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Published byFelicia Dixon Modified over 8 years ago
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Requirements and viewpoints for backhaul synchronization
微秒:microsecond draft-zhou-tictoc-ran-sync-req-01.txt Angela Zhou, Xiaodong Duan China Mobile
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Outline Synchronization Requirements
Recommendations for 1588v2 telecom profile Concerns on synchronization
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Synchronization in 2G/GSM
Current 2G/GSM Networks Future 2G/GSM Networks BTS BSC Ref. clock MS IP BSC PSN IP BTS Circuit Emulation E1 FE GE BTS BSC Ref. clock MS SDH E1 Sync Requirements in current 2G/GSM Networks SDH transport network need frequency sync: +/- 50ppm Base stations need frequency sync: +/- 0.05ppm Reference clock is distributed via an explicit transport at the physical layer: PDH/SDH Sync Requirements in future 2G/GSM Networks Packet switching network do not need strict synchronization Base stations need frequency sync: +/- 0.05ppm For base stations, Reference clock is distributed via PSN, need physical synchronization support (e.g. Sync Ethernet) or packet-based synchronization (e.g. 1588). Note: Previous SDH transport network maybe still exist for traditional base stations, sync requirement is the same as before. 2. Applications Description 2.1. Time Service Applications There are many applications in telecommunications that need to know the time with great precision. If there would be some services that require great precision such as position services, then RAN system has to provide precise time synchronization. In TDD mode of 2G/3G system, radio interface time synchronization is also needed for smooth handover. 2.2. Frequency Service Applications Cellular base-stations require a highly accurate frequency reference from which they derive transmission frequencies and operational timing however their transport is over E1/T1 or PSN, such as Ethernet IP and MPLS. The radio frequencies should be accurate. To use radio spectrum efficiently transmission frequencies which are allocated to a given base station and its neighbors had better not interfere with each other. There is an additional requirement derived from the need for smooth handover when a mobile station crosses from one cell to another.
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Synchronization in 3G/TD-SCDMA
Future 3G/TD-SCDMA Networks Current trail 3G/TD-SCDMA Networks RNC NodeB PSN FE GE Ref. clock RNC NodeB SDH ATM Sync Requirement in future 3G/TD-SCDMA Networks Packet switching network do not need strict synchronization Base stations need frequency sync: +/- 0.05ppm, and phase sync: +/- 3us For base stations, reference clock is distributed via PSN, need physical synchronization support (e.g. Sync Ethernet) for frequency sync or packet-based synchronization (e.g. 1588v2) for time/phase sync. Time sync between BTS and external reference clock: +/- 1.5us Sync Requirement in current 3G/TD-SCDMA Networks SDH transport network need frequency sync: +/- 50ppm For transport network, Reference clock is distributed via an explicit transport at the physical layer: PDH/SDH Base stations need frequency sync: +/- 0.05ppm, and phase sync: +/- 3us For base stations, reference clock is distributed via GPS. Time sync between BTS and GPS: +/- 1.5us 2. Applications Description 2.1. Time Service Applications There are many applications in telecommunications that need to know the time with great precision. If there would be some services that require great precision such as position services, then RAN system has to provide precise time synchronization. In TDD mode of 2G/3G system, radio interface time synchronization is also needed for smooth handover. 2.2. Frequency Service Applications Cellular base-stations require a highly accurate frequency reference from which they derive transmission frequencies and operational timing however their transport is over E1/T1 or PSN, such as Ethernet IP and MPLS. The radio frequencies should be accurate. To use radio spectrum efficiently transmission frequencies which are allocated to a given base station and its neighbors had better not interfere with each other. There is an additional requirement derived from the need for smooth handover when a mobile station crosses from one cell to another.
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Synchronization in 4G/TDD-LTE
Possible synchronization requirements in LTE Synchronization requirements in ALL-IP network Synchronization requirements in distributing Base Station (mesh topology among base stations) Synchronization requirements in distributing BBU & RRU Synchronization requirements in radio interfaces Note: synchronization requirement in LTE is under discussion. 2. Applications Description 2.1. Time Service Applications There are many applications in telecommunications that need to know the time with great precision. If there would be some services that require great precision such as position services, then RAN system has to provide precise time synchronization. In TDD mode of 2G/3G system, radio interface time synchronization is also needed for smooth handover. 2.2. Frequency Service Applications Cellular base-stations require a highly accurate frequency reference from which they derive transmission frequencies and operational timing however their transport is over E1/T1 or PSN, such as Ethernet IP and MPLS. The radio frequencies should be accurate. To use radio spectrum efficiently transmission frequencies which are allocated to a given base station and its neighbors had better not interfere with each other. There is an additional requirement derived from the need for smooth handover when a mobile station crosses from one cell to another. AGW eNB PSN Ref. clock
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Synchronization in different parts
Requirements schematic diagram Base station Base station controller UE Radio Interface SYNC Ref. Clock Network SYNC Node SYNC Synchronization requirements in different positions Layer Sub Items Frequency Accuracy Phase Accuracy Network Sync E1 50ppm - STM-N 4.6ppm PTN Not so strict Node Sync Controller-Base station If provide location service, TBD 50ppb(Time alignment over Iu) 1.5us(Time alignment over Iu) Inter-Base station 50ppb 3us(TD-SCDMA&TDD LTE) BS-Reference clock 1.5us(TD-SCDMA&TDD LTE) Radio interface GSM TD-SCDMA 3us TDD LTE
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Outline Synchronization Requirements
Recommendations for 1588v2 telecom profile Concerns on synchronization
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Time Alignment over Iu UE Node B Ref. Clock Iu RNC Client Network SYNC UE Master Node B Sync Ethernet for frequency sync and 1588v2 for time/phase sync The time sync accuracy among node B is 3us RNC pick up time information from Iu interface and distribute to node B by 1588v2 protocol The accuracy between node B and RNC should be 1.5us The peer-to-peer transparent clock type is more efficient in point-to-multipoint scenario The equipments along the clock transport should support 1588v2 transparent p2p clock type Iu 接口的同步精度未定义 除了p2p透明时钟是否考虑其他?
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External Reference Clock
Ref. Clock UE Node B RNC Network SYNC Client Client UE Node B Sync Ethernet for frequency sync and 1588v2 for time/phase sync The time sync accuracy among node B is 3us RNC and node B pick up time information from network by 1588v2 protocol The accuracy between node B and reference clock should be 1.5us RNC-node B sync is needed when there is position service The peer-to-peer transparent clock type is more efficient in point-to-multipoint scenario The equipments along the clock transport should support 1588v2 transparent p2p clock type RNC可不参与同步,除非特别的位置服务等
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Outline Synchronization Requirements
Recommendations for 1588v2 telecom profile Concerns on synchronization
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Concerns & Summary The requirements for RAN is clear and urgent
Radio Access Network is on the early stage of moving to IP transport Using GPS will affect the flexible deployment of BS, we really need a new synchronization technology to substitute GPS, epically though a simple Ethernet port How to distribute synchronization through packet based network? How to deploy different clock type in certain scenarios? Telecom profiles of 1588 should be standardized: network scale/ network load/ local clock accuracy Security The synchronization methods in next generation mobile network (LTE) and MESH/SON network should be paid more attention. At the same time, it is complex and more technologies in backhaul How to extend IEEE1588v2 or other synchronization technology so that it can be used smoothly in PBN and complex backhaul. Features needed for Backhaul nodes to support 1588v2 for high accuracy Different layers shall collaborate to meet the sync requirements form end to end, so what kind of mechanisms/protocols are need between different layer and technologies in backhaul? G.8261 是否需要强调1588v2?PBN?
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Thank you & Any questions?
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