## RELIABLE CHANNEL STATE INFORMATION IN MULTI-BEAM SATELLITE COMMUNICATIONS 

## Technical field 

The invention lies in the field of satellite communication systems, and relates in particular to a method and device for providing reliable channel state information for a plurality of carriers in a multi-beam satellite communication system relying on aggressive frequency reuse among its available carriers. 

## Background of the invention 

Communication satellites have evolved to provide broadband data transfer from a transmitting ground station via the satellite to a geographical area on the ground, which is defined by the area covered by the satellite’s transmission beam. Multibeam architectures have been proposed, in which information is simultaneously transmitted to a plurality of spot beams on the ground. 

In known approaches, all of the satellite’s beams are used to transmit data at the same time, while adjacent beams transmit at different frequencies and/or using different polarizations in order to reduce the co-channel interference. This approach fails to cope with heterogeneous data traffic demands in each ground spot, as the satellite resources are equally distributed over the beams, so that the per-beam offered capacity is fixed and the same for all beams. 

It has also been proposed to use beam hopping techniques, in which a first subset of beams, serving a first set of ground spots, is active at a given time and transmitting at a given frequency. Subsequently, the first subset of beams is not transmitting, and a second subset of beams, preferably serving a second set of ground spots, transmits at the same frequency. This approach allows to flexibly allocate scarce on-board resources over the service coverage. 

As an alternative, aggressive frequency reuse relies on the simultaneous transmission of signals on all available satellite beams, to receivers in all ground spots, on the same frequency. In order to mitigate spatial interference as well as co-channel interference, it has been suggested to use precoding at the transmitter gateway. Precoding takes the estimated interference levels into account, which the signal that is to be transmitted on a beam is likely to suffer. If, during transmission of the signal, the signal is indeed subject to the estimated interference, the precoding allows for a high probability of correct detection of the signal at a receiver located within the corresponding ground spot. For this approach to work efficiently, the channel state information that is estimated by the receivers and made available at the transmitter or at the gateway where the 

