De Bruyne, Jeffrey

Joseph, Wout

Martens, Luc

English

Ghent University Academic Bibliography

Extensions of the Capacity of Broadband AccessNetworksJeffrey De BruyneSupervisor(s): Wout Joseph, Luc MartensAbstract—A main challenge for broadband wired access networks (Hy-brid Fiber/Coax or HFC network studied in this paper) is the heavily in-creasing demand for bandwidth. Several methods can be proposed for en-hancing the offered bandwidth of these networks. In this paper, two of themare discussed: node splitting (pushing the fiber closer to the end user) andwireless extensions based on WiMAX.Keywords— Hybrid fiber/Coax networks, wireless broadband access,WiMAX, node splittingI. INTRODUCTIONDURING the last few years, there has been an increasingdemand for broadband network access. The different ca-ble operators deploy today triple-play services, the combinationof internet access, video (digital TV and Video on Demand),and telephony services. People use more and more these ser-vices, download content, and use peer-to-peer services, causinga heavily increase in the demand for bandwidth.Our research focuses on determining the most economical wayto exploit broadband HFC network access infrastructures inthe future to meet the broadband service demands. Improve-ment of current transmission technology as well as the studyof next-generation architecture models (such as Fiber-to-the-Home (FttH) and node splitting (bringing the fiber closer to thehome)) and new approaches such as wireless extensions are in-vestigated. In this paper node splitting and wireless extensionsbased on WiMAX (Worldwide Interoperability for MicrowaveAccess) are presented and analyzed.II. HYBRID FIBER COAX NETWORKSFig. 1 shows the tree-and-branch architecture of the currentHFC access network (typical in Belgium). The hub connectsthe backbone network to the HFC network. From the hub tothe optical node, two fibers are used to transport downlink (DL,traffic from backbone network to home user) and the uplink (UL,traffic from home user to backbone network) signal. From theoptical node, the signals are distributed through a thick low-losstrunk coaxial cable. At the bridger amplifier the signal is splitin different distribution lines. On the distribution lines, taps areused to connect drop cables to the homes. In most cases fourhouses are connected to one tap. Trunk and distribution ampli-fiers are used to compensate for the attenuation of the coaxialcable. Splitters are used to split the signal in equal parts (e.g., atwo-way splitter splits the signal of one coaxial cable into twoequal signals for two cables).The combined use of fiber and coaxial cable explains the termJ. De Bruyne is with the Information and Technology Depart-ment, IBBT/Ghent University (UGent), Gent, Belgium. E-mail: Jef-frey.DeBruyne@intec.UGent.be .Fig. 1. Architecture of an HFC access network‘Hybrid Fiber/Coax’ network. Fig. 1 illustrates that two compo-nents can be distinguished in such a branch-and-tree network:the branches and the junctions. The branches represent the coax-ial cable with a certain length, which is deployed undergroundor above ground (on pole or facade of house) and connectedto several homes through taps. The junctions represent the ini-tial node, the trunk and distribution amplifiers, and the splitters(above- or underground).III. METHODOLOGYTo meet future bandwidth demands, one can upgrade the cur-rent HFC network to a next-generation architecture model (e.g.,node splitting) or use new approaches such as wireless exten-sions in the HFC network (e.g., WiMAX).A. Node splittingWhen applying node splitting, fiber is brought towards se-lected junctions, which then act as new nodes serving a smallernumber of homes than the initial node (so that more bandwidthcan be provided per client). The selection of these junctionscannot be done arbitrarily: the most cost-efficient (= cheapest)node splitting architecture has to be determined. Only junctionswith amplifiers are considered as potential new nodes becausecable operators want to eliminate as much active componentsas possible. The CapEx as well as the OpEx are high for theactive components. The different ranges of houses used to splitthe networks into smaller parts are 128↔384, 64↔192, 32↔96.These are typical ranges that the cable providers want to applyto their access networks for node splitting (so an average of 256to 64 HPs per node).The tool to calculate the most cost-efficient node splitting of anarea is implemented in VisioTM using the macro-extension (Vi-sual Basic). The user can easily draw a network in Visio, definethe range, and execute the macro on the network to obtain theFig. 2. WiMAX Networkdesired new topology. Two different heuristic techniques areused for the node splitting. The new nodes selected by heuris-tic 1 and 2 are based on the maximum number of served homesand minimum relative cost, respectively.B. Wireless extensions: WiMAXWireless broadband connections may be a complement for‘last mile’ fixed access. They can be installed within days at rel-ative low costs, which make them faster to deploy and cheaper incomparison with their wired equivalents. WiMAX (WorldwideInteroperability for Microwave Access) based on the standardsIEEE 802.16 [1] and HiperMAN [2] promises an interoperablesystem and high data rates.Fig. 2 shows a typical setup for a WiMAX network. Differentbase station (BS) antennas can be positioned in an urban envi-ronment and act as a WiMAX Line-Of-Sight (LOS) backhaulnetwork. These BS are connected to the Internet through a fixedbackhaul network. The CPE (Customer Premises Equipment)at the end-user (e.g., Office building, residential houses, mobileclient) is connected to the BS, enabling communication with theInternet.IV. RESULTSA. Node splittingTABLE IRESULTS OF NODE SPLITTING FOR ALL RANGES FOR AN URBAN AREA INBELGIUMArea Range Both HeuristicsNew CostNodes [u]Urban1: 128↔384 5 1180.642: 64↔192 9 2237.643: 32↔96 22 6278.76Table I summarizes the results of the heuristic techniques ap-plied to an urban environment in Belgium for all ranges (withthe cost expressed in units [u]).When the ranges are divided by two, the cost almost doubles.The cost even increases with a factor 3 comparing range 2 withrange 3 (especially due to the larger distances between initialnode and new nodes, where the fiber has to be deployed).Fig. 3. DL throughput at different locations (• = location of BS)B. Wireless broadband access: WiMAXFig. 3 shows the observed throughput in DL, measured at 50different locations in an urban environment with the BS heighthBS = 45 m. The BS is indicated using a black circle. The blackline shows the direction of the main beam of the BS. Emptysquares indicate locations where no connection was possible.The maximum distance where connection is obtained, is about2.21 km. However, permanent connection with the BS is onlyguaranteed within a range of 1 km. A low correlation betweenDL throughput and distance can be observed, which illustratesthat the throughput is more related to environmental conditionsthan to distance. In DL and UL, a maximum throughput of8.19 Mbps and 11.8 Mbps are obtained, respectively.V. CONCLUSIONSIn this paper, two methods are proposed to extend currentHFC access networks for future bandwidth demands. By us-ing node splitting, the initial HFC access network is split intosmaller parts by deploying fiber closer to the end-user, whileWiMAX can be used as a wireless extension to the broadbandwired network. Both methods can deliver additional bandwidthto the end-user to meet future broadband demands, each with acertain cost. In the future, the network performance and expen-ditures of these and other methods (which deliver the requiredadditional bandwidth to the current HFC network) will be inves-tigated and compared to each other.ACKNOWLEDGMENTSThis work was supported by the IBBT-CIcK project, co-funded by the IBBT (Interdisciplinary institute for BroadBandTechnology), a research institute founded by the Flemish Gov-ernment in 2004, and the involved companies and institutions.W. Joseph is a Post-Doctoral Fellow of the FWO-V (ResearchFoundation Flanders).REFERENCES[1] IEEE Standard Std. 802.16-2004, IEEE Standard for Local and Metropoli-tan Area Networks, “Part 16: Air interface for fixed broadband wirelessaccess systems”, 2004.[2] ETSI, “ETSI Broadband Radio Access Networks (BRAN) HIPERMAN,Physical (PHY) layer, Standards TS 102 177”, 2003.   

Extensions of the capacity of broadband access networks

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Extensions of the capacity of broadband access networks

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