Why mobile systems need handover? Mobile systems are composed by cells which the coverage is limited. The mobility of the UE. Providing the continuous service the basic element in QoS. Tài liệu giúp hiểu các khái niệm handover trong 3G Hiểu về call flow trong 3G Hiểu về các khái niệm cơ bản trong handover Thuật toán handover
Internal WCDMA Handover Principle www.huawei.com HUAWEI TECHNOLOGIES CO., LTD Huawei Confidential Why mobile systems need handover? Mobile systems are composed by cells which the coverage is limited The mobility of the UE Providing the continuous service - the basic element in QoS HUAWEI TECHNOLOGIES CO., LTD Huawei Confidential Page TS25.331 Flow of Handover and Related Parameters TS25.133 Measurement Process TS25.215 Definitions of Measurement Indexes HUAWEI TECHNOLOGIES CO., LTD Huawei Confidential Page After studying this course, you will: Understand basic concepts about handover Understand the flow of soft handover Master basic parameters about soft handover Master soft handover decision algorithms HUAWEI TECHNOLOGIES CO., LTD Huawei Confidential Page Chapter Overview of Handover Chapter Handover Measurement Chapter Soft Handover Chapter Hard Handover HUAWEI TECHNOLOGIES CO., LTD Huawei Confidential Page Chapter Overview of Handover 1.1 Purposes of Handover 1.2 Modes and Status of the UE 1.3 Methods and Types of Handover 1.4 Comparison between Soft Handover and Hard Handover HUAWEI TECHNOLOGIES CO., LTD Huawei Confidential Page Purposes of Handover Providing the continuous service in mobile system is the basic element in QoS Providing continuous communication service is the main purpose of handover The load balance: sharing the resource The hierarchy divided by speed and service: high efficiency of using resource HUAWEI TECHNOLOGIES CO., LTD Huawei Confidential Page Chapter Overview of Handover 1.1 Purposes of Handover 1.2 Modes and Status of the UE 1.3 Methods and Types of Handover 1.4 Comparison between Soft Handover and Hard Handover HUAWEI TECHNOLOGIES CO., LTD Huawei Confidential Page UE Modes and Status URA_PCH DEAD IDLE RRC connection CELL_DCH HUAWEI TECHNOLOGIES CO., LTD CELL_PCH Huawei Confidential CELL_FACH Page UE Modes and Status (Status migration) - Reducing activities, DRX, saving power and resource RRC connection URA_PCH CELL_PCH URA Update After several Cell Updates Cell Update No traffic CELL_DCH CELL_FACH Low speed PS - Dedicated channel VP/Voice/PS These statuses are only applied in the UTRAN and UE They are transparent to the CN - Common channel, low speed service - Triggered by theCN SMS IDLE - Monitering the paging channel - Cell reselecting - Searching a PLMN - Find a cell to camps on DEAD HUAWEI TECHNOLOGIES CO., LTD Huawei Confidential Page Inter-frequency Hard Handover - Measurement and Event (Continued) Measurement Report Methods Event report − 2D event: The quality of current frequency is lower than a certain absolute threshold value It is used to start the compressed mode − 2F event: The quality of current frequency is higher than a certain absolute threshold value It is used to stop the compressed mode − 2B event: The quality of current frequency is lower than the absolute threshold value, and the quality of the neighbor frequency is higher than another absolute threshold value It is used in coverage handover trigger − 2C event: The quality of the neighbor frequency is higher than a certain absolute threshold value It is used in load handover trigger Periodic report HUAWEI TECHNOLOGIES CO., LTD Huawei Confidential Page Inter-frequency Hard Handover - Starting and Stopping of the Compression Mode Starting conditions of measurement 2D event: If the quality of the currently frequency is lower than a certain absolute threshold value, the compressed mode is started Use the velocity estimation algorithm to decide starting of inter-frequency handover measurement Stopping conditions of measurement 2F event After the best cell is changed, the new best cell does not have any interfrequency neighbor cell The timer of inter-frequency measurement expires The speed estimate status of the UE changes, and related inter-frequency handover measurement is disabled according to the hierarchical cell algorithm In hard handover, if the coverage reason is triggered, handover is stopped simultaneously HUAWEI TECHNOLOGIES CO., LTD Huawei Confidential Page Inter-frequency Hard Handover Flow Signaling flow TARGET NODEB SOARCE NODEB ALCAP ESTABLISHMENT ALCAP RELEASE HUAWEI TECHNOLOGIES CO., LTD Huawei Confidential Page Inter-frequency Hard Handover - Common Parameters Inter-frequency coverage handover parameters: Methods for report inter-frequency measurement: periodic or event Inter-frequency measurement variables: CPICH Ec/No or CPICH RSCP Inter-frequency measurement layer filtering coefficient, time to trigger, and hysteresis Starting and stopping threshold values of inter-frequency measurement: Configure it respectively for CPICH Ec/No, CPICH RSCP, and configure 2D, 2F event for CS and PS Inter-frequency coverage handover threshold value: quality threshold value of the target cell Quality threshold value of used frequency in inter-frequency hard handover Lowest access threshold value in inter-frequency handover HUAWEI TECHNOLOGIES CO., LTD Huawei Confidential Page Inter-frequency Hard Handover - Questions Why the compressed mode threshold for the CS and PS are configured different? If the UE uses the CS service and PS service at the same time, the 2D and 2F parameters of which service are used to decide starting the compressed mode? The Eb/No required by these two services are different, so the RSCPs are also different If the parameters of any service meet the threshold, the compressed mode is started Is the compressed mode started immediately after the UE sends the 2D parameter? The compressed mode is started after the RNC reconfigure the RB HUAWEI TECHNOLOGIES CO., LTD Huawei Confidential Page Chapter Hard Handover 4.1 Intra-frequency Hard Handover 4.2 Inter-frequency Hard Handover 4.3 Inter-RAT Hard Handover HUAWEI TECHNOLOGIES CO., LTD Huawei Confidential Page Inter-RAT Hard Handover Overview Measurement and Event Handover Decision Algorithm Handover Flow Common Parameters HUAWEI TECHNOLOGIES CO., LTD Huawei Confidential Page Inter-RAT Hard Handover - Overview Category WCDMA FDD < ） >GSM WCDMA FDD < ） >WCDMA TDD WCDMA FDD < ） >CDMA2000 Features The radio access technology (RAT) adopted in the system after handover is different Need compressed mode to assist measurement Advantages Coverage: Solve the problem of transition between different systems Capacity: Improve the utilization of old equipments to the greatest extent (2G->3G) Disadvantages The flow is complicated, and the requirement for compatibility of equipment is high The UE is complicated HUAWEI TECHNOLOGIES CO., LTD Huawei Confidential Page Inter-RAT Hard Handover - Measurement and Event Measurement in Inter-RAT hard handover (GSM measurement) Measurement types: − GSM Carrier RSSI − BSIC Identification − BSIC Reconfirmation Measurement processing: layer-1 filtering, layer-3 filtering HUAWEI TECHNOLOGIES CO., LTD Huawei Confidential Page Inter-RAT Hard Handover - Measurement and Event (Continued) Measurement Report − Event report ▪ 2D event: starting GSM measurement ▪ 2F event: stopping GSM measurement ▪ 3A event: The quality of WCDMA is lower than an absolute threshold but quality of a GSM neighbor cell is higher than another absolute threshold ▪ 3C event: The quality of a GSM neighbor cell is higher than an absolute threshold HUAWEI TECHNOLOGIES CO., LTD Huawei Confidential Page Inter-RAT Hard Handover - Decision Algorithm Decision of Inter-RAT handover Inter-RAT handover based on coverage − Event ▪ 3A event: The quality of the currently used frequency is lower than an absolute threshold value, but quality of a GSM cell is higher than another absolute threshold value − Periodic ▪ Evaluation: Confirm the status according to the GSM RSSI measurement value and the BSIC of the target cell in GSM and evaluate the cell of which the GSM RSSI exceeds the absolute threshold value If both conditions are met, consider the cell of which the BSIC is confirmed HUAWEI TECHNOLOGIES CO., LTD Huawei Confidential Page Inter-RAT Hard Handover - Decision Algorithm (Continued) Inter-RAT handover based on non-coverage − Event ▪ The 3C event means that the quality of the GSM cell is higher than an absolute threshold value HUAWEI TECHNOLOGIES CO., LTD Huawei Confidential Page Inter-RAT Handover Flow HUAWEI TECHNOLOGIES CO., LTD Huawei Confidential Page Inter-RAT Handover - Common Parameters Inter-RAT coverage handover parameters Starting and stopping thresholds of Inter-RAT measurement: They determine the thresholds of the 2D event and 2F event Configure CPICH Ec/No, CPICH RSCP for the CS service and PS service respectively Measurement variables for the 2D event and 2F event in Inter-RAT handover: Select CPICH Ec/No or PICH RSCP BSIC selection confirmation switch Inter-RAT coverage handover threshold: GSM RSSI threshold in Inter-RAT coverage handover Configure it for the CS service and PS service respectively Quality threshold of used frequency in Inter-RAT handover Configure time to trigger and hysteresis for each event respectively Penalty duration HUAWEI TECHNOLOGIES CO., LTD Huawei Confidential Page Summary - Categories of Handover According to the signaling characters − Soft handover (softer handover) − Hard handover According to the properties of source cell and target cell: − Intra-frequency handover − Inter-frequency handover − Inter-RAT handover (UMTS ↔ GSM/GPRS) According to the purpose of handover: − Based on Coverage − Based on Noncoverage HUAWEI TECHNOLOGIES CO., LTD Huawei Confidential Page ... Soft Handover and Hard Handover Item Soft Handover (Softer Handover) Hard Handover Number of radio links in the activate set Several One Interruption during handover No Yes Intra-frequency Intra-frequency... between soft handover, softer handover, and hard handover? Why intra-frequency handover is not always soft handover? How does handover gain arise? How much are various handover gains? HUAWEI... Intra-frequency Inter-frequency or Inter-RAT Frequencies in the cells before and after handover Handover gain Maximum-ratio combining or selective combining which can reduce the impact of fading and