Methods and systems for acquisition, reacquisiton and tracking of weak navigational signals
First Claim
1. A method of operating a navigational receiver under weak signal conditions, comprising:
- correlating a received signal with a local signal to obtain correlation samples;
grouping consecutive correlation samples into sub-blocks;
compensating the frequency and phase of the samples in each sub-block;
determining frequency components of the sub-blocks;
determining a frequency compensation based on the frequency components;
performing a long coherent integration over a block of consecutive sub-blocks; and
using a reference signal from an external communication system.
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Accused Products
Abstract
Provided herein are systems and methods for achieving long coherent integration in a navigational receiver to improve the sensitivity of the receiver and enable the receiver to acquire, reacquire and track signals under very weak signal conditions. In an embodiment, phase compensation is computed based on estimated Doppler frequency, rate of change of the Doppler frequency with time, and second order rate of change of the Doppler frequency. The Doppler frequency may be computed from an orbital model or ephemeris. This phase compensation is used to compensate samples of the input signal for changes in the phase due to the Doppler frequency. Frequency components of the phase-compensated samples are then computed using a frequency analysis such as a Fast Fourier Transform (FFT). The maximum frequency component is taken as an error frequency and used to compensate the samples of the input signal for residual frequency error.
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Citations
33 Claims
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1. A method of operating a navigational receiver under weak signal conditions, comprising:
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correlating a received signal with a local signal to obtain correlation samples; grouping consecutive correlation samples into sub-blocks; compensating the frequency and phase of the samples in each sub-block; determining frequency components of the sub-blocks; determining a frequency compensation based on the frequency components; performing a long coherent integration over a block of consecutive sub-blocks; and using a reference signal from an external communication system.
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2. A method of operating a navigational receiver under weak signal conditions, comprising:
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correlating a received signal with a local signal to obtain correlation samples; grouping consecutive correlation samples into sub-blocks; compensating the frequency and phase of the samples in each sub-block, wherein each sub-block is frequency and phase compensated by rotating all the samples of the sub-block by a phase of a reference sample within the sub-block; determining frequency components of the sub-blocks; determining a frequency compensation based on the frequency components; and performing a long coherent integration over a block of consecutive sub-blocks. - View Dependent Claims (3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22)
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23. A method of operating a navigational receiver under weak signal conditions, comprising:
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correlating a received signal with a local signal to obtain correlation samples; grouping consecutive correlation samples into sub-blocks; compensating the frequency and phase of the samples in each sub-block; determining frequency components of the sub-blocks; determining a frequency compensation based on the frequency components; and performing a long coherent integration over a block of consecutive sub-blocks, wherein a weighting factor is used with the said long integration.
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24. A method of operating a navigational receiver under weak signal conditions, comprising:
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correlating a received signal with a local signal to obtain correlation samples; grouping consecutive correlation samples into sub-blocks; compensating the frequency and phase of the samples in each sub-block; determining frequency components of the sub-blocks; determining a frequency compensation based on the frequency components; and
performing a long coherent integration over a block of consecutive sub-blocks, wherein both data aided and non-data aided methods of integration are used.
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25. A navigational satellite receiver, comprising:
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a radio frequency front-end for receiving satellite signals; a baseband section for processing the received signals into correlation samples; and a processor coupled to the baseband section, wherein the processor groups consecutive correlation samples into sub-blocks, compensates the frequency and phase of the samples in each sub-block wherein the processor frequency and phase compensates each sub-block by rotating all the samples of the sub-block by a phase of a reference sample within the sub-block, computes frequency components of the sub-blocks, computes a frequency compensation based on the frequency components, and performs a long coherent integration over a block of consecutive sub-blocks. - View Dependent Claims (26, 27, 28, 29, 30, 31, 32, 33)
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Specification