Pulse or digital communications – Equalizers – Automatic
Reexamination Certificate
1997-11-04
2001-08-07
Pham, Chi (Department: 2631)
Pulse or digital communications
Equalizers
Automatic
C375S340000, C375S350000
Reexamination Certificate
active
06272174
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention generally relates to the field of radio-frequency receivers, and more particularly to a method for increasing signal acquisition in global positioning system receivers.
Conventional global positioning system (GPS) receivers integrate the baseband quadrature components, implement a power detection function, and then follow this with post detection summation. If the frequency error is large, the signal will not be acquired because of the effective bandwidth of the coherent integration process. This requires multiple searches. A solution to the problem is to shorten the sampling interval and implement a banked filter process such as a Fast Fourier transform (FFT). The multiple outputs from the FFT can then be detected and summed in post detection filters. However, the Fast Fourier transform has several disadvantages. First, if the signal frequency falls between FFT frequency bins, it will be significantly attenuated. Second, if the signal frequency is near the outer edges of the FFT response, it will be attenuated by the integration process prior to sampling. Third, the FFT requires multiplication if more than four points are used. Fourth, utilization of an FFT typically produces frequency bins with frequencies up to plus and minus one-half the interval between samples, thereby causing the frequency bins on the extremes of the pattern to be unusable because of the attenuation caused by integration over the segment period.
SUMMARY OF THE INVENTION
Accordingly, it is a goal of this invention to provide an algorithm for a banked filter for reducing the acquisition time of global positioning system (GPS) receivers. The present invention provides low attenuation between frequency bins in which all of the frequency bins produce useful results and no multiplications are required to implement the algorithm.
Slight variations to the banked filter may be utilized having varying numbers of frequency bins. For example, designs having three, four, five and ten frequency bins may be implemented.
The invention is planned for most future military GPS receivers and for the application specific integrated circuits such as an acquisition correlation engine chip. Other applications may include extended range guided munition (ERGM), MAGR, and any other GPS products.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention as claimed.
The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate an embodiment of the invention and together with the general description, serve to explain the principles of the invention.
REFERENCES:
patent: 5257211 (1993-10-01), Noga
patent: 5375146 (1994-12-01), Chalmers
patent: 5537435 (1996-07-01), Carney et al.
patent: 5650785 (1997-07-01), Rodal
patent: 5706202 (1998-01-01), Itahara et al.
patent: 5809060 (1998-09-01), Cafarella et al.
patent: 5841811 (1998-11-01), Song
Corrielus Jean B
Eppele Kyle
Jensen Nathan O.
O'Shaughnessy James P.
Pham Chi
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