Phase-Optimized Constant Envelope Transmission (POCET) Method, Apparatus And System

• US 20110051783A1
• Filed: 08/25/2009
• Published: 03/03/2011
• Est. Priority Date: 08/25/2009
• Status: Active Grant

• Current Assignee: Aerospace Corporation
• Original Assignee: Aerospace Corporation
• Inventors: Dafesh, Philip A., Cahn, Charles Robert
• Granted Patent: US 8,774,315 B2
• Time in Patent Office: Days
• US Class Current: 375/146
• CPC Class Codes: G01S 19/02 Details of the space or ground control segments
• CPC Class Codes: H04B 1/0475 with means for limiting noise, interference or distortion H04B1/0483 takes precedence
• CPC Class Codes: H04B 1/707 using direct sequence modulation
• CPC Class Codes: H04B 1/7097 Interference-related aspects
• CPC Class Codes: H04B 1/7103 the interference being multiple access interference
• CPC Class Codes: H04B 2001/0491 with frequency synthesizers, frequency converters or modulators
• CPC Class Codes: H04B 2201/70706 with means for reducing the peak-to-average power ratio
• CPC Class Codes: H04B 2201/709709 Methods of preventing interference
• CPC Class Codes: H04J 13/0003 Code application, i.e. aspects relating to how codes are applied to form multiplexed channels
• CPC Class Codes: H04L 23/02 adapted for orthogonal signalling
• CPC Class Codes: H04L 27/12 Modulator circuits; Transmitter circuits
• CPC Class Codes: H04L 27/2007 in which the phase change within each symbol period is constrained coset coding H04L27/186

Abstract

An apparatus and method for generating a composite signal includes electronics configured to modulate a carrier utilizing a finite set of composite signal phases to generate a composite signal, the finite set of composite signal phases being determined through an optimization process that minimizes a constant envelope for the phase modulated carrier, subject to constraints on desired signal power levels of the signals to be combined and either zero or one or more relative phase relationships between the signals. The apparatus and method can be extended to generating an optimized composite signal of different frequencies.

Claims

1. An apparatus for generating a composite signal from a plurality of component signals, comprising:

electronics configured to modulate a carrier utilizing a finite set of composite signal phases to generate a composite signal, the finite set of composite signal phases being determined through an optimization process that minimizes a constant envelope of a phase-modulated carrier, subject to a plurality of intra-signal constraints for the component signals.

2. The apparatus for generating a composite signal of claim 1, wherein the optimization process is further subject to one or more inter-signal constraints between the component signals.

3. The apparatus for generating a composite signal of claim 1, wherein the component signals are satellite navigation signals.

4. The apparatus for generating a composite signal of claim 1, wherein a desired signal power level is determined from the average component signal correlation level for each of the component signals by averaging the composite signal over all possible phase states.

5. The apparatus for generating a composite signal of claim 4, wherein the intra-signal constraints are determined from the desired component signal power levels.

6. The apparatus for generating a composite signal of claim 1, wherein the optimization process includes optimization of an objective function, equal to a constant envelope, subject to constraints which include the intra-signal constraints for each of the component signals and either zero or one or more inter-signal constraints between the component signals.

7. The apparatus for generating a composite signal of claim 6, wherein an optimization algorithm is used to minimize the objective function.

8. The apparatus for generating a composite signal of claim 1, wherein the optimization process includes utilizing the penalty function method.

9. The apparatus for generating a composite signal of claim 1, wherein the composite signal is an Orthogonal Frequency Division Multiplexing (OFDM) waveform.

10. The apparatus for generating a composite signal of claim 1, wherein the composite signal is a Code Division Multiple Access (CDMA) waveform.

11. The apparatus for generating a composite signal of claim 1, wherein the component signals are PRN spreading codes.

12. The apparatus for generating a composite signal of claim 11, wherein the PRN spreading codes are at a plurality of different carrier frequencies.

13. The apparatus for generating a composite signal of claim 1, wherein the composite signal is derived from Frequency Division Multiple Access (FDMA) component signals.

14. The apparatus for generating a composite signal of claim 1, wherein each of the component signals is at a plurality of carrier frequencies.

15. The apparatus for generating a composite signal of claim 1, wherein the electronics include a modulator configured to utilize multiple finite sets of optimized phase tables, determined through additional optimization processes to accommodate different carrier frequencies.

16. The apparatus for generating a composite signal of claim 15, wherein a number of additional optimizations performed corresponds to a number of phase steps associated with the component signals at a plurality of different carrier frequencies.

17. The apparatus for generating a composite signal of claim 16, wherein the number of phase steps associated with the different carrier frequencies is determined by quantizing the continuous phase rotation of the carrier to ensure a negligible correlation loss.

18. An apparatus for generating a composite signal from a plurality of component signals, comprising:

electronics configured to modulate a carrier utilizing a finite set of composite signal phases to generate a composite signal, the finite set of composite signal phases being determined through an optimization process that minimizes a constant envelope of a phase-modulated carrier, subject to a plurality of constraints on desired signal power levels for the component signals.

19. The apparatus for generating a composite signal of claim 18, wherein the optimization process is further subject to one or more constraints on phase relationships between the component signals.

20. The apparatus for generating a composite signal of claim 18, wherein the component signals are satellite navigation signals.

21. The apparatus for generating a composite signal of claim 18, wherein a desired signal power level is determined from the average component signal correlation level for each of the component signals by averaging the composite signal over all possible phase states.

22. The apparatus for generating a composite signal of claim 21, wherein the constraints are determined from the desired component signal power levels.

23. The apparatus for generating a composite signal of claim 18, wherein the optimization process includes optimization of an objective function, equal to a constant envelope, subject to the constraints, which include intra-signal constraints for each of the component signals and either zero or one or more inter-signal constraints between the component signals.

24. The apparatus for generating a composite signal of claim 23, wherein an optimization algorithm is used to minimize the objective function.

25. The apparatus for generating a composite signal of claim 18, wherein the optimization process includes utilizing the penalty function method.

26. The apparatus for generating a composite signal of claim 18, wherein the composite signal is an Orthogonal Frequency Division Multiplexing (OFDM) waveform.

27. The apparatus for generating a composite signal of claim 18, wherein the composite signal is a Code Division Multiple Access (CDMA) waveform.

28. The apparatus for generating a composite signal of claim 18, wherein the component signals are PRN spreading codes.

29. The apparatus for generating a composite signal of claim 28, wherein the PRN spreading codes are at a plurality of different carrier frequencies.

30. The apparatus for generating a composite signal of claim 18, wherein the composite signal is derived from Frequency Division Multiple Access (FDMA) component signals.

31. The apparatus for generating a composite signal of claim 18, wherein each of the component signals is at a plurality of carrier frequencies.

32. The apparatus for generating a composite signal of claim 18, wherein the electronics include a modulator configured to utilize multiple finite sets of optimized phase tables, determined through additional optimization processes, to accommodate different carrier frequencies.

33. The apparatus for generating a composite signal of claim 32, wherein a number of additional optimizations performed corresponds to a number of phase steps associated with the component signals at a plurality of different carrier frequencies.

34. The apparatus for generating a composite signal of claim 33, wherein the number of phase steps associated with the different carrier frequencies is determined by quantizing the continuous phase rotation of the carrier to ensure a negligible correlation loss.

35. A method for generating a composite signal from a plurality of component signals, comprising the step of:

modulating a carrier utilizing a finite set of composite signal phases to generate a composite signal, the finite set of composite signal phases being determined through an optimization process that minimizes a constant envelope of a phase modulated carrier, subject to a plurality of constraints on desired signal power levels for the component signals, and either zero or one or more constraints on phase relationships between the component signals.

36. The method for generating a composite signal of claim 35, wherein the component signals are satellite navigation signals.

37. The method for generating a composite signal of claim 35, wherein the component signals are PRN spreading codes.

38. The method for generating a composite signal of claim 37 wherein the PRN spreading codes are at a plurality of different carrier frequencies.

39. The method for generating a composite signal of claim 35, wherein each of the component signals is at a plurality of carrier frequencies.

40. The method for generating a composite signal of claim 35, further including the step of:

utilizing multiple finite sets of optimized phase tables, determined through additional optimization processes, to accommodate different carrier frequencies.

41. A method for forming a composite signal, comprising the steps of:

enumerating M^N phase states for combining N signals with M possible signal phases;

formulating N intra-signal constraint equations, each as a function of the M^N phase states, to provide intra-signal constraints on the signals;

formulating K<

=N(N−

1)/2 inter-signal constraint equations, where K=0 or a positive integer, each as a function of the M^N phase states, to provide inter-signal constraints between the signals;

performing an optimization process to minimize a constant envelope for a phase modulated carrier, subject to the intra-signal constraints on the signals and the inter-signal constraints between the signals; and

modulating an RF carrier using phase states determined through the optimization process to produce a composite signal.

42. The method for forming a composite signal of claim 41, wherein performing an optimization process includes optimization of an objective function of the composite signal power.

43. The method for forming a composite signal of claim 42, wherein an optimization algorithm is used to minimize the objective function.

44. The method for forming a composite signal of claim 41, wherein performing an optimization process includes optimization of an objective function of the composite signal envelope.

45. The method for forming a composite signal of claim 44, wherein an optimization algorithm is used to minimize the objective function.

46. The method for forming a composite signal of claim 41, wherein performing an optimization process includes utilizing a penalty function method.

47. The method for forming a composite signal of claim 41, wherein the composite signal includes Orthogonal Frequency Division Multiplexing (OFDM) signals.

48. The method for forming a composite signal of claim 41, wherein the composite signal includes Code Division Multiple Access (CDMA) signals.

49. The method for generating a composite signal of claim 41, wherein the component signals are PRN spreading codes.

50. The method for generating a composite signal of claim 49, wherein the PRN spreading codes are at a plurality of different carrier frequencies.

51. The method for generating a composite signal of claim 41, wherein each of the component signals is at a plurality of carrier frequencies.

52. The method for forming a composite signal of claim 41, wherein the composite signal includes Frequency Division Multiple Access (FDMA) signals.

53. The method for forming a composite signal of claim 41, further including the step of:

performing additional optimization processes for different carrier frequencies.

54. The method for forming a composite signal of claim 53, wherein a number of additional optimizations performed corresponds to a number of phase steps associated with the different carrier frequencies.

55. The method for forming a composite signal of claim 54, wherein the number of phase steps associated with the different carrier frequencies is determined by quantizing the continuous phase rotation of the RF carrier to ensure a negligible correlation loss.