Research — Project Overview

Overview of the COMED Project

Project Scope and Goals

Fundamental building blocks of this infrastructure are big satellite networks, providing high quality communication services.

At the moment, satellite constellations with over 200 satellites are planned. With these quantities, satellites are becoming more and more industrial 'assembly-line' products in a market, where a competive price is of first-order importance.

This means a revolutionary change for the satellite industry which tradiontionally is oriented on bulding satellite in quantities of one or two pieces. These changes bring big chances but also a big risk in worldwide competition. The involvment of the German aerospace industry in the fast expanding but highly competetive multimedia market is of essential relevance for the entire German industry. A successful involvment in this multi-bilion Euro market means new jobs in this industry sector. The German Aerospace Center (DLR - Deutsches Zentrum fuer Luft- und Raumfahrt) supports a number of industry projects on the basis of Public Private Partnership, i.e., a public funding equivalent to the industry involvment.

The goal of these projects is the development of innovative technologies and production techniques for future satellite systems.

The projects in the COMED framework are oriented towards factors which are essential for the marketability of future satellite systems like:

• fast packet switching through an asynchronous transmission technique,
• on-board processing, i.e. low-cost and fast processing of information in the satellite,
• synchronisation and communication between the satellites by means of intersatellite-links,
• development of technologies for serial production of syb-systems and components, and
• reduction of the overall mass of the satellites by reduction of the component masses.

The COMED program is structured into two main parts:

• Satellite Bus (incl. satellite structures, power supply, control and steering);
• On-board Processing (incl. new switching technologies and system like ATM, optical Inter-Satellite Links, sub-systems and devices; coordinated by Bosch.

Involvement of the Satellite Group @ Fraunhofer FOKUS.cats

The first step in these studies is the specification of requirements for the on-board processing. This is based on the analysis of application scenarios; a list of typical applications as well as communication protocols and communication requirements are used to extract traffic models as input into simulations. On the basis of these studies, the protocol architecture for future multimedia satellite systems is developed, which includes protocol stacks for satellites and end systems as well as the partition of functionality between space and earth, between satellites, end users and Network Contol Centers (NCCs).

This leasds to an architectural design of the control and management plans - protocol architectures for user-satellite, satellite-satellite and satellite-NCC communication. A key aspect of the protocol architecture is the integration with existing fixed networks to enable seamless communication on a global basis. For this reason, the procols will be derived from exinstin ATM procols with modivications, nececssary due to the nature of satellite communication (long delays, high error rates, highly dynamic topology changes). A major part of the on-board processing is the resource management. This includes topics like air resouce management (up-link and down-link), access methods for multible access, data link control, medium access control, connection admission control and the interface between resource allocation modules and the protocol stacks. A key aspect in this area is the scalability of the system: a single satellite must suport any number from hundreds of users (in LEO constellation) up to hundreds of thousands of users (in GEO systems). Other aspects of the the FOKUS.cats involvement in COMED are security issues on the protocol level, mobility management and system management. The Satellite Group @ Fraunhofer FOKUS.cats will also take part in the realisation of a demonstrator and the tests of the latter.