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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