| 摘要 |
<p> Described is a satellite communication system 1 comprising a primary station 2, a communication satellite 3 and at least one secondary station 4. The primary station 2 transmits data signals 5 via the communication satellite 3 to the secondary station 4. The primary station 2 comprises a modulator 24 for modulating the data signals onto at least two differently FEC-encoded frequency carriers. The secondary station 4 comprises a tuner 32 for tuning to one of the frequency carriers in dependence on a tuning signal received from the primary station 2. The secondary station 4 further comprising signal quality determining means for determining at least an estimate of a signal quality of the frequency carrier presently tuned to. The secondary station 4 comprising retuning request transmit means for transmitting a retuning request signal to the primary station 2 when the estimate of the signal quality becomes lower than a predetermined threshold value. The primary station 2 comprises determining means for determining a frequency carrier with a better signal quality upon reception of the retuning request signal and tuning signal transmit means for transmitting the tuning signal indicating this frequency carrier to the secondary station 4. In this way, when the data signals 5 (which are modulated onto a certain frequency carrier) are received poorly (e.g. because of rain fading) the secondary station 4 can tune to a frequency carrier with a more robust FEC-encoding and the data signals 5 can be received without problems.</p> |
