Single- versus Dual-Carrier Transmission for Installed Submarine Cable Upgrades L. Molle, M. Nölle, C. Schubert (Fraunhofer Institute for Telecommunications, HHI) W. Wong, S. Webb, J. Schwartz (Xtera Communications) Lutz.Molle@hhi.fraunhofer.de Heinrich-Hertz-Institute Berlin www.hhi.fraunhofer.de
Presenter Profile Lutz Molle is a research associate at the Fraunhofer Institute for Telecommunications, Heinrich- Hertz-Institute Berlin (HHI) since 2005, where he is with the dept. Photonic Networks. He has been working on long-haul system design and upgrades of submarine systems. Lutz.Molle@hhi.fraunhofer.de
Introduction Fact: The ever-increasing capacity demand on back-bone networks Two ways for capacity increase on submarine infrastructure: New-builds Upgrades New & improved fibre, no DCF Fixed wet plant Larger bandwidth (C+L-band) Fixed bandwidth ( C-band) Coherent technology Coherent technology Advanced modulation (mqam) Lower-order modulation ( QPSK) 10Tb/s per fibre for >9000 km 3 Tb/s per fibre for > 9000 km More challenging, but Very long planning & lead time Quicker set up Very expensive Much lower cost This talk is on upgrades of 2 nd generation submarine links
What We ll Discuss Today Upgrade Aspects Transmission Link and 100G Test Equipment Single-carrier transmission on 3600-km link Single- & Dual-carrier transmission on 5600-km link Summary
Upgrade Paths for Legacy Links 2 nd generation systems were designed for 10G channels in 50GHz grid 10-fold capacity: replace old 10G channels by 100G-QPSK really? Possible problems (some) Q-margin low for 100G-QPSK at typ. delivered OSNR of 14 16dB Possible solutions (some) Stronger FEC Fewer channels (limited by nonlinearities) < 100Gb/s bitrate per channel Nonlinear impairments (e.g. SPM, phase flips, XpolM, ) Robust modulation (e.g. BPSK) Optimization of transmit pulse DSP (robust CPE, pilot symbols, MAP/MLSE decoding, DBP, ) This talk: Dual-carrier BPSK, RZ shaping, polarization interleaving
Investigated Wet Plant Links Two segments of 2 nd -gen. deployed submarine link, optical loop-back. NZDSF link, dispersion compensation by hybrid DCF/NZDSF spans Far End Terminal Station #1 Link #1 Link #2 2 1800km Near End Terminal Station 2 2900km Far End Terminal Station #2 Link Parameter Link #1 (loopback) Link #2 (loopback) Length 3600 km 5800 km No. of Repeaters 48 82 Repeater Spacing 75 km avg. 70 km avg. Repeater Output Repeater Bandwidth Repeater Noise Fig. 11 dbm 15 nm 5 db Link #2 Dispersion Map avg. dispersion slope ~0.07 ps/km/nm² 192.15 THz (1560.2 nm) 192.9 THz (1554.1 nm) 194.0 THz (1545.3 nm)
Channel spacing [GHz] Expected Linear Performance Maximum reach due to noise (ASE) accumulation along link: Maximum system length (in km) for 70km repeater spacing (BW EDFA = 14.0nm, P EDFA = 11.0dBm, NF EDFA = 5.0dB, fiber = 0.21dB/km) 59 29 1. Calculate required OSNR at FEC limit for used modulation format and bit rate 2. Add sufficient OSNR margin 3. Select proper channel spacing 4. Read maximum reach No. of Channels 53 47 41 35 29 23 12000 16000 18000 30000 10000 14000 25000 9000 8000 12000 20000 7000 9000 10000 16000 18000 5800 5800 6000 14000 5000 6000 7000 8000 12000 4000 10000 9000 5000 5800 3000 3000 7000 8000 4000 5800 6000 2000 5000 4000 2000 3000 33 37 42 50 60 76 e.g. 120Gb/s-DP-QPSK: Required OSNR* = 11.2 db Additional margin = 3.0 db Required link-osnr = 14.2 db Chanel spacing = 50 GHz 17 102 10 11 12 13 14 15 16 17 18 19 20 Required Rx-OSNR [db in 0.1nm] Reach is noise limited to ~7000 km with load of 35 100G-QPSK channels * req. OSNR for pre-(sd-)fec-ber = 1.8 10-2
20 l odd ILV 20 l even 100G Transmitter Test Equipment l1 RZ DP-IQ DGD EDFA 120Gb/s test channel: Dual-carrier BPSK or single-carrier QPSK DATA TDC EDFA 3dB to line l2 RZ DP-IQ DGD EDFA 3dB 100G QPSK 100G QPSK 100G Loading Channels blue mid red RZ-BPSK Pol-ILV 100G channel as dual-carrier DP-BPSK or single-carrier DP-QPSK Flexible RZ pulse carving, optional polarisation interleaving (pol-ilv) Insertion of test channel in loading comb in blue, mid or red band
Pol. Diversity 90 opt. Hybrid 100G Receiver Setup + Offline DSP EDFA from line 3dB RX 2 VOA EDFA opt. BPF OSNR EDFA LO Laser BD1 BD2 BD3 BD4 I X Q X I Y Q Y ADC: 4 80GS/s (8bit) PC for offline DSP Receiver DSP (Offline) Resampling Correction of optical frontend For dual-carrier : sub-carrier pre-filtering 14dB OSNR 120Gb/s DP-QPSK 60Gb/s DP-BPSK (1l) CD compensation LO offset correction Blind equalizer (CMA, DFE) Carrier recovery (V&V) Polarization-diversity coherent receiver High-bandwidth (36 GHz) real-time scope for ADC Offline-DSP for signal recovery and BER counting Differential decoding BER
Q (db) 100G Transmission on Link #1 (3600 km) Influence of RZ pulse shape for 100G single-carrier DP-QPSK Sweep over RZ pulse-width* Plain NRZ as ref. RZ-50 gains ~2 dbq Weak improvement with wider RZ-spectra (~0.5 dbq) Further tests: PC-RZ pulse 11 10.5 10 9.5 9 8.5 8 RZ-50 PC-RZ 7.5 NRZ 7 200 250 300 350 400 450 rms spectral width (pm) 500 * By adjustment of RZ-modulator bias. Only for MID-band channel, with Pol-ILV & const. channel power (RX-OSNR=19dB)
Q / db 100G Transmission on Link #1 (3600 km) Influence of Polarisation Interleaving for 100G single-carrier QPSK Sweep over channel power* RZ-50 w/o pol-ilv as reference Pol-ILV gains ~1 dbq PC-RZ gains ~0.8 dbq on top Increase of optimum Q value directly related to increase of non-linear limit * Only for RED-band channel 12 11 10 9 8 7 6 B2B FEC Pol-ILV RZ-50 RZ-50 Pol-ILV PC-RZ 5 11 13 15 17 19 21 23 OSNR (db in 0.1nm)
Q / db 100G Transmission on Link #2 (5600 km) Blue, mid and red band for 100G single- and dual-carrier format 100G single-carrier QPSK: about 2dB margin for red & blue band, <1dB@mid Blue and red band performance similar 100G dual-carrier BPSK: about 2.5 3 db higher optimum Q Simultaneous dual-carrier detection resulted in ~1.4dB lower optimum Q due to electrical bandwidth limitations Simultaneous detection still desirable for cost savings * 120-Gb/s Single-carrier PC-RZ-QPSK ** 120-Gb/s Dual-carrier PC-RZ-BPSK 12 11 10 9 8 7 6 B2B FEC Dual Carrier** Single Carrier* 5 11 13 15 17 19 21 23 OSNR / db in 0.1nm
Summary Field test of 100G single- vs. dual-carrier on NZDSF link Mid band most critical (as expected): ~1.5dB penalty 3600-km transmission of QPSK improved by optimised RZ pulse-shaping & Polarisation Interleaving 5400-km transmission of QPSK is nonlinearly limited 5400-km transmission of dual-carrier BPSK has about 2.5dB higher optimum Q (despite same linear performance) dual-carrier BPSK more robust against nonlinearities, but requires almost doubled hardware effort and results in lower spectral efficiency
Thank you for your attention!