Communications: directive radio wave systems and devices (e.g. – Directive – Including a satellite
Reexamination Certificate
2000-03-22
2001-10-23
Phan, Dao (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Including a satellite
C342S462000, C701S213000
Reexamination Certificate
active
06307504
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to satellite positioning systems which use augmentation or aiding from information regarding the altitude of a satellite positioning system receiver.
Conventional satellite positioning systems (SPS) such as the U.S. Global Positioning System (GPS) use signals from satellites to determine their position. Conventional SPS receivers normally determine their position by computing relative times of arrival of signals transmitted simultaneously from a multiplicity of GPS satellites which orbit the earth. These satellites transmit, as part of their message, both satellite positioning data as well as data on clock timing which specifies the position of a satellite at certain times; this data is often referred to as satellite ephemeris data. Conventional SPS receivers typically search for and acquire the SPS signals, read the ephemeris data for a multiplicity of satellites, determine pseudoranges to these satellites, and compute the location of the SPS receivers from the pseudoranges and the ephemeris data from the satellites.
Conventional SPS systems sometimes use altitude aiding to assist in two situations: a case of bad satellite geometry, or a lack of measurements for three dimensional positioning. For most cases, bad satellite geometry is caused by poor observability in the vertical direction. For instance, if the unit vectors to all of the satellites being used in the solution lie on a cone of arbitrary half-angle, then it is possible to place a plane on the top of the tips of the unit vectors if the unit vectors only span a two-dimensional space. The error in the third direction or dimension, which is perpendicular to the plane, is unobservable; this is referred to as a singularity condition. In urban canyon environments with tall buildings surrounding the GPS receiver antenna, the only satellites that are visible are those at high elevation angles. These signal conditions are similar to the singularity condition described herein. Also, large multi-path errors tend to cause large errors in the vertical direction.
Conventional altitude aiding is based on a pseudomeasurement of the altitude that can be visualized as a surface of a sphere with its center at the center of the earth. This sphere has a radius which includes the earth's radius and an altitude with respect to the earth's surface which is typically defined by an ellipsoid (WGS84 is one of the ellipsoidal models). There are numerous techniques which are available to perform altitude aiding, but all techniques rely on an a priori knowledge of the altitude required to define the surface of a sphere which is a magnitude of the altitude pseudomeasurement Typically, an estimated altitude can be manually supplied by the operator of the GPS receiver or can be set to some preset value, such as the surface of the earth or be set to an altitude from a previous three-dimensional solution.
Prior GPS technology has also used altitude aiding in the case where a mobile GPS receiver receives GPS signals but does not compute its position, and relies upon a basestation to perform the position calculations for it U.S. Pat. No. 5,225,842 describes such a system which uses altitude aiding in order to allow the use of only three GPS satellites. The estimated altitude is typically derived from mapping information such as a topological or geodetic database. In this configuration, the altitude information of a basestation may also be available.
A weakness of this approach is that an initial two-dimensional solution is typically made before an altitude aiding with a reasonable altitude estimate can be applied. The altitude can then be extracted from a vertical database as a function of latitude and longitude coordinates.
While the foregoing approaches provide certain advantages from the use of altitude information, they do not work well in the case of a distributed processing system where a mobile GPS receiver may be located in any position over a relatively large geographical area. Moreover, these prior approaches use altitude information with all available pseudoranges even if a particular pseudorange is faulty.
SUMMARY OF THE INVENTION
The present invention provides various methods and apparatuses for determining a position of a mobile satellite positioning system (SPS) receiver with the use of altitude information. In one example of a method of the present invention, a cell object information is determined. This cell object information comprises at least one of a cell object location or a cell object identification. In one example, the cell object may be a cell site and the identification may be an identifier of the cell site and the location may be the latitude and longitude of the cell site. An altitude is determined from the cell object information which is selected based upon a cell site transmitter which is in wireless communication with a cell based communication system which is coupled to (and typically integrated with) the mobile SPS receiver. That is, the altitude is determined from a cell object information which is associated with the cell site transmitter which is in communication with the communication system of the mobile SPS receiver. The position of the mobile SPS receiver is calculated using the altitude which is determined from the cell object information.
In another example of a method according to the present invention, an altitude pseudomeasurement is determined, and this pseudomeasurement uses an estimate of an altitude of the mobile SPS receiver. This estimate of the altitude may be derived from a cell based information source in a cell based communication system or may be an average altitude or other mathematical representation of altitude or altitudes of an area of coverage of a wireless basestation in a non-cell based system. In one implementation, a comparison of the estimate of the altitude to an altitude that is calculated from pseudoranges to SPS satellites (or from pseudoranges and the altitude pseudomeasurement) determines the condition of at least one pseudorange between an SPS satellite and the mobile SPS receiver. In another implementation, the altitude pseudomeasurement may be used as a redundant measurement (with pseudoranges to SPS satellites) and fault detection and isolation techniques may be employed using the redundant measurement to determine the condition (e.g. faulty or non-faulty) of at least one of the pseudoranges or a navigation solution. In one embodiment of this example, the position is determined from a position solution algorithm, and if the condition of a pseudorange is in a first state, such as a non-fault state, the at least one pseudorange is used in the position solution algorithm. A recomputation of a navigation solution may be performed using only non-faulty pseudoranges (after faulty pseudoranges have been identified and excluded from a re-computation of a navigation solution).
Various mobile SPS receivers and basestations are also described herein. Various other aspects and embodiments of the present invention are further described below.
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paten
Blakely & Sokoloff, Taylor & Zafman
Phan Dao
SnapTrack, Inc.
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