Communications: directive radio wave systems and devices (e.g. – Directive – Including a satellite
Reexamination Certificate
1998-09-19
2001-03-13
Tarcza, Thomas H. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Including a satellite
C342S357490, C701S215000
Reexamination Certificate
active
06201497
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to facilitating the use of radio signals for positioning and navigation where a barrier (solid or non-solid) precludes direct usage of public line-of-sight radio positioning
avigation beacons. Although several embodiments of the present invention are described herein, the focus is on the use of repeated geometrically non-linear Global Navigation Satellite System signals within a line-of-sight barrier.
DISCUSSION OF THE PRIOR ART
A common need of our society is to accurately track and record positions of aircraft, land vehicles, geographical landmarks, materials, buildings, animals, people, and other items. One system currently used to accomplish this goal in direct line-of-sight is use of public radio positioning
avigation signals and associated equipment. Radio positioning
avigation can be broadly defined as the use of radio waves to transmit information, which in turn can then be received and utilized to determine position and to navigate. Some radio positioning
avigation systems currently in use are Loran, Omega, LMN, DGPS, and Global Navigation Satellite Systems (GNSS) such as NAVSTAR, GLONASS (the Russian variant), and European systems (GNSS1, GNSS2, NAVSTAT and GRANAS). The radio navigation systems quickly becoming the standard worldwide are Global Navigation Satellite Systems (GNSS) including, in the United States, the NAVSTAR Global Positioning System.
The NAVSTAR GPS signal transmission system presently consists of twenty-four orbiting satellites, spaced in six separate circular orbits, with each accommodating four satellites. Of these, twenty-one are normally operational and three serve as spares. Each NAVSTAR GPS satellite reappears above the same ground reference approximately every twenty-three hours and fifty-six minutes. The spacing of satellites is designed to maximize probability that earth users will always have at least four satellites in good geometrical view for navigational use.
The basic method of position determination via radio positioning and navigation signals derives from the concept of triangulation. The term triangulation used herein refers to the general process of determining distance, a.k.a. range, from the present position to multiple known beacons, and mathematically solving for the point in space which satisfies these conditions. As applied to GNSS, the procedure requires calculation of signal travel time, which, when multiplied by the speed of light, renders distance.
In support of this computation, the normal radio signals transmitted by each broadcasting NAVSTAR GPS satellite are currently configured as follows: a 1575.42 MHZ “L1” carrier modulated by the 10.23 MHZ P-code (Precision), the 1.023 MHZ C/A-code (Coarse/Acquisition), and the 50 Hz navigation code; and a 1227.60 MHZ “L2” carrier modulated by the 10.23 MHZ P-code and the 50 Hz navigation code. Because the system was principally designed for military use, the P-code is classified, and the L2 carrier is not officially supported for civilian use.
Each satellite repeats its pre-defined, unique 1023-bit C/A-code every millisecond. This code identifies the sending satellite and, since the pattern is exactly known, the code-point at which the signal arrives serves as a marker for estimating arrival time (complex algorithms are applied for refining measurement accuracy).
The NAVSTAR GPS navigation message transmits various data including precise time information every six seconds, orbital parameters (ephemeris data), correction statistics, and satellite status. The basic data is divided among five frames over thirty seconds, with the total message spread over 12.5 minutes. The layout of data is designed such that once a receiver has accumulated the necessary background data, it acquires an update of precise time every six seconds from which navigation calculations can be made. The position of the satellite at time of transmission is computed based on its known orbital path along with current ephemeris data.
Initial range calculations are called “pseudoranges” since receiver clocks are not precisely synchronized to NAVSTAR GPS time, and propagation through the atmosphere introduces delays into the navigation signal propagation times. These result, respectively, in clock bias error and atmospheric bias error. Clock bias errors may be as large as several milliseconds.
Conventionally, a minimum of four GNSS satellites are sampled to determine a terrestrial position estimate (e.g. Cartesian X,Y,Z coordinates; or longitude, latitude, and altitude in any of various systems including WGS84, NAD83, NAD27, Indian, etc.). Three of the satellites are used for basic triangulation, and a fourth is used to solve for clock bias between the satellite system and the receiver. Ephemeris correction statistics from the navigation message assist in amelioration of atmospheric bias.
Other errors which affect GNSS position computations include receiver noise, signal reflections, shading, satellite path shifting, and in the case of NAVSTAR GPS, purposely induced accuracy degradation called selective availability (S/A).
A process known as differential positioning compensates for many of the errors which are common in radio positioning
avigation systems. An antenna at a known location receives line-of-sight (LOS) GNSS signals and broadcasts a signal with current correction adjustments for each satellite which can be received by any differential receiver within its signal range.
Location accuracy via GNSS is continually evolving. Standard GNSS receivers can typically produce position estimates within ±60-100 meter accuracy. Sub-meter accuracy of location can be achieved using differential positioning, known as DGPS. Some other techniques for improving accuracy are “Carrier-phase GPS”, “Augmented GPS”, and GPS Interferometry.
GNSS relies on no visual, magnetic, or other point of reference and this is particularly important in applications such as aviation and naval navigation that traverse polar regions where conventional magnetic navigational means are rendered less effective by local magnetic conditions. Magnetic deviations and anomalies common in standard radio positioning
avigation systems do not hinder GNSS. In addition, GNSS equipment is typically fabricated of standard, solid state electronic hardware, resulting in low cost, low maintenance systems, having few or no moving parts, and requiring no optics. GNSS does not have the calibration, alignment, and maintenance requirements of conventional inertial measuring units. Also, GNSS is available 24 hours per day on a worldwide basis.
During the development of the NAVSTAR GPS program the United States Government made decisions to extend its use to both domestic and international communities. Its applications range from navigation over the land, in the air, and on the seas, to precision surveys, the tracking of trains and trucks, and even locating undetonated mines left behind in the Gulf War. It is important to note that GNSS solutions are only accomplished when the GNSS receiver is in direct line-of-sight (LOS) with the orbiting GNSS satellites. In other words, if the GNSS receiver's antenna is used in heavily forested areas, in steep and narrow canyons, within a structure, or adjacent to the outer walls of buildings, the GNSS receiver will be unable to obtain a good repeatable reading, or in many cases, any reading at all.
What is needed is a system that relays GNSS signals beyond a line-of-sight barrier (LSB) and mathematically corrects satellite pseudorange calculations to account for geometrically nonlinear satellite signal paths. The result of such a system is accurate, consistent readings for multitudes of applications which need, or require, positioning and navigation information when out of the line of sight of a GNSS satellite system.
SUMMARY OF INVENTION
The present invention provides a system for use of GPS receivers separated by a barrier from being in the line of sight of orbiting GNSS satellites, hereinafter referred to as “within a line-of-sight barrier”. An e
Baych Leslie D.
Melick Bruce D.
Snyder David M.
DLB Limited
Harms Allan L.
Mull Fred H.
Tarcza Thomas H.
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