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NICOLE

An example of a satellite network for mobile users studied in NICOLE

The NICOLE is an ESA ARTES-1 project whose name stands for Next generation InteraCtive brOadcast mobiLe nEtworks. It deals with the design of the ground and space segment of a satellite network for mobile terminals that should be built in the mid-term, aboutfive years from now.

The consortium is composed by three members: Space Engineering, EUTELSAT and DLR. Space Engineering is the prime and deals with the system level analysis and the space segment. EUTELSAT is a space operator and has investigated the business case. DLR is involved in the design of the ground segment.

The analysed satellite network is composed by a wide range of elements (Fig. 1). The satellite is supported by a hub station and by a certain number of complementary ground components. The users can be, for example, handheld devices, vehicles, ships or airplanes.

DLR investigates a whole range of advanced ground segment techniques. The most relevant are:

• An iterative successive interference MUD

  MultiUser Detection (MUD): in the return link of a multibeam satellite system multiple users are received at the same time. The impact of mutual interference is very high for one-colour system and joint decoding by means of MUD can significantly mitigate the impact of the additional interference. DLR has focused on multistage Successive Interference Cancellation MUD (Fig. 2), which has optimal according to information theory. Moreover, the impact of real world impairments of satellite equipment (especially phase noise) has been taken into account.
• Interference Alignment: the new technique of interference alignment has raised significant interest in the past two years. It suggests a nearly optimal new way to achieve higher capacity both in the forward and return link of a satellite system. The core idea of Interference Alignment is to coordinate the transmitters so that they generate as little interference as possible to each other. One can prove that if the system is well posed, significantly higher capacity than the conventional T/FDMA approach is attainable. Techniques with and without channel state information at the transmitters (for the return and forward link, respectively) have been investigated as well.
• Upper Layer Coding: mobile users are characterized to very time varying land mobile satellite channels. The impact of the variability can be mitigated by the presence of upper layer coding. DLR has been investigating the design of high performance upper layer coding that hybridizes ratefull and rateless codes, in order to get the high performance of the former and the flexibility of the latter.