec/No of the common pilot channel of 10-1-26 Confidential Page 19 of 52
  20. 20. WCDMA RNO Handover Algorithm Analysis and Parameter Configuration Guidance For Intanal Use adjacent cells through the measurement by the UE, while the handover thresholds of various cells are also obtained through the RNC database, the load balancing control algorithm is transparent to handover algorithms, without any direct interface in between. When the loads become unbalanced among cells of different frequencies in the same Node B, the performance of the entire system may deteriorate. In this case, the load control algorithm will notify the handover algorithm to switch some UEs on heavy-load carries onto light-load carriers thus to balance the loads. At this time, the load control entity selects the specific UEs. Upon selecting the UEs, the load control entity sends the source cell information and the target cell information to the selected UEs’ Handover Control entities , and what the handover entity should to do is just to give out the handover command based on the message it has received. Load balancing between different NodeBs is transparent to the handover algorithm. Therefore, we mainly analyze handover requests caused by load balancing between different carriers in the same coverage area. In this kind of handover, the handover entity actually does not make any specific decision, but it only “forwards” the decision command made by the load control entity. In this kind of handover, two principles are followed for UE selection: (1) UEs in soft handover are not selected. Since the target cell’s synchronization information may be unavailable, the timming re-initiation hard handover procedure is used here. As RNC V1.2 does not support immediate macro diversity, if a UE in soft handover state is selected at this moment for load transfer, it will necessarily result in damage to the soft handover state of this UE, and increase call drop risk. (2) UEs with inconsistent SRNC and CRNC are not selected, because this kind of transfer involves signaling interworking on the Iur interface, while the Iur is an open interface, without this type of signaling. Upon receiving the load transfer signaling, the handover entity first implements handover decision to judge whether the two conditions previously mentioned are satisfied. If so, it will proceed with the next step of processing; otherwise, it will reject the request and indicate the reason. 2.2.6Cell Penalty The purpose of cell penalty caused by handover failure is to prevent the handover algorithm from deciding again on the handover of this UE to a cell that already has no more capacity. In order to avoid making redundant judgments, in case of a handover failure (including soft handover and hard handover), the involved UE will be restricted from initiating any further handover request to the same cell within the penalty time, and the event periodic reporting interval is required to be equal to the penalty time. Thus, after a handover failure, on one hand 10-1-26 Confidential Page 20 of 52
  21. 21. WCDMA RNO Handover Algorithm Analysis and Parameter Configuration Guidance For Intanal Use penalty is exerted on the target cell involved in the handover failure, and on the other the periodic reporting interval is made equal to the penalty time, so that large waste of processing capability is avoided. The Connection-oriented cell penalty algorithm is as follows: (1) The cell penalty algorithm is to deny any handover access to the cell in penalty within the specified period of time, namely, the involved UE is not allowed to initiate any further handover request to this cell. The penalty flag is set to 1; (2) After the penalty time expires, the penalty is released, and the penalty flag is set to 0. 2.2.7Active Set Synchronization Maintenance According to the 25.214 protocol, from the downlink receiving moment of the UE to the corresponding uplink transmission moment, there should be a 1024-chip delay, so as to ensure the normal 1-slot uplink and downlink power control, as shown below: Slot (2560 chips) DL DPCCH T TF T PILOT Data1 P CI Data2 PILOT Data1 P at UTRAN C C Propagation delay DL-UL timing Response offset (1024 chips) To TPC (*3) DL DPCCH T TF T PILOT Data1 P CI Data2 PILOT Data1 P at UE C C 512 chips DL SIR measurement (*1) Response to TPC UL DPCCH PILOT TFCI TPC PILOT at UE Slot (2560 chips) Propagation delay UL SIR measurement (*2) UL DPCCH PILOT TFCI TPC PILOT at UTRAN *1,2 The SIR measurement periods illustrated here are examples. Other ways of measurement are allowed to achieve accurate SIR estimation. *3 If there is not enough time for UTRAN to respond to the TPC, the action can be delayed until the next slot. Figure 9 Power Control Timing As illustrated in the diagram, when the UE complete receiving the downlink PILOT bit, it has the time of 512 chips to generate the TPC bit for downlink power control according to the PILOT 10-1-26 Confidential Page 21 of 52
  22. 22. WCDMA RNO Handover Algorithm Analysis and Parameter Configuration Guidance For Intanal Use bit. When the UE is in the soft handover state, the generation of the TPC bit should be based on the PILOT calculation of all links. However, in the actual system, because the selection of the downlink transmission time is obtained by the NodeB based on the RNC-configured frame offset and code offset after roundup by 256 chips (the minimum time resolution of the NodeB is 256 chips), there is an error of ±128 chips between the actual transmission time and the RNC- configured time. Plus errors in the UE movement speed and clock drift, there will be an error of ±(128+20) chips at the UE side. That is, when the Rx-Tx time difference is within the range of 1024±148 chips, the design of UE and NodeB should be able to satisfy the 1-slot power control requirement; when it is out of this range, the system will be unable to guarantee the 1-slot power control requirement, resulting in power control performance deterioration. The UE Rx-Tx time difference is measured once every 10 frames. When the Rx-Tx time difference is smaller than 876 (1024–148) chips, the UE-end processing time will be reduced, and, as result, it will be likely that the downlink 1-slot power control cannot be guaranteed; when the Rx-Tx time difference is greater than 1172 (1024+148) chips, the NodeB-end processing will be reduced, and it will be likely that the uplink 1-slot power control cannot be guaranteed. There are two UE internal measurement events for the measurement of the protocol- provided synchronization maintenance information: event 6F and event 6G, as described previously. Algorithm description: a) After the UE enters the CELL_DCH state, the algorithm enables the UE to report event 6F and event 6G through measurement control. b) The thresholds, delays and hysteresis values of events 6F and 6G are used as algorithm parameters, which can be adjusted through background configuration. c) Once event 6F or event 6G occurs on a radio link, the network side will release this radio link. D) The cell with its link released may retrigger other events and then new RL could be added to the active set. 2.2.8Direct Retry Algorithm When the UE requests to leave the IDLE mode and enter the CONNECTION mode, if the admission fails, another best cell will be selected for an access attempt based on the RACH measurement report previously reported by the UE. Such an access attempt is called direct retry. The direct retry algorithm needs the following parameters: 1) DRMaxNumber: the maximum direct retry times for each direct retry candidate cell 10-1-26 Confidential Page 22 of 52
  23. 23. WCDMA RNO Handover Algorithm Analysis and Parameter Configuration Guidance For Intanal Use 2) DRDCSThreshold: a basic threshold for entering the candidate set 3) MaxRelatingTime: the maximum time that the RACH measurement report can continue to be used 4) LinearFactor: the linear factor for the relative threshold and time interval during candidate set screening 5) MinSignalRequired: basic access threshold. Algorithm description: (1) The direct retry algorithm is effective only when the UE initiates RRC setup request. (2) The direct retry algorithm buffers the cell measurement value in the RACH measurement report of the UE, deletes the originally saved cell measurement information after the RNC receives a new RACH measurement report, buffers the cells of which the measurement signal CPICH Ec/No is greater than MinSignalRequierd (basic access threshold), and records the reporting time. (3) When the UE initiates an RRC setup requests, if the connection setup fails, the RNC will choose a new cell with the best quality for a further access attempt based on the cell measurement information in the RACH measurement report carried in the RRC CONNECTION REQUEST message, until all the available cells (candidate cells) fail and the number of attempts reaches the maximum retry times. (4) Candidate cells are picked up as follows: 1) Read the current system time, calculate the buffering time of the cell measurement value, and discards the cells of which the buffering time is bigger than MaxRelatingTime 2) Based on the measurement value in the buffered RACH report and the LinearFactor, convert the estimated value of the current cell signal quality: cell measurement value (CPICH Ec/ No) – buffer time (s) × LinearFactor (dB/s) 3) Put the cells of which the estimated quality value is greater than DRDCSThreshold into the candidate set of the direct retry algorithm. (5) Retry with the cell having the best estimated quality from the candidate set cells. If retry fails, continue to retry, until the number of attempts reaches the maximum retry times (DRMaxNumber). 2.2.9Principle for Generating Adjacent Cell List There are two adjacent cell list control methods: 1. Adjacent cell list control method based on the best cell 10-1-26 Confidential Page 23 of 52
  24. 24. WCDMA RNO Handover Algorithm Analysis and Parameter Configuration Guidance For Intanal Use When the adjacent cell list is controlled based on the best cell, the basic policy is as follows: (1) If there only one cell, the adjacent cell list will be controlled based on this cell; (2) If a cell is added by event 1D, after it is successfully added, the adjacent cell list will be controlled based on this cell; (3) If a cell is added by an event other than event 1D, the adjacent cell list will not be changed; (4) If the best cell has not been removed, the adjacent cell list will not be changed; (5) If the best cell has been removed, a new best cell will be selected based on the information obtained during the removal action, and the adjacent cell list will be modified after successful removal of the best cell; (6) If event 1D occurs on a cell in the active set, the adjacent cell list will be modified. (7) This method is relative simple, but is may bring the problem of inaccurate control for UEs under the macro diversity. 2. Control method based on all the cells in the active set A control method that can take the adjacent cells of all the cells in the active set is a good policy. The adjacent cell list is generated by means of the following method: Step 1: Add active set cells; Step 2: Add the common adjacent cells of the cells of all the active sets (3 active sets) into the adjacent cell list. If there are more than 32 adjacent cells after this action, remove randomly cells added in this step; Step 3: Add the common adjacent cells of every two active set cells into the adjacent cell list. If there are more than 32 adjacent cells after this action, remove randomly cells added in this step; Step 4: Consider adding the common adjacent cells of each active set cell into the adjacent cell list, starting from the adjacent cells of the best cell. If there are more than 32 adjacent cells after this action, remove cells by starting from the worst cell. Note: The RNC V1.2 version supports the adjacent cell list control method based on the best cell. 3 Handover Parameter Setting 10-1-26 Confidential Page 24 of 52
  25. 25. WCDMA RNO Handover Algorithm Analysis and Parameter Configuration Guidance For Intanal Use 3.1Description The MML client utility can be used for handover parameter setting. This utility provide convenient command navigation and function description, detailed usage and parameter descriptions of various commands. Figure 10 MML Client According to the functioning scope, handover algorithm parameter configuration commands are divided into categories: RNC-oriented global parameter configuration and cell-oriented parameter configuration. Handover common parameter configuration is RNC-oriented global parameter setting. Both RNC-oriented setting commands and cell-oriented setting commands are available for the configuration of intra-frequency handover measurement algorithm parameters, inter- frequency handover measurement algorithm parameters and inter-system handover measurement algorithm parameters. Generally, the adjustments of these parameters during network optimization are all cell-oriented settings, while RNC-oriented global parameter configuration commands facilitate modification of whole-network handover parameters. For one same parameter, the cell-oriented command has higher priority. 10-1-26 Confidential Page 25 of 52
  26. 26. WCDMA RNO Handover Algorithm Analysis and Parameter Configuration Guidance For Intanal Use 3.2Handover Common Parameters 3.2.1Maximum Number of Cells in Active Set Definition MaxCellInActiveSet, maximum number of cells in the active set Scope Per RNC Range and unit Integer(1..3) Working range Integer(1..3) Recommended value 3 Balance in setting Modification of value is not recommended. Modification/query To configure this RNC-oriented global handover parameter, use the command set hocomm; to view the current configuration of the parameter, use the command lst hocomm. 3.2.2Penalty Time Definition PenaltyTime, cell penalty time parameter, as described in Section 2.2.6. Scope Per RNC Range and unit Integer(1..255), s. Working range Integer(1..60) Recommended value 30, namely the penalty time is 30 seconds Balance in setting The setting of this parameter is related to traffic statistics. According to the general traffic statistics result, the average duration of a call is 60s, so the actual value range of this parameter is 1 to 60 seconds. If this value is too small, the resources will not be timely released, and therefore the penalty is meaningless; if this value is too big, radio links will fail to be timely added, and this is bad for link QoS improvement. Modification/query 10-1-26 Confidential Page 26 of 52
  27. 27. WCDMA RNO Handover Algorithm Analysis and Parameter Configuration Guidance For Intanal Use To configure this RNC-oriented global handover parameter, use the command set hocomm; to view the current configuration of the parameter, use the command lst hocomm. 3.2.3Event 6F Trigger Threshold Definition RxTxtoTrig6F, the trigger threshold of event 6F. Namely, if the time interval between the UE’s downlink receiving and the corresponding uplink transmission is greater than this absolute threshold, event 6F will be triggered. Scope Per RNC Range and unit Integer(768..1280), chip. Working range Integer(1024..1280)chip Recommended value 1172 Balance in setting The value of this parameter should not be too close to 1024; otherwise radio links will be removed too early. It is recommended that this parameter be adjusted within the range of 1172±3 chips. To guarantee the 1-slot power control, decrease the value of this parameter; otherwise, it could be increased. Modification/query To configure this RNC-oriented global handover parameter, use the command set hocomm; to view the current configuration of the parameter, use the command lst hocomm. 3.2.4Event 6G Trigger Threshold Definition RxTxtoTrig6G, absolute threshold for triggering event 6G. Scope Per RNC Range and unit Integer(768..1280), chip. Working range Integer(768..1024)chip Recommended value 876 Balance in setting 10-1-26 Confidential Page 27 of 52
  28. 28. WCDMA RNO Handover Algorithm Analysis and Parameter Configuration Guidance For Intanal Use The value of this parameter should not be too close to 1024; otherwise radio links will be removed too early. It is recommended that this parameter be adjusted within the range of 876±3 chips. To guarantee the 1-slot power control, increase the value of this parameter; otherwise, it could be increased. Modification/query To configure this RNC-oriented global handover parameter, use the command set hocomm; to view the current configuration of the parameter, use the command lst hocomm. 3.2.5Time-to-Trigger Parameters for Events 6F and 6G Definition Time-to-trigger parameters for event 6F and event 6G, including TrigTime6F and TrigTime6G. Scope Per RNC Range and unit Enum(D0, D10, D20, D40, D60, D80, D100, D120, D160, D200, D240, D320, D640, D1280, D2560, D5000), ms. Working range Enum(0, 10, 20, 40, 60, 80, 100, 120, 160, 200, 240, 320, 640, 1280, 2560, 5000)ms Recommended value D240. Balance in setting UE Rx-Tx time difference type1 is measured once per 100ms, with measurement accuracy being 1.5 chips. To avoid wrong judgment caused by measurement errors of the UE, a delay can be set in the event trigger time, so that the UE can perform measurement at least twice for judgment. The time delay on internal processing shall also be taken into consideration. We recommend that this parameter be set at 240ms. Modification/query To configure this RNC-oriented global handover parameter, use the command set hocomm; to view the current configuration of the parameter, use the command lst hocomm. 3.2.6BE Service Handover Rate Decision Threshold Definition BEBitRateThd. When the PS BE service rate exceeds this threshold, intra-frequency hard handover will be implemented; when it is lower than this threshold, soft handover will be implemented. Scope 10-1-26 Confidential Page 28 of 52
  29. 29. WCDMA RNO Handover Algorithm Analysis and Parameter Configuration Guidance For Intanal Use Per RNC Range and unit Enum (D8, D32, D64, D128, D144, D256, D384), corresponding to (8k, 32k, 64k, 128k, 144k, 256k, 384k) bps. Working range Enum(D8,D32,D64,D128,D144,D256,D384) Recommended value D64. Balance in setting It is the rate decision threshold deciding whether soft handover is to be implemented for the BE service. When the maximum rate of the BE service transmission channel is smaller than this threshold, the system will perform soft handover for the service user so as to ensure the QoS for the user; when the maximum rate of the BE service transmission channel exceeds this threshold, the system will implement intra-frequency hard handover for the service user so as to prevent excessive influence on the system capacity caused by soft handover. Modification/query To configure this RNC-oriented global handover parameter, use the command set hocomm; to view the current configuration of the parameter, use the command lst hocomm. 3.2.7Soft Handover Method Select Switch Definition SHOMechod, used to select the loose-mode algorithm or the relative threshold algorithm for soft handover decision. Scope Per RNC Range and unit Enum(SHO_METHOD1, SHO_METHOD2), soft handover algorithm 1, soft handover algorithm 2 Working range Enum(SHO_METHOD1, SHOMETHOD2) Recommended value Soft handover algorithm 2. Balance in setting Algorithm 1 is the loose-mode algorithm that adds a cell into the active set no matter the cell triggers event 1A or event 1E, and removes a cell only after it triggers both event 1B and event 1F simultaneously. Algorithm 2 is the relative threshold algorithm, which does 10-1-26 Confidential Page 29 of 52
  30. 30. WCDMA RNO Handover Algorithm Analysis and Parameter Configuration Guidance For Intanal Use not involve events 1E and 1F. It adds a cell into the active set as soon as it triggers event 1A, and removes a cell from the active set as soon as it triggers event 1B. Modification/query To configure this RNC-oriented global handover parameter, use the command set hocomm; to view the current configuration of the parameter, use the command lst hocomm. 3.2.8Handover Algorithm Switches Definition This parameter defines the switches of various algorithms related to connection-oriented handover. The specific algorithm parameters can function only after the corresponding algorithm switches being enabled. Scope Per RNC Range and unit 32 bits, 0~4294967295; each bit can be set at 0 or 1 to control a handover algorithm. Currently there are the 17 handover algorithm switches, arranged as follows from the lowest bit to the highest: Soft handover Compressed mode maintenance algorithm at soft handover synchronization Intra-frequency hard handover Inter-frequency hard handover 3G-2G inter-system hard handover 2G-3G inter-system hard handover Compressed mode Uplink compressed mode 6G & 6F measurement Cell penalty Location RTT enhanced location Relocation Relocation based on time delay optimization Relocation based on Iur transmission resource optimization CS UE relocation based on Iur transmission resource optimization Direct retry Working range Integer(0~32767) Recommended value 1159, namely 00000010010000111: 10-1-26 Confidential Page 30 of 52
  31. 31. WCDMA RNO Handover Algorithm Analysis and Parameter Configuration Guidance For Intanal Use Soft handover — On (1) Compressed mode maintenance algorithm at soft handover synchronization — On (1) Intra-frequency hard handover — On (1) Inter-frequency hard handover — Off (0) 3G-2G inter-system hard handover — Off (0) 2G-3G inter-system hard handover— Off (0) Compressed mode — Off (0) Uplink compressed mode — On (1) 6G & 6Fmeasurement — Off (0) Cell penalty — Off (0) Location — On (1) RTT enhanced location — Off (0) Relocation — Off (0) Relocation based on time delay optimization — Off (0) Relocation based on Iur transmission resource optimization — Off (0) CS UE relocation based on Iur transmission resource optimization — Off (0) Direct retry — Off (0) Balance in setting Corresponding configuration should be carried out based on the implementation of each version of algorithm. 1) Test compressed mode: compressed mode switch should be enabled. 2) Test inter-frequency hard handover: inter-frequency hard handover + compressed mode switch should be enabled. 3) Test inter-system hard handover : inter-system handover enabled + compressed mode switch should be enabled. 4) Test relocation: relocation enable switch — a main switch. When the main switch is off, the following three will not function Relocation based on time delay optimization enable switch Relocation based on Iur transmission resource optimization enable switch CS UE relocation based on Iur transmission resource optimization enable switch Modification/query For RNC-oriented settings, use the command set/lst corrmalgoswitch. 3.3Intra-Frequency Handover Measurement Algorithm Parameters 3.3.1Soft Handover Relative Thresholds Definition 10-1-26 Confidential Page 31 of 52
  32. 32. WCDMA RNO Handover Algorithm Analysis and Parameter Configuration Guidance For Intanal Use These parameters define the difference between the quality of a cell (currently it is evaluated with PCPICH Ec/No) and the overall quality of the active set (if w=0, then it is the quality of the best cell). The relative threshold parameters for soft handover include IntraRelThdFor1A (relative threshold for event 1A) and IntraRelThdFor1B (relative threshold for event 1B). Scope Per RNC/CELL Range and unit Integer(0~29), corresponding to 0 to 14.5dB; configuration step: 1 (0.5dB). Working range Integer(0~16) Recommended value 10, namely, 5dB. Balance in setting Settings of these parameters determine the size of the soft handover area and the soft handover subscriber proportion. In a CDMA system, it is required that the UE proportion in soft handover should be 30% to 40% so as to ensure smooth handover. Based on the simulation result, when the relative thresholds are set at 5dB, the proportion of UEs in the soft handover state (number of active set cells ≥ 2) is around 35%. It is recommended that this value be slightly bigger in the early stage of deployment (5 to 7dB). To save system resources, this figure can be gradually decreased with the growth of the number of subscribers, but it must be bigger than 3dB. The default configuration is 5dB. In addition, in special applications, different relative threshold values can be set for event 1A and event 1B to reduce the ping-pong effect and change the soft handover proportion in some special applications. For example, if the adjustment of the hysteresis values for events 1A and 1B is insufficient for good control of the ping-pong effect, the relative threshold for event 1B can be set larger than that for event A to reduce the ping-pong effect. However, the relative thresholds for events 1A and 1B should generally be kept consistent; instead, the time-to-trigger setting, L3 filter coefficient and hysteresis value should used to reduce the ping-pong effect. Modification/query To implement cell-oriented settings, use the commands add/mod/rmv/lst cellintrafreqho. Otherwise, use the RNC-oriented global settings configured with the command set intrafreqho as the configuration for the concerned cell. 3.3.2Soft Handover Absolute Thresholds Definition 10-1-26 Confidential Page 32 of 52
  33. 33. WCDMA RNO Handover Algorithm Analysis and Parameter Configuration Guidance For Intanal Use These parameters correspond to the signal strength that satisfies the basic QoS assurance. The soft handover absolute threshold parameters include IntraAblThdFor1E (absolute threshold for event 1E) and IntraAblThdFor1F (absolute threshold for event 1F). Scope Per RNC/CELL Range and unit Integer(-20..-10), dB. Working range Integer(-20..-10)dB Recommended value -18. Balance in setting This value is the absolute threshold value used in the measurement reports of events 1E and 1F in the soft handover algorithm, corresponding to the signal strength that satisfies the basic QoS assurance. This value affects the trigger of events 1E and 1F. Because an absolute threshold is only a necessary condition, but not a sufficient one, for access judgment, this value should be relative loose. With value settings in IS-95 and the lower threshold of -20dB, -18dB is deemed to be a reasonable value. Modification/query To implement cell-oriented settings, use the commands add/mod/rmv/lst cellintrafreqho. Otherwise, use the RNC-oriented global settings configured with the command set intrafreqho as the configuration for the concerned cell. 3.3.3Intra-Frequency Measurement Filter Coefficient (FilterCoef) Definition The measurement filtering coefficient used in L3 filtering of intra-frequency measurement report Scope Per RNC/CELL Range and unit Enum(D0, D1, D2, D3, D4, D5, D6, D7, D8, D9, D11, D13, D15, D17, D19), corresponding to (0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 11, 13, 15, 17, 19) Working range Enum(D0, D1, D2, D3, D4, D5, D6, D7, D8) Recommended value D5, namely 5 Balance in setting The following formula is used for the calculation of measurement value filtering: 10-1-26 Confidential Page 33 of 52
  34. 34. WCDMA RNO Handover Algorithm Analysis and Parameter Configuration Guidance For Intanal Use Fn = (1 − a ) ⋅ Fn −1 + a ⋅ M n Where, Fn: the updated measurement result after filtering processing. Fn-1: the old measurement result of the previous moment after filtering processing. Mn: The latest measurement value received from the physical layer. a = (1/2)(k/2), where, k is from IE "Filter coefficient", namely “FilterCoef” here. When k=0 and a=1, L3 filtering is not implemented. According to R2-000809, we recommend that the commonly used value of the filter coefficient be in the range of {0,1,2,3,4,5,6}. The bigger the filter coefficient is, the stronger the burr filtering capability will be, but the weaker the signal tracking capability will be. Therefore, a balance must be made. Calculated based on the typical handover area size [3], the distance between two NodeBs is 1000m, while calculated based on the 40%soft handover ratio of the entire system, the typical handover distance between two cells is about 150m. A mobile station that is moving at the speed of 20km/h goes across the handover area in averagely 20 to 30 seconds, while it takes only 5 to 6 seconds for a mobile station that is moving at the speed of 100km/h to go across the handover area. When such factors as hysteresis and trigger delay in event judgment are taken into account, the tacking time needs to be further reduced. Based on the analysis above, FilterCoef should be configured as follows: 5 as the default setting for intra-frequency filter coefficient, and this parameter can be adjusted according to the actual situation. In addition, for different cell coverage types, typical values are recommended as follows: a, if the cell covers urban area, the intra-frequency filter coefficient can be 7; b, if the cell covers suburbs, the intra-frequency filter coefficient can be 6; c, if the cell covers rural area, the intra-frequency filter coefficient can be 3. Table 1 Filter Coefficient vs. Intra-Frequency Tracking Time Filter 0 1 2 3 4 5 6 7 8 9 11 coefficient Iteration 1 2 3 5 7 10 15 21 30 42 85 times The table above lists the iteration times required when different filter coefficients are used to obtain 85% of the final output value. According to 25.133, in the CELL_DCH state, L1 reports the intra-frequency measurement result to L3 at a cycle of 200ms. When the iteration times are substituted with Intra-frequency tracking time, the table above will become: 0 1 2 3 4 5 6 7 8 9 11 Filter coefficient Intra- 0.2 0.4 0.6 1 1.4 2 3 4.2 6 8.4 17 frequency tracking time (s) 10-1-26 Confidential Page 34 of 52
  35. 35. WCDMA RNO Handover Algorithm Analysis and Parameter Configuration Guidance For Intanal Use Modification/query To implement cell-oriented settings, use the commands add/mod/rmv/lst cellintrafreqho. Otherwise, use the RNC-oriented global settings configured with the command set/lst intrafreqho as the configuration for the concerned cell. 3.3.4Hysteresis Related to Soft Handover Definition Hysteresis for event triggering, including Hystfor1A, Hystfor1B, Hystfor1C, Hystfor1D, Hystfor1E and Hystfor1F Scope Per RNC/CELL Range and unit Integer(0..15) , corresponding to 0..7.5dB; configuration step 1(0.5dB) Working range table 1Recommended Soft Handover Hysteresis Settings for Different Movement Speeds Speed (km/h) Range Recommended Value 5 6~10(3~5dB) 10(5dB) 50 4~10(2~5dB) 6(3dB) 120 2~6(1~3dB) 2(1dB) Typical configuration 4~10(2~5dB) 6(3dB) Recommended value 6(3dB) for events 1A and 1E, and 8(4dB) for events Balance in setting For UEs entering the soft handover area, increase of the hysteresis value means decrease of the soft handover range, while for UEs leaving the soft handover area, it means increase of the soft handover range. If the number of UEs entering the handover area is the same as the number of UEs leaving the handover area, there will be no influence on the actual soft handover proportion. The bigger the hysteresis value is, the stronger the signal fluctuation resistance capability will be, and thus the better the ping-pong effect will be suppressed, but the slower the handover algorithm can react on signal changes. Therefore, in the setting of this parameter, not only the radio environment (slow fading characteristic) but also the actual handover distance and the UE movement speed should be taken into due consideration. The setting of this parameter can be adjusted within the range of 2 to 5dB. As events that add cells to the active set, 1A and 1E are critical events. In order to ensure timely handover, the hysteresis value for event 1A can be smaller, but not be too smaller, than those for 1B, 1F, 1C and 1D; otherwise, the soft handover proportion will be affected. 10-1-26 Confidential Page 35 of 52
  36. 36. WCDMA RNO Handover Algorithm Analysis and Parameter Configuration Guidance For Intanal Use In addition, In addition, hysteresis adjustment should generally be considered together with the filter coefficient and time-to-trigger settings. Modification/query To implement cell-oriented settings, use the commands add/mod/rmv/lst cellintrafreqho. Otherwise, use the RNC-oriented global settings configured with the command set intrafreqho as the configuration for the concerned cell. 3.3.5Time-to-Trigger Parameters Related to Soft Handover Definition Time-to-trigger parameters, including TrigTime1A, TrigTime1B, TrigTime1C, TrigTime1D, TrigTime1E and TrigTime1F, corresponding to the six events for intra-frequency measurement respectively. Scope Per RNC/CELL Range and unit Enum(D0, D10, D20, D40, D60, D80, D100, D120, D160, D200, D240, D320, D640, D1280, D2560, D5000), corresponding to (0, 10, 20, 40, 60, 80, 100, 120, 160, 200, 240, 320, 640, 1280, 2560, 5000)ms Working range Enum(D0, D200, D240, D640, D1280, D2560, D5000) Recommended value table 2Recommended Time-to-Trigger Settings for Different Movement Speeds Speed (km/h) Range (ms) Recommended value (ms) 5 640, 1280 1280 50 240, 640 640 120 240, 640 640 Typical configuration 640, 1280 640 Balance in setting Simulation shows that the setting of the hysteresis value can effectively reduce the average handover times and mis-handover times, and thus can prevent the occurrence of unwanted handover. The bigger the hysteresis value is, the less the average handover timers will be. However, the increase of the hysteresis value will bring more risks of call drop. It is stipulated in TS 25.133V3.6.0 that the physical layer of intra-frequency measurement updates the measurement result every 200ms. Therefore, a time-to-trigger value below 200ms does not make any practical sense, and it should be as close as possible to an integral multiple of 200ms. In addition, simulation also shows that mobile stations moving at different speeds respond differently to the time-to-trigger value. The call drop rate is more sensitive to the time-to-trigger value when the mobile station is in high- speed movement, while it is less sensitive when the mobile station is in low-speed 10-1-26 Confidential Page 36 of 52
  37. 37. WCDMA RNO Handover Algorithm Analysis and Parameter Configuration Guidance For Intanal Use movement, and ping-pong handover and mis-handover are suppressed to a certain extent. Therefore, for cells where there are more high-speed moving mobile stations, this value can be relatively small, while for cells where there are more low-speed moving mobile stations, this value can be relatively big. Different types of events have different requirements on the time-to-trigger setting: events that add cells to the active set (event 1A and event 1E) generally require a small time-to-trigger setting, while events that replace cells in the active set (event 1C and event 1D) generally require low ping-pong handover and mis-handover and do have produce remarkable influence on the call drop rate. For the latter type of events, the time-to-trigger setting can be properly big. For events that remove cells from the active set (event 1Band event 1F), the time-to-trigger value is set mainly to reduce ping-pong handover; the initial setting can be the same as that for event 1A and event 1E, and can be properly adjusted based on the actual network statistics result. Modification/query To implement cell-oriented settings, use the commands add/mod/rmv/lst cellintrafreqho. Otherwise, use the RNC-oriented global settings configured with the command set intrafreqho as the configuration for the concerned cell. 3.3.6WEIGHT Definition Weighted factor (see formulas on Section 2.1.1) Scope Per RNC/CELL Range and unit Integer(0..20), corresponding to 0..2; step: 0.1 Working range Integer(0..10) Recommended value 10, namely 1 Balance in setting This parameter is used to determine the soft handover relative threshold based on the measurement value of each cell in the active set. The bigger this parameter is, the higher the relative threshold obtained under the same condition will be. When W=0, the determination of soft handover relative threshold is related to only the best cell in the active set. Modification/query 10-1-26 Confidential Page 37 of 52
  38. 38. WCDMA RNO Handover Algorithm Analysis and Parameter Configuration Guidance For Intanal Use To implement cell-oriented settings, use the commands add/mod/rmv/lst cellintrafreqho. Otherwise, use the RNC-oriented global settings configured with the command set intrafreqho as the configuration for the concerned cell. 3.3.7Detected Set Statistics Switch Definition DetectStatSwitch, used to control whether the UE measurement report contains the information of cells in the detected set, so as to provide statistics data for future network optimization. Scope Per RNC/CELL Range and unit Enum(ON, OFF) Working range Enum(ON,OFF) Recommended value OFF Balance in setting In the beginning of network operation, when you are not absolutely sure about the adjacent cell configuration, this switch can be set to ON so that missed adjacent cells can be detected and thus handover can be smoothly implemented. After network optimization, this switch can be set to OFF. Modification/query To implement cell-oriented settings, use the commands add/mod/rmv/lst cellintrafreqho. Otherwise, use the RNC-oriented global settings configured with the command set intrafreqho as the configuration for the concerned cell. 3.4Inter-Frequency Handover Algorithm Parameters 3.4.1Inter-Frequency Measurement Filter Coefficient (FilterCoef) Definition The measurement smoothening coefficient used in L3 filtering of inter-frequency measurement report Scope Per RNC/CELL Range and unit 10-1-26 Confidential Page 38 of 52
  39. 39. WCDMA RNO Handover Algorithm Analysis and Parameter Configuration Guidance For Intanal Use Enum(D0, D1, D2, D3, D4, D5, D6, D7, D8, D9, D11, D13, D15, D17, D19), corresponding to (0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 11, 13, 15, 17, 19) Working range Enum(D0, D1, D2, D3, D4, D5, D6, D7, D8) Recommended value D5, namely 5 Balance in setting The following formula is used for the calculation of measurement value filtering: Fn = (1 − a ) ⋅ Fn −1 + a ⋅ M n Where, Fn: the updated measurement result after filtering processing. Fn-1: the old measurement result of the previous moment after filtering processing. Mn: The latest measurement value received from the physical layer. a = (1/2)(k/2), where, k is from IE "Filter coefficient", namely “FilterCoef” here. When k=0 and a=1, L3 filtering is not implemented. According to R2-000809, we recommend that the commonly used value of the filter coefficient be in the range of {0,1,2,3,4,5,6}. The bigger the filter coefficient is, the stronger the burr filtering capability will be, but the weaker the signal tracking capability will be. Therefore, a balance must be made. For different cell coverage types, typical values are recommended as follows: a, if the cell covers urban area, the inter-frequency filter coefficient can be 7; b, if the cell covers suburbs, the inter-frequency filter coefficient can be 6; c, if the cell covers rural area, the inter-frequency filter coefficient can be 3. Modification/query To implement cell-oriented settings, use the commands add/mod/rmv/lst cellinterfreqho. Otherwise, use the RNC-oriented global settings configured with the command set interfreqho as the configuration for the concerned cell. 3.4.2Cell Location Property Definition CellProperty (cell location property), indicating whether the cell is located at the verge or center of the carrier coverage. Scope Per CELL Range and unit Enum(CARRIER_FREQUENCY_VERGE_CELL, CARRIER_FREQUENCY_CENTER_CELL), (cell located at carrier coverage verge / cell located at carrier coverage center) Working range 10-1-26 Confidential Page 39 of 52

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