Frekvenční a fázová synchronizace

Transkript

1 Proč je nutná synchronizace v mobilích sítích 1588v2 PTP, SyncE Master a Slave Clock, Boundary a Transparent Clock v systémech 1588v2, referenční body Stabilita obnovených hodin, měření wanderu a fáze

2 Proč je nutná synchronizace v mobilních sítích Why do mobile basestations need frequency synchronisation? Regulation and licensing of spectrum Interference with other basestations Handoff for mobiles moving between cells Quality of service Doppler effect Handset frequency acceptance ± 250ppb Basestation frequency accuracy ± 50ppb f c frequency

3 Doppler Shift f = f o. v At 320km/h (200mph), f = 300ppb c At 160km/h (100mph), f = 150ppb

4 GSM, UMTS (European 2G and 3G mobile standards): no requirement for time synchronisation Frekvenční a fázová synchronizace Time Synchronisation cdmaone, cdma2000 (N. American 2G and 3G mobile standards): Basestations must be within 3 s of system time (10 s holdover) Required for soft handoff Handset must see pilot signals from both basestations within a few microseconds of each other to handover properly Company ±3 s Confidential ±1km ±3 s ±1km

5 LTE Advanced: Small Cells Enhanced Inter-Cell Interference Co-ordination (eicic) Interference in small cell edge area Solution: Almost Blank Sub Frames macrocell reduces power temporarily so handsets can hear the small cell Time synchronisation of ±1 to 5 s required to co-ordinate ABSF

6 LTE Advanced: CoMP Co-ordinated Multipoint (CoMP) Several techniques for improving throughput and performance: Joint Transmission or Reception Co-ordinated Beamforming Dynamic Point Selection Dynamic Point Blanking All require time synchronisation in the order of ±1 to 5 s

7 LTE Synchronization Requirements LTE (FDD) ±50 ppb N/A ±16ppb (G ) LTE (TDD) LTE-A MBSFN LTE-A CoMP Network MIMO LTE-A eicic HetNet Coordination Small Cells ±50 ppb ±50 ppb ±50 ppb ±50 ppb ±100 ppb ±1.5µs (< 3km radius) ±5µs (> 3km radius) ±1 to 5µs implementation dependent N/A (FDD) ±1.5µs (TDD) ±1 to 5µs (eicic) ±16ppb (G ) ±1.1μs (G ) ±16ppb (G ) ±1.1μs (G ) ±33ppb ±1.1μs (G ) Home Cells ±250 ppb N/A (FDD) ±1.5µs (TDD) ±100ppb ±1.1μs (G )

8 Frekvenční synchronizace signály mají stejnou periodu, ale ne nutně fázi Fázový posun mezi začátkem referenčního signálu Fázová synchronizace signály začínají se stejný čas, ale ne nutně se stejnou periodou

9 Mobile Backhaul Synchronization Approach 1: Use the physical layer clock SyncE clocks (EEC) made identical to SECs in performance terms Up to 10 SSUs PRC Up to 20 SECs or EECs SSU Up to 20 SECs SSU SSU or EECs Approach 2: Use a packet timing protocol Packet timing protocols such as PTP or NTP used to deliver frequency Up to 10 SSUs Up to 20 SECs or EECs End Equipment M Packet Network S PRC Up to 20 SECs or EECs SSU Up to 20 SECs or EECs SSU SSU Packet Master and Slave End Equipment

10 Conventional timing (frequency) signal: A nominally periodic signal, generated by a clock: Significant instants Timing jitter and wander Packet timing signal: A nominally periodic signal, generated by a packet master clock: Significant instants F Payload 4 H 4 H F Payload 4 H 3 H F Payload 4 H 2 H F Payload 4 H 1 H Packets Packet Delay Variation

11 G.8260: Definitions and Terminology for Synchronization in Packet Networks (includes PDV metrics) Basic Aspects Network Requirements Clock Specifications Methodds and Architecture Profiles Frequency G.8261: Timing and Synchronization Aspects in Packet Networks (Frequency) G : PDV Network Limits Applicable to Packet- Based Methods (Frequency) G.8262: Timing Characteristics of a Synchronous Ethernet Equipment Slave Clock (EEC) G.8263: Timing Characteristics of Packet-Based Equipment Clocks (PEC) G.8264: Distribution of Timing Information through Packet Networks G.8265: Architecture and Requirements for Packet-Based Frequency Delivery G : Precision Time Protocol Telecom Profile for Frequency Synchronization Time/phase G.8271: Time and Phase Synchronization Aspects in Packet Networks G : Network Limits for Time/Phase (full timing support) G : Network Limits for Time/Phase (partial timing support) G.8272: Timing Characteristics of Primary Reference Time Clocks (PRTC) G.8273: Packet-Based Equipment Clocks for Time/Phase: Framework G : Telecom Grandmaster (T-GM) G : Telecom Boundary Clock (T-BC) G : Telecom Transparent Clock (T-TC) G : Telecom Time Slave Clock (T-TSC) G.8275: Architecture and Requirements for Packet-Based Time and Phase Delivery G : PTP Profile for Time and Phase Synchronization (full timing support) G : PTP Profile for Time and Phase Synchronization (partial timing support) Published 1 st version agreed Under development Options

12 Synchronous Ethernet (SyncE) Účelem SyncE je distribuovat informaci o frekvenci od PRC (Primary Reference Clock) prostřednictvím ethernetových zařízení. Hlavní činností SyncE rozhraní je získat synchronizační frekvenci z přicházejícího bitového streamu a předat ji systémovým hodinám EEC (Ethernet Equipment Clock) routru nebo switche, které pak tuto informaci šíří dál k dalšímu zařízení. Hlavní rozdíl mezi klasickým ethernetem a SyncE je ve vysílání hodin na TX portu routru/switche.

13 SyncE ITU-T G.8261 Používá k synchronizaci fyzickou vrstvu Získává hodinový signál bit stream Každý uzel obnovuje hodiny Nezávislý na použité síti (data jsou oddělená od synchronizace) EEC (Ethernet Equipment Clock)

14 Synchronous Ethernet (SyncE) Použitý vysoce stabilní interní oscilátor Ethernet Classic : ±100ppm. Synchronous Ethernet: ±4.6ppm ITU-T Standardy G.8261: Timing & Synchronisation in Packet Networks G.8262: Timing Characteristics for Synchronous Ethernet Equipment G.8264: Distribution of Timing Through Packet Networks (ESMC)

15 Precision Time Protocol (PTP) - IEEE 1588v2 Jakmile je ustanovena hierarchie Master/Slaver (BMCA) Announce message, může začít proces synchronizace hodin, pomocí výměny PTP zpráv, která se skládá ze dvou částí: Změřením propagation delay mezi Mastrem a Slavem. Sync Message obsahuje časovou značku kdy byla odeslaná Mastrem. Delay_Req_Message je identická jako Sync Message, ale odeslaná Slavem, obsahuje časovou značku kdy byla odeslaná Slavem. Delay_Resp_Message odeslaná Mastrem, obsahuje časovou značku kdy byla Delay_req_message doručená Mastru. t1 = Master Time čas vyslání Sync Message. t2 = Slave Time čas přijetí Sync Message. t3 = Slave Time čas vyslání Delay_Req Message. t4 = Master Time čas přijetí Delay_Req Message.

16 t1=10 Frekvenční a fázová synchronizace Master Slave Time = 10 s Time = 11 s Sync = 10s? Time = 5 s Follow up = 10s Time = 8 s t2=8 t4=19 Time = 17 s Time = 19 s Time = 23 s Time = 24 s Delay Req= 11s Delay Resp= 19s Sync = 23s? Follow up = 23s Delay = [(t2-t1) + (t4-t3)]/2 = [(19-11) + (8-10)]/2 = 3 Offset = (t2-t1) Delay = -5 Time = 11 s Time = 17 s Time = 23 s Time = 24 s t3=11 Slave čas upravený o offset a delay Zpráva Sync resp. Follow Up udávajá zpoždění Master->Slave (t-ms) Zprávay Delay_req a Delay_resp udávají zpoždění Slave->Master (t-sm) Jakákoliv asymetrie mezi (t-ms) a (t-sm) vnáší chybu do výpočtu korekce hodin!

17 Time Error Source Constant Time Error (cte) The fixed component is called Constant Time Error (cte) and comes from Link asymmetries and Node (T-GM, T-BC, T-TSC) asymmetries. Node asymmetry Link asymmetry Route asymmetry Dynamic Time Error (dte) The time-varying component is called Dynamic Time Error (dte) and comes primarily from Packet Delay Variation (PDV) caused by router queues, etc.

18 Approaches to Time Distribution 1. Full Timing Support Combined use of PTP for time and SyncE for frequency Every switch or router in the timing path must support PTP and SyncE (i.e. contain a Telecom Boundary Clock, T-BC) 2. Assisted Partial Timing Support Use of GNSS for time, supported by PTP for protection Some switches or routers in the timing path may support PTP (i.e. contain a BC or TC), but this is not mandatory 3. Partial Timing Support Use of PTP for both time and frequency distribution Some switches or routers in the timing path may support PTP (i.e. contain a BC or TC), but this is not mandatory

19 PTP with Full Timing Support GNSS Reference Point A Reference Point B Reference Point C Reference Point D all switch/routers on the path between T-GM and T-TSC contain a T-BC T-GM T-TSC PRTC Features PTP Grandmaster Packet Network PTP Slave End clock Every element in the path must be PTP aware T-BC case covered in standards, T-TC case under development Uses a combination of SyncE and PTP, where SyncE provides the frequency and PTP the phase/time

20 Slave Master Frekvenční a fázová synchronizace Boundary Clock Boundary Clocks reduce PDV accumulation by: PTP SyncE Master Slave EEC G Telecom Boundary Frequency Clock Time/Phase (T-BC) (T1/E1/SyncE) (1pps) PTP 1pps SyncE Terminating the PTP flow and recovering the reference time Generating a new PTP flow using the recovered time No direct transfer of PDV Slave/Master combination Telecom BCs use SyncE to: Improve stability Improve holdover

21 Slave Master Frekvenční a fázová synchronizace Packet Interfaces Siwtch/router Switch/Router Packet Interfaces Boundary Clock PTP Messages PTP Messages 1pps SyncE EEC SyncE

22 Q1 Frekvenční a fázová synchronizace Transparent Clock Transparent Clocks reduce PDV by; Calculating the time a PTP packet resides in the TC device (in nsec) and insert the value into the CorrectionField. Using the CorrectionField, the Slave or terminating BC can effectively remove the PDV introduced by the TC. Q2 Qn Packet Delay in TC Device inserted into CorrectionField TC CF Accuracy = 50ns (IEEE C )

23 PTP with Full Timing Support Benefits Controlled, deterministic environment suitable for both frequency and time/phase transfer Building block approach to network construction, with example time error budgets in G Profile, architecture and clock performance defined by ITU-T, published May 2014 Challenges All equipment in path needs to be PTP aware No control of asymmetry in the network

24 G Partial Timing Support Profile GNSS not all switch/routers on the path between T-GM and T-TSC contain a T-BC GNSS T-GM APTSC Features PRTC PTP Grandmaster Packet Network Objective is backup to GNSS, i.e. assisted holdover Combined GPS/PTP Slave End clock Can use GNSS when in service to monitor PTP service quality and measure network asymmetry PTP can maintain timebase when GNSS is out of service (e.g. due to jamming or antenna failure)

25 Benefits Frekvenční a fázová synchronizace PTP with Assisted Partial Timing Support Mutual co-operation between GNSS and PTP PTP provides an initial time fix to assist the GNSS during signal acquisition GNSS calibrates the PTP asymmetry, and monitors its suitability for service PTP can monitor GNSS timing quality, e.g. antenna failure, spoofing, jamming Operates over existing networks, including third party access networks that may not have built-in PTP support Profile, architecture and clock performance under definition in ITU-T Challenges Less deterministic path from T-GM to APTSC, because not every network element assists in the timing flow May need constraints on traffic load and span of the packet network Little agreement in ITU-T on the scope of the network, hence consent date keeps slipping

26 Use case: In-building Small Cells Features: GNSS antenna on roof, supplies synchronization to building (and possibly neighbouring buildings) Distributed to small cells using PTP over the building LAN No timing support provided (e.g. BCs or TCs)

27 PTP with Partial Timing Support GNSS not all switch/routers on the path between T-GM and T-TSC contain a T-BC T-GM PRTC Packet Network PTP Grandmaster Features Objective is to distribute time over a small PTP-unaware network Small network, potentially only a single in-building network Places GNSS source as close to the end clock as possible PTP Slave End clock

28 PTP with Partial Timing Support Benefits Simple deployment over existing networks Operators do not need to own or manage the network Can be leased from a third party, e.g. building owner Short network, so cable or fibre asymmetry small Profile, architecture and clock performance under definition in ITU-T Challenges Less deterministic path from T-GM to T-TSC, because not every network element assists in the timing flow Switches/routers not designed with PTP asymmetry in mind, so device asymmetry is uncontrolled May need constraints on traffic load and span of the packet network Little agreement in ITU-T on the scope of the network

29 G : Reference Points GPS Reference Point A Reference Point B Reference Point C Reference Point D T-GM T-TSC PRTC PTP Grandmaster Reference Point A: Packet Network PTP Slave End clock Time accuracy and stability at output of PRTC (defined in G.8272) Reference Point B: Packet timing interface at output of PTP GM (defined in G.8272; same as A) Reference Point C: Time accuracy and stability at input to end equipment (defined in G ) Reference Point D: End application requirements (e.g. air interface time/frequency specification)

30 G Network Reference Points A, B ±100ns (PRTC/T-GM) ±200ns dte (random network variation) Class A T-BCs: ±550ns cte (node asymmetry, ±50ns per node) ±250ns cte (link asymmetry compensation) C cte uses up 70% of the network equipment budget D Class B T-BCs: ±420ns cte (21 nodes, ±20ns per node) ±380ns cte (link asymmetry compensation) ±250ns (short term holdover) ±150ns (end application) ±1.1µs network equipment budget ±1.5µs end-to-end budget

31 - co je nutné měřit TIE Time Interval Error (ns) Fázový rozdíl mezi referenčním signálem a testovaným signálem v určitém čase. MTIE Maximum Time Interval Error (ns) Maximální rozkmit testovaného signálu vůči referenčnímu signálu, během celého testu. TDEV Time Deviation (ns) časová stabilita fáze v závislosti na času měření. Phase Error (TIE) MTIE t(1) t(2) t(3) t(4) t(5) TIE (ns) Reference Clock Observation time (n t 0 ) Test Signal MTIE (ns) *Faster playback is used to better explain the concept. t (s)

32 Juniper ACX 1100 Frekvenční a fázová synchronizace Clock Interface on Manufacturers Equipments Huawei BTS 3900 Juniper ACX 1100 has a SMC port which outputs 1pps signal ZTE BS 8700 PIN 18 for 10MHz signal. PIN 16 for GND

33 Clock Interface on Manufacturers Equipments Ericsson SIU (Cell Site Router) Symmetricom TP 2700 BNC port which outputs 1pps signal. Huawei ATN CX600/950B Huawei CX600 has both RJ45 and minibnc port that output E1 and 1pps signal.

34 TX300S, TX320,MTT320 RXT1200 Paragon - X Sentinel

35 (CSAC) Chip Scalled Atomic Clock Frekvenční a fázová synchronizace

36 MTT320 wander analysis GPS Reference Point A Reference Point B Reference Point C Reference Point D T- GM T-TSC PRTC PTP GM Packet Network PTP Slave End clock 1PPS

37 TX300 Master Slave emulation GPS Reference Point B Reference Point C Reference Point D T-TSC TX300 Master Emulation Packet Network PTP Slave TX300 Slave

38 Sentinel operating in Pseudo-Slave mode Antenna Sentinel Tester emulates PTP Pseudo-Slave 1588v2 GM 1G O/E or 100M E 2MHz/10MH/1PPS from enodeb RNC enodeb NETWORK Cell Site Router or Switch Base Station

39 Sentinel operating in Monitor mode Antenna Sentinel Tester in Transparent Mode 1588v2 GM 1G O/E or 100M E NETWORK RNC Cell Site Router or Switch A A B Taps or Splitter B enodeb Base Station

40 388mm Frekvenční a fázová synchronizace Color TFT, x 600 Antenna Frequency In/Out Ports 126mm 320mm Net Weight: < 6kg (13lb) Packet Module Clock Module Modular Design

41 Master Slave Emulation gives highest accuracy and repeatability for test bed Time Error measurements in CAT allow detailed insight into device performance.