Phase Synchronisation - Chronos Technology Ltd · Reference Point D: – Network limits based on...
Transcript of Phase Synchronisation - Chronos Technology Ltd · Reference Point D: – Network limits based on...
Phase Synchronisation – the standards and beyond…
Supporting Your Phase Network
3rd June 2015
Chris Farrow Technical Services Manager
©Chronos Technology: COMPANY PROPRIETARY
Contents
Intro
Stds overview –
– G.8275.1 focused on greenfield
– G.8275.2 more pragmatic approach
Testing, measuring
– TE cTE dTE
Summary
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Pre-G.811
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Pre-G.811
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Pre-G.811
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G.811 - finally
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G.811 & G.703
The most widely recognised Telecom sync stds?
– G.811 sync quality
– G.703 physical interfaces
the ubiquitous 2.048MHz & 2.048MBit/s
G.703 has been revised…
– … to add phase/time sync interfaces (sect. 17)
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Frequency Synchronisation
(actually syntonisation)
“Spinning” at the same rate
Frequency of clock signals, oscillators
(phase relationship is unimportant, although fixed (or at least
bounded))
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Frequency Synchronisation
(actually syntonisation)
In frequency distribution (e.g. SDH)
absolute phase is unimportant
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Phase Synchronisation
(actually synchronisation)
“Spinning” at the same rate, and aligned in phase
Frequency & phase of clock signals, oscillators
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Phase Synchronisation
(actually synchronisation)
In frequency & phase distribution
(e.g. CDMA-2000)
absolute phase is important
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Time Synchronisation
“Spinning” at the same rate, and aligned in phase
Frequency & phase of clock signals, oscillators
…and aware of the same time i.e. information is
associated with the passing of each cycle or tick
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Freq, Phase & Time - Summary
Syntonisation:
Clocks tick at the same rate
Phase Synchronisation:
Clocks tick at the same moment
ToD Synchronisation:
Clocks tick at the same
moment & are aware of the
same time & date.
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ITU G.826x & G.827x series
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Time Accuracy requirements
Level of
Accuracy
Range of
requirements Typical Applications
1 1 ms – 500 ms Billing, Alarms
2 5 µs – 100 µs IP Delay monitoring
3 1.5 µs - 5 µs
LTE TDD (large cell)
Wimax-TDD (some configurations)
4 1 µs - 1.5 µs UTRA-TDD,
LTE-TDD (small cell)
5 x ns - 1 µs
(x ffs) Wimax-TDD
(some configurations)
6 < x ns
(x ffs)
Some LTE-A features
(ffs 3GPP)
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The Relationship Between Phase & Time
800 1000 0
100
200
300
400
500
600
700
800
900
1000
0 200 400 600
Elapsed Time - Seconds
Ph
ase
, Tim
e In
terv
al E
rro
r (T
IE)
- n
s
Freq Offset 1x10-11
1000ns
Freq Offset 1x10-9
Freq Offset 1x10-10 100ns
10ns
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Requirements for phase
TDD modulation
Frames/Subframes/Timeslots
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Cs & Rb in “holdover”
“Caesium Stability”
– How long to slip a µS?
– At 1 x 10-11 (worst case PRC) it takes 105 seconds ~27.78 hours
– Over 12 years (Cs lifetime) total slip is ~379 x 106 seconds x 1 x 10-11 = 3787µS
– Rubidium ~1 order of magnitude worse ~2.78 hours
– [ At 10-12 would take 106 seconds ~11.6 days ]
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“You can’t escape UTC…”
UTC is the global timescale – Ensembled from the world’s primary National Labs
NPL, PTB, NIST etc.
Primary freq. stds TAI UTC
Referred to as a “paper clock” – “Circular-T”
The easiest, cheapest way to get UTC(k) is probably NTP
The most accurate, cost-effective is GPS
Somewhere, some backhaul provider/core network will be using GPS…
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Phase Performance Requirements
LTE-A
– eICIC eMBMS CoMP
ITU-T
– G.8275.1 PTP Profile for Phase & Time Delivery
full on-path support
– G.8275.2 PTP Profile for Phase & Time Delivery
partial on-path support
(assisted
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eICIC “enhanced inter-cell interference co-ordination”
Macro cell avoids scheduling in or reduces power in
“protected” subframes (ABS vs RPS)
Reduced interference from macro cell in “protected”
subframes
Advanced Rx in Ue required for range expansion – Cell size: Dense urban environment
– Time alignment: +/-5us required between macro and small cell
– Latency: No special demands
– Bandwidth: Low
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eMBMS
LTE “Evolved Multimedia Broadcast Multicast Service”
eMBMS requires SFN (a la DVB-T) – therefore requires
~1μS phase alignment
– (figures quoted from 1 to 32 μS – “dependent on implementation”)
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CoMP CoMP = Coordinated Multi-Point Transmission and
Reception, with two categories: – (1) Coherent Joint Processing (JP), aka “Network MIMO” and
– (2) Coordinated Scheduling (CS).
CoMP - Joint Processing
Transmission and/or reception from/to geographically
separated antennas. Traffic and control data transfer
between eNB via X2 interface (logical interface).
CoMP - Coordinated Scheduling (CS)
Dynamic allocation of air interface resources in
overlapping cells.
Control data exchange between eNB (incl. Pico-eNB) via
X2 interface (X2 for control data only).
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CoMP “Coordinated MulitPoint”
e.g. UL Joint reception (U1 L1 CoMP)
Baseband schedules UEs
Radio units receive transmitted data
Radios share received data and jointly process it – Cell size: Dense urban environment
– Time alignment: +/-1.5us required between cells
– Latency: <0.5ms one way
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Supporting the requirements:
ITU-T PRTC, T-GM, T-BC & T-TSC
specifications
ITU-T PTP Profiles for time/phase delivery
GNSS/GPS
Future – PHY enhancements
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G.8272 & the PRTC
PRC defines frequency source in
SONET/SDH
PRTC defines Time Source:
“Timing characteristics of primary reference time clocks”
PRTC=“Primary reference time clock”
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Telecom Profiles for time & phase –
G.8275.n
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Telecom Profile – G.8275.1 Time/Phase distribution
Full on-path support (+SyncE)
– Implies EVERY node is PTP aware,
BC initially, could include TC in the future
Implies T-GM (master clock only), T-BC and T-TSC
(Slave-Only Ordinary Clock). Uses Alternate BMCA.
Two-way only, both 1-step & 2-step, 16/s SY & DR
Multicast - both non-forwardable & forwardable
address 01-80-C2-00-00-0E and 01-1B-19-00-00-00
L2 - 802.3 ETH
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Telecom Profile – G.8275.2 (draft 03/15)
Time/Phase distribution
Partial on-path support
– Implies only some nodes are PTP aware, e.g. some BCs
L3, UDP, Unicast – OC only (BC & SyncE allowed options, but outside the scope)
Still under discussion, focus has been 8275.1
Packet Master
Clock Boundary Clock
Packet Slave Clock
time reference, Tin
PRTC
two-way packet timing signals
Tout +
fref (physical layer frequency reference for
protection)
fref
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Other significant standards
G.8260 (definitions)
FPP, minTDEV, MAFE
TE – cTE & dTE
Maximum/Minimum/Peak-to-peak average time error (maxATE, minATE, ppATE)
Asymmetry 1000/100M at opposing ends
BMCA
G.8273.4 – min reqs for partial timing support assisting GNSS clocks
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ITU Time Error Budget: Core to Edge model
±1.5 us end-to-end
±100 ns (PRTC)
±500 ns constant time error ±50 ns per node, 10 BC
±200 ns (dynamic time error - PDV)
±200 ns (network asymmetry compensation)
±200 ns (holdover budget)
±150 ns (eNodeB)
±50ns Slave clock
Time Error Budget PRTC to e.g. ENB
Standards
• G.8271
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Sync Flow & Network Limits
PRTC
T-GM
End Equipment
Packet Network PTP Slave
Packet Timing System
T-BC
EEC
T-BC
EEC
T-SC
EEC
T-BC
EEC
• Possible on geographically small network with few hops and good transport
• More problematic on geographically large networks with potentially noisy
transport, many hops, and complex asymmetry models
Sync Flow
Time error budget calculation
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Reference Points for Packet Timing
Reference Point A: – Network limits as for physical layer sync chain (EEC, SEC, SSU or
PRC limits)
Reference Point B: – Packet timing interface (not currently defined)
Reference Point C: – Packet timing interface, defined in terms of “Floor Packet Percentage”
(FPP)
Reference Point D: – Network limits based on traffic interface (for timing to end
application), or physical layer sync chain (for timing to the network)
PRC
PEC-
M
End Equipment
PTP Grandmaster
Packet Network Physical Layer Synchronization Network
PTP Slave
PEC-
S-F
Reference
Point
A
Reference
Point
B
Reference
Point
C
Reference
Point
D
Packet Timing System
Standards
• G.8261.1
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Time Error – maxTE, cTE & dTE
For applications that require time/phase alignment,
“Time Error” (TE) is defined
Split into 2 components:
– A fixed component – e.g due to link asymmetries in PTP
Constant Time Error - cTE
– A varying component – e.g. due to PDV in PTP
Dynamic Time Error – dTE
38
Standards
• G.8271.1
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Reference Network
Packet Slave Clock
(T-TSC)
Packet Master (T-GM)
End Application Time Clock
PRTC
Packet Network
• Common clock/timescale is GPS
UTC
• Simulation Reference Model:
• Chain of T-GM, 10 x T-BC, T-TSC
• Time Error “TE” measured reference points R1 – R5 (note R3=R4 if T-TSC is embedded)
• Typical target requirement – TED < 1.5µS
TED TE
C
TEB TEA GPS
R1 R2 R3 R4 R5
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G.8274.3 (draft)
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PHY enhancements
xDSL
– NTR – 8kHz reference from ATU-C to ATU-R
xPON
– Modem ranging
Standards groups looking at adding phase support to the PHY
– SG15/Q13 asked Q2 & Q9 for assistance
– Changed when?
– Greenfield use? 04/06/2015 ©Chronos Technology: COMPANY PROPRIETARY 41
Summary
Standards are changing
– To provide guidelines for Network Engineering
– To support service delivery, e.g. LTE-A
Phase/Time delivery to meet those requirements provides challenges
– In the delivery itself
– In the monitoring/measuring
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Thank you for listening
Chris Farrow Technical Services Manager
Website: www.phaseready.com
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Reference Material
Chris Farrow Technical Services Manager
Website: www.phaseready.com
Hybrid techniques & Ensembling,
timescales…
A new philosophy?
SyncE for OPS 8275.1/.2
SyncE as assistance to GPS
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