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Plastic optical fiber technology for reliable home networking: overview and results of the EU project pof-all

Plastic optical fiber technology for reliable home networking: overview and results of the EU project pof-all
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  IEEE Communications Magazine • August 2009 58 0163-6804/09/$25.00 © 2009 IEEE I NTRODUCTION Optical fiber access technology (e.g., fiber to the x [FTTx]), all different flavors of very-high-speeddigital subscriber line (VDSL), coaxial, andhybrid fiber coax (HFC) technologies, is carrying very high-bandwidth and high-quality-of-service(QoS) connections toward residential customerstoday, and in the near future will provide datarates of 100 Mb/s or higher. The development of solutions for the very last part of this network,sometimes called the  edge network (i.e., forshort-reach access inside customer premises andindividual living areas), has been mostly neglect-ed so far but, surprisingly, may become the bot-tleneck of the entire communication system.Supplying QoS and always available data con-nection at a high data rate to the very end of theedge network (customer devices) will be a keyrequirement for telecom operators and serviceproviders to successfully place their products onthe market. In addition, the reliability of the net- work for services like Internet Protocol TV(IPTV) and video on demand (VoD) is of utmostimportance to the customer, especially whenhigh-definition video content with low packeterror tolerance and low latency time is requested[1].Besides these technical requirements, twofundamental and somewhat parallel require-ments must be satisfied for these connections:low cost and extreme ease of installation. Ideal-ly, the final customer should be able to buildhis/her small network inside the building, with-out the need for a professional installer.Today, two approaches can be assumed forin-building networks [2]:• Wireless approach: Many radio-based datatransmission systems like wireless local areanetworks (WLANs, IEEE 802.11), Blue-tooth, GSM, HSDPA, and long-term evolu-tion (LTE) allow the user to have a finiterange of mobility accompanied by a medi-um and inconstant data rate. A BSTRACT The rising performance of broadband connec-tions for residential users, particularly in con- junction with fiber to the home, will present anew challenge for telecom operators in the shortand medium terms: how to deliver the high bitrate digital signals with high quality-of-service toall consumer devices scattered inside the build-ing of final users? Among the many differentsolutions for the home network, we review inthis article the use of polymer optical fibers forshort-reach and high-capacity optical communi-cations for residential customer premises. POFis an easy-to-install, low-cost, and eye-safe solu-tion for these networks, with the potential of being future-proof. In this article the state of theart in POF technology is presented by summariz-ing significant results achieved in the Europeanproject POF-ALL. Data transmission rates of more than 1 Gb/s over 50+ m and 100 Mb/sover 200+ m of standard step-index POF havebeen shown. T OPICSIN O PTICAL C OMMUNICATIONS Ingo Möllers and Dieter Jäger, Universität Duisburg-Essen, Germany Roberto Gaudino, Politecnico di Torino, Italy  Alessandro Nocivelli, Luceat S.p.A., Italy Hans Kragl, DieMount GmbH, Germany Olaf Ziemann, POF Application Center, Germany Norbert Weber, Fraunhofer IIS, Germany Ton Koonen, Eindhoven University of Technology, The NetherlandsCarlo Lezzi, Fastweb S.p.A., Italy  Andreas Bluschke, Teleconnect GmbH, Germany  Sebastian Randel, Siemens AG, Germany  Plastic Optical Fiber Technology forReliable Home Networking: Overviewand Results of the EU Project POF-ALL  IEEE Communications Magazine • August 2009  59 • Wireline approach: Unshielded twisted pair(UTP), coax, HomePNA, power line com-munication (PLC), optical fiber links (sili-ca/glass single-mode, silica/glass multimode,polymer optical fibers [POFs]) providepotentially higher data rates and QoS, butno mobility.When using a shared media approach (e.g.,today’s wireless, PLC, and coaxial LAN tech-nologies), the QoS cannot be fully guaranteed without a robust medium access control (MAC)strategy, as terminals are competing for theirshare of the total bandwidth available. Regard-ing cabled solutions, UTP is still the most fre-quently installed solution but, with respect torising metal prices and sensitivity to electromag-netic interference (EMI) as well as installationregulations to stay far from power lines, thissolution is not ideal in home networking.The combination of high demand in data rateand guaranteed QoS is easily met by opticalcommunications systems, together with completeEMI immunity and no regulatory problem withcoexistence in powerline ducts. Traditional silicafiber solutions could principally be used, butthey need to be installed by well trained andskilled technicians, which inhibits this solution tobe low-cost. For new cost-efficient installationsas well as reinstallations by do-it-yourself installers, POF could be a promising solution forhome networks.The first real field installations of POF-basedhome networks providing triple play services(IPTV, voice over IP [VoIP], and data) for fastEthernet have successfully been installed andtested by some telecom operators such as Swiss-com [3].While today POF transceivers are limited torelatively low bit rates (in the 100 Mb/s range),the goal for the POF-ALL project was defined toextend the limit to the gigabits per second rangeover several tens up to 100 m, and 100 Mb/stransmission distances to more than 200 m,respectively, by adapting higher order modulationschemes (e.g., pulse amplitude modulation [PAM]or multicarrier modulation [MCM]) and selectingsuitable optoelectronic components to meet spe-cific requirements of POF links. By demonstrat-ing these achievements, POF-ALL will be able toshow that installing POF into in-building net- works would be a future-proof solution. POF FOR  S HORT -R ANGE O PTICAL  C OMMUNICATION POF O VERVIEW AND  M ARKET Polymer or plastic optical fibers (POFs) havebeen largely used in industrial automation formore than 20 years in applications likePROFIBUS, INTERBUS, and SERCOS, and inharsh environments. Furthermore, POFs aredeployed in millions of vehicles serving a multi-media oriented systems transport (MOST) bus with data rates of 25 Mb/s, 50 Mb/s, and 150Mb/s (MOST150) [4]. For in-vehicle camera sys-tems, transmission via POF in the range of 1Gb/s is currently being studied. In recent yearsPOF also gathered importance in consumer ori-ented applications like optical audio signal trans-mission and is now challenging many coexistingtechnologies in the networking market.The success of POF has been driven mainlyby its technical characteristics. It is a low-costmaterial — standard POF is made of polymethyl-methacrylate (PMMA) — and it occupies lessspace and weight than copper [5]. Other advan-tages include complete galvanic isolation andimmunity to external EMI, which allows POF tobe installed adjacent to copper cables in thesame cable ducts or harnesses.The main advantage of POF for these mar-kets is that it is much easier to install than multi-mode glass fiber, thanks to its larger core.Standard POF has a 1 mm diameter, whichallows easy fiber cutting, termination, and hencelow-cost installation of the terminals. POF tech-nology is eye-safe, and the use of visible wave-lengths — the attenuation minima of POFs arein the visible region — eases the functionalitycheck of the network. Additionally, POF connections are extremelytolerant to residual dust on the terminal faces —a major issue, on the contrary, for glass fiberconnectors. Preparing POF connections with oreven without connectors, especially interestingfor do-it-yourself installations in apartments,requires no more than one minute and no spe-cial tools [6].Recent developments in POF and the tele-com markets have indicated that POF is begin-ning to make inroads in the telecom business.POF is enjoying significant growth in a widerange of applications due to its ease of use, largecore tolerances, and low cost. It is now used inmillions of small area networks, such as those inmany car models, and is rapidly growing in homenetworks and interconnection. The POF market was estimated to be worth over US$1.6 billion/  year by the end of 2008 (Beach Communica-tions) with an annual growth rate of more than20 percent. According to IMS Research, thehome networking market will more than doublein 2009, reaching an installed base of nearly 100million units compared to 42.5 million units in2005.The current home networking market hasmainly been driven by the availability of broad-band (> 1 Mb/s) connections to the wide areanetwork for Internet surfing and emailing. IPTVand VoD services with future high definitioncontent will accelerate the growth, although it isnot only the connection to the Internet worldthat counts. Interaction between devices in thebuilding and growing demand for intelligenthome automation, control, and new lifestyle fea-tures will lead to a rapidly growing market.Comparing the costs of POF with a still man-ageable amount of sold devices and fiber to cur-rent alternatives as UTP cabling, the fiber coststhemselves are currently comparable to the cop-per-based alternative, although for the entiresystem much lower installation costs for POF will compensate for slightly higher cost due tothe need of converters. With the perspective of growing markets for POF and demand for QoSand high data rates provided by a POF-basedbackbone, the costs will drop significantly. Cur-rent information regarding POF, its technology,and further information can be found in [7]. POF is enjoying  significant growth in a wide range of  applications due toits ease of use, largecore tolerances, and low costs. It is now used in millions of  small area networks, such as those inmany car models, and is rapidly  growing in homenetwork and interconnection.  IEEE Communications Magazine • August 2009 60 E DGE  N ETWORK  A RCHITECTURES Observing international housing conditions, thehome network appears to be quite heteroge-neous. While a majority of North Americans livein detached houses, in Europe apartment hous-ing is predominant, and in Asian cities multisto-ry buildings are common. For these differentneeds the topology of the edge network has tobe defined. Due to its capillarity, the edge net- work is the most expensive part of the accessnetwork. It includes interbuilding, intrabuilding,and apartment cable connections, as depicted inFig. 1. Different POF-based solutions are sug-gested for different types of data transmission.The equipment for each network type must meetspecific technical requirements (Table 1). Inter-and intrabuilding networks are mainly installedby telecom operators or home builders, whereasapartment networks are normally installed byprivate customers. T HE  POF-ALL P ROJECT The Paving the Optical Future with AffordableLightning-Fast Links (POF-ALL) project aims atdeveloping a technology to allow delivery of 100+ Mb/s symmetrically to residential users atcosts far lower than existing alternatives, thanksto the use of POF [9].POF-ALL shall prove that POF can radicallyease installation difficulties and reduce costs while providing ample bandwidth, making it aninteresting alternative for edge networks. It isexplicitly focused on large 1 mm core fibersbased on PMMA material, in either the tradi-tional step-index (SI-) version or the recentgraded-index (GI-) version. Two main technicaldirections are investigated in the POF-ALL pro- ject, and results of these research activities arepresented in this article:•Medium-range transmission at 100 Mb/s(fast Ethernet) over distances above 200 m,using standard 1 mm SI-POF, with a finaltarget of 300 m•Short-range transmission at high speed (1Gb/s and more) over distance > 50 m witha target of 100 m using 1 mm SI- or GI-POFTable 1 is a summary of the main specificattributes for the three network types and corre-sponding POF-based network solutions proposed within the two research fields of the POF-ALL project. T ECHNICAL  G OALS AND A CHIEVEMENTS The technical goals are divided into the tworesearch fields of the project: medium-range andshort-range developments. Each field is split intoone baseband and one orthogonal frequency-division multiplexing (OFDM) approach, fol-lowed by a view of components and fibers. M EDIUM  R ANGE  P ROGRESSION Baseband 8-PAM Approach — Since thebandwidth length product of a standard SI-POFis currently given at around 50 MHz ⋅ 100 m[10], true binary baseband non-return-to-zero(NRZ) modulation cannot achieve data rateshigher than 100 Mb/s at a distance far greaterthan 100 m. Consequently, multilevel basebandtransmission was developed to achieve 100 Mb/stransmission over 200+ m. Due to the strongmodal dispersion in 1 mm SI-POF over a dis-tance of 300 m, the available bandwidth is on theorder of around 15 MHz (maximum rates up to28 MHz). Thus, bandwidth-efficient multileveltransmission is required. A proprietary and opti-mized proprietary transmission protocol basedon direct baseband 8-PAM coupled with pre-and post-equalization is needed. The system that  Figure 1.  Definition of the edge network infrastructure (the different line colors indicate different segments of the network, see Table 1) [8].   Flat 5Room 2Flat 1Room 4House 1Apartmentbuilding 1SwitchFTTHRoom 1Room 3Room 2Room 4House 1SwitchFlat 3Flat 6Flat 2Digital videoinput (DVB-T,sat, cable,...)Flat 4FTTH, POFmanagementswitch +TV streamingInterbuilding network Intrabuilding network Apartment network  The technical goals are divided into thetwo research fieldsof the project: medium range and  short range developments. Each field is split intoone baseband and one OFDM approach, followed by a view on components  and fibers.  IEEE Communications Magazine • August 2009  61 has been proposed thus requires advanced digi-tal signal processing (DSP) algorithms and isbased on the following blocks (Fig. 2a):•Conversion of the input binary data streaminto 8-PAM, with (optionally) the additionof forward error correction (FEC) codingto improve transmission resilience.•Precompensation filtering on the 8-PAMsignal. This is performed by an 8-tap finiteimpulse response (FIR) filter with a high-pass response that partially precompensatesfor the bandwidth limitation of the POFchannel, and an ad hoc algorithm to com-pensate for the LED’s nonlinearity.•Digital-to-analog conversion of the resultingsignal, and application to a green (520 nm) wavelength LED with suitable driver hard- ware.•At the receiver side, detection of the incom-ing optical signal using a high-performancePIN photodiode followed by a trans-impedance amplifier and a (linear) auto-matic gain control circuit.•Analog-to-digital conversion, followed byDSP-like clock recovery and blind adaptiveequalization.•Demodulation from 8-PAM to binary.The advanced DSP proposed here is current-ly prototyped using a high-level field pro-grammable gate array (FPGA). It has beendemonstrated that this architecture is capable of transmitting 140 Mb/s line rate (for a net datarate equal to 100 Mb/s) over a full experimentalprototype of 200 m standard SI-POF. The result-ing transmission system was error-free after 200m, showing the eye diagram represented in Fig.2b. Additionally, a bit error rate (BER) of 10 –3 after 275 m was obtained. Using FEC, it can bemade error-free. This is a very good result thatoutperforms most demonstrations done in thepast. It was achieved thanks to a combination of the following technical solutions that allowed theavailable power budget to be greatly increased:•Use of green wavelength LED sources, where the POF attenuation is much lowerthan in the red region. Transmission overmore than 200 m would be absolutelyimpossible in the red, while in the green itgives a reasonable attenuation of approxi-mately 20 dB.•Improved sensitivity receiver, using the lat-est large area photodiodes.•Advanced digital signal processing, includ-ing the use of FECs. OFDM/VDSL Approach — Today, no commer-cial solutions are available for a highly band- width-efficient transmission method for SI-POFin the medium range (200+ m). The use of MCM, also called OFDM or discrete multitone(DMT), as a bandwidth-effective, noise protect-ed, and adaptive method for transmission overSI-POF has been investigated. Following theanalysis of the features of different MCM appli-cations (number of tones, tone spacing; bits pertone; required bandwidth; possible spectral effi-ciency, etc.) the choice is to use existing VDSL2as the basic technology for the required fast Eth-ernet transmission over 200+ m. The major fea-ture of MCM is the division of the spectralbandwidth into several thousands of equidistanttones with a signal-to-noise ratio (SNR) depend-ing on the number of bits modulated by quadra-ture amplitude modulation (QAM). With amaximal spectral efficiency of 15 b/s/Hz corre-sponding to 15 b/tone, VDSL2’s theoretical max-imum bit rate for a 17 MHz available bandwidth,4.3125 kHz tone spacing, and 4096 tones is, asthe sum for both directions, 245.76 Mb/s. For 30MHz, with double tone spacing and 3478 tones,417.36 Mb/s can be achieved. Furthermore,there are existing plans to transmit within abandwidth of 35.328 MHz (8192 tones and atone spacing of 4.3125 kHz). In this case themaximum aggregate bit rate would be 492 Mb/s.The idea to use MCM for fast Ethernet trans-mission over SI-POF was proposed in [11]. In2007 three generations of demonstrators werecreated. The block diagram of the demonstratoris shown in Fig. 3a. The first and second genera-tions are based on evaluation boards from aVDSL2 chip set manufacturer. For the thirdgeneration two printed circuit boards (PCBs) were developed, one for data processing and the  Table 1. Specifications and available POF-based solutions for edge network topologies.   Specifications POF-based solution Interbuildingnetwork • Connections between buildings or shortFTTH connections• Distance < 300 m• Data rate fixed: 100 Mb/s fast Ethernet• Transmission system based on VINAX-CPE, VDSL2 standard com p liantcircuit from Infineon for VDSL2 CPE a pp lications• 520 nm POF transceiver• System p rice is a pp roximately the same as the electrical VDSL2 system• The system requires high-quality POF connectors like EM-RJ or SC-RJand p rofessional installers.Intra-buildingnetwork • Connections from building entry to thea p artment entry• Distance: < 70 m• Data rate: 100 Mb/s fast Ethernet, p ros p ective 1 Gb/s• Pluggable 470 nm sim p lex POF small form p luggable (SFP) transceiverand switches with 100 Mb/s SFP p orts• Due to resistance of EMI, POF can use the existing ducts for electricalwiresA  p artmentnetwork • Connections from a p artment entry toconsumer device• Distance < 50 m• Data rate fixed: 1 Gb/s Ethernet• Subcarrier modulation-based transceiver• Due to resistance of EMI, POF can use the existing ducts for electricalwires  IEEE Communications Magazine • August 2009 62  Figure 2.  a) System setup.   AGC LED POF Analogue optoelectronics Analogue optoelectronics (a) (b)  .   0   0   1   0   1 . . . DC- balancing 8b/9b D/A converter Photodiode and TIA A/D converter LED driver FEC encoder RS(511,479) 8-PAM modulator Pre- equalizer (FIR) Digital signal processing blocks implemented inside a FPGA LED nonlinearity compensation *Clock recovery Adaptive equalizer FIR DLMS FEC decoder 8b/9b decoder 8-PAM demod Digital signal processing blocks implemented inside a FPGA Today, no commer-cial solutions are available for a highly bandwidth efficienttransmission method for SI-POF in themedium range(200+ m). The useof Multi Carrier Modulation, alsocalled OFDM or Dis-crete Multi Tone, as a bandwidth-effec-tive, noise protected, and adaptivemethod for transmis- sion over SI-POF hasbeen investigated.
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