| 摘要 |
A satellite communications system comprises a transmitter, a satellite transponder and a receiver. The transmitter transmits an uplink multi-level modulated signal (hierarchical modulation, layered modulation, etc.) to the satellite transponder, which broadcasts the multi-level modulated signal downlink to one, or more, receivers. The multi-level modulated signal comprises an upper layer and a lower layer. The lower layer conveys LDPC yes blocks, or LDPC frames, each LDPC block comprising S bits of data including a header portion and a data-bearing portion. The upper layer conveys shorter blocks, each shorter block comprising R bits of data, where R<S, the shorter block also comprising a header portion and a data-bearing portion. The transmitter synchronizes the start of transmission of each LDPC block to the start of transmission of a shorter block. The receiver uses the received shorter blocks to assist in searching for particular data in the lower layer portion of the received multi-level modulated signal. In particular, the receiver searches for synchronization data in the lower layer portion of the received signal upon detection of the header portion in a received shorter block.
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