Satellite Broadband Access Technology

Satellite access systems may be proprietary or standards-based. A standards-based approach has the promise of offering inter-operability between different vendor equipment, a wider range of equipment types, and the ability to re-use equipment in different networks.

The Digital Video Broadcast (DVB) Return Channel via Satellite system (DVB-RCS) is the key European standard published by the European Telecommunications Standards Institute (ETSI). The specification leverages the highly successful DVB standards for TV distribution to provide a bidirectional geostationary satellite network. Current DVB-RCS systems form a centralised star network where all communication passes via a Gateway terminal connected to the point of presence. The standard was amended in 2004 to allow systems to use a forward link with the more efficient DVB-S2 physical layer. The SatLabs forum addresses issues relating to deployment, interoperability, and management aspects of DVB-RCS.

As in many broadband technologies, capacity in the return link, from an RCS Terminal (RCST) to the Gateway, is not dedicated, but shared. In DVB-RCS the Network Control Centre (NCC), allocates capacity to the individual terminals based on a Service Level Agreement (SLA) and in response to explicit capacity requests (sent by RCSTs) or dynamically predicted traffic characteristics. A combination of methods is usually used to seek a compromise between offered Quality of Service (QoS) and efficient use of the satellite capacity.

Work is presently underway to define a next generation RCS system with improved efficiency. The proposed next generation standard, DVB-RCS2 is expected to be standardized in 2011. This improves the efficiency of return link and a redesign of the medium access control (MAC) layer and IP packet handling to make the system better integrated with ISP networks. DVB-RCS2 will also support commonly used IP based protocols and applications providing interoperability. Common specifications for critical components with the goal of allowing larger production volumes to reduce prices will also be developed. Together these are expected to increase performance and reduced the cost of terminal production and operation.

Satellite Broadband Access Service Provision

Current DVB-RCS networks support forward link rates of up to 80 Mbps (DVB-S2) per forward link with 2-20 Mbps per terminal and return link rates of up to 8 Mbps (256 kbps - 4 Mbps currently common) for several simultaneously logged-in terminals. Networks are typically aimed at user communities of 100’s to 1000’s of users per network.

The cost of access provision is determined by the ISP costs in the backhaul network and point of presence, the cost of the terminal and other equipment, and the cost of the satellite space segment.

The small satellite terminal market market has recently seen substantial growth. From shipments of fewer than 300,000 terminals per year in 2004, the market reached 750,000 shipped terminals in 2007. This increase is leading to a significant decrease in terminal unit price, to a price point below £300 per terminal. Benefits do arise for DVB-RCS systems, but the current European market, represents a small proportion of the global market, dominated by US proprietary systems (up to 2007, the world market share for DVB-RCS was of the order of 5%). 2007 saw a significant increase in DVB-RCS sales and compliant solutions are approaching price/performance competitiveness with proprietary solutions – especially if this is supported by the improvements developed in the DVB-RCS2.

The cost of satellite space segment represents the return on investment of design and manufacture of the satellite and it’s launch and (comparatively smaller) operational costs. The advances in terminal design have been matched by significant advances in satellite design – with the emergence of a new generation of spacecraft and the introduction of satellites with multiple spot beams that can provide much higher capacity. The launch of Hylas-1 and Hylas-2 will present an unprecedented increase in total available capacity across the UK.

Technology Strand in SIRA

Engineering research will be based on the European DVB-RCS Standard and the components needed to realise a next generation satellite broadband system (DVB-RCS2). This system needs to be cheaper, higher speed, and extensible to address new emerging markets. Immediate challenges focus on design of techniques, quality of service mechanisms and Internet integration. In recent years it has been recognised, that user-behaviour and the resulting traffic patterns have a profound impact on the service quality offered by an ISP, and the technologies to be selected. There is as yet little understanding of the way in which rural users will use new digital technology.

The SIRA project seeks to capture and understand user behaviour enabling us to derive better simulation models (application and traffic) and to interpret engineering performance. The project will explore protocol performance and system evolution and would drive research into techniques for Radio Resource Management (RRM), Quality of Service (QoS) mechanisms and Internet integration. We will be performing user lead piloting of new technology and services.

The project seeks to drive technology evolution, through carefully considered research combined with active engagement in the relevant standardisation bodies, we will influence the way in which this service is designed, delivered and operated for both professional and consumer use. Simulation models developed in the School of Engineering can be used to support the evaluation of new techniques.

The programme of research is designed so that it will result in both technological advances in the way communications infrastructure is engineered, and that the resulting service is responsive to user needs and results in greater inclusion of communities and business as a part of the Digital Economy.

Technology Strand Goals

  1. To deliver acceptable broadband experience at minimal cost of ownership/use
  2. Explore methods to support new applications and services (multi-service)
  3. Adapt and develop new applications
  4. Propose traffic management and QoS to virtualise the service
  5. Engineer new algorithms and techniques to optimise satellite usage
  6. Contribute to standardization efforts (ETSI, DVB, IETF, etc)

The research described here is supported by the award made by the RCUK Digital Economy programme to the dot.rural Digital Economy Hub; award reference: EP/G066051/1.