Noise Floor Independent Delay-Locked Loop Discriminator

• US 20090110134A1
• Filed: 10/24/2007
• Published: 04/30/2009
• Est. Priority Date: 10/24/2007
• Status: Active Grant

• Current Assignee: CSR Technology Incorporated (Qualcomm, Inc.)
• Original Assignee: CSR Technology Incorporated (Qualcomm, Inc.)
• Inventors: Xie, Gang, Yuan, Xiang
• Granted Patent: US 7,995,683 B2
• Time in Patent Office: Days
• US Class Current: 375/371
• CPC Class Codes: G01S 19/30 code related G01S19/246 takes precedence
• CPC Class Codes: G01S 19/37 Hardware or software details of the signal processing chain
• CPC Class Codes: H04B 1/7075 with code phase acquisition
• CPC Class Codes: H04B 1/7085 using a code tracking loop, e.g. a delay-locked loop
• CPC Class Codes: H04B 2201/70715 with application-specific features

Abstract

A system and method for providing code tracking in a CDMA based communications receiver. In example systems and methods, a CDMA receiver, such as a GPS receiver, receives a signal and demodulates the signal to yield a digital IF signal. The digital IF signal is down-converted to a received code signal. Early, prompt and late correlation results are determined by correlating the received code signal with early, prompt and late duplicates of the received code signal. The early, prompt and late correlation results are used to calculate a code phase error using a noise-floor independent function of all three correlation results.

Claims

1. A method for determining a phase error of a received communication signal, the method comprising:

determining an early correlation result between the received communication signal and a first copy of the received communication signal;

determining a prompt correlation result between the received communication signal and a second copy of the received communication signal, the second copy of the received communication signal phase-lagging the first copy by a correlator spacing;

determining a late correlation result between the received communication signal and a third copy of the received communication signal, the third copy of the received communication signal phase-lagging the second copy by the correlator spacing; and

using a noise-floor independent discriminator to generate an auto-correlation function having a peak correlation and calculating the phase error as a spacing between the prompt correlation and the peak correlation using a function of the prompt, early and late correlations independent of a noise floor estimate.

2. The method of claim 1 where the step of using the noise floor independent discriminator comprises:

calculating the phase error δ

_cp using;

3. The method of claim 1 where:

the received communications signal includes an in-phase signal, I, and a quadrature signal, Q;

the step of determining the early correlation result includes the steps of;

determining an I_E correlation of the in-phase signal, I, and the first copy of the received signal;

determining a Q_E correlation of the quadrature signal, Q, and the first copy of the received signal;

integrating the I_E correlation and the Q_E correlation, each over a predetection integration interval to generate smooth correlations I_ES, and Q_ES;

the step of determining the prompt correlation result includes the steps of;

determining an I_P correlation of the in-phase signal, I, and the second copy of the received signal;

determining a Q_P correlation of the quadrature signal, Q, and the second copy of the received signal;

integrating the I_P correlation and the Q_P correlation, each over a predetection integration interval to generate smooth correlations I_PS, and Q_PS;

the step of determining the late correlation result includes the steps of;

determining an I_L correlation of the in-phase signal, I, and the third copy of the received signal;

determining a Q_L correlation of the quadrature signal, Q, and the third copy of the received signal;

integrating the I_L correlation and the Q_L correlation, each over a predetection integration interval to generate smooth correlations I_LS, and Q_LS.

4. The method of claim 3 where:

the step of determining the early correlation result includes the steps of;

5. A method for implementing a code tracking loop in a CDMA receiver, the method comprising:

receiving a CDMA-based signal at a receiver front-end;

downconverting the CDMA-based signal to a digital IF signal;

removing a carrier from the digital IF signal to generate a received code signal;

determining an early correlation result between the received code signal and a first copy of the received code signal;

determining a prompt correlation result between the received code signal and a second copy of the received code signal, the second copy of the received code signal phase-lagging the first copy by a correlator spacing;

determining a late correlation result between the received code signal and a third copy of the received code signal, the third copy of the received code signal phase-lagging the second copy by the correlator spacing; and

using a noise-floor independent discriminator to generate an auto-correlation function having a peak correlation and calculating the phase error as a spacing between the prompt correlation and the peak correlation using a function of the prompt, early and late correlations independent of a noise floor estimate.

6. The method of claim 5 where the step of using the noise floor independent discriminator comprises:

calculating the phase error δ

_cp using;

7. The method of claim 5 where:

the received code signal includes an in-phase signal, I, and a quadrature signal, Q;

the step of determining the early correlation result includes the steps of;

determining an I_E correlation of the in-phase signal, I, and the first copy of the received code signal;

determining a Q_E correlation of the quadrature signal, Q, and the first copy of the received code signal;

integrating the I_E correlation and the Q_E correlation, each over a predetection integration interval to generate smooth early correlations I_ES, and Q_ES;

the step of determining the prompt correlation result includes the steps of;

determining an I_P correlation of the in-phase signal, I, and the second copy of the received code signal;

determining a Q_P correlation of the quadrature signal, Q, and the second copy of the received code signal;

integrating the I_P correlation and the Q_P correlation, each over a predetection integration interval to generate smooth prompt correlations I_PS, and Q_PS;

the step of determining the late correlation result includes the steps of;

determining an I_L correlation of the in-phase signal, I, and the third copy of the received code signal;

determining a Q_L correlation of the quadrature signal, Q, and the third copy of the received code signal;

integrating the I_L correlation and the Q_L correlation, each over a predetection integration interval to generate smooth late correlations I_LS, and Q_LS.

8. The method of claim 7 where:

the step of determining the early correlation result includes the steps of;

9. The method of claim 8 where the step of using the noise floor independent discriminator comprises:

calculating the phase error δ

_cp using;

10. The method of claim 8 where:

the received C/A code signal includes an in-phase signal, I, and a quadrature signal, Q;

the step of determining the early correlation result includes the steps of;

determining an I_E correlation of the in-phase signal, I, and the first copy of the received C/A code signal;

determining a Q_E correlation of the quadrature signal, Q, and the first copy of the received C/A code signal;

integrating the I_E correlation and the Q_E correlation, each over a predetection integration interval to generate smooth early correlations I_ES, and Q_ES;

the step of determining the prompt correlation result includes the steps of;

determining an I_P correlation of the in-phase signal, I, and the second copy of the received code C/A signal;

determining a Q_P correlation of the quadrature signal, Q, and the second copy of the received C/A code signal;

integrating the I_P correlation and the Q_P correlation, each over a predetection integration interval to generate smooth prompt correlations I_PS, and Q_PS;

the step of determining the late correlation result includes the steps of;

determining an I_L correlation of the in-phase signal, I, and the third copy of the received C/A code signal;

determining a Q_L correlation of the quadrature signal, Q, and the third copy of the received C/A code signal;

integrating the I_L correlation and the Q_L correlation, each over a predetection integration interval to generate smooth late correlations I_LS, and Q_LS.

11. The method of claim 10 where:

the step of determining the early correlation result includes the steps of;

8-1. A method for processing a received C/A code signal in a delay-locked loop, the method comprising:

determining an early correlation result between the received C/A code signal and a first copy of the received C/A code signal;

determining a prompt correlation result between the received C/A code signal and a second copy of the received C/A code signal, the second copy of the received C/A code signal phase-lagging the first copy by a correlator spacing;

determining a late correlation result between the received C/A code signal and a third copy of the received C/A code signal, the third copy of the received C/A code signal phase-lagging the second copy by the correlator spacing; and

using a noise-floor independent discriminator to generate an auto-correlation function having a peak correlation and calculating the phase error as a spacing between the prompt correlation and the peak correlation using a function of the prompt, early and late correlations independent of a noise floor estimate.

12. A system for code tracking in a CDMA system comprising:

a receiver front-end for receiving a CDMA-based communication signal and generating a digital IF signal;

a carrier removal function for down-converting the digital IF signal to a received C/A code signal having an in-phase signal, I, and a quadrature signal, Q;

a code replica generator for generating three replicas of the received C/A code signal, where the three copies of the received C/A code signal are a early code, a prompt code and a late code;

six code wipeoff correlators to determine a correlation between the in-phase signal, I, and each of the early code, the prompt code and the late code, and between the quadrature signal, Q, and each of the early code, the prompt code and the late code; and

a noise-floor independent delay-lock loop discriminator to calculate a prompt correlation result, an early correlation result and a late correlation result using the six correlations calculated by the six code wipeoff correlators, to generate an auto-correlation function having a peak correlation, and to calculate a phase error as a spacing between the prompt correlation result and the peak correlation using a function of the prompt, early and late correlations independent of a noise floor estimate.

13. The system of claim 12 where the noise floor independent discriminator calculates the phase error δ

_cp using;

14. The system of claim 12 where:

the early correlation result is determined by;

determining an I_E correlation of the in-phase signal, I, and the first copy of the received C/A code signal;

determining a Q_E correlation of the quadrature signal, Q, and

the first copy of the received C/A code signal;

integrating the I_E correlation and the Q_E correlation, each over a predetection integration interval to generate smooth early correlations I_ES, and Q_ES;

the prompt correlation result is determined by;

determining an I_p correlation of the in-phase signal, I, and the second copy of the received code C/A signal;

determining a Q_P correlation of the quadrature signal, Q, and the second copy of the received C/A code signal;

integrating the I_p correlation and the Q_P correlation, each over a predetection integration interval to generate smooth prompt correlations I_PS, and Q_PS;

the late correlation result is determined by;

determining an I_L correlation of the in-phase signal, I, and the third copy of the received C/A code signal;

determining a Q_L correlation of the quadrature signal, Q, and the third copy of the received C/A code signal;

integrating the I_L correlation and the Q_L correlation, each over a predetection integration interval to generate smooth late correlations I_LS, and Q_LS.

15. The system of claim 14 where:

the early correlation result is determined by;

16. A discriminator in a delay-locked loop function comprising:

at least one signal input for receiving an early correlation result from correlating a received code signal and an early code, the early code being a first copy of the received code signal that phase-leads the received code signal by one correlator spacing;

at least one signal input for receiving a prompt correlation result from correlating the received code signal with a prompt code, the prompt code being a second copy of the received code signal that lags the early code in phase by one correlator spacing;

at least one signal input for receiving a late correlation result from correlating the received code signal with a late code, the late code being a third copy of the received code signal that lags the prompt code in phase by one correlator spacing;

an auto-correlation function having a peak correlation; and

a phase error detector to calculate the phase error as a spacing between the prompt correlation result and the peak correlation using a function of the prompt, early and late correlations independent of a noise floor estimate.

17. The discriminator of claim 16 where the phase error detector calculates the phase error δ

_cp using;

18. The system of claim 17 where:

the received code signal includes an in-phase signal, I, and a quadrature signal, Q;

the early correlation result is determined by;

determining an I_E correlation of the in-phase signal, I, and the first copy of the received C/A code signal;

determining a Q_E correlation of the quadrature signal, Q, and the first copy of the received C/A code signal;

integrating the I_E correlation and the Q_E correlation, each over a predetection integration interval to generate smooth early correlations I_ES, and Q_ES;

the prompt correlation result is determined by;

determining an I_P correlation of the in-phase signal, I, and the second copy of the received code C/A signal;

determining a Q_P correlation of the quadrature signal, Q, and the second copy of the received C/A code signal;

integrating the I_p correlation and the Q_p correlation, each over a predetection integration interval to generate smooth prompt correlations I_PS, and Q_PS;

the late correlation result is determined by;

determining an I_L correlation of the in-phase signal, I, and the third copy of the received C/A code signal;

determining a Q_L correlation of the quadrature signal, Q, and the third copy of the received C/A code signal;

integrating the I_L correlation and the Q_L correlation, each over a predetection integration interval to generate smooth late correlations I_LS, and Q_LS.

19. The system of claim 18 where:

the early correlation result is determined by;