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US 7,120,191 B2Granted
Method and apparatus for acquiring a ranging signal of a positioning system
AssigneeNokia Corporation
InventorDavid Akopian
Life of this patent
Estimating the term…
Abstract
A method and corresponding apparatus for accurately determining the offset of the carrier frequency of a received signal from a nominal frequency (the offset due to for example Doppler shifting), such as is done in a ranging receiver when acquiring or tracking a signal transmitted by a beacon (such as a satellite) of a positioning system. The method amplifies a conventional correlation by performing a special noncoherent integration of the real and imaginary components of the output of a conventional (coherent) correlation calculation, resulting in a complex phasor having a phase that bears information about the offset of the carrier frequency from the nominal carrier frequency.
Claims10
A method for determining information about a carrier frequency of a signal transmitted by a possibly moving transmitter, the signal having a code component and a carrier component at the carrier frequency, the method comprising:
- a) responding to successive approximately carrier-demodulated received signal fragments of the signal, and providing a set of correlation results indicating information about a correlation of the successive approximately carrier-demodulated received signal fragments with phase-shifted replicas of the code component, wherein the successive approximately carrier-demodulated received signal fragments are formed using different possible offsets from a nominal carrier frequency, and further wherein each element of the set is provided as a phasor having a magnitude and a phase;
- and
- b) responding to the set of phasors, selecting the phasor having a magnitude distinguishing it from all the other elements of the set, and determining the phase of the selected phasor;
- wherein providing the set of correlation results includes performing a coherent integration of the successive approximately carrier-demodulated received signal fragments, and performing a non-coherent integration in which phasor results of the coherent integrations are combined without regard to phase;
- and
- further wherein performing the non-coherent integration involves multiplying each element of a matrix of correlation results provided using a coherent integration of a first signal fragment, by the complex conjugate of a corresponding element for an immediately preceding signal fragment.
3 more elements
An apparatus for determining information about a carrier frequency of a signal transmitted by a possibly moving transmitter, the signal having a code component and a carrier component at the carrier frequency, the apparatus comprising:
- a) means, responsive to successive approximately carrier-demodulated received signal fragments of the signal, for providing a set of correlation results indicating information about a correlation of the successive approximately carrier-demodulated received signal fragments with phase-shifted replicas of the code component, wherein the successive approximately carrier-demodulated received signal fragments are formed using different possible offsets from a nominal carrier frequency, and further wherein each element of the set is provided as a phasor having a phase and a magnitude;
- and
- b) means, responsive to the set of phasors, for selecting the phasor having a magnitude distinguishing it from all the other elements of the set, and determining the phase of the selected phasor, and for providing information about the carrier frequency based on the phase of the selected phasor;
- wherein the means for providing the set of correlation results includes means for performing a coherent integration of the successive responsive to the carrier-demodulated received signal fragments, and also means, responsive to the coherent integrations, for providing a non-coherent integration in which phasor results of the coherent integrations are combined without regard to phase;
- and
- further wherein the means for performing the non-coherent integration multiplies each element of a matrix of correlation results provided using a coherent integration of a first received signal fragment, by the complex conjugate of a corresponding element for an immediately preceding received signal fragment.
3 more elements
A system, including:
- a transmitter for transmitting a signal having a code component and a carrier component, and a ranging receiver for receiving the signal and for determining information about the carrier frequency of the signal, the ranging receiver characterized in that it comprises:
- a) means, responsive to successive approximately carrier-demodulated received signal fragments of the signal, for providing a set of correlation results indicating information about a correlation of the successive approximately carrier-demodulated received signal fragments with phase shifted replicas of the code component, wherein the successive approximately carrier-demodulated received signal fragments are formed using different possible offsets from a nominal carrier frequency, and further wherein each element of the set is provided as a phasor having a phase and a magnitude;
- and
- b) means, responsive to the matrix of phasors, for selecting the phasor having a magnitude distinguishing it from all the other elements of the set, and determining the phase of the selected phasor, and for providing information about the carrier frequency based on the phase of the selected phasor;
- wherein the means for providing the set of correlation results includes means, for performing a coherent integration of the successive approximately carrier-demodulated received signal fragments, and also means, responsive to the coherent integrations, for providing a non-coherent integration in which phasor results of the coherent integrations are combined without regard to phase;
- and
- further wherein the means for performing the non-coherent integration multiplies each element of a matrix of correlation results provided using a coherent integration of a first received signal fragment, by the complex conjugate of a corresponding element for an immediately preceding received signal fragment.
4 more elements
An apparatus for determining information about a carrier frequency of a signal transmitted by a possibly moving transmitter, the signal having a code component and a carrier component at the carrier frequency, the apparatus comprising:
- a) a first module responsive to successive approximately carrier-demodulated received signal fragments of the signal, for providing a set of correlation results indicating information about a correlation of the successive approximately carrier-demodulated received signal fragments with phase-shifted replicas of the code component, wherein the successive approximately carrier-demodulated received signal fragments are formed using different possible offsets from a nominal carrier frequency, and further wherein each element of the set is provided as a phasor having a phase and a magnitude;
- and
- b) a second module responsive to the set of phasors, for selecting the phasor having a magnitude distinguishing it from all the other elements of the set, and determining the phase of the selected phasor, and for providing information about the carrier frequency based on the phase of the selected phasor;
- wherein the first module includes a first submodule for performing a coherent integration of the successive approximately carrier-demodulated received signal fragments, and also a second submodule, responsive to the coherent integrations, for providing a non-coherent integration in which phasor results of the coherent integrations are combined without regard to phase;
- and
- further wherein the second sub-module for performing the non-coherent integration multiplies each element of a matrix of correlation results provided using a coherent integration of a first received signal fragment, by the complex conjugate of a corresponding element for an immediately preceding received signal fragment.
3 more elements
Dependencies are inferred from the claim text.