Patent Application
20110307171
A well-known problem with GPS signals is that they are not always available to a GPS receiver.
Areas where a GPS signal cannot be detected or where its signal strength is too weak to be used by a GPS receiver 230 are considered herein to be areas of poor GPS visibility. When the GPS signal is lost or too weak as happens in an area of poor GPS visibility, GPS navigation is not possible. A method or an apparatus for locating or deriving a geographical location upon the loss of a GPS signal would be an improvement over the prior art.
The apparatus in
The computer 310 can be coupled to so-called on-board memory as well as memory that is accessible via the address, data and control bus 320 for the computer 310. Address, data and control busses for computers are well-known in the art and couple the computer to a GPS receiver 230. A description of the nature and operation of a computer bus is omitted for brevity.
In addition to being coupled to the GPS receiver 230, the computer 310 also communicates via the bus 320 with a two-way wireless communication device that provides a data link 330. The computer is therefore coupled to the data link device. In one embodiment, the data link device 330 can be embodied as a cellular telephone. In other embodiments a transceiver compatible with the I.E.E.E. standards 802.11(a), (b), (g) or (n) can be used. A WI-MAX transceiver or other two-way data communications device can also be used.
An electronic compass 340 provides a digital representation of the direction in which the vehicle moves. A vehicle speed sensor 350 provides a digital representation of the vehicle's instantaneous speed. A timer is provided by the computer 310. The compass, speed and time are considered to be sensor data that is provided by corresponding sensors/hardware well known to those of ordinary skill. A digitized map data base 360 and a user interface 370 are also coupled to the computer 310 via the bus 320, as is a cell phone tower database 380.
The on-board computer 310 executes program instructions that are stored in memory. The instructions imbue the computer with the ability to perform two similar methods of GPS location refinement in environments with a low GPS satellite visibility, both of which are depicted in
If a map or maps of the nearby terrain can be stored locally, i.e. within the computer 310 or accessible to it, program execution proceeds to step 420, where the first step of a first method of GPS location refinement determines whether the GPS receiver 230 is entering into an area of poor GPS signal visibility. An area of poor GPS signal visibility is considered to be one where GPS satellite signal strength is too weak for a GPS receiver to use or where the signals are missing.
Areas of poor GPS visibility can be determined simply by measuring the received signal strength. In an alternate embodiment however, the map database 360 stores information that identifies areas that are known to have weak or missing GPS signals. By using GPS location information continuously or nearly continuously, the computer 310 can determine whether entry into an area of poor GPS visibility is imminent or whether it has already happened.
At step 420, if the GPS SSI indicates that signal loss is not imminent, a location is determined using GPS as indicated by step 422
At step 432, the determined location is used to display the vehicle's location, area landmarks, points of interest, etc. on a display device. The determined location is also provided various other on-board applications for use inside the vehicle 240, an example of which includes the so-called “ON-STAR” vehicle tracking system.
Referring again to step 420, if it is determined that the vehicle 240 is inside or entering an area of poor signal strength, the first location refine methodology downloads a map of the surrounding area using the last known good coordinates from the GPS receiver, if such a map is not already stored in the map database 360. The download of local area features and map data is provided by the data link device 330. The resolution of the downloaded map is a design choice and will effectively determine the time required to download the data necessary to determine using subsequent steps where the vehicle 240 is located.
At step 426, a second test is performed to determine whether the GPS signal has in fact been lost or is unusable. If the GPS signal has not been lost, program control returns to step 422 where the location is determined using GPS signals as before. If the GPS signal has been lost, at step 428 the vehicle's current location is estimated using the last known good GPS location and on-board sensors. The on-board sensors used for estimating the vehicles current location include the vehicle's electronic compass 340, speed sensor 350 and a timer.
The current location can be calculated or estimated using a compass, timer and a speed sensor to determine how far a vehicle has gone in various different directions. The calculation of displacement is a simple computation.
At step 430, the estimated current location that is determined using the on-board sensors is compared to maps stored in the map database 360. The map-matching step 430 checks the validity/accuracy of the calculated location against local terrain information in the maps. If for example the estimated location places the vehicle inside a building, body of water or other impossible location, software in the computer 310 can perform a best-fit correction of the estimated location. At step 432 the corrected location determined in step 430 is used for the on-board applications as described above. From step 432, program execution returns to step 420 in order to re-check whether the vehicle is still located within an area of poor GPS signal visibility.
Not all GPS-enabled navigation systems store local copies of maps. Some GPS-based navigation systems use a GPS receiver to determine latitude and longitude but rely on maps that are downloaded to the vehicle in real time and which are then displayed on a screen with the current location data determined using a GPS signal.
In
If it is determined at step 440 that the GPS signal is lost, the on-board computer 310 estimates the vehicles current location using the most recently-available GPS location and the aforementioned on-board sensors 340, 350 and a timer function provided by the computer 310 or an external timer not shown.
The estimated or calculated location is transferred by the wireless data link device 330 to a remotely-located server at step 448. Not shown in
The server performs map matching as described with step 430 and sends the updated location back to the vehicle 240 via the wireless data link 330 as indicated by step 450.
Having received the updated location response a step 450, the method next displays and makes that updated location available for use by vehicle on-board applications as described above.
The map matching called out in step 430 and performed by the receiver as a result of step 448 is well known and described in various prior art publications. See for example the article entitled “IN-VEHICLE ROUTE GUIDANCE SYSTEMS USING MAP MATCHED DEAD RECKONING” by W. Clay Collier CH2811-8/90/0000/0359 copyright 1990 I.E.E.E. see also the article entitled “THE TRAVEL PILOT: A SECOND-GENERATION AUTOMOTIVE NAVIGATION SYSTEM,” by James L. Buxton, et al., published in the I.E.E.E. Transactions on Vehicular Technology, Volume 40, No. 1, February 1991 at page 41.
Paraphrased, map matching is a process by which small vectors present in an observed track are combined to produce larger vectors. The process essentially concactinates co-linear segments and breaks the concagnation at points where the vehicle has turned. The result of segmentation is a segmented track congruent with an observed track but composed of fewer elements.
Map matching compares a segmented track against a map database and a planned route to follow the progress of the vehicle and to correct for errors in the dead-reckoning process. The output of a map matching process is a list containing the current position, a current heading, a current speed, and a current map segment being traveled. Each element of the list corresponds directly to a node in the map database a current position and a degree of certainty are derived by comparing the segmented track to the map database and a planned route to find the path in the database which most closely matches the route in the segmented track. This is accomplished using a search tree called the historical track. The route of the historical track is the last location in which the vehicles location was known with a high degree of certainty such as just prior to GPS signal loss.
Those of ordinary skill in the art will recognize that areas of poor GPS visibility can be stored in the map database 360 as they are encountered. Over time, an accurate record of locations or areas of poor GPS visibility will be created in the map database. Over time, the steps of determining whether entry into such an area is imminent can be made simply by reading the database and comparing a current location to a previously-determined or known area of poor GPS visibility. This would allow optional configuration without data link 330.
The apparatus and method described herein is for purposes of illustration only. The true scope of the invention is set forth in the appurtenant claims.
