COFDM DCM communications systems with preferred labeling diversity formats

A transmitter-apparatus configured for transmitting coded orthogonal frequency-division modulation (COFDM) dual-carrier-modulation (DCM) signal via a communication channel, the lower-frequency and upper-frequency sidebands of which said COFDM DCM signal convey the same data but do not mirror each other in frequency around a mid-channel frequency between them, said transmitter apparatus comprising:

• coding apparatus for forward-error-correction (FEC) coding digital data that is to be transmitted and arranging the resulting FEC-coded data in successive map labels for quadrature-amplitude-modulation (QAM) symbols;
• a pair of QAM mappers consisting of a first QAM mapper and a second QAM mapper, said first QAM mapper configured for generating complex coordinates of a first set of successive QAM symbols respectively responsive to said successive map labels in accordance with a first mapping pattern, and said second QAM mapper configured for generating complex coordinates of a second set of successive QAM symbols respectively responsive to said successive map labels in accordance with a second mapping pattern, said first and second mapping patterns differing so as to afford labeling diversity between said first and second sets of successive QAM symbols;
• a COFDM symbol generator connected for arranging successive ones of said first set of QAM symbols in first prescribed spectral order in first halves of successive COFDM symbols and arranging successive ones of said second set of QAM symbols in second prescribed spectral order in second halves of said successive COFDM symbols;
• a generator of COFDM DCM radio-frequency signal, the lower-frequency sideband of which conveys said first set of successive QAM symbols and the upper-frequency sideband of which conveys said second set of successive QAM symbols;
• and
• a power amplifier connected for amplifying said COFDM DCM radio-frequency signal before its transmission.