Concepts and Solutions for improving the Performance of HFC Networks

Transcription

1 FP White Paper Concepts and Solutions for improving the Performance of HFC Networks 2 May 2010 ReDeSign Research for Development of Future Interactive Generations of Hybrid Fiber Coax Networks Information for Publication: Version: final Status: Public (PU)

2 Executive summary Hybrid Fibre Coax (or HFC ) networks were originally designed to provide broadcast services to cable customers by means of analogue signals. In recent decades, networks were upgraded to broadband telecommunication infrastructures capable of carrying all kinds of electronic media services mainly via digital transmission. Huge investments were necessary to make this evolution happen. Strong competition from incumbent telecommunication networks and emerging infrastructures FttH providers is now challenging cable operators to push forward the technological evolution of HFC networks in order to maintain their position as providers of one of the most cost effective components in the European broadband infrastructure. In order to address these issues, the FP7 ReDeSign project focused on new technologies allowing operators to extend the life expectancy of current HFC network architectures as well as on strategies helping them to migrate to Next Generation architectures. The achievements of the project, which were published in deliverables and other documentations were communicated directly with the operators community through regular Operators Forum meetings, to vendors through an implementers workshop as well as to the European trade association of operators and the USbased CableLabs. Most importantly for the ReDeSign work, liaisons were agreed with the recognised standardisation body CENELEC, the standards developing organisation DVB, and the Society of Broadband Engineers SCTE ensuring the findings and results could be implemented in specifications and standards as quickly as possible. Major research achievements of the project include the project s contribution to the DVB efforts producing a new physical layer for digital transmissions in cable networks (DVB-C2). The new technology has the potential for replacing DVB-C which is implemented in millions of devices world-wide. One of the major contributions of the project here was a simulation platform used in DVB for performance investigation and system verification. In addition, the development of a new prototype amplifier based on state-of-the art (Gallium Nitride GaN) semiconductor technology allows operators to further increase the capacity in their networks in complement with DVB- C2 and other new HFC upgrade techniques such as network segmentation. Implementing the results produced by ReDeSign could thus increase network capacity from 5 to 7 Gbps and beyond. Looking at longer-term evolution, several approaches were short-listed and advantages and disadvantages were described. This resulted in a clear advice to the cable industry to migrate to a common approach starting with the implementation in greenfield situations of an FttH architecture and migrate in brownfield situations (i.e. where there is an existing HFC network in place) to this architecture via deeper fibre solutions such as FttLA (Fibre to the Last Amplifier) complying with various prerequisites driving down the cost per bit transmitted. 2...

3 Concepts and Solutions for improving the Performance of HFC Networks Authors: Bart Brusse (ContestConsultancy) Rui Castro (ZON TV Cabo) Carsten Engelke (ANGA) Manfred Geilert (BLANKOM Digital) Tim Gyselings (ALCATEL-Lucent Bell) Dirk Jaeger (TU Braunschweig, IfN) Maciej Muzalewski (VECTOR) Jan De Nijs (TNO) Contents 1 Introduction The European Cable Industry a brief analysis ReDeSign and its major objectives Current architectures and future service requirements Advancements for today s technologies Advanced physical layer (DVB-C2) Implications of high-scale signal introduction in HFC networks Next Generation broadband amplifiers Future Generations HFC architectures Conclusions, dissemination of results and outlook Acknowledgements The document and further information can be found at the web site of the project:

4 1 Introduction Cable networks are an important part of Europe s broadband infrastructure as they provide millions of citizens with High Speed Internet, voice telephony, and digital TV services. Moreover, as research carried out by the ReDeSign project shows, cable operators have the potential for increasing this role even more, as the nature of their networks enables them to meet mid to longer term challenges with relatively moderate investments. This will enable them to provide very High Speed Data services to their customers in a very cost effective and hence competitive way, thus boosting the development of the information society as a whole. This White Paper provides a brief overview of the current potential and market position of cable networks and documents the research and results carried out by Re- DeSign as well as the objectives the project started out with. In this respect, chapter 4 highlights the results of a survey carried out among operators with the aim to gather information about the current state of cable network architecture across Europe as well as on future service requirements. The results of this survey establish the starting point for the technical work carried out by ReDeSign. The first part of this technical work focused on technical solutions addressing short to middle-term capacity shortages potentially arising in some regional markets. Results of this activity that were largely carried out around a new transmission technology (DVB-C2) as a central concept can be found in chapter 5. Subsequently, chapter 6 documents the second part of the activities carried out by ReDeSign which concentrated on longer-term architectural evolution and the migration path towards the Next Generation HFC infrastructure. Chapters 7 and 8 finally summarise the results of the project and underline that it has been successful in achieving its objectives and hence in defining the cost effective scenarios that will allow the cable industry to preserve and even increase the considerable economic and societal value it has managed to build up through the years. 2 The European Cable Industry a brief analysis The history of cable started in the middle of the last century with the installation of small Community Antenna TV (CATV) systems providing analogue multichannel TV and radio services. Through the years these cable islands were interconnected by broadband systems and merged into large two-way telecommunication infrastructures by combining the traditional Radio Frequency (RF) technology with optical fibre components. These kinds of networks are referred to as HFC networks. They are capable of providing a huge variety of multimedia services based on a cable communication platform called DOCSIS. The cable industry therefore clearly represents a large economic and societal value. In order to preserve this value also on the longer term, cable operators need to further evolve their technical cable infrastructures to ensure compliance with their continuously changing business requirements. One strong pre-requisite to stay competitive is the effective use of the frequency spectrum available; an example of which showing a mixture of analogue and digital signals is depicted in Figure 1. It can be 4...

5 Figure 1: Example of an RF frequency spectrum usage in today s HFC networks seen that the frequency spectrum is almost fully occupied. Therefore, new methods are needed to increase the spectral efficiency per signal and channel, respectively Today, 73 million homes in the European Union receive services via HFC networks. 3 ReDeSign and its major objectives In line with the issues described above, the aim of ReDeSign was to determine the most cost effective way to further enhance HFC infrastructures in consideration of commercial and technical requirements which operators expect to emerge in the timeframe. For that purpose a consortium was formed consisting of cable equipment manufacturers, network operators, and research institutions. Two work streams were set up to develop technical solutions for short to middle-term network enhancements, on the one hand, and concepts focussing on middle to longer term issues, on the other hand. Major objective of the first work stream was to develop concrete technical solutions exploring the full capabilities of the coaxial networks by applying state-of-the-art transmission techniques systems and by enhancing the performance of amplifiers. In the second work stream, the main aim was to evaluate several longer term evolutional concepts for the traditional HFC network and to define the most attractive and cost-effective longer term migration path for cable operators. 4 Current architectures and future service requirements As a result of historic, economic, and regulatory differences, HFC networks across Europe are far away from being coherent in a technical sense. Moreover, the nature and quantity of services offered to consumers may differ between regional markets, as may the views on the future development of these offerings. For both work-stream activities it was of utmost importance to define the existing technical differences as well as the varying expectations of cable operators for their future major business requirements. Such fundamental knowledge was gathered by ReDeSign by means of a survey carried out among the European cable operator community. It was the first time that a detailed study on these topics was successfully executed providing meaningful re- 5...

6 Larger nodes, tree-andbranch Larger nodes, hybrid Larger nodes, star Smaller nodes, tree-andbranch Smaller nodes, hybrid Smaller nodes, star Figure 2: Market share of different access network topologies in Europe sults. Based on the responses from cable operators serving almost a third of all European cable customers, cable reference architectures were defined. In addition, the differences in commercial developments between regional markets in Europe were used as bases for determining relevant technical requirements for these markets. Data emerging from the questionnaire revealed that technical differences were to find predominantly in the coaxial parts of HFC networks as explained in Figure 2. Two thirds of subscribers are connected to cable networks which could be characterised as a so called tree-and-branch or hybrid network with a large number of customers being serviced from a single fibre node. This architecture builds the basis for ReDeSign s subsequent technical developments. Furthermore, the survey results revealed considerable differences between current service levels and packages in regional markets, however anticipated a convergence between these markets on the longer term. This meant that although requirements for solutions addressing short to middle term capacity issues would most likely differ between markets, a migration path towards a single concept replacing the various existing HFC architectures on the longer term could be feasible. 5 Advancements for today s technologies One of the most important business perspectives of cable operators is to continue using their cable networks for a number of years rather than switching to a new topology. One short-term business demand identified was to enhance the transmission efficiency which could be achieved by an increase of the spectral efficiency resulting in a transport of more bits per Hz bandwidth and per channel, respectively. With DVB-C2, a new physical layer was developed which has the potential to replace the antiquated DVB-C technology used today in many million devices world-wide. 5.1 Advanced physical layer (DVB-C2) The ReDeSign project entered the DVB process developing an advanced physical layer technology for the transmission of digital signals in HFC networks at an early stage. The contributions generated by the project partners in terms of computer simulations were essential for the definition of the final DVB-C2 solution. Core techniques adopted were a flexibly configurable LDPC channel coding as well as a Data- 6...

7 Figure 3: Spectral efficiency as function of signal-to-noise ratio generated by computer simulations Slice based OFDM concept which constitutes a novelty in HFC downstream transmission. The major improvements provided by DVB-C2 compared to its predecessor DVB-C can be summarised by an increased robustness against transmission impairments of 7 db (see Figure 3 horizontal red arrow) and an increased spectral efficiency of some 60 % (see Figure 3 right vertical arrow) allowing the transmission of more than 80 Mbps in a conventional 8 MHz cable channel. The simulation results showed that the new OFDM concept provides a very flexible applicability of DVB-C2. The bandwidth of the signal, for instance, can be flexibly assigned and extends the traditional channel bandwidth. This feature helps overcome the difficulties provided by the different channel patterns of analogue signals (7 MHz) and digital signals (8 MHz) when switching from analogue to digital transmission. Another example is the capability to bundle 12.5 channels to a frequency band of 100 MHz while allowing for the establishment of a 1 Gbps connection providing a total network capacity of 7 Gpbs and beyond. 5.2 Implications of high-scale signal introduction in HFC networks As described in the last sub-chapter, the support of a higher spectral efficiency was one of the major reasons why a 4096-QAM constellation was applied in DVB-C2. Adequate high signal levels which are needed to deploy signals using this highefficiency mode are limited by the non-linear transmission effects mainly caused by the saturation of the amplifiers used in a network. The question whether European networks support a 4096-QAM transmission is fair and was investigated by ReDeSign by means of network simulations. The simulation considered technical specifications of the components used in HFC networks which were provided by European cable operators to emulate their worstcase amplifier cascade topologies. In total 4 cascades were studied ranging from an 7...

8 60 Node + 5 Amps Node + 15 Amps SNRDVB-C2 (db) QAM 4096 QAM margin 4 db 2 nd (CSO) 3 rd (CTB) order model 4 th 5 th order model DVB-C2 Carrier Level (dbµv) Figure 4: SNR ratio of the DVB-C2 signals in dependence of the DVB-C2 carrier level for 4 amplifier cascades of different length. Optical Node combined with a cascade of 2 amplifiers up to an Optical Node with 15 amplifiers connected. For all cascades a load comprising 20 analogue TV channels, 30 DVB-C channels, and 43 DVB-C2 was assumed. For the analogue TV and DVB-C signals fixed signal levels of 69 dbµv and 65 dbµv, respectively, were applied, which are common figures used in practice. The DVB-C2 level was varied from about 55 dbµv up to some 75 dbµv. At lower levels, the DVB-C2 signals did not contribute to the generation of intermodulation products and the signal-to-noise ratio (SNR) of those signals increased with increasing DVB-C2 signal level. In contrast, at a level above 65 dbµv, the distortion became noticeable, resulting in a decline of the SNR. Results of the simulations for 2 cascades are shown in Figure 4. As a first deployment rule, the maximum DVB-C2 level should not surpass the level representing the maximum of the respective SNR curve. The traditional model for determining intermodulation is based on 2 nd and 3 rd order non-linear components. ReDeSign however worked out that degradation of digital signals is dominated by 4 th and 5 th order nonlinear components and the traditional model was extended accordingly. The new model is submitted to the standardisation work of CENELEC. 5.3 Next Generation broadband amplifiers One of the most important parameters used for the simulations explained in the above sub-chapter is the power level used for the transmission of signals in HFC networks. Assuming that amplifiers operate in their linear transfer range as intended, high signal levels entail high signal-to-noise ratios as shown in Figure 4 whereas high signal-to-noise ratios allow high efficient spectrum utilisation as seen in Figure 3. Consequently, amplifiers providing high output levels while keeping the level of noise and intermodulation low are supportive to more efficient spectrum utilization through the introduction of DVB-C2 high-efficiency modes. This objective was achieved by a new amplifier prototype which was developed, produced, and verified in the course of the ReDeSign work. The prototype was implemented on the basis of a state-of-the-art Gallium Nitride (GaN) semiconductor hybrid 8...

9 Figure 5: CINR (Carrier-to-Intermodulation Noise Ratio) comparison of new amplifier with a GaN hybrid versus traditional amplifier based on GaAs power output stage circuit. This novelty in broadband amplifier designs is optimised for full digital or mixed digital/analogue signal load which is present in HFC networks today. The comparison with traditional amplifier output stages based on GaAs silicon shows a 3 db improved Carrier-to-Intermodulation Noise Ratio (CNIR) behaviour (see Figure 5), an identical power consumption provided. This feature of the new GaN amplifier could also be used to save system power complying with the Green IT requirements set out by the European Union to reduce power consumption of telecommunication networks. 6 Future generations HFC architectures HFC access networks have evolved from traditional architectures as explained at the beginning of the document. They have been upgraded taking into account the business requirements of operators. The basic structures of the networks including cable and other network elements, however, were maintained to a large extent. Emerging technologies such as the cable communication platform DOCSIS operating on top of the physical network were designed to cope with the prerequisites set out by the underlying network technology. For brownfield situations it was therefore not possible to design an optimized communication system but to evolve a system according to changing operational and business requirements. This phenomenon is a principle drawback valid for all kinds of telecommunication networks and not only for HFC. It does not allow reducing the cost per transmitted bit to a level provided by modern architectures such as FttH, for instance. However, it does have the huge benefit of saving a significant amount of capital expenses due to the capability utilising existing infrastructure and thus prevent expensive digging, as indicated in Figure 6. The situation in greenfield areas is differ- 9...

10 Investment [$] 40% growth 60% growth GPON 1:128 GPON 1: Figure 6: Estimation of average investment cost for FttH (GPON) against HFC upgrade cost, assuming 40% and 60% annual growth in capacity requirements ent. As no network is in place, the optimal solution has to be chosen. It was found in terms of an FttH approach based on passive optical network technology and realised either via GPON or via RFoG technology depending on the specific situation of the MSO. The results of ReDeSign unambiguously show that current HFC infrastructures have a high performance and are scalable due to the implementation of deeper fibre solutions combining the roll-out of fibre closer to the customer and the splitting of nodes to serve smaller clusters. Developments such as DVB-C2 complement deep fibre technologies and increase the utilisation of the coax capacity. Existing coaxial cables have a good transmission performance and suit the bit rate requirements for various years to come in case the cable lengths can be made sufficiently short and used at the last meters only. However, the DOCSIS platform existing today was not developed for this kind of networks and, thus, will not provide an adequate cost-per-bit ratio in the long term. The next generation cable communications system which is not developed yet has to take into account related and further requirements such as power consumption and central office density. Within the project, alternative solutions for coax transmission were studied, offering better cost, power, and density results. Different approaches are followed and evaluated, in theory but also with practical roll-outs. One of the approaches is optimising the current DOCSIS CMTS method in terms of density. Another approach is to stretch the modular CMTS approach as standardised in DOCSIS 3.0 to the outside plant via micro-eqam or micro-cmts on the field. Another approach is to look for alternative coax transmission technologies in the access network, inspired by MOCA, WiMax, etc., called Ethernet over Coax. Today it is clear that the different approaches have pros and cons and none of them is outstanding. The ReDeSign project believes that there is a lot of added value in the DOCSIS approach offering a lot of functionality and optimisation for traffic management but also service support. However, the current DOCSIS 3.0 standard is a very exhaustive and complex standard entailing implementations which are not cost and power efficient compared to other shared access technologies. A new version of 10...

11 DOCSIS with a reduced set of features and more straightforward to implement, which could possibly make use of a new more optimal PHY layer such as DVB-C2, is probably the best way forward to guarantee a success for the NG-HFC network in the next 10 years. 7 Conclusions, dissemination of results and outlook HFC cable networks evolved from their original structure optimised for the support of broadcast services to modern telecommunication infrastructures. Enormous investments were made by the Cable industry to actualise this development. In order to foster the competitiveness of cable against other telecommunication infrastructures also in the future, HFC networks need to comply with dedicated business requirements and thus have to be developed permanently. A major objective in this context is to lower operational costs while keeping the existing access parts of the networks in place. A replacement of HFC by FttH appears not to be economically viable against a much more cost effective upgrade of the networks, although for greenfield situations it would appear to be the preferable solution. Nevertheless, it would be worthwhile for the Cable Industry to agree on and migrate to a common NG-HFC architecture. Looking at short to middle-term aspects, one of the major activities developed by ReDeSign focussed on the implementation of DVB-C2 and identification of operational issues. Simulation results here show that the DVB-C2 high efficiency mode using 4096-QAM could be applied in today s HFC networks, generating an efficiency increase of some 60 %. An even higher increase could be created if complementary measures are introduced at the same time. For example, a new generation broadband amplifier was developed, generating additional gain and reducing power consumption in networks. The active participation of ReDeSign researchers in the standardisation efforts of DVB and CENELEC has been fundamental for the project to pass its output through standardisation processes and to encourage the implementation of its results in innovative technology and equipment. For this purpose, Liaison agreements were set up with DVB, CENELEC, and SCTE. In order to speed up the uptake of its results, the project also established regular Operators Forum meetings with the participation of almost 30 operators in total, representing more than 50% of the European cable market in terms of subscribers. For the manufacturing community finally a DVB-C2 Implementers Workshop was organised in coordination with the DVB Project and ReDeSign member ANGA. Further dissemination activities include scientific publications as well as presentations in research and industry events which took place world-wide from Lisbon to Los Angeles and Shanghai. 8 Acknowledgements The members of the ReDeSign Consortium thank the European Commission for cofounding the work carried out in the project during 1 January 2008 and 30 June