MRC antenna diversity for FM IBOC digital signals
View Patent ↗A radio receiver includes a first signal path including a first tuner configured to receive a first signal from a first antenna, and a first demodulator configured to demodulate symbols from an output of the first tuner to produce first branch metrics derived from the demodulated symbols; a second signal path including a second tuner configured to receive a second signal from a second antenna, and a second demodulator configured to demodulate symbols from an output of the second tuner to produce second branch metrics derived from the demodulated symbols; a combiner for maximum ratio combining the first branch metrics and the second branch metrics; and processing circuitry to process the combined first and second branch metrics to produce an output signal.
1. A radio receiver comprising:
a first signal path including a first tuner configured to receive a first signal from a first antenna, and a first demodulator configured to demodulate symbols from an output of the first tuner to produce first branch metrics derived from the demodulated symbols;
a second signal path including a second tuner configured to receive a second signal from a second antenna, and a second demodulator configured to demodulate symbols from an output of the second tuner to produce second branch metrics derived from the demodulated symbols;
a combiner for maximum ratio combining the first branch metrics and the second branch metrics, wherein the first and second branch metrics are synchronized by indexing; and
processing circuitry to process the combined first and second branch metrics to produce an output signal.
2. The radio receiver of claim 1 , wherein the indexing occurs prior to the deinterleaving.
3. The radio receiver of claim 1 , wherein indexing is used to identify the first and second branch metrics by a symbol number.
4. The radio receiver of claim 1 , wherein when one of the signal paths has no branch metrics available, the branch metrics of that signal path are zeroed.
5. The radio receiver of claim 1 , wherein the first and second demodulators adjust the magnitudes of the first and second branch metrics in response to signal-to-noise ratios of the first and second signals.
6. The radio receiver of claim 1 , wherein the combiner sums corresponding, synchronized branch metrics from the first and second signal paths.
7. The radio receiver of claim 1 , wherein the processing circuitry includes a deinterleaver and a Viterbi decoder, and wherein like-indexed branch metrics are added when the corresponding symbols are available from the first and second signal paths.
8. The radio receiver of claim 1 , wherein each of the signal paths independently acquires and tracks a signal received by one of the antennas.
9. The radio receiver of claim 8 , wherein symbol and frequency tracking for each signal path flywheels over temporary fades or outages.
10. The radio receiver of claim 1 , wherein the first and second antennas are configured to receive an FM IBOC signal.
11. The radio receiver of claim 1 , wherein the processing circuitry processes the second branch metrics to produce a data output signal.
12. A radio receiver comprising:
a first signal path including a first tuner configured to receive a first signal from a first antenna, and a first demodulator configured to demodulate symbols from an output of the first tuner to produce first branch metrics derived from the demodulated symbols;
a second signal path including a second tuner configured to receive a second signal from a second antenna, and a second demodulator configured to demodulate symbols from an output of the second tuner to produce second branch metrics derived from the demodulated symbols;
a combiner for maximum ratio combining the first branch metrics and the second branch metrics;
processing circuitry to process the combined first and second branch metrics to produce an output signal;
a third signal path including a third tuner configured to receive the second signal from the second antenna, and a third demodulator configured to demodulate symbols from an output of the third tuner; and
processing circuitry to process an output of the third demodulator to produce a data output signal.
13. A radio receiver comprising:
a first signal path including a first tuner configured to receive a first signal from a first antenna, and a first demodulator configured to demodulate symbols from an output of the first tuner to produce first branch metrics derived from the demodulated symbols;
a second signal path including a second tuner configured to receive a second signal from a second antenna, and a second demodulator configured to demodulate symbols from an output of the second tuner to produce second branch metrics derived from the demodulated symbols;
a combiner for maximum ratio combining the first branch metrics and the second branch metrics;
processing circuitry to process the combined first and second branch metrics to produce an output signal;
a third signal path including a third tuner configured to receive the second signal from the second antenna, and a third demodulator configured to demodulate symbols from an output of the third tuner to produce third branch metrics derived from the demodulated symbols;
a fourth signal path including a fourth tuner configured to receive the first signal from the first antenna, and a fourth demodulator configured to demodulate symbols from an output of the fourth tuner to produce fourth branch metrics derived from the demodulated symbols;
a second combiner for maximum ratio combining the third branch metrics and the forth branch metrics; and
processing circuitry to process the combined third and fourth branch metrics to produce a data output signal.
14. The radio receiver of claim 1 , wherein each of the signal paths includes a preacquisition filter.
15. The radio receiver of claim 14 , wherein each of the signal paths includes a decimation filter preceding the preacquisition filter.
16. A method comprising:
receiving a signal on a first antenna;
producing first branch metrics derived from the signal in a first signal path;
receiving the signal on a second antenna;
producing second branch metrics derived from the signal in a second signal path;
synchronizing the first and second branch metrics are synchronized by indexing;
maximum ratio combining the first branch metrics and the second branch metrics; and
processing the combined first and second branch metrics to produce an output signal.
17. The method of claim 16 , wherein the first and second signal paths adjust the magnitudes of the first and second branch metrics in response to a signal-to-noise ratio of the signal in the first and second signal paths.
18. The method of claim 16 , wherein the maximum ratio combining step sums corresponding, synchronized branch metrics from the first and second signal paths.
19. The method of claim 16 , wherein the first and second branch metrics are synchronized prior to deinterleaving.
20. The method of claim 16 , wherein the processing step is performed by processing circuitry including a deinterleaver and a Viterbi decoder; and like-indexed branch metrics are added when the corresponding symbols are available from the first and second signal paths.
21. The method of claim 16 , wherein each of the signal paths independently acquires and tracks a signal received by one of the antennas.
22. The method of claim 21 , wherein symbol and frequency tracking for each signal path flywheels over temporary fades or outages.
23. The method of claim 16 , wherein the first and second signal paths are configured to receive an FM IBOC signal.
24. The method of claim 16 , wherein when one of the signal paths has no branch metrics available, the branch metrics of that signal path are zeroed.
25. The method of claim 16 , further comprising:
using a digital signal quality metric as a bad-track detector in at least one of the signal paths.
26. The method of claim 25 , wherein the branch metrics are zeroed when the digital signal quality metric drops below a threshold.
27. The method of claim 26 , wherein the threshold is reduced for operation at lower signal-to-noise ratios.
28. The method of claim 16 , further comprising:
forcing a reacquisition when a filtered digital signal quality metric drops below a threshold for a predetermined number of consecutive symbols.
29. The method of claim 16 , wherein the signal paths are independent.
30. The method of claim 16 , further comprising:
warping at least one of the branch metrics at low signal-to-noise ratios to improve maximum ratio combining performance when a signal in one or both signal paths are degraded.
31. The method of claim 16 , further comprising:
using a maximum ratio combining arbitration scheme for the two signal paths.
32. The method of claim 16 , wherein the maximum ratio combining uses shared tracking information from the two signal paths.
33. The method of claim 16 , further comprising:
processing the second branch metrics to produce a data output signal.
34. A method comprising:
receiving a signal on a first antenna;
producing first branch metrics derived from the signal in a first signal path;
receiving the signal on a second antenna;
producing second branch metrics derived from the signal in a second signal path;
maximum ratio combining the first branch metrics and the second branch metrics;
processing the combined first and second branch metrics to produce an output signal;
producing third branch metrics derived from a signal in a third signal path; and
processing the third branch metrics to produce a data output signal.
35. A method comprising:
receiving a signal on a first antenna;
producing first branch metrics derived from the signal in a first signal path;
receiving the signal on a second antenna;
producing second branch metrics derived from the signal in a second signal path;
maximum ratio combining the first branch metrics and the second branch metrics;
processing the combined first and second branch metrics to produce an output signal;
producing third branch metrics derived from a signal in a third signal path;
producing fourth branch metrics derived from a signal in a fourth signal path;
maximum ratio combining the third branch metrics and the fourth branch metrics; and
processing the combined third and fourth branch metrics to produce a data output signal.
36. The method of claim 16 , wherein symbol tracking using reference subcarriers is started after an initial subframe is found.
37. The method of claim 36 , wherein a reacquisition is invoked within about 0.5 seconds after a digital signal quality metric if the initial subframe is not found.
38. The method of claim 16 , wherein symbol tracking is performed using a digital signal quality metric until an initial subframe is found.