Results
The DLR Institute of Communications and Navigation developed a network coding protocol (NETCOP) to save bandwidth in a bidirectional communication between two satellite terminals. This protocol has been demonstrated with two video-conferencing terminals communicating via a transparent satellite (EUTELSAT EUROBIRD 3) and a central hub station. The network coding employed in the central hub station achieved bandwidth savings of up to 47% in the forward link from the hub to the terminals. It was the worldwide first demonstration of network coding in a satellite system. Furthermore, the DLR Institute of Communications and Navigation developed and demonstrated in a lab system with 50 virtual terminals a reliable multicast protocol with a random linear Fountain code in GF(256). The multicast data throughput could be significantly increased compared to a standard selective-repeat-ARQ protocol. A possible application of this multicast protocol is software or file distribution to multiple terminals. Furthermore, the DLR Institute of Communications and Navigation developed and demonstrated a multiuser detection algorithm, i.e. an iterative successive interference cancellation algorithm that allows the decoding of two overlapping user signals. This algorithm enables a parallel transmission of two interfering signals, e.g. caused by partially or fully overlapping frequency bands. This method helps to use the available spectrum more efficiently.
The NEXT project aimed to develop and to demonstrate network coding (NC) techniques for satellite interactive communication systems. Three major scenarios were taken into account: network coding for a bidirectional communication between two satellite terminals to save bandwidth in the downlink/forward link, multiuser detection for two transmitting terminals to save bandwidth in the uplink, and reliable multicast to increase the data throughput in unreliable satellite channels. For these three scenarios algorithms and protocols have been developed and validated by lab-demonstrations. The development was carried in cooperation with the Lehrstuhl für Nachrichtentechnik (LNT) of TUM, and with IQ wireless GmbH, Berlin. The experiments take benefit from state-of-the-art channel coding techniques, and pave the way to future demonstrations with the advanced payload to the H2Sat satellite.
Satellite bandwidth is a precious resource and makes bit transmission costs high compared to the transmission costs of terrestrial systems. It is therefore crucial to develop and introduce bandwidth saving techniques that are suitable for satellite communication systems. The project NEXT- “Network Coding Satellite Experiment” aimed at such bandwidth saving techniques in three different scenarios:
The basic principle is shown in the picture. The network coding operation onboard the satellite reduces – in case of a symmetric traffic – the required downlink bandwidth by up to 50%. Typical applications for such scenarios are e.g. a bidirectional video communication between two satellite terminals, an interconnection of geographically separated communication, or computer networks (backhauling via satellite).
The basic principle is shown in the picture.
The network coding operation onboard the satellite reduces – in case of a symmetric traffic – the required downlink bandwidth by up to 50%. Typical applications for such scenarios are e.g. a bidirectional video communication between two satellite terminals, an interconnection of geographically separated communication, or computer networks (backhauling via satellite).
The basic principle is shown in the following picture. The data file to be distributed is segmented. The receiving terminals signal back the information about the missing data segments. Network coding will be used for the repetition of the data segments to reduce the amount of data to be retransmitted.
Two signals interfere with each other. The detection of the two interfering signals will be done by a multiuser detection algorithm based on interference cancellation principles.
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