Frekvenční a fázová synchronizacení-a-fázová-syn… · Frekvenční a fázová synchronizace GSM, UMTS (European 2G and 3G mobile standards): •no requirement for time synchronisation

Frekvenční a fázová synchronizace

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

Frekvenční a fázová synchronizace 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

Basestation frequency accuracy ± 50ppb

Handset frequency acceptance ± 250ppb

frequency fc


f = fo . v

c

At 320km/h (200mph), f = 300ppb

At 160km/h (100mph), f = 150ppb

Doppler Shift


GSM, UMTS (European 2G and 3G mobile standards):

•no requirement for time synchronisation

cdmaOne, cdma2000 (N. American 2G and 3G mobile standards):

•Basestations must be within 3s of system time (10s holdover)

•Required for “soft handoff” •Handset must see pilot signals from both basestations within a few microseconds of each other to handover properly

Company Confidential ±3s ±1km ±3s ±1km

Time Synchronisation


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 5s required to co-ordinate ABSF


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 5s

LTE Advanced: CoMP


LTE (FDD) ±50 ppb N/A ±16ppb (G.8261.1)

LTE (TDD) ±50 ppb ±1.5µs (< 3km radius)

±5µs (> 3km radius)

±16ppb (G.8261.1)

±1.1μs (G.8271.1)

LTE-A MBSFN ±50 ppb

±1 to 5µs

implementation

dependent

±16ppb (G.8261.1)

±1.1μs (G.8271.1)

LTE-A CoMP Network MIMO

±50 ppb

LTE-A eICIC HetNet Coordination

±50 ppb

Small Cells ±100 ppb

N/A (FDD)

±1.5µs (TDD)

±1 to 5µs (eICIC)

±33ppb

±1.1μs (G.8271.1)

Home Cells ±250 ppb N/A (FDD)

±1.5µs (TDD)

±100ppb

±1.1μs (G.8271.1)

LTE Synchronization Requirements


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


Mobile Backhaul Synchronization • Approach 1: Use the physical layer clock

• SyncE clocks (EEC) made identical to SECs in performance terms

PRC Up to 20 SECs or EECs

SSU SSU SSU

Up to 10 SSUs

Up to 20 SECs or EECs


End Equipment

• Approach 2: Use a packet timing protocol

• Packet timing protocols such as PTP or NTP used to deliver frequency

SSU

S M Packet

Network

Packet Master and Slave PRC Up to 20 SECs or EECs

SSU SSU

Up to 10 SSUs


End Equipment


•Conventional timing (frequency) signal: • A nominally periodic signal, generated by a clock:

•Packet timing signal: • A nominally periodic signal, generated by a packet master clock:

Significant instants

Timing jitter and wander

Packets

Significant instants

Packet Delay Variation

Payload 4 H Payload 4 H Payload 4 H Payload 4 H Payload 4 H F Payload 3 H F Payload 2 H F Payload 1 H F


Frequency Time/phase

G.8265.1: Precision Time Protocol Telecom Profile for Frequency Synchronization

G.8275.1: PTP Profile for Time and Phase Synchronization (full timing support)

G.8261.1: PDV Network Limits Applicable to Packet-Based Methods (Frequency)

G.8271.1: Network Limits for Time/Phase (full timing support)

G.8273.1: Telecom Grandmaster (T-GM)

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.8260: Definitions and Terminology for Synchronization in Packet Networks (includes PDV metrics)

G.8272: Timing Characteristics of Primary Reference Time Clocks (PRTC)

G.8273.2: Telecom Boundary Clock (T-BC)

G.8273.3: Telecom Transparent Clock (T-TC)

G.8273.4: Telecom Time Slave Clock (T-TSC)

Published 1st version agreed

G.8275: Architecture and Requirements for Packet-Based Time and Phase Delivery

G.8265: Architecture and Requirements for Packet-Based Frequency Delivery

Under development

G.8275.2: PTP Profile for Time and Phase Synchronization (partial timing support)

G.8271.2: Network Limits for Time/Phase (partial timing support)

G.8261: Timing and Synchronization Aspects in Packet Networks (Frequency)

G.8271: Time and Phase Synchronization Aspects in Packet Networks

G.8273: Packet-Based Equipment Clocks for Time/Phase: Framework

Options

Methodds and Architecture

Basic Aspects

Network Requirements

Clock Specifications

Profiles


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.


• 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)

SyncE ITU-T G.8261


• 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)

Synchronous Ethernet (SyncE)


• 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.

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.

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.

Precision Time Protocol (PTP) - IEEE 1588v2

Frekvenční a fázová synchronizace Master Slave

Time = 10 s Time = 5 s Sync = 10s?

Follow up = 10s

Time = 11 s

Time = 8 s

Time = 17 s Time = 11 s

Time = 19 s


Delay = [(t2-t1) + (t4-t3)]/2 = [(19-11) + (8-10)]/2 = 3 Offset = (t2-t1) – Delay = -5


Sync = 23s ? Follow up = 23s

Delay Req= 11s

Delay Resp= 19s

t1=10

t2=8

t3=11

t4=19

Slave čas upravený o offset a delay

Time = 24 s

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!

Frekvenční a fázová synchronizace Time Error Source

The fixed component is called Constant Time Error (cTE) and comes from Link asymmetries and Node (T-GM, T-BC, T-TSC) asymmetries.

The time-varying component is called Dynamic Time Error (dTE) and comes primarily from Packet Delay Variation (PDV) caused by router queues, etc.

Constant Time Error (cTE)

Dynamic Time Error (dTE)

• Node asymmetry

• Link asymmetry

• Route asymmetry

Frekvenční a fázová synchronizace 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


PTP with Full Timing Support

T-GM

End clock PTP Grandmaster

Packet Network PTP Slave

T-TSC

Reference Point A

Reference Point B

Reference Point C

Reference Point D

PRTC

GNSS

all switch/routers on the path between T-GM and T-TSC contain a T-BC

Features

•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

http://www.google.co.uk/url?sa=i&rct=j&q=clock face with hands&source=images&cd=&cad=rja&docid=1hOsQakcRp6U0M&tbnid=SgBnp2TS04ab8M:&ved=0CAUQjRw&url=http://carpatys.com/clockface-jpg.html&ei=zrPnUaTIGoew0QWDroDgAg&psig=AFQjCNH2akkaTAmfr4Kyd3TmQbU-epIWJA&ust=1374225720108736



G.8273.2 Telecom Boundary Clock (T-BC)

Slav

e

Mas

ter

EEC

SyncE SyncE

1pps

PTP PTP

Slave

Master

Time/Phase (1pps)

Frequency (T1/E1/SyncE)

Boundary Clocks reduce PDV accumulation by:

•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

Boundary Clock



Packet Interfaces Siwtch/router

Switch/Router

Packet Interfaces

Boundary Clock

Slav

e

Mas

ter

1pps

EEC SyncE SyncE

PTP Messages PTP Messages



Q1

Q2

Qn

Packet Delay in TC Device inserted into CorrectionField

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.

TC CF Accuracy = 50ns (IEEE C 37.238)

Transparent Clock


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.8271.1

•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

PTP with Full Timing Support


End clock Combined GPS/PTP Slave

APTSC

GNSS

T-GM

PTP Grandmaster

Packet Network PRTC

GNSS

not all switch/routers on the path between T-GM and T-TSC contain a T-BC

Features

•Objective is backup to GNSS, i.e. “assisted holdover”

•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)

G.8275.2 “Partial Timing Support” Profile




Benefits

•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

PTP with Assisted Partial Timing Support


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)

Use case: In-building Small Cells


End clock PTP Slave

T-GM

PTP Grandmaster Packet Network PRTC

GNSS

not all switch/routers on the path between T-GM and T-TSC contain a T-BC

PTP with Partial Timing Support

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




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

PTP with Partial Timing Support


T-GM

End clock PTP Grandmaster


T-TSC

Reference Point

A

Reference Point

B

Reference Point

C

Reference Point

D

PRTC

GPS

Reference Point A:

• 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.8271.1)

Reference Point D:

• End application requirements (e.g. air interface time/frequency specification)

G.8271.1: Reference Points



Frekvenční a fázová synchronizace G.8271.1 Network Reference Points

±250ns (short term holdover)

±150ns (end application)

D

±1.1µs network equipment budget

±1.5µs end-to-end budget

±200ns dTE (random network

variation)

±100ns (PRTC/T-GM)

A, B

cTE uses up 70% of the network equipment budget

C

Class A T-BCs:

Class B T-BCs:

±250ns cTE (link asymmetry compensation)

±550ns cTE (node asymmetry, ±50ns per node)

±380ns cTE (link asymmetry compensation)

±420ns cTE (21 nodes, ±20ns per node)


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.

- co je nutné měřit

t(1)

t(2)

t(3)

t(4)

t(5)

TIE (ns)

t (s)

Ob

servation

time (n

·t0 )

MTIE (ns)

*Faster playback is used to better explain the concept.

Reference Clock

Test Signal

Phase Error (TIE)

MTIE

Frekvenční a fázová synchronizace Clock Interface on Manufacturers’ Equipments

Juniper ACX 1100

Juniper ACX 1100 has a SMC port which outputs 1pps signal

ZTE BS 8700

PIN 18 for 10MHz signal. PIN 16 for GND

Huawei BTS 3900


Ericsson SIU (Cell Site Router) Symmetricom TP 2700

Huawei ATN CX600/950B

BNC port which outputs 1pps signal.

Huawei CX600 has both RJ45 and miniBNC port that output E1 and 1pps signal.

Clock Interface on Manufacturers’ Equipments


TX300S, TX320,MTT320 RXT1200 Paragon - X

Sentinel


(CSAC) Chip Scalled Atomic Clock


T-GM

End clock PTP GM


T-TSC

Reference Point

A

Reference Point

B

Reference Point

C

Reference Point

D

PRTC

GPS

MTT320 wander analysis

1PPS







Reference Point D

TX300 Slave TX300 Master

Emulation Packet Network PTP Slave

T-TSC

Reference Point B

Reference Point C

GPS

TX300 Master Slave emulation



eNodeB

1G O/E or 100M E

1588v2 GM

2MHz/10MH/1PPS from eNodeB

Cell Site Router or Switch Base Station

RNC

NETWORK

Antenna Sentinel Tester emulates PTP Pseudo-Slave

Sentinel operating in Pseudo-Slave mode


eNodeB

1G O/E or 100M E

Cell Site Router or Switch Base Station

RNC

NETWORK

Sentinel Tester in Transparent Mode

Taps or Splitter

A A B

B

Antenna

1588v2 GM

Sentinel operating in Monitor mode


Net Weight: < 6kg (13lb)

Modular Design Clock Module

Packet Module

Frequency In/Out Ports Color TFT, 8.4” 800 x 600 Antenna

38

8m

m

320mm

12

6m

m


•Master Slave Emulation gives highest accuracy and repeatability for test bed

•Time Error measurements in CAT allow detailed insight into device performance.

Documents

Frekvenční a fázová synchronizacení-a-fázová-syn… · Frekvenční a fázová synchronizace GSM, UMTS (European 2G and 3G mobile standards): •no requirement for time synchronisation