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

[email protected]

©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

04/06/2015 ©Chronos Technology: COMPANY PROPRIETARY 2

Pre-G.811


Pre-G.811


Pre-G.811


G.811 - finally



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)


Frequency Synchronisation

(actually syntonisation)

“Spinning” at the same rate

Frequency of clock signals, oscillators

(phase relationship is unimportant, although fixed (or at least

bounded))


Frequency Synchronisation

(actually syntonisation)

In frequency distribution (e.g. SDH)

absolute phase is unimportant


Phase Synchronisation

(actually synchronisation)

“Spinning” at the same rate, and aligned in phase

Frequency & phase of clock signals, oscillators


Phase Synchronisation

(actually synchronisation)

In frequency & phase distribution

(e.g. CDMA-2000)

absolute phase is important


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


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.


ITU G.826x & G.827x series


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)


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


Requirements for phase

TDD modulation

Frames/Subframes/Timeslots


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 ]


“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…


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


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


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”)


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).


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

– Bandwidth: 1Gbps per antenna, internal RBS interface 04/06/2015 ©Chronos Technology: COMPANY PROPRIETARY 28

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


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”


Telecom Profiles for time & phase –

G.8275.n


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


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

fref 04/06/2015 ©Chronos Technology: COMPANY PROPRIETARY 33

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


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


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


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


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

04/06/2015 ©Chronos Technology: COMPANY PROPRIETARY

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


G.8274.3 (draft)

04/06/2015 ©Chronos Technology: COMPANY PROPRIETARY 40 Assisted partial timing support slave clock functional model

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



Thank you for listening


[email protected]

Website: www.phaseready.com

mailto:[email protected]

http://www.phaseready.com/

https://twitter.com/PhaseReady

http://www.linkedin.com/groups?gid=4885361&trk=hb_side_g

https://www.facebook.com/pages/Phase-Ready/347662155351336?ref=tn_tnmn


Reference Material


[email protected]

Website: www.phaseready.com

mailto:[email protected]

http://www.phaseready.com/

https://twitter.com/PhaseReady

http://www.linkedin.com/groups?gid=4885361&trk=hb_side_g

https://www.facebook.com/pages/Phase-Ready/347662155351336?ref=tn_tnmn

Hybrid techniques & Ensembling,

timescales…

A new philosophy?

SyncE for OPS 8275.1/.2

SyncE as assistance to GPS


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