Method and apparatus for digital audio broadcasting and reception

• US 5,278,844 A
• Filed: 04/11/1991
• Issued: 01/11/1994
• Est. Priority Date: 04/11/1991
• Status: Expired due to Term

• Current Assignee: iBiquity Digital Corporation (Xperi Inc.)
• Original Assignee: USA Digital Radio, Inc. (Xperi Inc.)
• Inventors: Murphy, John L., Rich, Mark J.
• Primary Examiner(s): Beausoliel, Jr., Robert W.
• Assistant Examiner(s): Snyder, Glenn
• Application Number:
  US07/683,918
• Time in Patent Office: 1,006 Days
• Field of Search: 371/37.1, 371/43, 375/52, 375/53, 375/83, 375/100
• US Class Current: 714/778
• CPC Class Codes: H04H 20/31 using in-band signals, e.g. subsonic or cue signal
• CPC Class Codes: H04H 20/95 characterised by a specific format, e.g. an encoded audio stream
• CPC Class Codes: H04H 2201/183 FM digital or hybrid
• CPC Class Codes: H04H 40/18 Arrangements characterised by circuits or components specially adapted for receiving
• CPC Class Codes: H04H 40/54 generating subcarriers
• CPC Class Codes: H04H 60/07 characterised by processes or methods for the generation
• CPC Class Codes: H04L 1/0057 Block codes H04L1/0061, H04L1/0064 take precedence
• CPC Class Codes: H04L 1/0071 Use of interleaving interleaving per se H03M13/27
• CPC Class Codes: H04L 2001/0093 Point-to-multipoint
• CPC Class Codes: H04L 27/2601 Multicarrier modulation systems

Abstract

A radio broadcasting system is provided for transmitting and receiving through free space a fully coherent multicarrier modulated digital signal which is especially adapted to be resistive to multipath degradation. The multicarrier modulated signal is a synthesized vector-modulated signal which is a quadrature phase shift keyed (QPSK) modulated set of synthesized carriers phase coherent with each other and each occupying a spectrum replicated multiple times within a bandwidth with no more than two bits per vector. An efficient channel coding consisting of large block size, high efficiency block coding, such as BCH 255, 239 code, is employed in connection with time interleaving of bits to mitigate the effects of frequency selective multipath and broadband multipath. The broadcast system is designed to be used in support of compressed digital audio programming material. In a demodulation process according to the invention, a demodulator is operative to phase lock to a reconstructed or otherwise coherent pilot tone or equivalent clock, to coherently demodulate the digital signal, to deinterleave, to decode the block encoded signal and to format the recovered data stream for source decoding.

Claims

1. A system for broadcast transmission and reception of digitized program material, said broadcast system comprising:

a 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 a BCH code having at least 200 data bits and no more than 20 check bits 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, said second signal processing means being 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; and

means for translating said intermediate frequency carrier signal to an output carrier and broadcasting said output carrier through atmospheric free-space; and

a plurality of receivers, each receiver comprising;

means for acquiring a replica of said multitone QPSK modulated block encoded signal through atmospheric free-space, said atmospheric free-space being subject to multipath such that said replica is inclusive of transmission errors;

third signal processing means coupled to receive said replica of said replica of said multitone QPSK modulated block encoded signal for coherently demodulating said replica of said multitone QPSK modulated signal into a replica of said block encoded signal; and

fourth signal processing means 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.

2. The system according to claim 1, wherein said BCH block code is a type having 239 data bits in a 255 bit block.

3. The system according to claim 1 wherein said first signal processing means further includes means for interleaving in time said block encoded digitized program material to temporally spread said program material and wherein said fourth signal processing means includes means for deinterleaving in time said program material with correction bits in order to enhance resistance to said selected short-interval-dependent data errors.

4. The system according to claim 3 wherein said second signal processing means comprises a digital signal processing means employing a fast Fourier transform.

5. A transmitter system for a system for broadcast transmission and reception of digitized program material, 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 a BCH code having at least 200 data bits and no more than 20 check bits 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, said second signal processing means being 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; and

means for translating said intermediate frequency carrier signal to an output carrier and broadcasting said output carrier through atmospheric free-space.

6. The transmitter according to claim 5 wherein said first signal processing means further includes means for interleaving in time said block encoded digitized program material to temporally spread said program material in order to enhance resistance to said selected short-interval-dependent data errors.

7. The transmitter according to claim 5, wherein said BCH block code is a type having 239 data bits in a 255 bit block.

8. A receiver system for a system for broadcast transmission and reception of digitized program material in the form of a multitone QPSK modulated signal, wherein said digitized program material is encoded according to a BCH block code having at least 200 data bits and no more than 20 data bits in a block encoded signal, said receiver system comprising:

means for acquiring a replica of said multitone QPSK modulated block encoded signal through atmospheric free-space, said atmospheric free-space being subject to multipath such that said replica is inclusive of transmission errors;

first signal processing means coupled to receive said replica of said replica of said multitone QPSK modulated block encoded signal for coherently demodulating said replica of said multitone QPSK modulated signal into a replica of said block encoded signal; and

second signal processing means 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.

9. The receiver system according to claim 8, wherein said block encoded signal is further interleaved in time according to an interleaving scheme, said receiver further comprising:

means for deinterleaving in time said program material with correction in order to enhance resistance to said selected short-interval-dependent data errors.

10. The receiver system according to claim 8, wherein said BCH block code is a type having 239 data bits in a 255 bit block.

11. The system according to claim 8 wherein said second signal processing means comprises a digital signal processing means employing a fast Fourier transform.

12. A method for transmitting, in a broadcast transmission and reception system, digitized program material, 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 a BCH code having at least 200 data bits and no more than 20 check bits to produce a digital representation of a block encoded signal;

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, 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;

translating said intermediate frequency carrier signal to an output carrier; and

broadcasting said output carrier through atmospheric free-space.

13. The method according to claim 12 wherein said further including the step of interleaving in time said block encoded digitized program material to temporally spread said program material in order to enhance resistance to said selected short-interval-dependent data errors.

14. The method according to claim 12, wherein said BCH block code is a type having 239 data bits in a 255 bit block.

15. A method for receiving an analog signal and digitized program material in the form of a multitone QPSK modulated signal, wherein said digitized program material is encoded according to a BCH block code having at least 200 data bits and no more than 20 check bits in a block encoded signal, said method comprising the steps of:

acquiring a replica of said multitone QPSK modulated block encoded signal through atmospheric free-space, said atmospheric free-space being subject to multipath such that said replica is inclusive of transmission errors;

coherently demodulating said replica of said multitone QPSK modulated signal into a replica of said block encoded signal; and

decoding said replica 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.

16. The method according to claim 15, wherein said block encoded signal is further interleaved in time according to an interleaving scheme, said method further comprising:

deinterleaving in time said program material with correction in order to enhance resistance to said selected short-interval-dependent data errors.

17. The method according to claim 15, wherein said BCH block code is a type having 239 data bits in a 255 bit block.