Access network systems for future mobile backhaul networks Nov. 6, 2012 Seiji Yoshida NTT Network Technology Laboratories NTT Corporation 1
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 2
Mobile traffic growth in Japan Launches of LTE services and rapid spread of smart phones and tablet devices have accelerated mobile traffic growth in Japan. Total mobile traffic (PB/month) 80 60 40 20 0 Downstream Upstream Jun Sep Dec Mar Jun Sep Dec Mar Jun / 2010 / 2011 / 2012 Month/Year 2.21 times/year 2.27 times/year 3 Data from information & communications Statistics database By Ministry of Internal Affairs and Communications in Japan
Future mobile base station configuration To increase spatial capacity, planned cell size will decrease along with small cells over-laid on traffic hot spot areas. Today s mobile base station configuration Future mobile base station configuration X10 # of base stations in urban areas HetNet configuration Densified Macro cells (planned) Cell size BS Overlaid Small cells (Micro, Pico, Femto) (unplanned) 4
Cloud RAN (C-RAN) C-RAN is architectural goal towards BBU consolidation, which could effectively reduce CAPEX/OPEX and power consumption. Today s mobile fronthaul/backhaul architecture Mobile Network C-RAN architecture Mobile Network Mobile Backhaul enodeb BBU RRU BBU BBU Access Network Access Network Optical MUX/DEMUX BBU BBU consolidation Mobile Fronthaul ~20 km Dark Fiber Digital RoF WDM-PON etc 1 Digital RoF 2 N 3 RRU RRU RRU RRU RRU RRU RRU RRU RRH RRH RRH: Remote Radio Head RRU: Remote Radio Unit BBU: Baseband Unit RoF: Radio over Fiber 5
Access network for small cell base stations Requirements for future mobile fronthaul will be different for different types of base station architecture. Type (A): C-RAN Mobile Backhaul Mobile Fronthaul EPC PSN (Carrier Ethernet, etc.) BBU Dark fiber / RRH UE IP packet signal enodeb/ BBU pool Digital RoF signal Type (B): Distributed APs (antennas) with BBU Mobile Backhaul Mobile Fronthaul EPC PSN: Packet Switched Network PON: Passive Optical Network EPC: Evolved Packet Core PSN (Carrier Ethernet, etc.) IP packet signal enodeb Proxy/ GW Act as proxy in place of APs against EPC 6 PSN (Carrier Ethernet, PON etc) IP packet signal BBU AP BBU BBU AP: Access Point GW: Gateway UE
Mobile fronthaul for small cell base stations Mainly applicable cell type Signal type Architecture (toady s technologies) Requirement for transmission delay Effectiveness of BBU consolidation CoMP Options Type (A) C-RAN Macro Cell Digital RoF (CPRI/OBSAI) Dark fiber WDM-PON OTN, etc Severe both in delay and delay variation High NW-MIMO Joint Transmission, etc Type (B) Distributed APs with BBUs Small Cell Packet-based signal (IP, Ethernet) PSN (Ethernet, TDM-PON, etc) relaxed Low Joint Transmission, etc Cost challenge CPRI transceiver SoC (MPU&DSP) CPRI: Common Public Radio Interface CoMP: Coordinated Multi-Point transmission and reception 7 OBSAI: Open Base Station Architecture Initiative
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. 8
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) solutions to 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 9
Synchronous Access Network Systems Sync-E and PTP are applied only for access networks in first stage, while core network infrastructures remain unchanged. GPS Synchronized to CSN Clock Signal Clock Signal Synchronized to CSN Clock Supply Networks BTS etc. Carrier Ethernet Networks BTS etc. Correction of Transmission delay Access (Synchronous) Core (Asynchronous) Access (Synchronous) GPS: Global Positioning System BTS: Base Transceiver Station : Optical Line Terminal : Optical Network Unit 10
Synchronous Access Network Systems 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 second ToD: Time of day ESMC: Ethernet Synchronization Message Channel 11
Overview of Synchronous Access Network Systems PTP MC PRC/PRTC switching Clock/Timing Supply network Ethernet GPS Receiver GPS ToD 1PPS Ext. Clock SNI #1 #0 Clock Card OSU #2 OSU #1 Redundant clock cards conduct Holdover operation OSU #N Ether-IF 10MHz 1PPS Phase/time & frequency synchronization at Ethernet UNI UNI Network synchronization via SNI Control Card Synchronous operation management Compensation of timing offset due to transmission delay ToD Dedicated interface for frequency & phase/time synchronization 12
Hybrid sync operation of Sync-E & PTP/802.1AS Coherent Hybrid Operation Central Office GPS Receiver 10 MHz 1PPS /ToD GPS receiver GPS receiver Network PRTC PTP/Sync-E Ethernet Network Incoherent Hybrid Operation PRC Clock supply networks GPS Receiver 64 khz + 8 khz Composite clock 1PPS /ToD Clock Supply GPS receiver PTP/Sync-E GPS Receiver Ethernet 1PPS /ToD 13 Network GPS receiver
10G-EPON Correction of timing offset in access line Multi-Point Control Protocol (MPCP) Ref. Time LocalTimer Gate LocalTimer Report IEEE802.1AS Ref. Time LocalTimer TimeSync message LocalTimer Aggregated media converter Precision Time Protocol (PTP) Ref. Time LocalTimer Sync message Delay req. Delay response LocalTimer 14
PTP Implementation Synchronous access network systems works as PTP boundary clock. In aggregated media converters, PTP is also used for timing offset correction in access line. 10G-EPON IEEE802.1AS PTP S PON IF PON IF PTP M UNI CPE PTP S Aggregated media converters PTP S PTP M PTP PTP S PTP M UNI CPE PTP S media converter media converter 15
10G-EPON Access Systems 10G-EPON 10G-EPON Front view Rear view ANI ToD 1PPS 10 MHz UNI (GbE) UNI (10 GbE) D-sub 9pin (NMEA-0183) 16
Aggregated media converters access systems Control card 10 MHz 1PPS ToD DCS PTP/Sync-E OSU card Clock Card #0 Clock Card #1 D-sub 9pin (NMEA-0183) 17
Frequency Synchronization Characteristics MTIE(s) 10 1 G.823 SEC Mask 50 ppb G.811 PRC Mask 0.1 ppb 100 n Measured data 0.001 ppb 10 n 20 ns 1 n 100 m 1 10 100 1k 10 k 100 k Observation interval(seconds) Long-term TIE is around 20 ns and FFO is < 0.001 ppb. PTP sync messages need to be exchanged only once in 10 5 seconds to achieve +-100-ns phase/time accuracy in hybrid operation. FFO: Fractional Frequency Offset TIE: Time Interval Error MTIE: Maximum Time Interval Error 18
Temperature cycling test Temp. cycling pattern 40ºC 0ºC 3.0 h 1.0 h 3.0 h 1.0 h (1) Access transmission line(optical fiber) (2) Thermostatic chamber Thermostatic chamber SMF 20 km (31ps/km/ºC) Temp. (ºC) 40 Temp. (ºC) 0 40 TIE 0 TIE 10ns /div 10ns /div 0 12 24 36 48 60 Elapsed Time(hours) SMF: Single Mode Fiber 19 0 8 16 24 30 Elapsed Time(hours)
Time/Phase Synchronization Characteristics [10G-EPON/802.1AS] *10 5 times overwriting Phase shift < 60 ns GPS output (Trigger) 0-km output 20-km output 10 ns/div 20
Time Synchronization Characteristics [Media converter/ptp] Phase shift 10 ns 10 ns 100 ns 100 min. Elapsed Time 21
Summary Issues to be considered in future mobile networks were discussed. We developed two types of synchronous access network systems,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. 22