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The August 21, 2003 Issue Provided by System Dynamics Inc.
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Celeria: Wireless Access To Cable Networks

A Guest Article by Inés Vidal Castiñeira

Note from the Editors: We are delighted to continue our series of guest articles by broadband experts with this contribution from Euskaltel, a full service cable and telephone operator in the Basque Country, in the north of Spain. Although Euskaltel already had a fiber ring infrastructure from which they reached end users with HFC and twisted pair, this approach was not cost effective for serving small municipalities. Instead, they developed a wireless approach to deliver digital video, cable modem and voice services to these customers. This LMDS-based approach provides the same services delivered over wires to urban users, consistent with Euskaltel’s backbone architecture, and using the same equipment at both the headend and the user premises for both wired and wireless customers.

Inés Vidal Castiñeira, Manager, Wireless Access for Broadband Services in Cable Networks, has been involved in and managing new services projects within the Technology Department. She has also been deeply involved with regional, national and international engineering and development projects. Inés graduated as a Telecommunications Engineer from the Bilbao Industrial and Telecommunications Engineering College, specializing in Telematics. Inés also participated in IAESTE, a student technical exchange program, during which she worked in Poland and Austria.


Cable service in Spain is quite recent. In 1998 Telefonica’s monopoly was broken and 12 companies entered the market to provide telecommunication services over cable networks. They all got licenses in different areas of the country and committed to reach the majority of the customers in their areas in 15 years time.

Euskaltel is one of those cable operators born with the liberalization of the Spanish market. We are a Cableco and Telco Operator in the Basque Country in the north of Spain. We offer digital television, internet access (both narrowband and cable modem) and telephone service to residential customers and voice and data services to corporate customers, as well as ISP services.

We are deploying an overlay network, using a fiber to the cabinet (FTTC) scheme. We deliver TV and cable modem services with hybrid fiber-coax (HFC) and telephone services with copper twisted pair.

Our network is hierarchically organized into rings. The top level ones contain the main nodes and the equipment for service provision, and the bottom ones have the nodes closest to the user. For residential customers, each user node is planned for approximately 500 homes.

The Basque country, with around 2.1 million inhabitants and 700,000 households, is an area of contrasts. While five major cities have 42% of the population, 127,000 homes are in 184 small municipalities, with a population density below 100 homes/Km2. It is easy to serve the major cities, but the small municipalities make it very difficult to achieve economic profitability and meet the coverage commitments associated with our licenses.

Because of the long distance to our network nodes and the lower income in these smaller municipalities, an important part of our natural market would have to wait to be reached by our network if we used the same wired approach as in the larger communities. We therefore decided to develop a wireless approach to reach these markets faster.


The objective of the Celeria project is to offer the standard “triple-play” service (telephony, cable modem and digital TV) to a broader market, without changing our network structure and with reasonable investments.

That is, we aimed:

  • to reduce the investment necessary to deploy our network in low-density environments, or where traditional deployment is not advisable (such as the older parts of towns);
  • keeping the same offer from the user point of view; and
  • using the same equipment, both at our headend and at the user premises.

Innovation In Euskaltel

The Department of Technology is in charge of research and development in Euskaltel. We provide the technological strategies for the company in the mid-to-long term, based on the business objectives of the Company.

We currently participate in several regional, national and international projects to deal with the need for new products and strategies to reach the customers. This includes Advanced IP-Services Platforms and several Broadband Radio Access systems:

  • Wireless Access for Corporate Customers (industrial areas. LMDS 26 GHz)
  • Wireless Access for Residential Clients (LMDS 28 GHz)
  • Wireless LAN 802.11b, including roaming
  • Satellite Interactive Services (DVB-RCS)

The Project

The Celeria project started in the beginning of 2001, as an initiative of the Spanish Ministry of Science and Technology, Euskaltel and R, the cable operator servicing Galicia. We have developed a new concept in radio access solutions, meeting the frequency requirements imposed by the Spanish authorities and the needs of cable operators. The result is the first commercial LMDS system operating at 28 Ghz that allows DVB-C (digital video) and DOCSIS (cable modem) carriers to be successfully delivered to the customer’s home.

The DVB-C and DOCSIS carriers allow the provision of the same digital TV and cable modem services we offer to clients with HFC access. But an important part of the package, voice services – provided over copper twisted pair to our HFC customers -- would not be included for wireless customers. Introducing an additional carrier for voice would mean changing the whole telephonic schema of the company.

Instead, we decided to adopt VoIP technologies to deliver voice services over the wireless network. We chose CableLabs’ PacketCable specification for real-time services over two-way cable networks since it is based on DOCSIS architecture, thus leading to minor changes to our network. The adoption of the PacketCable solution required installing EMTA (Embedded Multimedia Terminal Adaptor) functionality at the customer premises to carry voice traffic over the cable modem data link, and installation of a voice gateway at our headend premises. Suppliers such as Thomson, Arris and Motorola already include EMTA capabilities in some of their cable modems, simplifying the customer solution.

We installed a VoIP gateway from Nuera to convey the telephone traffic from the IP network to the PSTN switch. The gateway is connected to the DOCSIS cable modem termination system (CMTS) at our cable headend; it extracts the voice traffic introduced into the network by the EMTA, transforms it into V5.2 and routes it to our circuit-switched telephone infrastructure.

This system provides carrier class telephony. All the telephone traffic between the EMTA at the customer premises and the VoIP gateway at our headend follows PacketCable standards. It flows over a controlled IP network with QoS enabled by DOCSIS 1.1. All telephone traffic, even traffic local to the IP network, goes through the switch, allowing us to use the same accounting scheme provided for our wired-access customers.

The Celeria service is a pre-commercial trial and is currently deployed in Derio, a small municipality near Bilbao airport and the Euskaltel offices. The 40 users are regular customers, who have signed up to receive voice calls, cable modem service and a basic digital TV offering. In the trial, there is no charge for the basic services, but the users are charged for premium TV services such as PPV and for any voice calls exceeding 12 €.

The decision as to whether Euskaltel will deploy this type of access network will be made by year end. Euskaltel’s commitment is to cover approximately 90% of the population of the Basque Country, which will be done deploying its standard HFC network in about 90 municipalities. Any additional/rural deployments are dependent upon the plans being drafted by different public administrations. In particular, open questions include:

  • Whether there is a requirement to provide digital television in these municipalities. If not, there are less costly technologies, e.g. operating at 3.5 Ghz, to provide telephony and broadband, but not digital TV.
  • The role of the incumbent operator in those plans (universal service).
  • The availability of public funding for other deployments.

Network Architecture

Celeria architecture --> Click for larger pictureThe picture shows the network architecture created for the trial:

The CATV Headend, the CMTS and the Telephony switch are the same we use to provide the service through our wired network, and only the new VoIP gateway was added to the original scheme.

We use eleven DVB-C carriers for conventional wired DTV service. These same carriers are mixed with a CM /DOCSIS carrier in the 710-822 MHz band, and constitute the downstream carried over the radio interface; the upstream consists only of the CM carrier. We used a QAM 64 modulation scheme for the downstream and QPSK for the upstream.

The transmission takes place in the 28 GHz LMDS bands defined for the trial by the Spanish regulatory institutions. For full-scale deployment, this frequency assignment will be revised to allow planning for a cellular deployment and the provision of the whole service offering of cable operators.

IKUSI subscriber and base station antennas --> Click for larger pictureThe LDMS system to transmit and receive in these bands was developed for the trial by IKUSI, a leading RF company based in the Basque Country. The Base Station and the User equipment (aerial + transceiver), can be seen in the figure.

After the air interface, the same equipment (DVB Set-Top Box and DOCSIS CM/EMTA) is used in the same way as in homes with HFC access. In fact, the home installation necessary for service provision is the same we use for customers with cable access, avoiding the need to train special staff for customer installation. This approach also facilitates conversion to wired service if an area with radio access becomes accessible to cable, just by changing the signal input point.


For the trial, 11 DVB-C digital television and one DOCSIS carriers were broadcast in a 90º sector. Tests revealed that the signal characteristics received at the customer premises were comparable to those transmitted through the HFC network, and that the signal-to-noise ratios were acceptable up to 2 Km from the base station.

A wireless deployment of this type would permit Euskaltel and many other operators to reach rural and other difficult areas, helping the democratization of access to broadband services.

We do not view this LMDS radio access to cable networks as a global substitute for traditional HFC access. Instead, we think it may provide a good option to shorten the time necessary for cable operators to reach areas that would require large investments for wired access, while allowing a transition to conventional access when the areas accessed initially through wireless are reached by HFC.

Celeria will allow operators to offer the same services earlier and cheaper, with a simple migration to HFC when traditional deployment reaches these areas.

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