MULTIPLE SYMBOL NONCOHERENT SOFT OUTPUT DETECTOR

• US 20120275546A1
• Filed: 03/07/2012
• Published: 11/01/2012
• Est. Priority Date: 03/07/2011
• Status: Active Grant

• Current Assignee: Mojix Inc
• Original Assignee: Mojix Inc
• Inventors: Divsalar, Dariush
• Granted Patent: US 9,602,316 B2
• Time in Patent Office: Days
• US Class Current: 375/324
• CPC Class Codes: H04L 25/03171 Arrangements involving maximum a posteriori probability [MAP] detection

Abstract

Multiple symbol noncoherent soft output detectors in accordance with embodiments of the invention are disclosed. In a number of embodiments, the multiple symbol noncoherent soft output detector uses soft metrics based on the Log Likelihood Ratio (LLR) of each symbol to provide information concerning the reliability of each detected symbol. One embodiment of the invention includes a receiver configured to receive and sample a phase modulated input signal, and a multiple symbol noncoherent soft output detector configured to receive the sampled input signal and to generate a soft metric indicative of the reliability of a detected symbol based upon observations over multiple symbols.

Claims

1. A receiver system, comprising:

a receiver configured to receive and sample a phase modulated input signal; and

a multiple symbol noncoherent soft output detector configured to receive the sampled input signal and to generate a soft metric indicative of the reliability of a detected symbol based upon observations over multiple symbols.

2. The receiver system of claim 1, wherein the soft metric is based on the Log Likelihood Ratio of the detected symbol based upon observations over multiple symbols.

3. The receiver system of claim 2, wherein the observations include at least one known symbol.

4. The receiver system of claim 2, wherein the observations include observations over a three symbol sequence.

5. The receiver system of claim 1, wherein:

the phase modulated input signal comprises data that is phase modulated on a carrier; and

the multiple symbol noncoherent soft output detector assumes that carrier phase of the input signal is constant over the time duration of the observations.

6. The receiver system of claim 5, wherein the phase modulated input signal is a binary phase modulated signal.

7. The receiver system of claim 5, wherein the phase modulated input signal is a Multiple-Phase-Shift Keying modulated signal.

8. The receiver system of claim 1, wherein:

the multiple symbol noncoherent soft output detector comprises a plurality of matched filters having different numbers of samples configured to integrate the samples during each half-symbol period; and

the multiple symbol noncoherent soft output detector is configured to use the outputs of each of the plurality of matched filters to determine the most likely symbol duration.

9. A combined receiver system, comprising:

a plurality of receivers configured to receive and sample an input signal, where the input signal comprises data that is phase modulated onto a carrier;

a plurality of multiple symbol noncoherent soft output detectors configured to receive a sampled input signal from one of the plurality of receivers and to generate a soft metric indicative of the reliability of a detected symbol based upon observations over multiple symbols; and

a combiner configured to receive the soft metrics from the plurality of multiple symbol noncoherent soft output detectors and to detect data based upon the soft metrics.

10. The combined receiver system of claim 9, wherein the combiner is configured to detect data by combining the soft metrics.

11. The combined receiver system of claim 9, wherein the combiner is configured to select at least one of the soft metrics from the plurality of multiple symbol noncoherent soft output detectors based upon a threshold level of reliability.

12. The combined receiver system of claim 9, wherein the soft metrics generated by the plurality of multiple symbol noncoherent soft output detectors are based on the Log Likelihood Ratio of the detected symbol based upon observations over multiple symbols.

13. The combined receiver system of claim 12, wherein the observations include at least one known symbol.

14. The combined receiver system of claim 12, wherein the observations include observations over a three symbol sequence.

15. The combined receiver system of claim 9, wherein each of the plurality of multiple symbol noncoherent soft output detectors assumes that carrier phase of the input signal is constant over the time duration of the observations.

16. The combined receiver system of claim 15, wherein the phase modulated input signal is a binary phase modulated signal.

17. The combined receiver system of claim 15, wherein the phase modulated input signal is a Multiple-Phase-Shift Keying modulated signal.

18. The combined receiver system of claim 9, wherein:

each of the plurality of multiple symbol noncoherent soft output detectors comprises a plurality of matched filters having different numbers of samples configured to integrate the samples during each half-symbol period; and

each of the plurality of multiple symbol noncoherent soft output detectors is configured to use the outputs of each of the plurality of matched filters to determine the most likely symbol duration.

19. A radio frequency identification (RFID) receiver system configured to detect phase modulated data transmitted by RFID tags, the RFID receiver system comprising:

an antenna configured to receive a phase modulated signal comprising symbols transmitted by an RFID tag;

a receiver configured to sample the phase modulated signal; and

a multiple symbol noncoherent soft output detector configured to receive the sampled input signal and to generate soft metrics indicative of the reliability of a detected symbol based upon observations over multiple symbols.

20. The RFID receiver system of claim 19, wherein the soft metric is based on the Log Likelihood Ratio of the detected symbol based upon observations over multiple symbols.

21. The RFID receiver system of claim 20, wherein the phase modulated input signal is an FM0 modulated signal.

22. The RFID receiver system of claim 21, wherein the FM0 modulated input signal comprises a known preamble sequence and an unknown data sequence.

23. The RFID receiver system of claim 22, wherein the observations include observations over at least one symbol in the preamble sequence and at least one symbol in the unknown data sequence.

24. The RFID receiver system of claim 23, wherein the observations include observations over the entire preamble and at least three symbols in the unknown data sequence.

25. The RFID receiver system of claim 22, wherein:

the FM0 modulated input signal further comprises a known pilot sequence; and

the observations include observations over the entire pilot and preamble and at least three symbols in the unknown data sequence.

26. The RFID receiver system of claim 22, wherein the multiple symbol noncoherent soft output detector assumes that carrier phase of the input signal is constant over the time duration of the observations.

27. The RFID receiver system of claim 20, wherein:

the multiple symbol noncoherent soft output detector comprises a plurality of matched filters having different numbers of samples configured to integrate the samples during each half-symbol period; and

the multiple symbol noncoherent soft output detector is configured to use the outputs of each of the plurality of matched filters to determine the most likely symbol duration.

28. The RFID receiver system of claim 20, wherein the multiple symbol noncoherent soft output detector is configured to detect RFID tag transmission collisions based upon the LLRs of the detected symbols.

29. The RFID receiver system of claim 20, wherein the phase modulated signal comprising symbols transmitted by an RFID tag is a phase modulated signal comprising symbols backscattered by an RFID tag.

30. A combined radio frequency identification (RFID) receiver system configured to detect phase modulated data transmitted by an RFID tag, the RFID receiver system comprising:

a plurality of antennas configured to receive an input signal transmitted by an RFID tag, where the input signal comprises data that is phase modulated onto a carrier;

a plurality of receivers configured to sample the phase modulated signal from least one of the plurality of antennas;

a plurality of multiple symbol noncoherent soft output detectors configured to receive the sampled input signal from one of the plurality of receivers and to generate soft metrics indicative of the reliability of a detected symbol based upon observations over multiple symbols; and

a combiner configured to receive the soft metrics from the plurality of multiple symbol noncoherent soft output detectors and to detect data based upon the soft metrics.

31. The combined RFID receiver system of claim 30, wherein the combiner is configured to detect data by combining the soft metrics.

32. The combined RFID receiver system of claim 30, wherein the combiner is configured to select at least one of the soft metrics from the plurality of multiple symbol noncoherent soft output detectors based upon a threshold level of reliability.

33. The combined RFID receiver system of claim 30, wherein the soft metrics generated by the plurality of multiple symbol noncoherent soft output detectors are based on the Log Likelihood Ratio of the detected symbol based upon observations over multiple symbols.

34. The combined RFID receiver system of claim 30, wherein the phase modulated input signal is an FM0 modulated input signal.

35. The combined RFID receiver system of claim 34, wherein the FM0 modulated input signal comprises a known preamble sequence and an unknown data sequence.

36. The combined RFID receiver system of claim 35, wherein the observations include observations over at least one symbol in the preamble sequence and at least one symbol in the unknown data sequence.

37. The combined RFID receiver system of claim 36, wherein the observations include observations over the entire preamble and at least three symbols in the unknown data sequence.

38. The combined RFID receiver system of claim 37, wherein:

the FM0 modulated input signal further comprises a known pilot sequence; and

the observations include observations over the entire pilot and preamble and at least three symbols in the unknown data sequence.

39. The combined RFID receiver system of claim 33, wherein the phase modulated signal comprising symbols transmitted by an RFID tag is a phase modulated signal comprising symbols backscattered by an RFID tag.