Downconvert and average identification of biphase coded signal carrier

Abstract

An improved apparatus and method for determining the carrier frequency in a biphase coded signal such as the course acquisition code signal in a global position sensing system. The described system may also be used for other purposes. The described system is based on use of the conventional data signal squaring or frequency doubling step to remove biphase coding but performs a series of frequency reducing steps prior to applying the Fourier transformation sequence. The frequency reducing steps include heterodyne mixing and signal averaging. These frequency-reducing steps diminish the speed and capacity requirements imposed on the Fourier transformation sequence and thereby decrease the cost and complexity of the overall system.

Description

RIGHTS OF THE GOVERNMENT[0001]The invention described herein may be manufactured and used by or for the Government of the United States for all governmental purposes without the payment of any royalty.BACKGROUND OF THE INVENTION[0002]In order to acquire and process a biphase-coded signal such as the NAVSTAR / global position system (GPS) Coarse / Acquisition or Clear / Acquisition [C / A] code signal one needs to find the carrier frequency and the initial phase in the suppressed carrier signal received from a GPS satellite. The purpose of the acquisition system usually employed in a GPS receiver is to accomplish just these carrier frequency and initial phase determination functions in a signal, which actually has no carrier presence. Such an acquisition system in fact needs to perform a two-dimensional searching, i.e., searching in time and searching in frequency. This operation is time consuming; however, if one of the quantities is identified the other can be obtained rather easily becaus...

AI Technical Summary

Benefits of technology

"The present invention provides a simplified method for determining the carrier frequency of a biphase coded signal using frequency doubling. This method involves converting the signal to a digital format, squaring the data, and removing the DC component. The method can be used in real-time or off-line modes and can be implemented as a software or hardware algorithm. The invention also provides a composite lowered frequency representation of the biphase code-modulated input signal, which simplifies the identification of carrier frequency components. The technical effects of the invention include simplifying the overall frequency determination process and reducing the complexity of the carrier frequency determination arrangement."

Problems solved by technology

This operation is time consuming; however, if one of the quantities is identified the other can be obtained rather easily because the search then becomes one-dimensional in nature.

In a real world environment with noise-inclusive signals this squaring process has the effect of increasing the noise component in the processed signal, especially under conditions where the noise is of greater magnitude than the signal and the bandwidth is relatively large.

To perform Fourier transformation on a long data record is however complicated and time consuming.

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