Requirements and viewpoints for backhaul synchronization

draft-zhou-tictoc-ran-sync-req-00.txt

Angela Zhou, Xiaodong DuanChina Mobile

Outline

• Synchronization Requirements

• Mobile backhaul network

• Concerns on synchronization

Synchronization in 2G/GSM• Current 2G/GSM Networks

• Sync Requirements in current 2G/GSM Networks

– SDH transport network need frequency sync: +/- 50ppm

– Base stations need frequency sync: +/- 0.05ppm

– Reference clock is distributed via an explicit transport at the physical layer: PDH/SDH

• Future 2G/GSM Networks

• Sync Requirements in future 2G/GSM Networks

– Packet switching network do not need strict synchronization

– Base stations need frequency sync: +/- 0.05ppm– For base stations, Reference clock is distributed via

PSN, need physical synchronization support (e.g. Sync Ethernet) or packet-based synchronization (e.g. 1588).

Note: Previous SDH transport network maybe still exist for traditional base stations, sync requirement is the same as before.

BTS BSC

Ref. clockMS

SDH

E1 E1

BTSBSC

Ref. clock

MS

IP BSC

MS

PSN

IP BTS

Circuit Emulation

E1 E1

FE GE

Synchronization in 3G/TD-SCDMA• Current trail 3G/TD-SCDMA Networks

• Sync Requirement in current 3G/TD-SCDMA Networks

– SDH transport network need frequency sync: +/- 50ppm

– For transport network, Reference clock is distributed via an explicit transport at the physical layer: PDH/SDH

– Base stations need frequency sync: +/- 0.05ppm, and phase sync: +/- 3us

– For base stations, reference clock is distributed via GPS

• Future 3G/TD-SCDMA Networks

• Sync Requirement in future 3G/TD-SCDMA Networks

– Packet switching network do not need strict synchronization

– Base stations need frequency sync: +/- 0.05ppm, and phase sync: +/- 3us

– For base stations, reference clock is distributed via PSN, need physical synchronization support (e.g. Sync Ethernet) for frequency sync or packet-based synchronization (e.g. 1588) for time/phase sync.

RNC

NodeB

NodeB SDH

ATM

ATMRNC

NodeB

NodeB PSN

FE

GE

Ref. clock

Synchronization in 4G/TDD-LTE/FDD-LTE

• Possible synchronization requirements in LTE– Synchronization requirements in ALL-IP network– Synchronization requirements in distributing Base Station

(mesh topology among base stations)– Synchronization requirements in distributing BBU & RRU– Synchronization requirements in radio interfaces

Note: synchronization requirement in LTE is under discussion.

AGW

eNB

eNB

PSN

Ref. clock

eNB

eNB

eNB

eNB

eNB

Synchronization in different partsBase station Base

station controller

Base station

UE

UE

RadioInterface

SYNC

Ref. Clock

Network SYNCNode SYNC

• Requirements schematic diagram

• Synchronization requirements in different positions

Layer Sub Items Frequency Accuracy Phase Accuracy

Network Sync E1 50ppm -

STM-N 4.6ppm -

PTN Not so strict -

Node Sync Controller-Base station

50ppb(If base station pick up time from base station controller)

3us(if base station pick up time from base station controller)

Inter-Base station 50ppb(If base station pick up time from other base station)

3us(If base station pick up time from other base station)

Radio interface GSM 50ppb -

WCDMA 50ppb -

TD-SCDMA 50ppb 3us

TDD LTE 50ppb TBD

FDD LTE 50ppb -

Outline

• Synchronization Requirements

• Mobile backhaul network

• Concerns on synchronization

Mobile backhaul• Mobile backhaul could be based on

– Carrier Ethernet (e.g. 802.1ad, PBB-TE)– IP/MPLS (e.g. PW, VPLS, L3VPN ,IP routing)– T-MPLS– Others

• Each transport technique can fit certain scenario respectively, and they could be used in different network layers (access/aggregation/core).

Mobile backhaul• Mobile backhaul network

Base station

IP/MPLScore

Base stationcontrollerPBTBase

station

802.1ad

Base station

DLS

PON

Base stationcontroller

Base station

IP/MPLScore

Base stationcontrollerTMPLSBase

station

TMPLS

Base stationcontroller

TMPLS

Base stationcontrollerBase

station

IP/MPLScore

Base stationcontrollerBase

stationMPLS AGGVLL/VPLS

MPLS Access

802.1ad

CoreAggrAccess

SON & Self-backhauling

AGW 1AGW 2

New BSJoin

Ref. Clock

• Self Organization Network– Some BSs are configured

only by it’s mother BS for both sync and radio resource

• Self-backhauling– Using in-band connection

between BSs for backhaul

Outline

• Synchronization Requirements

• Mobile backhaul network

• Concerns on synchronization

Concerns & Summary• The requirements for RAN is clear and urgent

– Radio Access Network is on the early stage of moving to IP transport– Using GPS will affect the flexible deployment of BS, we really need a new

synchronization technology to substitute GPS, epically though a simple Ethernet port

– How to distribute synchronization through packet based network? Can 1588 meet our requirements? Telecom profiles of 1588 should be standardized:

• network scale/ network load/ local clock accuracy• Security

– The synchronization methods in next generation mobile network (LTE) and MESH/SON network should be paid more attention.

• At the same time, it is complex and more technologies in backhaul– How to extend IEEE1588 or other synchronization technology so that it can be

used smoothly in PBN and complex backhaul.– Features needed for Backhaul nodes to support 1588 for high accuracy– Different layers shall collaborate to meet the sync requirements form end to end,

so what kind of mechanisms/protocols are need between different layer and technologies in backhaul?

Thank you&Any questions?