SYSTEM AND METHOD FOR ACCURATE DOWNLINK POWER CONTROL OF COMPOSITE QPSK MODULATED SIGNALS

• US 20100034313A1
• Filed: 08/08/2008
• Published: 02/11/2010
• Est. Priority Date: 08/08/2008
• Status: Active Grant

• Current Assignee: The Boeing Co.
• Original Assignee: The Boeing Co.
• Inventors: Benavides, Armando
• Granted Patent: US 8,189,708 B2
• Time in Patent Office: Days
• US Class Current: 375/268
• CPC Class Codes: H04L 27/2071 in which the data are represented by the carrier phase, e.g. systems with differential coding

Abstract

A method for controlling code power levels of individual codes of a composite quadrature phase shift keyed (QPSK) signal. The method may involve obtaining a sample of the composite QPSK signal; separating the individual codes from the composite QPSK signal; analyzing the individual codes against corresponding commanded code power settings for the individual codes; and determining a code power correction signal needed for each of the individual codes needed to adjust a code power for each of the individual codes to match their corresponding commanded code power settings.

Claims

1. A method for controlling code power levels of individual codes of a quadrature phase shift keyed (QPSK) composite signal, the method comprising:

obtaining a sample of said composite QPSK signal;

separating said individual codes from said composite QPSK signal;

analyzing said individual codes against corresponding commanded code power settings for said individual codes; and

determining a code power correction signal needed for each of said individual codes needed to adjust a code power for each of said individual codes to match their said corresponding commanded code power settings.

2. The method of claim 1, further comprising using said code power correction for each of said individual codes to adjust a code power level of each of said individual codes.

3. The method of claim 1, wherein said individual codes of said QPSK signal comprises four individual codes.

4. The method of claim 1, wherein said separating said individual codes from said QPSK signal comprises initially dividing said sampled QPSK signal into first and second signals having approximately equal power, said first signal comprising an I-channel signal that does not have a phase shift with respect to zero degrees phase, and said second signal comprising a Q-channel signal that has a ninety degree phase shift with respect to said I-channel signal.

5. The method of claim 4, wherein said separating said individual codes from said QPSK signal comprises phase detecting and demodulating said first and second signals independently of one another.

6. The method of claim 5, wherein said separating said individual codes from said QPSK signal further comprises independently detecting a peak level of said first signal and a peak level of said second level.

7. The method of claim 6, wherein said separating said individual codes from said composite QPSK signal further comprises using an exclusive OR-gate to receive first and second navigation data codes being used to help form said composite QPSK signal, and using said codes to control a pair of sample and hold circuits receiving said first signal to thus generate a pair of sampled, peak signals relating to said first and second navigation data codes.

8. The method of claim 7, wherein said separating said individual codes from said composite QPSK signal further comprises using an exclusive OR-gate to receive third and fourth navigation data codes being used to help form said composite QPSK signal, and using said codes to control an additional pair of sample and hold circuits receiving said second signal, to thus generate an additional pair of sampled, peak signals relating to said third and fourth navigation data codes.

9. The method of claim 8, wherein said separating said individual codes from said composite QPSK signal further comprises filtering and analog-to-digital converting each of said sampled, peak signals to produce four digital signals corresponding to said four navigation data codes that are indicative of an actual code power being used for each of said four navigation data codes being transmitted from said satellite.

10. The method of claim 9, further comprising using a processor to receive said four digital signals and to compare said four digital signals to four commanded power codes, and to generate said code power correction signals that are applied to a transmitter of said satellite being used to transmit said composite QPSK signal, to thus modify a power level of each of said individual codes being used to form said composite QPSK signal.

11. The method of claim 10, wherein said method forms a closed loop system to generate said code power correction signals in real time.

13. The method of claim 1, wherein said method forms a closed loop system for generating and applying said code power correction signals, in real time, to a transmitter transmitting said composite QPSK signal.

12. A method for controlling code power levels of four individual codes of a quadrature phase shift keyed composite (QPSK) signal being transmitted from a satellite, the method comprising:

obtaining a sample of said composite QPSK signal;

separating said sample into first and second signals, said first signal including components of said composite QPSK signal that are ninety degrees out of phase with respect to a zero degree phase, and said second signal including components of said composite QPSK signal that are in phase with said zero degree phase;

phase detecting said first and second signals to produce demodulated first and second signals;

further processing said demodulated first and second signals to generate four sampled, peak signals corresponding to first, second third and fourth navigation data codes being generated by a navigation data unit being used with said satellite;

analyzing said four sampled, peak signals in relation to corresponding commanded code power settings for said four navigation data codes; and

determining a code power correction signal needed for each of said four navigation data codes needed to adjust a code power for each of said navigation data codes to match corresponding commanded code power settings for each of said navigation data codes.

14. The method of claim 12, wherein further processing said demodulated first and second signals comprises using a first exclusive OR-gate and said first and second navigation data codes to generate first and second ones of said sampled, peak signals.

15. The method of claim 14, wherein further processing said demodulated second and third signals comprises using a second exclusive OR-gate and said third and fourth navigation data codes to generate first and second ones of said sampled, peak signals.

16. The method of claim 15, wherein determining said code power correction signal for each of said four navigation data codes comprises using a microprocessor to generate and apply said four code power correction signals to signal attenuators used in a transmitter of said satellite.

17. A system for controlling code power levels of individual codes of a composite quadrature phase shift keyed (QPSK) signal being transmitted from a satellite, the system comprising:

a power divider for splitting a sampled portion of said composite QPSK signal into first and second signals of equal power;

a first subsystem for phase detecting, demodulating and analyzing said first signal, and analyzing first and second navigation data codes being applied by a transmitter of said satellite in forming said composite QPSK signal, and generating first and second sampled, peak signals relating to peak power levels of said first and second navigation data codes;

a second subsystem for phase detecting, demodulating and analyzing said second signal, and analyzing and third and fourth navigation data codes being applied by said transmitter to form said composite QPSK signal, and generating third and fourth sampled, peak signals relating to peak power levels of said third and fourth navigation data codes; and

a processor for further analyzing said first, second, third and fourth peak sampled navigation data codes and commanded navigation data codes, and generating power correction signals needed to adjust a power level of each one of said first, second, third and fourth navigation data codes being used to form said composite QPSK signal.

18. The system of claim 17, wherein:

said first subsystem includes a first peak detector for detecting a peak of said first signal; and

said second subsystem includes a second peak detector for detecting a peak of said second signal.

19. The system of claim 18, wherein:

said first subsystem includes a first exclusive OR-gate for receiving said first and second navigation data codes, and a first sample-and-hold circuit for receiving an output from said first peak detector; and

said second subsystem includes a second exclusive OR-gate for receiving said third and fourth navigation data codes, and a second sample-and-hold circuit for receiving an output from said second peak detector.

20. The system of claim 19, wherein said processor comprises a microprocessor that generates said power correction signals, and wherein said power correction signals are applied to independent signal attenuators of said transmitter.