New FTTH Architectures for NG-PON-2 ... This network implements an alternative architecture of the conventional tree WDM/TDM-PON, consisting on the.
New FTTH Architectures for NG-PON-2 Josep Prat1 OSA member, Jose A. Lázaro1, Konstantinos Kanonakis2, Ioannis Tomkos2 OSA member 1: Univ. Politècn. de Catalunya (UPC), Dept. Signal Theory Comm., Jordi Girona, D4-S107, 08034 Barcelona 2: Research and Education Laboratory in Information Technologies, Athens Abstract: Three new relevant architectures for the Second Next Generation Passive Optical Networks (NGPON2), based on hybrid topologies, OFDM and UD-WDM, are discussed, as a step forward in PON performances and functionalities.
©2008 Optical Society of America OCIS codes: (060.2330) Fiber optics communications, (060.4250) Networks.
1. Introduction. Passive Optical Networks for access systems are evolving towards offering higher bandwidths to more users sharing a common infrastructure in cost-sensitive scenarios, with respect to currently deployed G/E-PON systems. Longer reach, higher scalability and simpler integration with radio access are features that are also pursued. The first architecture presented employs both the optical and the electrical domains by means of combined TDM and WDM multiplexing, inherited from transport networks, in a metro/access topology,; the second makes intensive use of the electrical frequency multiplexing (OFDM) over the fiber and the third makes exploits the wavelength multiplexing, with very narrow channel spacing (ultra-dense-WDM). The three systems can operate over the typical tree topology but also over more complex ones like hybrid ring/trees. The cost limitation in the access arena compels to intensify the research in the three directions to find out the future-proof solutions. 2. Hybrid WDM/TDM-PON This network implements an alternative architecture of the conventional tree WDM/TDM-PON, consisting on the organization of the optical distribution network as a WDM bidirectional ring and TDM access trees, interconnected by means of cascadeable optical passive Add&Drop remote nodes (RN), as shown in Fig 1. This network, proposed in the European SARDANA project [1], aims at serving more than 1000 users spread along distances up to 100 km, at 10 Gbit/s, with 100 Mb/s to 1 Gb/s per user in a flexible scalable way. The ring+tree topology can be considered as a natural evolution, from the conventional situation where Metro and Access networks are connected by heterogeneous O/E/O equipment at the interfaces between the FTTH OLTs and the Metro network nodes, towards an optically integrated Metro-Access network. In this case, covering similar geographical area, users and services, but concentrating electronic equipment at a unique CO, and implementing an all-optical passive alternative, operating as a resilient 1:K D1,…, Dm TDM over WDM overlay. Depending on the scenario, RN2 the ring+tree mixed topology optimizes the usage of the RN1 U 1,…, U2N fiber infrastructure in the ODN, and also offers TDM TREE Central RNi enhanced scalability and flexible distribution, as new Upstream Signals Office 1:K RNs can be installed. ONU WDM RING RSOA This network transparently merges TDM single-fiber RNj tree sections with a main WDM double-fiber-ring by U1,…, U2N means of the passive RNs. The high power budget is PIN/APD 1:K RNN compensated by remotely-pumped fibre amplification. Bidirectional Transmission RNN-1 The 100 km WDM ring transports e.g. 32 wavelengths with splitting factor of 1:K=32 each. Protection and D m+1,…, D2N Downstream Signals traffic balancing properties of the network are provided Fig 1: Network architecture and implemented test-bed comprising a by the ring configuration and the internal design of the Remote Node and Reflective SOA as colorless ONU. RNs, in the case of fiber-cut. 3. OFDM-PON OFDMA (Orthogonal Frequency Division Multiple Access) technology/protocols can introduce ultra high capacity, even reaching the 100Gbps regime, in extended reach optical access network architecture as proposed in the European ACCORDANCE project [2]. OFDM is implemented through the proper mix of state-of-the-art photonics and electronics. Such architecture is not only intended to offer improved performance compared to evolving TDMAPON solutions but also inherently provide the opportunity for convergence between optical, radio and copper-based access.
Although OFDM has been used in radio and copperbased communications, it is only recently that is making its way into optics and is expected to increase the system reach and transmission rates without increasing the required cost/complexity of optoelectronic components. ACCORDANCE hence aims to realize the concept of introducing OFDMA-based technology and protocols (Physical and Medium Access Control layer) to provide a variety of desirable characteristics, such as increased aggregate bandwidth and scalability, enhanced resource allocation flexibility, longer reach, lower equipment cost/complexity and lower power consumption, while also supporting multi-wavelength operation. In addition, it enables the convergence of the optical infrastructure with standard wireless solutions, thus offering a way to integrate dominant wired and wireless technologies in a hybrid access network supporting seamless ubiquitous broadband services.
Segment 1: Copper-based Access (DSL) ONU 1
Segment 2: Hybrid Optical/Wireless
BS 1 (ONU 2)
ONU 3
ONU 1
Segment 3: OFDMA/DSCA PON
ONU 2
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ONU 3
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ONU 1 ONU 3 ONU 2
Segment 4: Pure Wireless (e.g. WiMax, LTE)
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Segment 5: Legacy (e.g. GPON, EPON) and NG Optical Access
Fig 2: Network architecture and implemented test-bed comprising a Remote Node and Reflective SOA as colorless ONU.
4. Ultra-Dense-WDM-PON An alternative to the exploitation of the electrical-over-optical domains could consist of the direct intensive use of the optical spectrum, while minimizing the electronics requirements in terms of bandwidth and power consumption. This can be achieved by ultra-dense WDM multiplexing, with very narrow filtering techniques or by coherent homodyne detection [3]. New developments in photonics and signal processing can enable this next-generation large-scale access networks based on ultra-dense wavelength division multiplexing (U-DWDM) targeting more than 1000 users on a single architectural platform with low-cost deployment. Pure optical OFDM is a step further in this direction [2]. 5. Discussion As commented, the three proposals offer different performances and functionality (summarized in the Table 1, and compared to 10G-PON), which can be of interest in a wide range of scenarios or applications, once the technological hurdles are solved in current worldwide research initiatives. These hurdles are generally related to the up-stream transmission and ONU design. Figure 3 allocates the NGPON systems in this frame. A great improvement in spectral efficiency is obtained with the proposed systems, what can translate into relevant power and cost savings. As access networks aim at an efficient utilization of resources, and being the optical and electronic spectra the most valuable resources that communications have. Table 1. Typical main parameters of the ngPON2 architectures (average values). XG-PON WDM/TDM-PON OFDM-PON ** UD-WDM User data* 50 MBit/s 50M-1G Bit/s 100 MBit/s 1 GBit/s Aggregated bit rate 10 GBit/s 10 GBit/s 10 - 100 GBit/s 1 - 2 GBit/s ONU El. Bandwidth kHz - 10GHz kHz - 10GHz Fi – Fi+50MHz MHz - 1 GHz Electrical Spectrum Eff.(up) 0.5% 0.5% - 10% 200%*** 100 - 200% Number of users 32 1024 128 1000 Wavelength Channels 1-2 32 1-8 1000 Wavelength Spacing 50 - 100 GHz 10 - 100 GHz 3 - 5 GHz Optical Spectrum Eff. (up) 20% 1% - 80% 20 - 60% Passive distance reach 20 km 100 km 20 km 100 km simple Added features protection, wired&wireless electronics, scalability, metro- convergence, complex optics access converg. SC-DBA Issues Optical remote Up-stream OBI Wavel.tuning, pump power polarization
Fig. 3. Electrical/Optical spectrum efficiency allocation.
1000% SC-OFDM UD-WDM
100% Electrical 10% Spectrum Efficien.
1%
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0.1% 0.1%
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* Symmetrical PON; ** 16QAM; *** Only odd carriers used. This work is supported by the European FP7-ICT projects: SARDANA" (GA-217122) and ACCORDANCE (GA-248654).
References [1] [2] [3]
European 7th Framework Programme project SARDANA (www.ict-sardana.eu). European 7th Framework Programme project ACCORDANCE (www.ict-accordance.eu). J. M. Fabrega and J. Prat, “Simple Low Cost PSK Receiver”, ECOC’2007, paper 7.2.5
O-OFDM
10%
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Optical Spectrum Efficiency
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