Method and apparatus for digital audio broadcasting and reception

A transmitter system for a system for broadcast transmission and reception of an analog signal and digitized program material, including means for producing an analog frequency modulated (fm) signal form a composite baseband signal, and a transmitter for transmission of at least said analog fm signal, wherein said composite broadband signal includes a single unmodulated pilot tone, said transmitter system comprising:

• first signal processing means coupled to accept digitized program material from a source of digitized program material for encoding said digitized program material according to an error-correcting block code of predetermined length and predetermined error correcting capability to produce a digital representation of a block encoded signal;
• second signal processing means for generating an equivalent of a plurality of equivalent tones which are spaced equally at a baseband between 0 Hz and a selected maximum frequency, each of said equivalent tones being at a frequency which is an integer multiple of a base frequency tone and each one of said equivalent tones being constrained to be phase coherent with said unmodulated pilot tone by means of a master clock, said second signal processing being means coupled to accept said digital representation of said block-encoded signal for quadrature phase shift key (QPSK) modulating each one of said equivalent tones with said digital representation of said block-encoded signal thereby to distribute said digital representation of said block-encoded signal over substantially all of said equivalent tones in order to produce a multitone QPSK modulated signal at a selected intermediate frequency carrier signal;
• means for linearly combining said analog fm signal and said multitone QPSK modulated signal, said multitone QPSK modulated signal having a magnitude when combined with said analog fm signal of at least 100 times less than the magnitude of said analog fm signal, to produce a combined information signal;
• and
• means for broadcasting said combined information through atmospheric free-space.

A receiver system for a system for broadcast transmission and reception of an analog signal and digitized program material in the form of a multitone QPSK modulated signal, including means for producing an analog frequency modulated (fm) signal from a composite baseband signal, and a transmitter for transmission of at least said analog fm signal, wherein said composite baseband signal includes a single unmodulated pilot tone, and wherein said digitized program material is encoded according to a block code in a block encoded signal, said receiver system comprising:

• means for acquiring a replica of a combined information signal through atmospheric free-space, said atmospheric free-space being subject to multipath such that said replica is inclusive of transmission errors;
• means coupled to said acquiring means for splitting said replica of said combined information signal into a first signal path and a second signal path;
• frequency (fm) demodulating means in said first signal path for extracting a replica of said unmodulated pilot tone;
• means in said second signal path for separating a replica of a multitone QPSK modulated signal substantially from said combined information signal;
• first signal processing means in said second signal path coupled to receive said replica of said unmodulated pilot tone and said replica of said multitone QPSK modulated signal for coherently demodulating said replica of said multitone QPSK modulated signal into a replica of said digitized program material;
• and
• second signal processing means in said second signal path for decoding said replica of said digital representation of said block encoded signal into output program material with correction of selected short-interval-dependent data errors, narrow-band frequency-dependent data errors and long-interval broadband frequency dependent data errors, such as induced by multipath effects, said output program material being a substantial duplicate of said digitized program material.

A method for broadcast transmission and reception of an analog signal and digitized program material, employing means for producing an analog frequency modulated (fm) signal from a composite baseband signal, and a transmitter for transmission of at least said analog fm signal, wherein said composite baseband signal includes a single unmodulated pilot tone, said method comprising the steps of:

• encoding, in first signal processing means coupled to accept digitized program material from a source of digitized program material, said digitized program material according to an error-correcting block code of predetermined length and predetermined error correcting capability to produce a digital representation of a block encoded signal;
• generating in second signal processing means an equivalent of a plurality of equivalent tones which are spaced equally at a baseband between 0 Hz and a selected maximum frequency, each of said equivalent tones being at a frequency which is an integer multiple of a base frequency tone and each one of said equivalent tones being constrained to be phase coherent with said unmodulated pilot tone by means of a master clock, and quadrature phase shift key (QPSK) modulating each one of said equivalent tones with said digital representation of said block-encoded signal thereby to distribute said digital representation of said block-encoded signal over substantially all of said equivalent tones in order to produce a multitone QPSK modulated signal at a selected intermediate frequency carrier signal;
• linearly combining said analog fm signal and said multitone QPSK modulated signal, said multitone QPSK modulated signal having a magnitude when combined with said analog fm signal of at least 100 times less than the magnitude of said analog fm signal, to produce a combined information signal;
• broadcasting said combined information signal through atmospheric free-space;
• acquiring at each of a plurality of receiving locations a replica of said combined information signal through atmospheric free-space, said atmospheric free-space being subject to multipath such that said replica is inclusive of transmission errors;
• splitting said replica of said combined information signal into a first signal path and a second signal path;
• extracting a replica of said unmodulated pilot tone from said first signal path;
• separating a replica of said multitone QPSK modulated signal substantially from said combined information signal in said second signal path;
• coherently demodulating said replica of said multitone QPSK modulated signal into a replica of said digital representation of said block encoded signal in said second signal path using said replica of said unmodulated pilot tone and said replica of said multitone QPSK modulated signal;
• and
• decoding a replica of said digital representation of said block encoded signal into output program material with correction of selected short-interval-dependent data errors, narrow-band frequency-dependent data errors and long-interval broadband frequency dependent data errors, such as induced by multipath effects, said output program material being a substantial duplicate of said digitized program material.

A method for transmitting, in a broadcast transmission and reception system, an analog signal and digitized program material, including an analog frequency modulated (fm) signal from a composite baseband signal, wherein said composite baseband signal includes a single unmodulated pilot tone, said method comprising the steps of:

• encoding, in first signal processing means coupled to accept digitized program material from a source of digitized program material, said digitized program material according to an error-correcting block code of predetermined length and predetermined error correcting capability to produce a digital representation of a block encoded signal;
• generating in second signal processing means an equivalent of a plurality of equivalent tones which are spaced equally at a baseband between 0 Hz and a selected maximum frequency, each of said equivalent tones being at a frequency which is an integer multiple of a base frequency tone and each one of said equivalent tones being constrained to be phase coherent with said unmodulated pilot tone by means of a master clock, and quadrature phase shift key (QPSK) modulating each one of said equivalent tones with said digital representation of said block-encoded signal thereby to distribute said digital representation of said block-encoded signal over substantially all of said equivalent tones in order to produce a multitone QPSK modulated signal at a selected intermediate frequency carrier signal;
• linearly combining said analog fm signal and said multitone QPSK modulated signal, said multitone QPSK modulated signal having a magnitude when combined with said analog fm signal of at least 100 times less than the magnitude of said analog fm signal, to produce a combined information signal;
• and,
• broadcasting said combined information through atmospheric free-space.

A method for receiving an analog signal and digitized program material in the form of a multitone QPSK modulated signal, wherein a composite baseband signal of said analog signal includes a single unmodulated pilot tone, and wherein said digitized program material is encoded according to a block code in a block encoded signal, said method comprising the steps of:

• acquiring a replica of a combined information signal through atmospheric free-space, said atmospheric free-space being subject to multipath such that said replica is inclusive of transmission errors;
• splitting said replica of said combined information signal into a first signal path and a second signal path;
• extracting a replica of said unmodulated pilot tone from said replica of said combined information signal, said unmodulated pilot tone having an amplitude at least 100 times greater than said multitone QPSK modulated signal;
• separating a replica of said multitone QPSK modulated signal substantially from said combined information signal in said second signal path;
• and
• coherently demodulating said replica of said multitone QPSK modulated signal into a replica of said digital representation of said block encoded signal upon reference to said unmodulated pilot tone at a signal level at least 100 times greater than said digitized program material in said replica of said combined information signal;
• and
• decoding said replica of said digital representation of said block encoded signal into output program material with correction of selected data errors, said output program material being a substantial duplicate of said digitized program material.