Forward error correction coding for hybrid AM in-band on-channel digital audio broadcasting systems
View Patent ↗An AM compatible digital audio broadcasting signal comprises an analog modulated carrier signal centrally positioned in a radio channel, wherein the analog modulated carrier signal is modulated by an analog signal, and a plurality of digitally modulated subcarrier signals in the radio channel, wherein the digitally modulated subcarrier signals are modulated using complementary pattern-mapped trellis code modulation including a code mapped to overlapping partitions. Time diversity can be included between the analog modulated carrier signal and the plurality of digitally modulated subcarrier signals, and/or between groups of the digitally modulated subcarrier signals. A broadcasting method, and transmitters and receivers and that utilize the signal are also provided.
1. A receiver for receiving an AM compatible digital audio broadcasting signal, the receiver comprising:
an antenna for receiving a composite signal comprising an analog modulated carrier signal centrally positioned in a radio channel, wherein the analog modulated carrier signal is modulated by an analog signal, and a plurality of digitally modulated subcarrier signals in the radio channel, wherein the digitally modulated subcarrier signals are modulated using complementary pattern-mapped trellis code modulation including a code mapped to overlapping partitions; and
means for producing an output in response to the composite signal;
wherein in a first operating mode the analog modulated carrier signal and the plurality of digitally modulated subcarrier signals are in a 20 kHz channel and the analog modulated signal is delayed with respect to the plurality of digitally modulated subcarrier sianals, and in a second operating mode the analog modulated carrier signal and the plurality of digitally modulated subcarrier signals are in a 30 kHz channel and a first group of the plurality of digitally modulated subcarrier signals are delayed with respect to a second group of the plurality of digitally modulated subcarrier signals.
2. The receiver of claim 1 , wherein the code comprises:
a complementary punctured convolutional code.
3. The receiver of claim 1 , wherein:
the composite signal and the data service signal are processed on interleaver block boundaries.
4. A method of broadcasting an AM compatible digital audio broadcasting signal, the method comprising the steps of:
producing an analog modulated carrier signal centrally positioned in a radio channel, wherein the analog modulated carrier signal is modulated by an analog signal;
producing a plurality of digitally modulated subcarrier signals in the radio channel, wherein the digitally modulated subcarrier signals are modulated using complementary pattern-mapped trellis code modulation (CPTCM) including a code mapped to overlapping partitions; and
transmitting the analog modulated carrier signal and the plurality of digitally modulated subcarrier signals;
wherein in a first operating mode the analog modulated carrier signal and the plurality of digitally modulated subcarrier signals are in a 20 kHz channel and the analog modulated signal is delayed with respect to the plurality of digitally modulated subcarrier signals, and in a second operating mode the analog modulated carrier signal and the plurality of digitally modulated subcarrier signals are in a 30 kHz channel and a first group of the plurality of digitally modulated subcarrier signals are delayed with respect to a second group of the plurality of digitally modulated subcarrier signals.
5. The method of claim 4 , wherein the code comprises:
a complementary punctured convolutional code.
6. A method of broadcasting an AM compatible digital audio broadcasting signal, the method comprising the steps of:
producing an analog modulated carrier signal centrally positioned in a radio channel, wherein the analog modulated carrier signal is modulated by an analog signal:
producing a plurality of digitally modulated subcarrier signals in the radio channel, wherein the digitally modulated subcarrier signals are modulated using complementary pattern-mapped trellis code modulation (CPTCM) including a code mapped to overlapping partitions; and
transmitting the analog modulated carrier signal and the plurality of digitally modulated subcarrier signals;
wherein the analog modulated carrier signal and the plurality of digitally modulated subcarrier signals are in a 30 kHz channel, the method further comprising the step of:
eliminating or suppressing the subcarriers in an upper partition of subcarriers, or the subcarriers in a lower partition of subcarriers, or the subcarriers in both the upper partition of subcarriers and the lower partition of subcarriers depending upon interference conditions.
7. A receiver for receiving an AM compatible digital audio broadcasting signal, the receiver comprising:
an antenna for receiving a composite signal comprising an analog modulated carrier signal centrally positioned in a radio channel, wherein the analog modulated carrier signal is modulated by an analog signal, and a plurality of digitally modulated subcarrier signals in the radio channel, wherein the digitally modulated subcarrier signals are modulated using complementary pattern-mapped trellis code modulation including a code mapped to overlapping partitions; and
an output device for producing an output in response to the composite signal;
wherein in a first operating mode the analog modulated carrier signal and the plurality of digitally modulated subcarrier signals are in a 20 kHz channel and the analog modulated signal is delayed with respect to the plurality of digitally modulated subcarrier signals, and in a second operating mode the analog modulated carrier signal and the plurality of digitally modulated subcarrier signals are in a 30 kHz channel and a first group of the plurality of digitally modulated subcarrier signals are delayed with respect to a second group of the plurality of digitally modulated subcarrier signals.
8. The receiver of claim 7 , wherein the code comprises:
a complementary punctured convolutional code.
9. The receiver of claim 7 , wherein:
the composite signal and the data service signal are processed on interleaver block boundaries.
10. A method of broadcasting an AM compatible digital audio broadcasting signal, the method comprising the steps of:
producing an analog modulated carrier signal centrally positioned in a radio channel, wherein the analog modulated carrier signal is modulated by an analog signal;
producing a first plurality of subcarrier signals in a first portion of the radio channel and a second plurality of subcarrier signals in a second portion of the radio channel, wherein the first and second pluralities of subcarrier signals are complementary modulated subcarrier signals and have a power spectral density below the analog modulated carrier by a first margin;
producing a third plurality of subcarrier signals in a third portion of the radio channel and a fourth plurality of subcarrier signals in a fourth portion of the radio channel, wherein the third and fourth pluralities of subcarrier signals are complementary modulated subcarrier signals and have a power spectral density below the analog modulated carrier by a second margin;
producing a fifth plurality of subcarrier signals in a fifth portion of the radio channel and a sixth plurality of subcarrier signals in a sixth portion of the radio channel, wherein the fifth and sixth pluralities of subcarrier signals have a power spectral density below the analog modulated carrier by a third margin;
wherein the first, second, third, fourth, fifth and sixth pluralities of subcarrier signals are modulated by one or more digital signals, the first margin is larger than the second margin, and the second margin is larger than the third margin; and
transmitting the first, second, third, fourth, fifth and sixth pluralities of subcarrier signals.
11. The method of claim 10 , wherein:
the digital signals are complementary pattern mapped signals.
12. The method of claim 10 , wherein:
the first and second pluralities of subcarrier signals are QPSK modulated; and
the third, fourth, fifth and sixth pluralities of subcarrier signals are 16-QAM modulated.
13. The method of claim 10 , wherein:
the first portion of the radio channel encompasses frequencies between about 0 kHz and about +6 kHz from the analog modulated carrier;
the second portion of the radio channel encompasses frequencies between about 0 kHz and about −6 kHz from the analog modulated carrier;
the third portion of the radio channel encompasses frequencies between about +6 kHz and about +7 kHz from the analog modulated carrier;
the fourth portion of the radio channel encompasses frequencies between about −6 kHz and about −7 kHz from the analog modulated carrier;
the fifth portion of the radio channel encompasses frequencies between about +7 kHz and about +10 kHz from the analog modulated carrier; and
the sixth portion of the radio channel encompasses frequencies between about −7 kHz and about −10 kHz from the analog modulated carrier.
14. The method of claim 10 , further comprising the steps of:
producing a seventh plurality of subcarrier signals in a seventh portion of the radio channel and an eighth plurality of subcarrier signals in an eighth portion of the radio channel, wherein the seventh and eighth pluralities of subcarrier signals have a power spectral density at least 40 dBc below the analog modulated carrier;
wherein the seventh and eighth pluralities of subcarrier signals are modulated by the one or more digital signals; and
transmitting the seventh and eighth pluralities of subcarrier signals.
15. The method of claim 14 , wherein:
the digital signals are 25 kbps signals coded at a rate of 4/5.
16. The method of claim 14 , wherein:
the seventh portion of the radio channel encompasses frequencies between about +10 kHz and about +15 kHz from the analog modulated carrier; and
the eighth portion of the radio channel encompasses frequencies between about −10 kHz and about −15 kHz from the analog modulated carrier.
17. The method of claim 14 , further comprising the step of:
eliminating or suppressing the seventh plurality of subcarriers, or the eighth plurality of subcarriers, or the seventh plurality of subcarriers and the eighth plurality of subcarriers depending upon interference conditions.