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On-board switching

GT to GT data transmission in case of classical bent pipe satellite.

On-board switching and multi-beam satellite systems

Multi-beam satellite systems with bent-pipe satellites are gaining tremendous attention from the industry and the research organisations since they enable to cover a wide area with a multitude of narrow, high gain beams, and to highly increase the total system capacity by reusing the same frequency slots in different non adjacent beams. Nevertheless, in such systems, ground terminal to ground terminal(s) communication is only performed via two consecutive satellite hops, all data being first transmitted from the transmission ground terminal to an intermediate gateway and then forwarded to the reception ground terminal(s).

GT to GT data transmission in case of satellite with on-board witching

On-board switching is a technology enabling to support a single satellite hop network topology in multi-beam satellite systems. In the payload of the satellite, the on-board switch is responsible for the establishment of physical or logical paths between its inputs and outputs usually associated with the up-link and down-link beams respectively.

Advantages and draw-backs of on-board switching

On-board switching therefore considerably enhances the resource utilization and performance of the multi-beam satellite systems and displays the following advantages:

• Support of a single satellite hop full meshed network topology for ground terminal to ground terminal(s) data connection,

• Frequency plan applied to the considered coverage area (cluster size 4)

  Halving of transmission delay in end-to-end ground terminals data connections,
• Halving of the radio resources involved in end-to-end ground terminals data connections, and therefore increase of the overall satellite system transmission capacity,
• Active on-board support of traffic differentiation and Quality of Service (QoS),
• On-board duplication of traffic bursts for efficient multicast support, and therefore optimization of the radio resources usage for multicast traffic transport,

Nevertheless, several critical issues should unfortunately be tackled when satellite systems with on-board switching are designed:

• Schematic representation of the network architecture as well as the main network entities

  Complexity of the payload and of the general satellite system architecture,
• Losses and Delays generated by the on-board switch in case of contention at its outputs: this occurs when the amount of traffic instantaneously destined to the outputs of the on-board switch exceeds the associated transmission capacity,
• Pertinence of on-board switching only for some specific applications, such as meshed network of corporate users or support of peer-to-peer applications,

In addition, multi-beam satellite systems suffer also from Co-Channel Interference due to the reuse of the same frequency in different up-link and down-link beams and the imperfect transmission and reception properties of the satellite antennas.

On-board switching DLR related work

The work carried out at DLR in the field of on-board switching consists in:

• General reference scenario definition for multi-beam satellite systems with on-board switching,
• Study of different on-board switch architectures (regenerative, transparent or hybrid, with input, output or shared on-board buffering),
• On-board QoS support and integration with terrestrial QoS mechanisms (IntServ and DiffServ),
• On-board QoS aware, ad-hoc scheduling algorithms,
• On-board advanced down-link transmission resources management and dynamic down-link resource attribution for contention resolution,
• On-board management and minimization of the down-link interferences,

On-board switching related researches have been carried out in the framework of two ESA projects:

• Integrated Resources and QoS Management for DVB-RCS Networks,
• Validation Model of an Ultra-Fast On-Board Processor for Meshed Packet Networks [ULISS LINK]