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 RAN : Radio Access Network core network metro cell (200 m diam.) EPC centralized BBU IP backhaul CPRI fronthaul macro cell (1 km diam.) conventional RAN cloud RAN IP backhaul or CPRI fronthaul ? = conventional RAN or cloud RAN ? … most likely both of them

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

Backhauling and fronthauling bandwidth in LTE IP peak bandwidth per site typ. for macro cell CPRI bandwidth per site * 8/15 in case of WCDMA typ. for macro cell 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

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)

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

IP backhaul by 10G-PON : urban area, macro cells 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) ) max. 20 km power splitter Central Office eNBs 1 4 Router 2 8 OLT ONT CO serving area: diam. 6 km macro cell: diam. 1 km

IP backhaul (ct‘d) : urban area, macro + metro cells 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 split each (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 CO serving area: diam. 6 km macro cell: diam. 1 km metro cells max. 20 km hybrid splitter: 10G - power splitter GPON - cyclic AWG Central Office eNBs 1 2 8 metro (8 x 64) macro (32 x) 10G-PON GPON macro area 16 dipl exer power splitter l 10G + lj GPON 4 Router WDM1r (diplexer) GPON #1 … #8 10G PON cyclic AWG OLTs

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

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

Enable BBU pooling, but not via CPRI : alternatives IP backhauling core network EPC classical eNB PDCP RLC RF MAC PHY BIP variable increased optical link bandwidth split within L2 core network EPC central unit (cluster) PDCP RLC MAC slim eNB RF PHY ≥ BIP variable split within L1 core network EPC central unit (cluster) PDCP RLC MAC PHY extended RRH RF e.g. 0.2 * BCPRI fixed CPRI fronthauling core network EPC central unit (cluster) PDCP RLC MAC PHY CPRI RRH RF BCPRI fixed - simpler remote unit - possible pooling gains

Back-Up

Conventional Approach Example XG-PON1 upstream, 4 Wavelength Subbands SB1 – SB4 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.

TWDM 40/10G with ultra-low cost WDM upstream (ALU proposal, ECOC 2011) wavelength sets 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 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