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Access network systems for future mobile backhaul networks
Nov. 6, 2012
Seiji Yoshida
NTT Network Technology LaboratoriesNTT Corporation
Copyright(c)2012 NTT Corp. All Rights Reserved.2
Outline
Mobile Traffic Growth in Japan
Future Mobile Base Station Configurations
Development of Synchronous Access Network Systems
• 10G-EPON• Aggregated Media Converters• Frequency Synchronization Characteristics • Temperature Cycling Test• Time/Phase Synchronization Characteristics
Summary
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Mobile traffic growth in Japan
Data from information & communications Statistics database By Ministry of Internal Affairs and Communications in Japan
Month/Year
Jun/ 2010
Sep Dec Mar/ 2011
Jun Sep Dec Mar/ 2012
Jun0
20
40
60
80
Tota
l mo
bile
tra
ffic
(P
B/m
on
th)
Downstream
Upstream
Launches of LTE services and rapid spread of smart phones and tabletdevices have accelerated mobile traffic growth in Japan.
2.21 times/year
2.27 times/year
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Future mobile base station configuration
Today’s mobile base station configuration
Future mobile base station configuration
Cell size BS
HetNet configuration
OverlaidSmall cells(Micro, Pico, Femto)(unplanned)
X10 # ofbase stations
in urban areas
To increase spatial capacity, planned cell size will decrease along with small cells over-laid on traffic “hot spot” areas.
DensifiedMacro cells(planned)
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RRU
BBU
Mobile Network
RRU RRU RRU
~20 km
AccessNetwork
RRUeNodeBBBU
Dark Fiber
Digital RoF
RRU RRU RRURRU
1 2N
Today’s mobile fronthaul/backhaul architecture
3
BBU consolidation
OpticalMUX/DEMUX
RRH: Remote Radio HeadRRU: Remote Radio Unit
MobileBackhaul
MobileFronthaul
BBU BBU
Digital RoF
WDM-PONetc
Cloud RAN (C-RAN)
C-RAN is architectural goal towards BBU consolidation, which could effectively reduce CAPEX/OPEX and power consumption.
AccessNetwork
RRH
Mobile Network
C-RAN architecture
RRH
BBU: Baseband UnitRoF: Radio over Fiber
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PSN(Carrier
Ethernet, PON etc)
PSN(Carrier
Ethernet, PON etc)
6
Type (A): C-RAN
RRHEPC
eNodeB/ BBU pool
PSN(Carrier
Ethernet, etc.)
PSN(Carrier
Ethernet, etc.)
Mobile Backhaul
UE
AP
EPC
Digital RoF signal
Act as proxy in place of APs against EPC
BBU
Dark fiber /
Access network for small cell base stations
Requirements for future mobile fronthaul will be different for different types of base station architecture.
Mobile Fronthaul
Mobile Backhaul Mobile Fronthaul
Type (B): Distributed APs (antennas) with BBU
IP packet signal
eNodeBProxy/GW
IP packet signal
IP packet signal
UEBBU
BBU
BBU
PSN(Carrier
Ethernet, etc.)
PSN(Carrier
Ethernet, etc.)
PSN: Packet Switched NetworkPON: Passive Optical NetworkEPC: Evolved Packet Core
AP: Access PointGW: Gateway
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Type (A)C-RAN
Type (B)Distributed APs with BBUs
Mainly applicable cell type
Macro Cell Small Cell
Signal typeDigital RoF
(CPRI/OBSAI)Packet-based signal
(IP, Ethernet)
Architecture(toady’s technologies)
• Dark fiber• WDM-PON• OTN, etc
PSN(Ethernet, TDM-PON,
etc)
Requirement for transmission delay
Severe both in delay and delay variation
relaxed
Effectiveness of BBU consolidation
High Low
CoMP OptionsNW-MIMO
Joint Transmission, etcJoint Transmission, etc
Cost challenge CPRI transceiver SoC (MPU&DSP)
Mobile fronthaul for small cell base stations
CPRI: Common Public Radio InterfaceCoMP: Coordinated Multi-Point transmission and reception
OBSAI: Open Base Station Architecture Initiative
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Technical Challenges
C-RAN
• Increasing bandwidth of digital RoF segments in accordance with wireless bandwidth increment towards LTE-advanced.e.g. LTE 10MHz 2x2 MIMO 1.2 Gbps DRoF signal
• Bandwidth compression of CPRI signal.• Limitation of distance between BBU and RRHs.• CPRI transmission over public networks.
- CPRI could not be electrically multiplexed as in PSN.• Redundancy of CPRI transmission path.
Distributed APs
• Distribution of time/frequency to APs over PSN.• Transmission latency reduction.• Enhancement of cost effectiveness.
- SoCs will be key devices for cost reduction.• Vendor lock-in.
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Our Scope
We expect future mobile fronthaul/backhaul architecture will be a mixture of Types (A) & (B).
Applying synchronous Ethernet technologies (Sync-E & PTP) to access network systems as short-term (STEP-1) solutionsto provide phase/time & frequency synchronization to mobile base stations for PSN-based mobile fronthaul/backhaul architecture.
In C-RAN, transmitting DRoF signals from each RRH to BBU might be important issue.Cost-effective measures other than using dark fibers require further study.
Sync-E: Synchronous Ethernet PTP: Precision Time Protocol (IEEE1588v2) PSN: Packet Switched Network
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Carrier EthernetNetworks
ONU OLTBTSetc.
Synchronizedto CSN
Clock SupplyNetworks
OLT ONU
Core(Asynchronous)
Access(Synchronous)
ClockSignal
BTSetc.
GPS
Correction ofTransmission delay
ClockSignal
Access(Synchronous)
Synchronizedto CSN
Synchronous Access Network Systems
Sync-E and PTP are applied only for access networks in first stage, while core network infrastructures remain unchanged.
GPS: Global Positioning System OLT: Optical Line TerminalBTS: Base Transceiver Station ONU: Optical Network Unit
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We have developed two types of synchronous access systems(10G-EPON and aggregated media converters), which can be applied for both consumer and enterprise network services.
Coherent/Incoherent hybrid sync operation (Sync-E / PTP, Sync-E / 802.1AS) used to achieve highly precise time/phase sync.
Support of multiple reference clock/timing sources.(PRC/PRTC, GPS, and Ether-IF)
Target accuracy is ±100 ns for phase/time synchronization.- Assuming application for LTE-advanced CoMP (co-operative
multi-cell multiuser MIMO).
Clock card redundancy.
Holdover capability for both time/phase & frequency.
UNI for providing frequency and phase/time synchronization to CPEs.- Ethernet-IF (Sync-E, PTP) and 1PPS/ToD/Clock interface.
SSM (ESMC) is supported at UNI as well as inside access systems.PRC: Primary Reference Clock PRTC: Primary Reference Time Clock PPS: Pulse per secondToD: Time of day ESMC: Ethernet Synchronization Message Channel
Synchronous Access Network Systems
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Ethernet
OLT
ONU
ControlCard
OSU #1
Clock/TimingSupply network
GPSReceiver
ToD
1PPS
OSU #2
OSU #N
PTPMC
ToD
10MHz
1PPS
Ether-IF
GPS
Ext.Clock
Redundant clockcards conductHoldover operation
Phase/time & frequencysynchronization at Ethernet UNI
Dedicated interface for frequency & phase/time synchronization
Compensation of timing offset due to transmission delay
Synchronousoperationmanagement
Networksynchronizationvia SNI
PRC/PRTCswitching
SNI
UNI
12
Overview of Synchronous Access Network Systems
ClockCard
#0
#1
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GPSReceiver
GPSReceiver
PRC
GPSReceiver
PRTC
13
Hybrid sync operation of Sync-E & PTP/802.1AS Coherent Hybrid Operation
Incoherent Hybrid Operation
OLT ONU
10 MHz
1PPS/ToD
64 kHz + 8 kHzComposite clock
1PPS/ToD
Clock supply networks
1PPS/ToD
Ethernet
GPS receiver
GPS receiver
Network
Network
Clock Supply
GPS receiver
Network
GPS receiver
OLT ONU
OLT ONU
OLT ONU
CentralOffice
Ethernet
PTP/Sync-E
PTP/Sync-E
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Correction of timing offset in access line
10G-EPON
Aggregated media converter
OLT ONURef. Time Gate
Report
LocalTimer LocalTimer
OLT ONURef. Time TimeSync message
LocalTimer LocalTimer
OLT ONURef. Time Sync messageLocalTimer LocalTimer
• Multi-Point Control Protocol (MPCP)
• IEEE802.1AS
• Precision Time Protocol (PTP)
Delay req.Delay response
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PTP Implementation
OLT ONU
Synchronous access network systems works as PTP boundary clock. In aggregated media converters, PTP is also used for timing offset correction in access line.
PTPS
PTPM
UNI
OLT ONU
UNI
PTPS
PTPM
IEEE802.1AS
PTPS
PTPM
PTP
10G-EPON
Aggregated media converters
CPE
CPE
PTPS
PTPS
PONIF
PONIF
media converter media converter
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10G-EPON Access Systems
10G-EPONOLT
10G-EPONONU
Frontview
Rearview
1PPS
10 MHzToD UNI(10 GbE)
ANI
D-sub 9pin(NMEA-0183)
UNI(GbE)
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Aggregated media converters access systems
OLT
10 MHz
1PPS
ToD
DCS
PTP/Sync-E
ONUControl card
Clock Card#1
Clock Card#0
OSU card D-sub 9pin(NMEA-0183)
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Frequency Synchronization Characteristics
MTIE(s)
1 n
10 n
100 n
1
10
100 m 1 10 100 1k 10 k 100 k
Observation interval(seconds)
G.823 SECMask
G.811 PRCMask
0.1 ppb
50 ppb
0.001 ppb
Measured data
• Long-term TIE is around 20 ns and FFO is < 0.001 ppb.
• PTP sync messages need to be exchanged only once in 105 seconds to achieve +-100-ns phase/time accuracy in hybrid operation.
20 ns
FFO: Fractional Frequency Offset TIE: Time Interval Error MTIE: Maximum Time Interval Error
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Temperature cycling test
ONU
(1) Access transmission line(optical fiber) (2) ONU
SMF 20 km(31ps/km/ºC)
OLT ONUOLT
Thermostatic chamberThermostatic chamber
Elapsed Time(hours)
TIE
0
40
Temp.(ºC)
10ns/div
0 6012 24 36 48
40ºC
3.0 h1.0 h
3.0 h1.0 h
0ºC
TIE
0
40
10ns/div
0 308 16 24Elapsed Time(hours)
Temp. cyclingpattern
Temp.(ºC)
SMF: Single Mode Fiber
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Time/Phase Synchronization Characteristics[10G-EPON/802.1AS]
GPS output(Trigger)
0-km ONU output
20-km ONU output
10 ns/div
*105 times overwriting
Phase shift < 60 ns
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Time Synchronization Characteristics[Media converter/PTP]
21
100 ns
Elapsed Time
Phase shift
100 min.
10 ns 10 ns
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Summary
• Issues to be considered in future mobile networks were discussed.
• We developed two types of synchronous access networksystems,10G-EPON and aggregated media converters.
• Sync-E/PTP and Sync-E/802.1AS hybrid operation was implemented and highly accurate phase/time synchronization(<100 ns) was achieved.