UE Level Oscillating Handover Minimization Feature Description 119/221 04-LZA 701 6014/1 Uen AM Copyright © Ericsson AB 2016-2019, 2021. All rights reserved. No part of this document may be reproduced in any form without the written permission of the copyright owner. Disclaimer The contents of this document are subject to revision without notice due to continued progress in methodology, design and manufacturing. Ericsson shall have no liability for any error or damage of any kind resulting from the use of this document. Trademark List All trademarks mentioned herein are the property of their respective owners. These are shown in the document Trademark Information. 119/221 04-LZA 701 6014/1 Uen AM | 2021-01-08 Contents Contents 1 UE Level Oscillating Handover Minimization Overview 1 2 Dependencies of UE Level Oscillating Handover Minimization 2 3 Feature Operation of UE Level Oscillating Handover Minimization Process Steps 3 3.1 5 4 Network Impact of UE Level Oscillating Handover Minimization 10 5 Parameters of UE Level Oscillating Handover Minimization 11 6 Performance of UE Level Oscillating Handover Minimization 12 7 Activate UE Level Oscillating Handover Minimization 14 8 Deactivate UE Level Oscillating Handover Minimization 15 119/221 04-LZA 701 6014/1 Uen AM | 2021-01-08 UE Level Oscillating Handover Minimization 119/221 04-LZA 701 6014/1 Uen AM | 2021-01-08 1 UE Level Oscillating Handover Minimization Overview The UE Level Oscillating Handover Minimization feature enables the UE to perform a handover to the best cell earlier. Access Type: Feature Identity: Value Package Name: Value Package Identity: Node Type: Licensing: LTE FAJ 121 1885 Self-Organizing Networks FAJ 801 0435 Baseband Radio Node Licensed feature. One license for each radio. Summary The UE Level Oscillating Handover Minimization feature decreases the number of unnecessary handovers in a radio network. This decreases the signaling load and increases throughput. In a radio network where the HOM is configured to a high value, the UE Level Oscillating Handover Minimization feature makes it possible to decrease the configured HOM. The number of handovers does not increase. The benefit is that the UE performs a handover to the best cell earlier. Additional Information For information on the preferred state and parameter settings of this feature, see RAN Parameter Recommendations Lists. 119/221 04-LZA 701 6014/1 Uen AM | 2021-01-08 1 UE Level Oscillating Handover Minimization 2 Dependencies of UE Level Oscillating Handover Minimization The UE Level Oscillating Handover Minimization feature has handover features as prerequisites. Table 1 Feature Dependencies Feature Relationship Description Intra-LTE Handover (FAJ 121 0489) Prerequisite This feature modifies intra-LTE handover behavior. Coverage-Triggered Inter-Frequency Handover (FAJ 121 0877) Prerequisite This feature modifies inter-frequency handover behavior. Category M Connected Mode Mobility Related (Part of LTE Basic) When the Category M Connected Mode Mobility feature is active, the functions of this feature also apply to Category M1 UEs. Hardware No special hardware requirement for this feature. Network Requirements No network requirements for this feature. 2 119/221 04-LZA 701 6014/1 Uen AM | 2021-01-08 3 Feature Operation of UE Level Oscillating Handover Minimization The purpose of the UE Level Oscillating Handover Minimization feature is to reduce the number of unnecessary handovers by preventing fast handovers and repeated handovers to the same cell. Feature Operation Sequence Diagram Last Cell Current Cell Handover TL Handover TC Potential Handover L0000529A Figure 1 Time Measurements for the Decision Process and Performance Measurements The handover decision process is different for intra-frequency and interfrequency relations. The intra-frequency handover decision has the following specifications: — The process is triggered by an Event A3 measurement. — The node calculates the time in the current cell. — The node checks the handover oscillation rules. — The outcome is one of the following: — Attempt the handover — Reject the handover — Apply an offset to the HOM 119/221 04-LZA 701 6014/1 Uen AM | 2021-01-08 3 UE Level Oscillating Handover Minimization If the decision is to apply an offset, the process continues in the following way: — The HOM is calculated. — The offset is added to the HOM. — The handover condition is checked. The result is one of the following decisions: • Attempt the handover • Reject the handover The inter-frequency handover decision has the following specifications: — The process is triggered by an Event A5 measurement. — The node calculates the time in current cell. — The node checks the handover oscillation rules. — The outcome is one of the following decisions: — Attempt the handover — Reject the handover — Apply an offset to the HOT If the decision is to apply an offset, the process continues in the following way: — The HOT is calculated. — The offset is added to the HOT. — The handover condition is checked. The result is one of the following decisions: 4 • Attempt the handover • Reject the handover 119/221 04-LZA 701 6014/1 Uen AM | 2021-01-08 A mobility measurement report is received Measure time in current cell Apply handover oscillation prevention rules [Action is “Reject Handover”] [Action is “Attempt Handover”] [Action is “Apply Offset”] Calculate handover margin Calculate signal quality improvement [Signal quality improvement < handover margin + offset] [Signal quality improvement >= handover margin + offset] Do not attempt handover Attempt handover L0000528A Figure 2 Handover Oscillation Decision Process This decision process modifies the handover sequence described in Intra-LTE Handover. 3.1 Process Steps The UE Level Oscillating Handover Minimization feature minimizes the number of unnecessary handovers with prevention functions. For every UE, the node measures the time in the current cell and keeps a record of the time in last cell. The node then bases the handover decision on these values. Table 2 Handover Oscillation Prevention Rules Time in Current Cell (TC) Time in Action Last Cell (TL) Rule TC < T1(2) - Prevention of Very Fast (1) 119/221 04-LZA 701 6014/1 Uen AM | 2021-01-08 Reject handover. 5 UE Level Oscillating Handover Minimization Time in Current Cell (TC) (1) Time in Action Last Cell (TL) Rule Handovers on page 7 T1 ≤ TC < T2(3) TL < T2 Apply an extra 2 dB handover margin offset, offset2 for handover back to the last cell. Prevention of Fast Intra-Frequency Handovers on page 7 T1 ≤ TC < T2 TL ≥T2 Apply an extra 1 dB handover margin offset, offset1 for handover to the last cell. Prevention of Fast Inter-Frequency Handovers on page 8 T2 ≤ TC < T3(4) TL < T2 Apply an extra 2 dB handover margin offset, offset2 for handover back to the last cell. Prevention of Repeated Oscillating Handover to a Neighbor on page 8 T2 ≤ TC < T3 TL ≥ T2 Attempt handover as in design base. T3 ≤ TC - Attempt handover as in design base. (1) (2) Time limit 1 = 200 ms (3) Time limit 2 = 2,000 ms (4) Time limit 3 = 5,000 ms Handover Time Measurements and Handover Oscillation Detection The time in the current cell is a time interval. It starts when the RLC and the MAC layer of the Uu link is established between the UE and the node. It is measured until the handover attempt decision that the node makes when it receives the RRC measurement report. The time in the last cell measurement is fetched from the UE History provided in the X2-AP or S1-AP HANDOVER REQUEST message, from the last cell. At every handover out, the time in the current cell is measured and compared to time limit2. If the time in the current cell is less than time limit2, a handover oscillation has occurred and is counted by the EUtranCellRelation.pmHoOscInterF or EUtranCellRelation.pmHoOscIntraF Performance Management counters. When a handover preparation is implemented, EUtranCellRelation.pmHoOscQci1 is also issued, if a QCI1 bearer is established for the UE. 6 119/221 04-LZA 701 6014/1 Uen AM | 2021-01-08 The signal strengths in the current cell and the neighbor cell are measured in dB or dBm, depending on the trigger quantity of the neighbor relations. Table 3 Trigger Quantity Measurement Unit RSRQ dB RSRP dBm For more information about RRC, see 3GPP TS 36.331. For more information about X2AP, see 3GPP TS 36.423. For more information about S1AP, see 3GPP TS 36.413. Prevention of Very Fast Handovers When the UE Level Oscillation Handover Minimization feature is active, the node never performs a very fast handover of a UE. The limit for very fast handovers is time limit1. According to the standard process, if the UE is in the current cell for less than time limit1, and the UE sends an RRC mobility measurement report, a handover is triggered. Because of the prevention rule, the node does not attempt a handover in these cases. Prevention of Fast Intra-Frequency Handovers The node uses an increased HOM for fast handovers without reconfiguring the measurements in the UE. Without the UE Level Oscillating Handover Minimization feature, the node configures the UE with a specified HOM. The UE sends an Event A3 measurement report if the signal strength of a target cell is higher than the signal strength of the serving cell. The HOM is calculated using the formula in the following equation: HOM = a3offset − cellIndividualOffsetEUtran + hysteresisA3 The reception of an Event A3 measurement report causes the node to attempt the handover of the UE to the target cell. For more information about the Event A3 measurement reports, see Intra-LTE Handover. With this feature enabled, if the time in the current cell is less than time limit2, and the last cell is the same as the target cell, the node applies offset1 to the HOM. The node applies the extra offset by calculating the HOM, and checking whether the condition in the following equation is valid: SN> SC + HOM + Offset1 119/221 04-LZA 701 6014/1 Uen AM | 2021-01-08 7 UE Level Oscillating Handover Minimization Signal strength in the current cell and signal strength in the neighbor cell are retrieved from the Event A3 measurement report. If the equation is valid, the handover is attempted, otherwise the handover is prevented. Prevention of Fast Inter-Frequency Handovers For the prevention of fast handovers, the node increases the inter-frequency HOT with offset1. Offset1 has the same value for the prevention of fast interfrequency handovers and for the prevention of fast intra-frequency handovers. The HOT is calculated using one of the following equations, depending on the trigger quantity used for the Event A5 measurement reports: — If RSRP is used, the equation is the following: HOT = a5Threshold2RSRP − cellIndividualOffsetEUtran + hysteresisA5 — If RSRQ is used, the equation is the following: HOT = a5Threshold2RSRQ − cellIndividualOffsetEUtran + hysteresisA5 This is done by the node without reconfiguring the measurements in the UE. Under certain conditions, the node configures the UE to send an Event A5 measurement report if the signal strength of a target cell is higher than the HOT. For more information about the Event A5 measurement reports, trigger quantities, and other conditions that are not affected by the UE Level Oscillating Handover Minimization feature, see Coverage-Triggered Inter-Frequency Handover. After receiving an Event A5 measurement report, the node attempts the handover of the UE to the target cell according to the standard process. With this feature enabled, if the time in current cell is less than time limit2, and the last cell is the same as the target cell, the node applies offset1 to the HOT. The node applies the extra offset by calculating the HOT, and checking if the condition in the following equation is valid. SN is retrieved from the Event A5 measurement report. SN> HOT + Offset1 If it is valid, handover is attempted, otherwise handover is prevented. Prevention of Repeated Oscillating Handover to a Neighbor The node prevents a repeated fast handover to a neighbor by using offset2, if the following conditions apply: — Time in the last cell is less than time limit2. — Time in the current cell is less than time limit3. 8 119/221 04-LZA 701 6014/1 Uen AM | 2021-01-08 In this case, offset2 is used for both inter-frequency and intra-frequency handover in the same way as described for offset1 in Prevention of Fast IntraFrequency Handovers on page 7 and Prevention of Fast Inter-Frequency Handovers on page 8. 119/221 04-LZA 701 6014/1 Uen AM | 2021-01-08 9 UE Level Oscillating Handover Minimization 4 Network Impact of UE Level Oscillating Handover Minimization The UE Level Oscillating Handover Minimization feature makes it possible to increase capacity in the network, and decrease unnecessary handovers. Performance and Capacity The UE Level Oscillating Handover Minimization feature enables increased capacity in the network in many scenarios. The increase is made possible by allowing the operator to configure a smaller HOM without increasing the rate of unnecessary handovers. Interfaces No impact. Other Network Elements The UE Level Oscillating Handover Minimization feature reduces the number of unnecessary handovers in the network in many scenarios. 10 119/221 04-LZA 701 6014/1 Uen AM | 2021-01-08 5 Parameters of UE Level Oscillating Handover Minimization The UE Level Oscillating Handover Minimization feature affects MOM attributes by adding offsets. Table 4 Parameters Parameter Type Description a3offset Affected In certain prevention processes, an offset is added to this parameter for one UE. The offset does not affect the parameter value registered in the MOM. a5Threshold2RSRP Affected In certain prevention processes, an offset is added to this parameter for one UE. The offset does not affect the parameter value registered in the MOM. a5Threshold2RSRQ Affected In certain prevention processes, an offset is added to this parameter for one UE. The offset does not affect the parameter value registered in the MOM. 119/221 04-LZA 701 6014/1 Uen AM | 2021-01-08 11 UE Level Oscillating Handover Minimization 6 Performance of UE Level Oscillating Handover Minimization The UE Level Oscillating Handover Minimization feature has KPIs for downlink and uplink throughput calculation, counters for handover calculation and performance management events. KPIs Table 5 KPIs KPI Description Downlink Throughput Indicates the average downlink throughput for each UE. Uplink Throughput Indicates the average uplink throughput for each UE. E-RAB Retainability Indicates the retainability of each UE in connected mode. Counters — EUtranCellRelation.pmHoOscInterF — EUtranCellRelation.pmHoOscIntraF — EUtranCellRelation.pmHoOscQci1 For a given neighbor relation, only one of EUtranCellRelation.pmHoOscInterF and EUtranCellRelation.pmHoOscIntraF steps, depending on the type of the relation. The counters are also available when the UE Level Oscillating Handover Minimization feature is not activated. Events Table 6 PM Events Event Event Parameter INTERNAL_EVENT_SON_UE_OSCILLATION_ PREVENTED EVENT_PARAM_NEIGHBOR_CGI INTERNAL_EVENT_SON_OSCILLATION_DET ECTED EVENT_PARAM_HO_PREV_CAUSE EVENT_PARAM_HO_SOURCE_OR_TARGET_TYPE EVENT_PARAM_NEIGHBOR_CGI EVENT_PARAM_ERAB_QCI1_IND 12 119/221 04-LZA 701 6014/1 Uen AM | 2021-01-08 For a full list with detailed information about PM events, see the list files in the List Files library folder. 119/221 04-LZA 701 6014/1 Uen AM | 2021-01-08 13 UE Level Oscillating Handover Minimization 7 Activate UE Level Oscillating Handover Minimization To use the feature, it must be activated following the usual feature activation procedure. Prerequisites — The license key is installed in the node. — Coverage-Triggered Inter-Frequency Handover feature is activated. — Continuous Cell Trace Recording (CCTR) is activated since at least one week. This ensures there is troubleshooting data available if something goes wrong. Steps 1. Set the FeatureState.featureState attribute to ACTIVATED in the FeatureState=CXC4011157 MO instance. After This Task Let the CCTR be active for one week, for continued collection of troubleshooting data. 14 119/221 04-LZA 701 6014/1 Uen AM | 2021-01-08 8 Deactivate UE Level Oscillating Handover Minimization If the feature is no longer needed, it can be deactivated following the usual feature deactivation procedure. It must also be deactivated before the activation of any conflicting feature. Prerequisites Continuous Cell Trace Recording (CCTR) is activated since at least one week. This ensures there is troubleshooting data available if something goes wrong. Steps 1. Set the FeatureState.featureState attribute to DEACTIVATED in the FeatureState=CXC4011157 MO instance. After This Task Let the CCTR be active for one week, for continued collection of troubleshooting data. 119/221 04-LZA 701 6014/1 Uen AM | 2021-01-08 15
