Geneva, 28 May 2010

Examples of Time Transport

Michel Ouellette

Technical Advisor

Huawei Technologies Co., Ltd.

Joint ITU-T/IEEE Workshop on The Future of Ethernet Transport

(Geneva, 28 May 2010)

Outline

LTE-Advanced Time Synchronization Examples

Time Distribution over Packet Transport Network

Latest Field Trials

Performance Results & Voice/Data Service Results

Summary

2

LTE-Advanced Network Synchronization Overview

S1

X2

UN

UU

Over-the-Air Synchronization Error

Network Based Synchronization Error

(frequency and/or time)

eNB

Relay

Node

UE

Backhaul Network

LTE

Switching Centers

LTE / LTE-A phase/time specs are beyond current GSM/UMTS frequency

specs (50ppb) imposing further requirements on the transport network

3GPP TR36.814 defines further advancements for LTE

3

LTE-AdvancedCoordinated Multi-Point Transmission*

Radio transmissions from multiple base

stations radiate at the same time (spatial multiplexing), giving better cell edge performance and higher data rates

Broadcast service on the air interface

Accurate time synchronization required

at base station (GPS, IEEE1588-time, etc.) for aligning radio transmissions

Time difference = max{ t0-(∆1+t1) , t0-(∆2+t2) } ≤ x µsec

LTE

Switching Centers

t2

Time Difference

t1

∆∆∆∆1∆∆∆∆

2222t0

Backhaul

Network

eNB

*Illustrative example4

LTE-AdvancedRelay Function*

Relay used to improve the coverage of high data rates sites, temporary network deployment, coverage in new areas, etc.

The relay node (RN) is wirelessly connected to radio-access network via a donor cell (eNB).

The UE may need to get timing info from RN over the air, and where the RN also obtains timing over the air from the donor eNB.

Some relay nodes have strigent time alignment such as Example 2

RN nodes might be equipped with GPS or is synchronized via the radio interface

Donor eNB might be equipped with GPS or is synchronized via IEEE1588-time

t1

t2

∆∆∆∆1

Example 1

t1

t2

∆∆∆∆1

RN

RN

UE

UE

donoreNB

donoreNB

*Illustrative example5

Example 2

Field Trial TopologyCity-Wide Time Distribution, Joint with China Mobile

Requirement at NodeB: < ± 1.5usec of cumulative time error

1PPS + ToD

WorkingBITS

(Time Source)

10GE Core Ring(Packet Transport Network with IEEE1588)

Ethernet

GE GE

1PPS+ToD(output)

GE Access Rings withIEEE1588

1PPS+ToD

1PPS+ToD

FE

ProtectedBITS

(Time Source)

1PPS+ToD

1PPS+ToD

FE

NodeB

BMCA Master-Slave hierarchy

(time reference chain)Boundary clocks in each device

NodeB

M

M

S

P

S

M

M

M MS

S

S

MM

M

S S

P

6

BC

BC

BC

Field Trial SetupTime Distribution

One Core 10GE ring with 6 Access GE ringApproximately 75 nodes, covering one city, multi-vendor equipment

Two Time Reference SourcesDual mode GPS/Beidou receivers, connected to packet transport nodes via Gigabit Ethernet interface (running IEEE1588) or direct 1PPS+ToD interface

Packet Transport NodesIEEE1588 Boundary Clock & Best-Master Clock Algorithm. IEEE1588 terminated in each port, 10GE & GE timestamping (similar in spirit to 802.3bf architecture)Synchronous Ethernet & ESMC channel for frequency distributionIEEE1588 time and SyncE frequency reference chain are congruentFiber asymmetry compensated section-by-section

NodeB base stationsReceive time synchronization from Fast Ethernet interface (running IEEE1588) or direct 1PPS+ToD coaxial input.NodeB can output 1PPS interface for measurement purposes

TrafficPTN carries real voice/data services

Measurement equipmentTimeAcc 1PPS+ToD analyzer, call quality drive test tool and voice call generator

Test ScenariosLong term cumulative time error performanceTime Reference protection switch, PTN protection switchBMCA master-slave hierarchy, SyncE reference switchQuality of voice/data service, handoff and call completion

7

Performance ResultsCumulative Time Error (nsec) versus Time at NodeB

Delay compensation of every single element is necessary

-5

0

5

10

15

20

25

30

35

40

1 29 57 85 113 141 169 197 225 253 281 309 337 365 393 421 449 477 505 533 561 589

105

110

115

120

125

130

135

140

145

1 33 65 97 129 161 193 225 257 289 321 353 385 417 449 481 513 545 577 609

nsec

nsec

Scenario2: BITS uses 1PPS+ToD to provide time to packet transport, and BTS uses 1PPS+ToD interface

to recover time

Results: NodeB not capable of compensating (at the time of the trial) for 1PPS+ToD coaxial cable

delay and internal delay

Scenario1: BITS uses 1PPS+ToD to provide time to packet transport, and BTS uses IEEE1588 FE to recover time

Result: Acceptable performance

8

Performance ResultsLong term Cumulative Time Error (36 hours)

Long-term cumulative time error < ± 1.5usec

0 – 12 hours

12 - 24 hours

24 - 36 hours

9

nsec

nsec

nsec

Voice/Data Quality Results

Drive testsBetween NodeBs supporting IEEE1588 time syncBetween NodeBs supporting IEEE1588 and NodeBs supporting GPS

Voice/Data Services under test & Handoff performanceAMR voice, VP and PS384 (various wireless codecs)Eg., AMR traffic: 100-seconds call with 10-seconds intervalDrive speed: 40 – 60km/hour

Tests (reference C1065 – Geneva June 2010)Successful handoff ratio between adjacent base stations: 100%Call completion ratio: 100%Average voice MOS (mean opinion score): 3.46

Drive test routes10

Summary

Accurate Phase/Time distribution over large-scale Packet Transport Network is progressing within Q13, primarily serving wireless radio interfaces requirementsVarious Field Trials

IEEE1588 distribution over Packet Transport NetworkIEEE1588 distribution over Optical Transport Network

Field trials using Boundary Clocks & Best Master Clock show good results

Cumulative time error < ±1.5 usec for TD-SCDMA NodeBPacket impairments: reference switch, protection switchGood voice & data quality of service

Successful handoff and call completion

Additional references:C599, ZTE/CMCC, Geneva, October 2009WD29, Huawei/CMCC, Lannion, December 2009C1065, ZTE/Huawei/CMCC/CATR, Geneva, June 2010C1064/65, ZTE/CMCC/CATR, Geneva, June 2010

11

Additional Slides

Additional performance results

Time distribution via IEEE1588

Frequency distribution Synchronous Ethernet

Boundary Clock

12

Trial Results

2 time synchronization reference chains

A chain consists of 15 nodes

Each node implements IEEE1588 (for

time) and Synchronous Ethernet (for

frequency)

Default Best Master Clock Algorithm used

to establish Master-Slave hierarchy and

electing new GrandMaster during failure

GM1 is the initial GrandMaster of the

network

1PPS signal (cumulative time error) and

2.048MHz signal (time interval error)

used for time and frequency

measurements

M: Master portS: Slave port (only 1 per switch)

P: Passive port

GM: GrandMaster

GPS reference

GPS

10GERAN

1PPS

Time Tester

GERAN

GPS

BITS1 BITS2

1PPS+ToD 1PPS+ToD

Fiber

Chain #152 km

Chain #2

43km

M

M

M

M

M

M

M

M

S

S

S

S

S

S

S

S

PM

MP

GM1 GM2

13

Frequency and Time ResultsPerformance of two Boundary Clocks

connected via single GE link

Frequency

(SyncE)

±±±± 3 nsec on 2.048MHz output

~= 10-11 frequency offset

���� PRC traceable results

±±±± 2 nsec 1PPS pk-to-pk jitter

+ 3 nsec static time error due

in part to fiber asymmetry

Time

(IEEE1588)

14

Frequency and Time ResultsProtection scenario from Chain#1 to Chain#2

Master failure done by disconnecting 1PPS interface/cable from GM1

Master2 is the new GrandMaster, produceed by BMCA & the exchange of Announce messages. Time is distributed through Chain #2

Chain #1 Time error performance

(±±±± 15 nsec)

Chain #2 Time error performance

(±±±± 20 nsec)

Protection Switchfrom Chain 1 ���� 2 Phase Transient

(~ 60 nsec)

+ 80nsec Static Time Error

(eg., fiber asymmetry,

timestamping error,

temperature)

15

Results demonstrate the robustness and performance when using

IEEE1588 node-by-node time synchronization

Boundary Clock System

Boundary Clock is similar in concept to current SDH/SONET/SyncEsynchronization system (deal with time and not just frequency)

PHYTimestamp

Capture(T1, T4)

MAC

PHY

Line Card

(1588 Slave Port)

PHYTimestamp

Capture(T2, T3)

MAC Switch

Fabric

1588

Clock

1588

Software

(T1, T2, T3, T4)BMCA, etc.

timestamp, id

(T2, T3)

1PPS + local time

SyncEEEC

SyncE

RX clock

Timing Card

Line Card

(1588 Master Port)

Ext Sync InputSystem Clock

1PPS + local time

PHY

16