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 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