US 5,414,729 AGranted

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

AssigneeNovAtel Communications Ltd.

InventorPatrick Fenton

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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.

Claims19

Dependent claims

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.

6 more elements

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.

10 more elements

Dependencies are inferred from the claim text.