When every nanosecond counts
www.sevensols.com
Ultra-accurate time transfer based on the IEEE-1588 High Accuracy Profile.
A high scalability and resilience approach
Summary
• The road to 5G
• Limitations of the IEEE 1588 – 2008 (PTPv2)
• The upcoming IEEE 1588 revision: High Accuracy profile
• Scalability and resiliency
• Performance data
• Live demo
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The road to 5G
• Timing and synchronization is critical to improve current telecom service
capabilities
• Dedicated timing network: Necessary? It depends...
– Interconnection with common reference (GNSS, UTC(k), …)
GNSS
Time Server Backhaul Network
CU DU
RRU
±100 ns
±70 ns ±20 ns ±10 ns
< 10 Km < 2 Km
3Data taken from Dr. Han Li, China Mobile. WSTS 2017
Limitations of the IEEE 1588 – 2008 (PTPv2)
• Several “telecom” profiles.
• Per-link calibration is mandatory.
• Accuracy and precision is not enough.
• Heavily affected by Packet Delay Variation (PDV).
• Best Master Clock Algorithm (BMCA) is unsecure. You must trust the
source.
• Asymmetry needs to be measured and taking into account.
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The upcoming standard: High Accuracy profile
• Main ideas coming from White Rabbit (WR) Protocol
• WR born at CERN and tested through several years
• WR brought to industry by Seven Solutions already in 2010
• IEEE1588 with HA expected in 2018/2019.
• 3rd default PTP Profile included in Annex J of the IEEE1588
• HA allows:
– Clock sync (L1 synchronization)
– Timestamp enhancement through phase detection
– Automatic precise evaluation of link asymmetry.
• Fully compatible with PTPv2
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The upcoming standard: High Accuracy profile
125.00 MHz
124.98 MHZ
125.03 MHz
125.00 MHz
125.00 MHZ
125.00 MHz
• Sub-nanosecond accuracy of synchronization. L1-Sync + Phase difference
measurement.
• Calibration procedures and dynamic evaluation of medium asymmetry.
• Low bandwidth utilization for time synchronization
• Hops of over 80 Km (validated with WR implementation on longer links)
• As with PTPv2, switchover and holdover techniques can be used
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5G Network example
Network frequencyReference
(PRC/Cesium)
Phase/timereference
Fronthaul II Backhaul/core network
RRURRU
CU
CU
CU
Fronthaul I
CU: Centralized UnitDU: Distributed Unit (5-10 per CU)RRU: Remote Radio Unit (10-20 per DU)
DUDU
DU
DU DU
DU
DU
RRU
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Scalability and resiliency
• Possibility to have multiple grandmasters connected to
independent time sources: GNSS, UTC (k), multiport
device. (Maciej. PhD. 2016, J. L. Gutierrez et al. EFTF. 2016)
• 15 hops maintaining sub-nanosecond (Seven Solutions. ITSF
2016, Torres-Gonzalez et al., ISPCS 2016)
• Up to 120Km per hop (see next results)
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Performance data
Synchronization performance of the current WR implementation
that is representative to the future HA implementations.
24 hours
20 KmHA profile
Compatible DeviceHA profile
Compatible Device
Counter20 ps
resolution
PPS PPS
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Performance data
10
10000 20000 30000 40000 50000 60000 70000 80000
Performance data
1,E-10
1,E-10
1,E-10
2,E-10
2,E-10
2,E-10
2,E-10
2,E-10
3,E-10
1 10 100 1000 10000 100000
Tim
e Er
ror
(s)
Seconds
MTIE
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Performance data
1,E-12
1,E-11
1,E-10
1 10 100 1000 10000 100000
Tim
e D
evia
tio
n (
s)
Seconds
TDEV
12
Performance data
GM
CU
DU
RRU
16 hours
GPS-DO
PPS
10 MHz
20 Km
20 Km
20 Km
Counter20 ps
resolution
PPS
PPS
HA profileCompatible Device
HA profileCompatible Device
HA profileCompatible Device
HA profileCompatible Device
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Performance data
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Performance data
1,00E-10
1,20E-10
1,40E-10
1,60E-10
1,80E-10
2,00E-10
2,20E-10
2,40E-10
2,60E-10
1 10 100 1000 10000 100000
Tim
e Er
ror
(s)
Seconds
MTIE
15
Performance data
1,E-12
1,E-11
1,E-10
1 10 100 1000 10000 100000
Tim
e D
evia
tio
n (
s)
Seconds
TDEV
16
Performance data
18 hours
GPS-DO
PPS
10 MHz
50 Km
70 Km
Counter20 ps
resolution
PPS
PPS
HA profileCompatible Device
HA profileCompatible Device
HA profileCompatible Device
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Performance data
-100
-75
-50
-25
0
25
50
75
100
0 3000 6000 9000 12000 15000 18000 21000 24000 27000 30000 33000 36000 39000 42000 45000 48000 51000 54000
Tim
e er
ror
(ps)
Seconds
Time Error on 120 Km, 2 hops
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Performance data
1,00E-10
1,10E-10
1,20E-10
1,30E-10
1,40E-10
1,50E-10
1,60E-10
1,70E-10
1,80E-10
1,90E-10
2,00E-10
1 10 100 1000 10000 100000 1000000
Tim
e Er
ror
(s)
Seconds
MTIE
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Performance data
1,E-12
1,E-11
1,E-10
1 10 100 1000 10000 100000 1000000
Tim
e D
evia
tio
n (
s)
Seconds
TDEV
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Live demo
Location A Location B
20/50/70 Km
Location A
Location B
GPS-DOPPS
10 MHz
WR-ZEN TP-32BNCWR-SWITCH
SF7322
PTP
WR-ZEN TP-32BNC
WR
WR
PPS
PPS
PPS
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Conclusions
• WR and HA match 5G time transfer requirements
– Distance scalability with low time error budget (nanosecond)
– Validated in the presented results
– Live trials already in place
• High Accuracy profile:
– Intensively based on White Rabbit approach (developed and promoted
by CERN)
– Clock distribution (L1 synchronization)
– Phase offset measurement
• We have a live set up in the booth
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