Method and apparatus for digital audio broadcasting and reception

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:

• generating in first 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 ones 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 digitized program material over substantially all of said equivalent tones in order to produce a multitone QPSK modulated signal at a selected intermediate frequency carrier;
• 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 through atmospheric free-space;
• acquiring 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, 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 to extract said digitized program material 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, said output program material being a substantial duplicate of said digitized program material.

A transmitter 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 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 transmitter system comprising:

• first 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, said second signal processing being means coupled to accept a digital representation of a program signal for quadrature phase shift key (QPSK) modulating each of said equivalent tones with said digital representation of said program signal thereby to distribute said digital representation of said program signal over substantially all of said equivalent tones in order to produce a multitone QPSK modulated signal at a selected intermediate frequency carrier;
• means for linearly combining said analog fm signal and said multitone QPSK modulated signal, said multitone 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 for a system for broadcast transmission and reception of a combined information signal comprising an analog signal and digitized program material in 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, wherein said combined information signal comprises said analog fm signal and said multitone QPSK modulated signal, and wherein said analog fm signal and said multitone QPSK modulated signal are sufficiently close to one another in frequency to overlap in spectrum, said receiver comprising:

• means for acquiring 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;
• 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, said replica of said unmodulated pilot tone being of a signal level at least 100 times greater than said multitone QPSK modulated signal;
• means in said second signal path for separating a replica of said multitone QPSK modulated signal substantially from said combined information signal, including means for cancelling said replica of said analog fm signal in said second signal path in order to permit reuse of common spectrum;
• and
• 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 to extract 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:

• generating in first 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, and quadrature phase shift key (QPSK) modulating each of said equivalent tones with said digitized program material thereby to distribute said digitized program material over substantially all of said equivalent tones in order to produce a multitone QPSK modulated signal at a selected intermediate frequency carrier;
• 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, in a broadcast transmission and reception system, a combined information signal of an analog signal and digitized program material in a multitone QPSK modulated signal, including an analog frequency modulated (fm) signal of a composite baseband signal, wherein said composite baseband signal includes a single unmodulated pilot tone, wherein said combined information signal comprises and analog fm signal and said multitone QPSK modulated signal, and wherein said analog fm signal and said multitone QPSK modulated signal are sufficiently close to one another in frequency to overlap in spectrum, said method comprising the steps of:

• acquiring 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 the, 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, including cancelling said replica of said analog fm signal in said second signal path in order to permit reuse of common spectrum;
• and
• coherently demodulating said replica of said multitone QPSK modulated signal in said second signal path upon reference to said replica of said unmodulated pilot tone to extract said digitized program material.