Patent Description:
For example, it is possible for satellite signals to reflect off of nearby structures before being received by the navigation system antenna or detector. Such reflections increase the distance travelled by the signal before reaching the antenna or detector compared to a signal travelling directly from the satellite to the antenna or detector. Since a known position of the satellite from which such a signal originates is used for determining the location of the vehicle, any intermediate reflection and resulting increased signal travel distance can introduce errors in the vehicle location determination.

The publication <CIT> discloses a vehicle locating system that can detect the occurrence of a multipath error in a Global Positioning System (GPS) signal path. Two pseudo distances to the same GPS satellite are calculated by using a first and a second GPS antenna. Corrective data for differential GPS (DGPS) are received by an FM antenna, an FM receiver and a decoder and outputted to a CPU. When a difference between the two pseudo distances is above a first predetermined value and a change in the corrective data is below a second predetermined value, the CPU judges that a multipath error occurs.

An illustrative example embodiment of a system includes a detector configured to detect a signal from a source and provide first signal information regarding a distance a detected signal traveled between the source and the detector, wherein the at least one detector is associated with a vehicle. A processor is configured to determine whether the first signal information corresponds to a direct signal path between the detector and the source or the first signal information corresponds to a reflected signal based on second signal information from at least one other detector, wherein the at least one other detector is movable relative to the vehicle. The processor determines a location of the detector based on the first signal information only when the first signal information corresponds to the direct signal path between the detector and the source. The processor is further configured to determine a position of the at least one other detector relative to the vehicle, determine a position of the vehicle relative to the at least one source, determine whether at least one portion of the vehicle obstructs a direct signal path between the at least one source and the at least one other detector based on the determined positions, and determine that the at least one other detector does not have a direct signal path between the at least one other detector and the at least one source and that the second signal information corresponds to a reflected signal between the at least one source and the at least one other detector when the at least one portion of the vehicle obstructs the direct signal path.

In an example embodiment including at least one of the features of the system of the previous paragraph, the first signal information comprises a pseudo range between the at least one source and the at least one detector, and the second signal information comprises a distance traveled by a reflected signal between the at least one source and the at least one other detector.

In an example embodiment including at least one of the features of the system of any of the previous paragraphs, the processor is configured to determine that the first signal information corresponds to a reflected signal by determining a difference between the pseudo range of the first signal information and the distance of the second signal information and determining that the determined difference is below a threshold.

In an example embodiment including at least one of the features of the system of any of the previous paragraphs, the processor is configured to determine that the first signal information corresponds to a reflected signal by determining that the pseudo range of the first signal information is greater than the distance of the second signal information.

In an example embodiment including at least one of the features of the system of any of the previous paragraphs, the determined location is a location of the vehicle.

In an example embodiment including at least one of the features of the system of any of the previous paragraphs, the at least one portion of the vehicle comprises a vehicle roof and the processor uses information regarding at least one of a size of the roof and a shape of the roof to determine that the roof obstructs the direct signal path between the at least one source and the at least one other detector.

In an example embodiment including at least one of the features of the system of any of the previous paragraphs, the at least one source is a satellite having a known location within an earth centered earth fixed reference frame.

An illustrative example embodiment of a method includes: detecting a signal from at least one source, generating first signal information regarding a distance the detected signal traveled between the at least one source and at least one detector, wherein the at least one detector is associated with a vehicle, and determining whether the first signal information corresponds to a direct signal path between the at least one detector and the at least one source or the first signal information corresponds to a reflected signal based on second signal information from at least one other detector, wherein the at least one other detector is movable relative to the vehicle, and determining a location of the at least one detector based on the first signal information when the first signal information corresponds to the direct signal path between the at least one detector and the at least one source. The method further comprises determining a position of the at least one other detector relative to the vehicle, determining a position of the vehicle relative to the at least one source, determining whether at least one portion of the vehicle obstructs a direct signal path between the at least one source and the at least one other detector based on the determined positions, determining that the at least one other detector does not have a direct signal path between the at least one other detector and the at least one source and that the second signal information corresponds to a reflected signal between the at least one source and the at least one other detector when the at least one portion of the vehicle obstructs the direct signal path.

In an example embodiment including at least one of the features of the method of the previous paragraph, the first signal information comprises a pseudo range between the at least one source and the at least one detector and the second signal information comprises a distance traveled by a reflected signal between the at least one source and the at least one other detector.

An example embodiment including at least one of the features of the method of any of the previous paragraphs includes determining that the first signal information corresponds to a reflected signal by determining a difference between the pseudo range of the first signal information and the distance of the second signal information and determining that the determined difference is below a threshold.

An example embodiment including at least one of the features of the method of any of the previous paragraphs includes determining that the first signal information corresponds to a reflected signal by determining that the pseudo range of the first signal information is greater than the distance of the second signal information.

In an example embodiment including at least one of the features of the method of any of the previous paragraphs, the method comprises determining a location of the vehicle based on the determined location of the at least one detector.

<FIG> schematically illustrates a system <NUM> including a detector <NUM> and a processor <NUM>. The detector <NUM> includes an antenna or another device capable of detecting a signal from at least one source. In the embodiment shown in <FIG> the detector <NUM> is configured to detect satellite signals from a satellite <NUM>. Only one satellite is shown for discussion purposes but the detector <NUM> will often detect multiple satellites. The detector <NUM> is configured to generate first signal information regarding a distance that a detected signal travels between the satellite <NUM> and the detector <NUM>.

The processor <NUM> includes a computing device and associated memory. The processor <NUM> in some embodiments is a device dedicated to processing signals from the detector <NUM> while in other embodiments the processor <NUM> is a device that performs other functions that may be unrelated to processing signals from the detector <NUM>. The processor <NUM> is configured to determine whether the first signal information from the detector <NUM> corresponds to a direct signal path between the detector <NUM> and the satellite <NUM> or if the first signal information corresponds to a reflected signal. The processor <NUM> makes this determination based upon second signal information from at least one other detector <NUM> that provides the second signal information. When the detector <NUM> does not have a direct signal path between it and the satellite <NUM>, any second signal information from the detector <NUM> regarding a signal detected from the satellite <NUM> is the result of a reflected signal detected by the detector <NUM>.

In the embodiment shown in <FIG>, the system <NUM> is associated with a vehicle <NUM> and is useful for determining a location of the vehicle <NUM>. The detector <NUM> is located within the vehicle <NUM> such that one or more portions of the vehicle <NUM> obstructs a direct signal path between the detector <NUM> and the satellite <NUM> under at least some conditions.

The condition shown in <FIG> includes a direct signal path <NUM> from the satellite <NUM> to the detector <NUM>. First signal information from the detector <NUM> resulting from detecting a signal that travels along the direct signal path <NUM> is useful for determining a location of the detector <NUM> and the vehicle <NUM> because the satellite <NUM> has a known position relative to an earth centered earth fixed (ECEF) reference frame.

In the condition shown in <FIG>, it is also possible for the detector <NUM> to detect a signal from the satellite <NUM> that is a reflected signal, which should not be used for making location determinations because the distance traveled by a reflected signal will introduce errors into the location determination, which is based in part on the known location of the satellite <NUM>. For example, a signal from the satellite <NUM> may travel along the path shown at <NUM> and reflect off a structure <NUM>, such as a building nearby the path of the vehicle <NUM>. The reflected signal may follow a path as schematically shown at <NUM> and be detected by the detector <NUM>. The distance traveled by the signal following the path <NUM>, <NUM> is different than the distance of a signal following the direct signal path <NUM> between the satellite <NUM> and the detector <NUM>. The processor <NUM> utilizes first signal information from the detector corresponding to a signal following the direct signal path <NUM> but does not use first signal information from the detector <NUM> resulting from a reflected signal detected by the detector <NUM>.

The processor <NUM> uses second signal information from at least one other detector, such as the detector <NUM> situated in the vehicle <NUM>, to determine whether the first signal information corresponds to a reflected signal. Given the current location of the satellite <NUM> and the position of the vehicle <NUM> relative to the satellite <NUM>, no direct signal path exists between the satellite <NUM> and the detector <NUM>. The potential direct signal path <NUM> is obstructed by the roof <NUM> of the vehicle <NUM>. The position of the detector <NUM> in the vehicle <NUM> does allow for the detector <NUM> to detect a reflected signal from the satellite <NUM>. For example, a signal following the path schematically shown at <NUM>, reflecting off the structure <NUM> and then following the path schematically shown at <NUM> may pass through the windshield of the vehicle <NUM> and be detected by the detector <NUM>. The processor <NUM> receives second signal information from the detector <NUM> indicating or corresponding to the distance traveled by the reflected signal following the path <NUM>, <NUM>. The processor <NUM> uses such second signal information for determining whether first signal information from the detector <NUM> should be used for purposes of determining a location of the detector <NUM> and the vehicle <NUM>.

<FIG> includes a flowchart diagram <NUM> that summarizes an example method of determining the location. At <NUM>, the detector <NUM> detects a signal from the satellite <NUM>. At <NUM>, the detector <NUM> generates first signal information regarding the distance the detected signal traveled between the satellite <NUM> and the detector <NUM>. In this example embodiment, the first signal information comprises a pseudo range corresponding to the distance the signal traveled. The first signal information is provided to the processor <NUM>. At <NUM>, the processor <NUM> determines whether the first signal information corresponds to a direct signal path distance or a reflected distance based on second signal information from the detector <NUM>, which is another pseudo range in this example. The processor <NUM> determines a difference between the distance of the first signal information and the distance of the second signal information. The processor <NUM> determines whether the difference between the distances of the first signal information and the second signal information is below a threshold or within a preselected range. When the second signal information is known to correspond to a reflected signal and the distance of the first signal information is sufficiently close to the distance of the reflected signal, the processor <NUM> determines that the first signal information is the result of the detector <NUM> detecting a reflected signal rather than a signal following a direct signal path between the satellite <NUM> and the detector <NUM>.

For example, when the location of interest is the location of the vehicle <NUM>, it can be assumed that any nearby structure <NUM> from which a satellite signal may reflect resulting in a reflected signal is at least <NUM> meters away from the vehicle <NUM>. A reflected signal likely will travel through such a spacing twice resulting in about three meters difference between the distance traveled by the reflected signal and a direct signal path that does not involve a reflection off that nearby structure <NUM>. In this example, whenever the difference between the distances of the first signal information and the second signal information is within three meters, the processor <NUM> determines that the pseudo range or distance of the first signal information is the result of a reflected signal because the second signal information is known to be the result of detecting a reflected signal.

At <NUM>, the processor <NUM> determines the location of the detector <NUM> or the vehicle <NUM> based on the first signal information when the first signal information corresponds to detecting a signal received along a direct signal path. In some embodiments any signal that appears to be a reflected signal is rejected or excluded from the information used to determine the location of the vehicle <NUM> but some embodiments include using such signal information when a sufficiently reliable correction or adjustment can be made by the processor <NUM>.

In some embodiments forming part of the prior art and not forming part of the present invention the detector <NUM> is part of the system <NUM> and situated in a known position on the vehicle <NUM> where the detector <NUM> is likely to only be able to detect reflected signals from the satellite <NUM>. For example, the detector <NUM> may be situated relative to the interior of the vehicle <NUM> where the detector <NUM> will be effectively shielded by the roof of the vehicle <NUM> from any direct signal paths from the satellite <NUM> or other satellites that may be used for location determinations. In such embodiments forming part of the prior art and not forming part of the present invention, the second signal information from the detector <NUM> is always known to correspond to a reflected signal.

In other embodiments, the detector <NUM> may be situated on the vehicle <NUM> in a location where a direct satellite signal path may be obstructed depending on the relative position of the vehicle <NUM> and the satellite <NUM>. For example, there may be conditions under which the detector <NUM> has a direct line of sight through the windshield of the vehicle <NUM> to one or more satellites depending on the relative positions between such satellites and the vehicle <NUM>.

<FIG> includes a flowchart diagram <NUM> that summarizes an example technique by which the processor <NUM> determines whether second signal information from the detector <NUM> corresponds to a reflected signal. At <NUM>, the processor <NUM> determines a position of the detector <NUM> relative to the vehicle. This may be accomplished in different ways known to those skilled in the art depending on the embodiment. In embodiments forming part of the prior art and not forming part of the present invention, when the detector <NUM> is in a dedicated location on or in the vehicle <NUM>, the position of the detector <NUM> is known. In other embodiments, the detector <NUM> is moveable relative to the vehicle <NUM>, such as when the detector <NUM> is a personal communication device that has GPS capability, such as a cell phone. The processor <NUM> in such embodiments utilizes known locating techniques for locating a position of the detector <NUM> relative to the vehicle <NUM>. In an example, the position of the moveable detector relative to the vehicle is determined using radio frequency transmissions from the detector that are received by a plurality of antennas distributed about the vehicle. In this example, the plurality of antennas may be components of a passive entry/passive start (PEPS) system that may be installed on the vehicle. Details for determining the position of the moveable detector are disclosed in <CIT>.

At <NUM>, the processor <NUM> determines a location of the vehicle <NUM> relative to the satellite <NUM>. This may be accomplished, for example, by using a last known position or location of the vehicle <NUM> and the currently known position of the satellite <NUM>, which is available through a known GNSS almanac to which the processor <NUM> has access. Based on that relationship and the position of the detector <NUM> relative to the vehicle <NUM>, the processor <NUM> is able to determine whether a portion of the vehicle <NUM> obstructs a direct signal path between the satellite <NUM> and the detector <NUM>, which provides the second signal information at <NUM>.

In some embodiments, the processor <NUM> is provided with information regarding the size, shape or both of the vehicle roof <NUM> and uses that information combined with the relative positions of the vehicle <NUM> and the satellite <NUM> for determining when the roof <NUM> would obstruct a direct signal path between the detector <NUM> and the satellite <NUM>.

The illustrated example embodiment provides enhanced accuracy for location determinations, such as locating a vehicle. Accurate vehicle location is useful for guided navigation or autonomous vehicle control. By eliminating reflected signals from location determinations, the example system increases the accuracy and reliability of location determinations allowing for satisfying more stringent margin of error requirements.

The various features of the disclosed embodiments are not necessarily limited to the arrangements that are shown. Other combinations of the disclosed features are possible to realize additional or different embodiments.

Claim 1:
A system (<NUM>), comprising:
at least one detector (<NUM>) configured to detect a signal from at least one source (<NUM>) and provide first signal information regarding a distance a detected signal traveled between the at least one source (<NUM>) and the at least one detector (<NUM>), wherein the at least one detector (<NUM>) is associated with a vehicle (<NUM>); and
a processor (<NUM>) that is configured to
determine whether the first signal information corresponds to a direct signal path (<NUM>) between the at least one detector (<NUM>) and the at least one source (<NUM>) or the first signal information corresponds to a reflected signal (<NUM>, <NUM>) based on second signal information from at least one other detector (<NUM>), wherein the at least one other detector (<NUM>) is movable relative to the vehicle (<NUM>), and
determine a location of the at least one detector (<NUM>) based on the first signal information when the first signal information corresponds to the direct signal path (<NUM>) between the at least one detector (<NUM>) and the at least one source (<NUM>),
characterized by
the processor (<NUM>) being further configured to
determine a position of the at least one other detector (<NUM>) relative to the vehicle (<NUM>);
determine a position of the vehicle (<NUM>) relative to the at least one source (<NUM>);
determine whether at least one portion of the vehicle (<NUM>) obstructs a direct signal path (<NUM>) between the at least one source (<NUM>) and the at least one other detector (<NUM>) based on the determined positions; and
determine that the at least one other detector (<NUM>) does not have a direct signal path between the at least one other detector (<NUM>) and the at least one source (<NUM>) and that the second signal information corresponds to a reflected signal (<NUM>, <NUM>) between the at least one source (<NUM>) and the at least one other detector (<NUM>) when the at least one portion of the vehicle obstructs the direct signal path (<NUM>).