In-band on-channel digital broadcasting

• US 5,465,396 A
• Filed: 01/12/1993
• Issued: 11/07/1995
• Est. Priority Date: 01/12/1993
• Status: Expired due to Term

• Current Assignee: iBiquity Digital Corporation (Xperi Inc.)
• Original Assignee: USA Digital Radio Partners, L.P. (Xperi Inc.)
• Inventors: Solie, Leland P., Hunsinger, Billie J., Vigil, A. J.
• Primary Examiner(s): Pham, Chi H.
• Assistant Examiner(s): WISLER, MARK
• Application Number:
  US08/003,189
• Time in Patent Office: 1,029 Days
• Field of Search: 455/102, 455/70, 455/68, 455/61, 455/71, 455/142, 455/143, 455/108, 455/202, 455/46, 455/205, 375/41, 375/43, 375/12, 375/14, 375/103, 375/268, 375/270, 375/230, 375/232, 375/350, 375/300, 375/301, 375/320, 375/321, 329/317, 329/318, 329/366, 329/336, 381/10, 381/13
• US Class Current: 455/61
• CPC Class Codes: H04H 20/30 by a single channel
• CPC Class Codes: H04H 2201/183 FM digital or hybrid
• CPC Class Codes: H04H 2201/20 digital audio broadcasting [DAB]
• CPC Class Codes: H04H 60/11 Arrangements for counter-measures when a portion of broadcast information is unavailable
• CPC Class Codes: H04L 5/023 Multiplexing of multicarrier modulation signals multicarrier modulation H04L27/2601

Abstract

A system for combining AM and FM transmissions. In-band, On-channel, FM Digital Audio Broadcast (IBOC FM-DAB) allows simultaneous transmission of DAB and FM over existing FM allocations without interfering with conventional analog FM signals. The utility of existing FM spectrum allocations is therefore enhanced.

Claims

1. A method for broadcasting information in a composite signal from a transmitter to one or more receivers, comprising:

a) frequency modulating an FM message to generate an FM waveform;

b) multiplying said FM waveform by an AM message to generate a suppressed carrier AM over FM signal;

c) combining said suppressed carrier AM over FM signal with said FM waveform to generate a large carrier AM over FM composite signal;

d) transmitting said large carrier AM over FM composite signal;

e) receiving said large carrier AM over FM composite signal;

f) recovering one of said FM message and an AM waveform corresponding to said AM message over FM composite signal.

2. The method of claim 1 wherein the recovering step comprises the steps of selecting one of said AM and FM waveforms from said large carrier AM over FM composite signal and demodulating the selected waveform.

3. The method of claim 1 wherein the recovering step comprises the steps of:

a) isolating said FM waveform from said large carrier AM over FM composite signal to generate an FM only signal; and

b) demodulating said FM only signal to recover said FM message.

4. The method of claim 1 wherein the recovering step comprises the steps of:

a) isolating said AM message from said large carrier AM over FM composite signal to generate an AM only signal; and

b) demodulating said AM only signal to recover said AM message.

5. The method of claim 1, further comprising the steps of:

a) emphasizing a raw AM message to generate said AM message, for subsequent use in multiplying said FM waveform; and

b) deemphasizing said recovered AM message with deemphasis filter to generate an AM message after deemphasis.

6. A method for transmitting information, comprising the steps of:

a) frequency modulating an FM message to generate an FM waveform;

b) multiplying said FM waveform by an AM message to generate a suppressed carrier AM over FM signal;

c) summing said suppressed carrier AM over FM signal with said FM waveform to generate a large carrier AM over FM signal; and

d) transmitting said large carrier AM over FM signal.

7. A method for transmitting information, comprising:

a) frequency modulating an FM message to generate an FM waveform;

b) multiplying an AM message with a local oscillator signal to generate a double sideband suppressed carrier AM signal;

c) summing the local oscillator signal and the double sideband suppressed carrier AM signal to generate a double sideband large carrier AM signal;

d) multiplying the FM waveform with the local oscillator signal to generate a first intermediate signal;

e) band-pass filtering the first intermediate signal to produce an FM waveform at sum frequency signal;

f) multiplying the FM waveform at sum frequency signal with the double sideband large carrier AM signal to produce a second intermediate signal;

g) band-pass filtering the second intermediate signal to produce a double sideband large carrier AM over FM signal; and

h) transmitting said double sideband large carrier AM over FM signal.

8. A method for recovering signals from a transmitted large carrier AM over FM signal incorporating an AM message and an FM message, comprising:

a) receiving the large carrier AM over FM signal;

b) obtaining an FM only signal;

c) multiplying said FM only signal with a local oscillator signal to generate a first product signal;

d) generating from the first product signal a high IF FM signal;

e) combining the high IF FM signal with the large carrier AM over FM signal to produce a second product signal;

f) generating from the second product signal an AM only signal; and

g) demodulating said AM only signal to recover said AM message.

9. The method of claim 8 wherein the step of generating from the first product signal an FM at high IF signal comprises band pass filtering said first product signal.

10. The method of claim 8 where the step of combining the FM at high IF signal with the large carrier AM over FM signal to produce a second product signal comprises multiplying the FM at high IF signal with the large carrier AM over FM signal.

11. The method of claim 8 wherein the step of generating from the second product signal an AM only signal comprises band-pass filtering the second product signal.

12. The method of claim 8 further including cancellation of cross interference.

13. A method for recovering signals from a transmitted large carrier AM over FM signal incorporating an AM message and an FM message, comprising:

a) receiving the large carrier AM over FM signal;

b) generating, from said large carrier AM over FM signal, a suppressed carrier AM over FM signal;

c) generating, from said large carrier AM over FM signal, an FM only waveform; and

d) demodulating the large carrier AM over FM signal, wherein said demodulating step comprises combining said suppressed carrier AM over FM signal and said FM only waveform to produce a product signal and generating from said product signal said AM message.

14. A method for mitigating the deleterious effects of multipath on a received signal, comprising:

a) receiving an amplitude modulated message upon a frequency modulated signal;

b) canceling the frequency modulated signal from the received signal and generating a raw AM message signal and an instantaneous frequency estimate signal;

c) generating a polynomial with a plurality of coefficients for producing an FM to AM conversion interference estimate signal;

d) subtracting the FM to AM conversion interference estimate signal from the raw AM message signal to produce a clean AM message signal;

e) measuring and integrating the cross correlation between said clean AM message signal and each term of the polynomial; and

f) adjusting the coefficients of the polynomial, thereby driving the FM to AM interference in the clean AM message signal to zero.

15. A method for recovering signals from a transmitted large carrier AM over FM signal incorporating an AM message and an FM message, comprising:

a) receiving the large carrier AM over FM signal;

b) generating, from said large carrier AM over FM signal, a suppressed carrier AM over FM signal;

c) generating, from said large carrier AM over FM signal, an FM only waveform;

d) demodulating the large carrier AM over FM signal, wherein said demodulating step comprises combining said suppressed carrier AM over FM signal and said FM only waveform to produce a product signal and generating from said product signal said AM message;

e) instantaneously tracking the frequency of said FM only waveform; and

f) generating, from said frequency of said FM only waveform, said FM message.

16. A method for mitigating the deleterious effects of multipath on a received signal, comprising:

a) receiving an amplitude modulated message upon a frequency modulated signal;

b) canceling the frequency modulated signal from the received signal and generating a raw AM message signal and an instantaneous frequency estimate signal;

c) generating a running estimate of an FM to AM conversion interference signal to be expected from the instantaneous frequency estimate signal by comparison of the instantaneous frequency estimate signal and the raw AM message signal with data stored in a look-up table; and

d) subtracting the FM to AM conversion interference signal from the raw AM message signal to produce a clean AM message signal.

17. A method for recovering signals from a transmitted large carrier AM over FM signal incorporating an AM message and an FM message, comprising:

a) receiving the large carrier AM over FM signal; and

b) isolating an AM waveform from said large carrier AM over FM signal to generate an AM only signal, said isolating step comprising;

obtaining an FM only signal; and

multiplying the large carrier AM over FM signal with said FM only signal to generate a product signal; and

c) generating from the product signal an envelope of the AM only signal.