Iterative-diversity COFDM broadcasting with improved shaping gain

摘要

Transmitter apparatus to broadcast coded orthogonal frequency-division multiplexed (COFDM) radio-frequency carriers conveying low-density parity-check (LPDC) coding transmits the same coded DTV signals twice some time apart. The coded DTV signals of initial transmissions and of final transmissions are mapped to quadrature amplitude modulation (QAM) of the COFDM carriers according to first and second patterns, respectively. Bits that map to lattice points in the first mapping pattern more likely to experience error are mapped to lattice points in the second mapping pattern less likely to experience error. Bits that map to lattice points in the second mapping pattern more likely to experience error are mapped to lattice points in the first mapping pattern less likely to experience error. Receiver apparatus combines the earlier and later transmissions of twice-transmitted COFDM signals as part of iterative procedures for de-mapping QAM and decoding the LDPC coding of the DTV signals.

主权项

1. A method for preparing packets of digital data to be transmitted by a COFDM broadcast transmitter so as to facilitate iterative-diversity reception by COFDM broadcast receivers of suitable design, said method comprising steps of:
forward-error-correction (FEC) coding successive frames of digital data to generate respective FEC codewords, each having the same prescribed number of bits; writing said FEC codewords to temporary storage locations within a digital memory to be temporarily stored therein for a number at least one of COFDM symbol intervals; twice reading said FEC codewords from said temporary storage locations within said digital memory, initially reading portions of FEC codewords in each of successive CODM symbols in a first time-sequential order from said temporary storage locations, and finally reading said portions of said FEC codewords in each of successive CODM symbols in a second time-sequential order from said temporary storage locations some time after their being initially read; mapping the bits of each portion of said FEC codeword initially read from said temporary storage locations to modulation symbol constellations to generate digital coordinates descriptive of successive ones of said modulation symbol constellations; mapping the bits of each said portion of said FEC codeword finally read from said temporary storage locations to modulation symbol constellations to generate digital coordinates descriptive of successive ones of said modulation symbol constellations, said mapping of said bits of each said FEC codeword finally read from said temporary storage locations to said modulation symbol constellations differing from said mapping of said bits of each said FEC codeword initially read from said temporary storage locations to said modulation symbol constellations, those bits of each said FEC codeword mapped less robustly to said modulation symbol constellations when initially read from said temporary storage locations being mapped more robustly to said modulation symbol constellations when finally read from said temporary storage locations, those bits of each said FEC codeword mapped more robustly to said modulation symbol constellations when initially read from said temporary storage locations being mapped less robustly to said modulation symbol constellations when finally read from said temporary storage locations; and generating a modulated carrier wave responsive to said digital coordinates descriptive of successive ones of said modulation symbol constellations mapping each said FEC codeword as twice read from said temporary storage locations within said digital memory, said modulated carrier wave to be transmitted by said broadcast transmitter.