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OPTICAL ARCHITECTURES FOR MOBILE BACK- AND FRONTHAULING

OPTICAL ARCHITECTURES FOR MOBILE BACK- AND FRONTHAULING. Thomas Pfeiffer, Frank Schaich - Alcatel-Lucent Bell Labs Stuttgart OFC/NFOEC wireless backhauling workshop - Los Angeles, 5.3.2012. Backhauling or fronthauling ?. EPC : Evolved Packet Core BBU : Baseband Unit

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OPTICAL ARCHITECTURES FOR MOBILE BACK- AND FRONTHAULING

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  1. OPTICAL ARCHITECTURES FORMOBILE BACK- AND FRONTHAULING Thomas Pfeiffer, Frank Schaich - Alcatel-Lucent Bell Labs StuttgartOFC/NFOEC wireless backhauling workshop - Los Angeles, 5.3.2012

  2. Backhauling or fronthauling ? EPC : Evolved Packet CoreBBU : Baseband Unit RAN : Radio Access Network centralizedBBU metro cell(200 m diam.) cloud RAN CPRIfronthaul IP backhaul macro cell(1 km diam.) IP backhaul EPC conventional RAN IP backhaul or CPRI fronthaul ? =conventional RAN or cloud RAN ?… most likely both of them core network

  3. Choice of transmission technology : optical only Fiber transmission systems • protocol : IP, CPRI, others (digital; RoF not considered here) direct or over PON, Ethernet, … • multiplexing : TDM, WDM, TWDM, … • topology : ptp, ptmp, ring • architecture: dedicated ? overlay ? shared with FTTx ? Metrics • technical metrics : • bandwidth (scaleability, user statistics), latency, jitter • environmental factors : temperature, humidity, mechanical • location factors : availability of local powering, footprint, accesseability • economic metrics : • infrastructure : ownership, availability of dark fibers, digging cost, leasing cost, opportunity for sharing • location factors : power supply and power consumption, rights of way

  4. Backhauling and fronthauling bandwidth in LTE IP peak bandwidth per site CPRI bandwidth per site typ. for macro cell typ. for macro cell * 8/15 in case ofWCDMA • IP backhauling = variable bitrate • antennas may be grouped (e.g. beamforming) : each group counts as one single element • - user traffic statistics apply : - shown above are achievable peak rates on air i/f - avged. values may be less by an order of mag • CPRI fronthauling = constant bitrate- each antenna counts separately (individual streams)- 8B/10B can be removed for transport over Ethernet • compression can be applied to reduce to 1:3

  5. Impact from traffic statistics Backhaul and fronthaul network dimensions and architecture shall account for traffic statistics • traffic statistics per cell  statistical multiplex gain on IP backhaul • variations of total cell traffic over the day  load sharing (pooling gain) in cloud RAN taken from Alcatel-Lucent Technology lightRadioTM White Paper „Economic analysis“ (2011)

  6. Latency in LTE : limited by synchronous UL HARQ The allowed RRH eNB transmission time is limited to <<1 msecIt comes at the expense of a reduced processing time in the eNB UE RRH eNB UE eNB round trip time (10 µsec / km)+ transport systemprocessing time n Orig. TX n Orig. TX 3 msec fixed delaydefined by LTE standard eNB processing 1. PHY: UL frame decoding 2. MAC: ACK/NACK creation 3. PHY: DL frame creation n+4 reduced time for eNB processing NACK n+4 NACK n+8 1st RTX n+8 1st RTX t [ms] t [ms] t [ms] t [ms] t [ms]

  7. IP backhaul by 10G-PON : urban area, macro cells macro cell:diam. 1 km serving area:diam. 6 km Serving area around traditional CO • 32 macro cells, backhauled by single dedicated 10G-PON - peak rate = 10Gbps per site;  sufficient even for extreme loads - average rate = 320 Mbps per site  can be increased by using multiple 10G-PONs, WDM-stacked - link length = 20 km  reaches any site within the area over realistic cable routes Possible migration towards serving from consolidated Super-CO • via WDM stacking : hybrid WDM/TDM long reach 10G-PONs (cf. PIEMAN, MUSE, SARDANA for example architectures + upcoming NGPON2 standardisation for specs (tbd) ) CO Central Office eNBs 1 2 max. 20 km ONT Router OLT 1 powersplitter 4 powersplitter 8

  8. IP backhaul (ct‘d) : urban area, macro + metro cells macro cell:diam. 1 km serving area:diam. 6 km Scenario: serving area around CO with • 32 macro cells: 10G peak / 320M avge.  10G-PON, 1:32 split(3 sectors * 8 antennas * 100 MHz) (XGPON1 or XGPON2) • 16 metros per macro : 1.7G peak / 26M avge.  8 x GPON, 1:64 spliteach(1 sector * 4 antennas * 100 MHz) (stacking via low cost WDM)low cost WDM-PON by cyclic wavelength allocation within 40 nm band cf. Pöhlmann, Pfeiffer: ECOC 2011, paper We.9.C.1 metrocells CO Central Office eNBs 1 max. 20 km 2 OLTs WDM1r(diplexer) 10GPON 1 macro (32 x) 10G-PON 4 1 l 10G +lj GPON diplexer Router 2 8 powersplitter GPON #1 … #8 metro (8 x 64) GPON powersplitter 16 cyclicAWG hybrid splitter:10G - power splitter GPON - cyclic AWG macro area

  9. Centralized processing : variants and benefits • BBU clustering : move BBU hardware from BTS into common central space • simplified hardware at antenna sites (footprint, electrical power) and in BBU (indoor specs) • „zero latency“ links between BBUs allow for implementing CoMP and ICIC algorithms • BBU pooling : share hardware elements between multiple colocated BBUs • additional benefit : ease of load-sharing between clusters • Either variant requires CPRI links to remote antenna sites • transmission bandwidths easily reach levels that render TDM-PON unattractive • small split factors (1:2 or 1:4) • constant bitrate, i.e. no statistical multiplex gain • strict latency limits (<<1 msec) require zero framing/buffering etc. delays • most viable solutions employ ptp-links via • fiber, if available … • wavelength : ptp-WDM overlay on TDM-PON or „pure“ WDM-PON

  10. CPRI fronthaul via WDM overlay on LR-PON(ACCORDANCE project) MCO … Metro Central Office RN … remote node

  11. Enable BBU pooling, but not via CPRI : alternatives IP backhauling classical eNB EPC PDCPRLC MAC PHY RF corenetwork corenetwork corenetwork corenetwork BIPvariable increased optical link bandwidth split within L2 central unit (cluster) slim eNB EPC PDCPRLC MAC MAC PHY RF ≥ BIPvariable split within L1 extended RRH central unit (cluster) EPC PDCPRLC MAC PHY PHY RF e.g. 0.2 * BCPRIfixed CPRI fronthauling - simpler remote unit- possible pooling gains central unit (cluster) RRH EPC PDCPRLC MAC PHY CPRI CPRI RF BCPRIfixed

  12. Back-Up

  13. Conventional Approach Example XG-PON1 upstream, 4 Wavelength Subbands SB1 – SB4 SB4 SB2 SB1 SB3 1260nm 1265nm 1270nm 1275nm 1280nm • Wavelength band is separated in four subbands for wavelength stacking Randomly distributed DFB laser wavelengths in the 20nm band 1260nm 1265nm 1270nm 1275nm 1280nm DFB laser wavelength can be tuned by heating or cooling by ≈ 0.08nm/K. Tuning range up to 3nm.

  14. TWDM 40/10G with ultra-low cost WDM upstream(ALU proposal, ECOC 2011) • WSDM (wavelength set division multiplexing) • Operational principle: • - cyclic optical filter at Rx, 50 or 100 GHz grid • narrow range Tx tuneability instead of full band • accomplished by integrated heater stripe (no TEC) • otherwise conventional transmitter technology wavelength sets • Downstream : 4 x 10G TDM DWDM channels, 100GHz spacing, 1575-1580nm band • - OLT : l-stabilised DFB transmitter • - ONU : FP based tunable filter • Upstream : 4 x 2.5G TDMA wavelength sets, 50GHz grid, 1260-1280nm band • - OLT : filtered with cylical AWG • - ONU : partially tunable DFB with integrated heater

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