Pseudorandom noise ranging receiver which compensates for multipath distortion by making use of multiple correlator time delay spacing

• US 5,414,729 A
• Filed: 11/29/1993
• Issued: 05/09/1995
• Est. Priority Date: 01/24/1992
• Status: Expired due to Term

• Current Assignee: Novatel Incorporated (Hexagon AB)
• Original Assignee: Novatel Communications Ltd (Hexagon AB)
• Inventors: Fenton, Patrick
• Primary Examiner(s): Cain, David C.
• Application Number:
  US08/158,511
• Time in Patent Office: 526 Days
• Field of Search: 375/1, 380/34, 380/46, 342/357
• US Class Current: 375/149
• CPC Class Codes: G01S 19/22 Multipath-related issues
• CPC Class Codes: H04B 1/7085 using a code tracking loop, e.g. a delay-locked loop
• CPC Class Codes: H04B 1/709 Correlator structure

Abstract

A receiver for pseudorandom noise (PRN) encoded signals consisting of a sampling circuit, multiple carrier and code synchronizing circuits, and multiple digital correlators. The sampling circuit provides digital samples of a received composite signal to each of the several receiver channel circuits. The synchronizing circuits are preferably non-coherent, in the sense that they track any phase shifts in the received signal and adjust the frequency and phase of a locally generated carrier reference signal accordingly, even in the presence of Doppler or ionospheric distortion. The multiple correlators in each channel correlates the digital samples with locally generated PRN codes having multiple offsets, to produce a plurality of correlation signals. The plurality of correlation signals are fed to a parameter estimator, from which the delay and phase parameters of the direct path signal, as well as any multipath signals, may be estimated, and from which a range measurement may be corrected.

Claims

1. A receiver for demodulating and decoding a composite radio frequency (RF) signal consisting of a plurality of transmitted pseudorandom noise (PRN) encoded signals comprising:

an RF downconverter, connected to receive the composite RF signal and to provide a composite intermediate frequency (IF) signal;

means for generating a local sample clock signal;

a sampling circuit, connected to receive the composite IF signal and the local sample clock signal, and to provide digital in-phase (I) samples and quadrature (Q) samples of the composite IF signal;

a plurality of channel circuits, each channel circuit for demodulating and decoding one of the transmitted PRN encoded signals, and connected in parallel with the other channel circuits such that the each channel circuit receives the I samples and Q samples at the same time as the other channel circuits, wherein each channel circuit further comprises;

a PRN code signal generator, connected to receive a synchronizing adjustment signal and to provide a local reference PRN code signal;

means for decoding the I and Q sample signals, connected to receive the I samples, the Q samples, and the local reference PRN code signal, the decoding means for multiplying the I and Q samples by the local reference PRN code signal, and providing decoded I and Q samples;

autocorrelation means, connected to receive the decoded I and Q samples, for determining the autocorrelation power level at multiple code phase delays; and

parameter estimator means, connected to receive the autocorrelation power level at multiple code phase delays, for determining paramenters of a direct path signal to the receiver.

2. A receiver as in claim 1 wherein each channel circuit further comprises:

means for providing an expected carrier phase signal;

a synchronizing circuit, connected to receive the sample clock signal, the expected carrier phase signal, and a synchronizing adjustment signal, and connected to provide an accumulated carrier phase signal and a PRN code phase control signal, the accumulated carrier phase signal and PRN code phase signals being synchronous with each other;

carrier rotation means, connected to receive the I samples, the Q samples, and the accumulated carrier phase signal, for phase-rotating the I and Q samples by an amount indicated by the accumulated carrier phase signal;

wherein the autocorrelation means provides the synchoronizing adjustment signal to the synchronizing circuit, and

wherein the PRN code phase signal is provided to the PRN code signal generator.

3. A receiver as in claim 1 wherein the autocorrelation power level is determined at more than three code phase delay points.

4. A receiver as in claim 1 wherein the direct path signal parameter being estimated is a direct path code tracking error.

5. A receiver as in claim 1 wherein the direct path signal parameter being estimated is a direct path carrier phase tracking error.

6. A receiver as in claim 1 wherein the parameter estimator means also estimates the phase tracking error of one or more multipath signals.

7. A receiver as in claim 1 wherein the parameter estimator means also estimates the carrier tracking error of one or more multipath signals.

8. A receiver as in claim 1 wherein the autocorrelation power level at multiple code phase delays is determined by a like multiple number of physical correlator circuits.

9. A receiver as in claim 1 wherein the autocorrelation power level at multiple code phase delays is determined by a adjusting the code delay spacing of one or more physical correlator circuits.

10. A receiver for demodulating and decoding a composite radio frequency (RF) signal consisting of a plurality of transmitted pseudorandom noise (PRN) encoded signals comprising:

an RF downconverter, connected to receive the composite RF signal and to provide a composite intermediate frequency (IF) signal;

means for generating a local sample clock signal;

a sampling circuit, connected to receive the composite IF signal and the local sample clock signal, and to provide digital in-phase (I) samples and quadrature (Q) samples of the composite IF signal;

a plurality of channel circuits, each channel circuit for demodulating and decoding one of the transmitted PRN encoded signals, and connected in parallel with the other channel circuits, such that each channel circuit receives the I samples and Q samples at the same time as the other channel circuits, wherein each channel circuit further comprises;

means for providing an expected carrier phase signal;

a synchronizing circuit, connected to receive the sample clock signal, the expected carrier phase signal, and a synchronizing adjustment signal, and connected to provide an accumulated carrier phase signal and a PRN code phase control signal, the accumulated carrier phase signal and code phase signals being synchronous with each other;

a PRN code signal generator, connected to receive the PRN code phase control signal and to provide a local reference PRN code signal;

decoding and carrier rotation means, including means for simultaneously demodulating and decoding the I and Q sample signals, connected to receive the I samples, the Q samples, the local reference PRN code signal, and the accumulated carrier phase signal, the demodulating means for phase-rotating the I and Q samples by an amount indicated by the carrier phase signal, and the decoding means for multiplying the I and Q samples by the local reference PRN code signal, and providing decoded I and Q samples;

correlation means, connected to receive the decoded I and Q samples, for determining multiple correlation power levels for at least three code phase delays;

parameter estimating means, connected to receive the multiple correlation power levels, and for providing and estimate of a direct path time delay and one or more multipath time delays to the receiver; and

means for providing the synchronizing adjustment signal to the synchronizing circuit by comparing the estimates of the direct path time delay and the one or more multipath time delays, wherein

a first and second code phase delay are dynamically narrowed by being set to a predetermined wide correlator delay equal to a PRN code chip time during an initial PRN code lock acquisition period, and by being set thereafter to a predetermined narrow correlator delay equal to a fraction of a PRN code chip time.

11. A method for demodulating and decoding a composite signal consisting of a plurality of transmitted pseudorandom noise (PRN) encoded signals comprising:

sampling the composite signal in synchronism with a local sample clock signal, and thereby providing digital in-phase (I) samples and quadrature (Q) samples of the composite signal;

feeding the I samples and Q samples to a plurality of channel circuits, each channel circuit connected in parallel with the other channel circuits such that each channel circuit receives the I samples and Q samples at the same time as the other channel circuits;

within each channel circuit;

generating a local reference PRN code signal in response to a synchronizing adjustment signal;

decoding the I and Q samples, by multiplying the I and Q samples by the local reference PRN code signal, and in response thereto, producing decoded I and Q samples;

determining the correlation power level of the I and Q samples at multiple code phase delays; and

estimating the parameters of a direct signal path to the receiver from the correlation power levels at the multiple code phase delays.

12. A method as in claim 11 further comprising:

providing an expected carrier phase signal;

producing an accumulated carrier phase signal and a PRN code phase control signal which are synchronous with one another, by combining the sample clock signal, the expected carrier phase signal, and a synchronizing adjustment signal; and

phase-rotating the I and Q samples by an amount indicated by the accumulated carrier phase signal.

13. A method as in claim 11 wherein the correlation power level is determined at more than three code phase delays.

14. A method as in claim 11 wherein the direct path signal parameter being estimated is a direct path code tracking error.

15. A method as in claim 11 wherein the direct path signal parameter being estimated is a direct path carrier phase tracking error.

16. A method as in claim 11 wherein a phase tracking error of one or more multipath signals is also estimated.

17. A method as in claim 11 wherein a carrier tracking error of one or more multipath signals is also estimated.

18. A method as in claim 11 wherein the autocorrelation power level at multiple code phase delays is determined by a like multiple number of physical correlator circuits.

19. A receiver as in claim 11 wherein the autocorrelation power level at multiple code phase delays is determined by a adjusting the code delay spacing of one or more physical correlator circuits.