Data processing: vehicles – navigation – and relative location – Navigation – Employing position determining equipment
Reexamination Certificate
1998-08-10
2001-01-30
Chin, Gary (Department: 3661)
Data processing: vehicles, navigation, and relative location
Navigation
Employing position determining equipment
C342S357490, C342S357490
Reexamination Certificate
active
06182011
ABSTRACT:
ORIGIN OF THE INVENTION
The invention described herein was made by an employee of the United States Government. This invention may be manufactured and used by or for the Government for governmental purposes without the payment of any royalties thereon or therefor.
TECHNICAL FIELD
The present invention relates generally to a method and apparatus for determining the position of an object, and more particularly to a method and apparatus for determining the position of an object using a low cost global positioning satellite receiver, such as balloon radiosondes, sonobuoys, ships, land vehicles and other objects on or near the earth's surface, using satellites of the Global Positioning System (GPS).
BACKGROUND ART
A very low cost GPS receiver is highly desirable in any application which involves a mobile segment and a fixed segment in which there is a telemetry link such as a cellular telephone system or balloon radiosondes.
For instance, a cost effective method to accurately locate a Cell phone user who has made a 911 telephone call is highly desirable.
In addition, many thousands of balloon radiosondes are launched yearly in the world. Most of these are launched from commercial airports twice daily to gather meteorological data, such as data on winds aloft for flight planning purposes. Another large user of balloon radiosondes are the armed forces who need to know winds aloft in connection with artillery and missile trajectory projections. Currently, most balloon radiosondes use one of the following to determine balloon position:
Loran Transponder
Omega Transponder
Radar Tracking
Radiotheodolite Tracking.
Both Loran and Omega are scheduled for termination within the next 20 years. Radar tracking is prohibitively expensive for most synoptic applications. Radiotheodolite tracking systems are expensive to maintain and suffer from multi-path problems at low tracking elevations. Accordingly, a need for a low cost global positioning satellite receiver has arisen.
The United States government has placed a number of satellites in orbit as part of the Global Positioning System (GPS). A GPS receiver simultaneously or sequentially receives signals from four or more satellites to determine various parameters, such as time, receiver position and velocity. Each satellite transmits two L-band signals known as L
1
(1.57542 GHz) and L
2
(1.2277 GHz), using a spread spectrum technique in which the carriers are bi-phase modulated with a pseudo random number (PRN) sequence or code. The L
2
band transmits a code available only to authorized users and is not used in the current invention. In fact, the L
1
carrier is modulated with two PRN codes, a coarse, acquisition (C/A) code and a precision (P) code and is available to any user, military or civilian. Each satellite is assigned a unique C/A and P code sequence. For the purpose of the following Disclosure, we are only interested in the C/A code modulation of the L
1
carrier.
In order to determine position in three dimensions, a receiver must simultaneously or sequentially track at least four satellites. A GPS receiver is able to track a given GPS satellite when it can synchronize an internally generated replica of the C/A code with the C/A code being transmitted by the satellite. In a typical GPS receiver, the L
1
signal is received by an antenna, bandpass filtered, amplified by a low noise amplifier (LNA) and then down converted to an intermediate frequency (IF) by mixing with the multiplied output of a voltage controlled oscillator (VCO). The resulting IF signal is then de-spread or correlated with an internally generated version of the satellite's C/A code sequence. A raw pseudo-range is determined by observing where in the C/A code sequence that correlation occurs at some instant in time. “Raw” refers to the determination of position prior to microprocessor compensation for clock errors, atmospheric effects, and other known factors. At least four Pseudo-ranges are processed to determine a receiver's position.
Virtually all conventional GPS receiver designs make use of a Costas Loop to decode a 50 bit per second navigation message and also use either a Costas Loop or a separate carrier tracking loop to phase lock a local oscillator to the satellite carrier and to compensate for Doppler effects.
Additionally, a codeless GPS receiver has been developed for use in balloon radiosondes as a low cost alternative to a traditional code tracking receiver. In the codeless receiver, the L
1
signal is stripped of its bi-phase modulation by means of a squaring technique and then carrier Doppler information is analyzed to determine receiver velocity and position. By converting the GPS signal into two quadrature components and then multiplying the two quadrature components together, the
180_spread spectrum code is removed from the carrier frequency. The multiplied result is bandpass filtered to pass two times the expected Doppler frequency shift from which velocity information is subsequently derived.
Finally, a method is known to the art in which the wideband spread spectrum L
1
signals from a plurality of satellites is frequency compressed and its Fourier components analyzed to extract velocity and position information.
The limitations of GPS technologies currently known to the art contribute to the complexity and cost of current receivers. Correlation must be performed at a down-converted frequency, requiring a local oscillator and mixer. The alternative codeless technique suffers from a signal-to-noise inefficiency which impairs the accuracy of determining position and velocity.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a method for determining the position of an object.
It is another object of the present invention to provide an apparatus for determining the position of an object.
It is yet another object of the present invention to provide a method for determining the position of an object using a global positioning satellites.
It is also an object of the present invent on to provide a low cost apparatus for determining the position of an object using a global positioning satellites.
It is an additional object of the present invention to provide a low cost method and apparatus for determining the position of an object using a global positioning satellites that does not perform correlation on a down-converted signal.
It is a further object of the present invention to provide a low cost method and apparatus for determining the position of an object using a global positioning satellites that has good signal-to-noise efficiency in order to accurately determine position and velocity of the object.
These and other objects can be achieved according to the principles of the present invention wherein a method for generating pseudo-range data and pseudo-range rates in a global positioning satellite receiver for transmission to a ground station sequentially generates pseudo-random noise codes corresponding to known satellite codes in response to address signals received from a microprocessor, generates a de-spread signal by de-spreading a radio frequency signal in response to the generated pseudo-random noise codes, detects when the de-spread signal is indicative of correlation between the radio frequency signal and the generated pseudo-random noise codes, and generates pseudo range data upon correlation.
Additionally, these and other objects can be achieved according to the principles of the present invention wherein a global positioning satellite receiver having an antenna for receiving a L
1
signal from a satellite and a preamplifier for converting the L
1
signal to a radio frequency signal wherein the global positioning satellite receiver generates pseudo-range data and pseudo-range rates for transmission to a ground station and incorporates a pseudo-random noise code generator for sequentially generating pseudo-random noise codes corresponding to known satellite codes in response to address signals received from a microprocessor, a correlation mixer for de-spreading the radio frequency s
Chin Gary
The United States of America as represented by the Administrator
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