COFDM broadcasting with single-time retransmission of COFDM symbols

摘要

Transmitter apparatus to broadcast coded orthogonal frequency-division multiplexed (COFDM) radio-frequency carriers conveying digital television (DTV) signals encoded using Bose-Chaudhuri-Hocquenghem (BCH) coding concatenated with subsequent low-density parity-check coding (LPDC) transmits the same coded DTV signals twice some time apart. The coded DTV signals are mapped to quadrature amplitude modulation (QAM) of the COFDM carriers. Preferably, the circular Fourier transforms of COFDM symbols in the earlier transmissions are rotated one half revolution respective to the circular Fourier transforms of corresponding COFDM symbols in the later transmissions. 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 concatenated BCH-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 coding successive frames of digital data to generate respective low-density parity-check codewords, each having the same prescribed number of bits; mapping the bits of each said low-density parity-check codeword to modulation symbol constellations to generate digital coordinates descriptive of successive ones of said modulation symbol constellations arranged in normal time-sequential order; writing said digital coordinates descriptive of said modulation symbol constellations 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 digital coordinates descriptive of successive ones of said modulation symbol constellations from said temporary storage locations within said digital memory, initially reading said digital coordinates descriptive of said modulation symbol constellations in each of successive CODM symbols in a first time-sequential order from said temporary storage locations, and finally reading said digital coordinates descriptive of said modulation symbol constellations in each of successive CODM symbols in a second time-sequential order from said temporary storage locations some time after their being initially read, said first time-sequential order differing from said second time-sequential order in that initial and final portions of each COFDM symbol in said initial reading thereof are in reverse order from their order in said final reading thereof; and generating a modulated carrier wave responsive to said digital coordinates descriptive of successive ones of said modulation symbol constellations as twice read from said temporary storage locations within said digital memory, said modulated carrier wave to be transmitted by said broadcast transmitter.