From TDMA to WDM-PON
Sjur Fredriksen
Aril Schultzen
Intro
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“PON in Adolescence: From TDMA to WDM-PON”
Grobe, Klaus et al.;
IEEE Applications & Practice: Topics in optical communications
January 2008, Pages: 26-34
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Many proposals for WDM-PONs
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Cost and performance are important aspects for success
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bandwidth per user, splitting ratio and maximum reach
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The article used as source is analysing these proposals
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Heavy subject, we’ll try to go easy on you
Preliminary Knowledge
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OLT = Optical Line Termination (central)
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ONU = Optical Network Unit (end-user)
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Power Budget = budgeted loss
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Fiber attenuation
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Couplers
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Splicers
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Connectors
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Muxes/demuxes
TDMA
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Time Division Multiple Access
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Multiple signals over the same frequency / wavelength
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Uses time-slots
Timeslots
Frequency
Time
Source: www.wirelesscommunication.nl/reference/chaptr04/multi/tdma.htm
WDM
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Wavelength-Division Multiplexing
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One fiber = multiple wavelengths (wl)
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Multiple wl = broader bandwidth
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Separation gives better security
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Cost effective upgrade
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Better usage of available fiber
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More often used with amplifiers than TDMA
Source: WDM operating principle.svg By Xens (Own work)
[CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons
GPON (ITU-T G.984)
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Gigabit PON
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Popular in Europe and North America
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In Norway: Telenor / Canal Digital / Get
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High bandwidth efficiency
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Lower build cost because better fiber utilization
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Supports IP, ATM and TDM payloads
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Uses TDMA
EPON (IEEE802.3ab)
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Ethernet PON
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Popular in Japan and Korea
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Lower bandwidth efficiency compared to GPON (less payload)
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Natively supports Ethernet
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Integrated into Ethernet in the First Mile (EFM) and Operation, administration
and maintenance (OAM) approach
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Uses TDMA
GPON vs EPON
Source: “PON in Adolescence: From TDMA to WDM-PON”, page 27
*Table shows costs normalized with respect to GPON.
Next Generation of PONs
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TDMA based PON can’t cope with future bandwidth needs
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Use of passive splitters imposes loss
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limits attainable link lengths
These problems can be mitigated with WDM PONs
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enhanced privacy
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enhanced bandwidth
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can be combined with TDMA based PON
Next up, some architectures.
Splitter WDM-PON
Source: “PON in Adolescence: From TDMA to WDM-PON”, page 28
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DS Wavelengths are broadcasted
Passive splitter (attenuation)
Individual ONUs with individual wl (DS/US)
AWG
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Arrayed Waveguide Gratings
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Optical (de)multiplexers in WDM systems
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Light waves of different length interfere linearly with each other
Source: Arrayed-Waveguide-Grating.svg By Dr. Schorsch (self made illustration.)
[GFDL (http://www.gnu.org/copyleft/fdl.html) or CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/)], via Wikimedia Commons
AWG-based wavelength routing PON
Source: “PON in Adolescence: From TDMA to WDM-PON”, page 28
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DS Wavelengths are broadcasted
AWG router instead of splitter (lower attenuation)
Simpler ONUs, still need for different TX wavelengths
Wavelength routing with spectrum sliced LED
Source: “PON in Adolescence: From TDMA to WDM-PON”, page 28
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Broadcasted DS wavelength
Identical ONU design with common US (AWG slices)
LED suffers from poor power budget in SM fiber
Limited US bandwidth
Colorless ONUs for single fiber (RSOA/REAM/IL-FP)
Source: “PON in Adolescence: From TDMA to WDM-PON”, page 29
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Colorless ONUs reduces cost
Single fiber reduces cost
Dedicated seed, limited number of ONUs
Colorless ONU using FSK/OOK with RSOA in ONU
Source: “PON in Adolescence: From TDMA to WDM-PON”, page 29
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Reuse OLT TX in ONU for TX data
Constant Envelope signal must be used in OLT (FSK)
FSK removed and OOK used in US
Simple CWDM PON based on CWDM SFP
Source: “PON in Adolescence: From TDMA to WDM-PON”, page 29
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Another type of mux/demux - Thin-film filters
CWDM SFPs to use different wavelengths
Low cost transceivers, but more expensive ONUs
Requires low water-peak fibers to support all channels
Architecture summary
Source: “PON in Adolescence: From TDMA to WDM-PON”, page 31
WDM-PON Application
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Extend range
Higher bandwidth
Higher splitting ratios
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(above 1:100) amplification is needed
Because of all these factors it can be used in unified metro and backhaul
networks
Structure today
Source: “PON in Adolescence: From TDMA to WDM-PON”, page 33
Structure of tomorrow
Source: “PON in Adolescence: From TDMA to WDM-PON”, page 33
Conclusion
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Next step PONs are WDM-PONs with TDMA techniques
Higher reach, splitting ratios and bandwidth than GPON/EPON
Supports various fiber topologies
Enables evolution to unified access and backhaul
Combination with DWDM and TDMA to optimize cost