Frame structure for a QAM system

摘要

A novel framing method for a variable net bit rate digital communications system that utilizes a set of different QAM constellations and punctured trellis code combinations, each combination designated as a mode. This frame structure has a variable integral number of QAM symbols per frame depending on the selected mode, but the number of bytes and Reed-Solomon packets per frame is constant. This is achieved even though the number of data bits per QAM symbol for some modes is fractional. Also the number of trellis coder puncture pattern cycles per frame is an integer for all modes. This arrangement simplifies the synchronization of receiver processing blocks such as the Viterbi decoder, de-randomizer, byte de-interleaver, and Reed-Solomon decoder.

主权项

1. A method for variable net bit rate digital communications comprising:
generating a forward error correction (FEC) data frame from one or more interleaved Reed-Solomon (RS) packets, each RS packet encoding a plurality of data bytes; modulating a plurality of bits of the FEC data frame using a punctured trellis coder that is operated at a selected code rate, the code rate being selected based on white noise performance of a digital communications system; mapping the modulated bits to quadrature amplitude modulation (QAM) symbols using a QAM constellation selected from a set of candidate QAM constellations; and providing a transmission frame comprising the QAM symbols and a indication of a transmission mode, the transmission mode identifying the selected code rate and the QAM constellation selected from the set of candidate QAM constellations, wherein a constant number of RS packets is provided in each of a plurality of transmission frames regardless of transmission mode selected for the each transmission frame.