Method and system for determining the altitude of a mobile wireless device

A method and system for determining the three-dimensional location of a mobile wireless device. In one implementation, the device is a cellular telephone making a 911 call from one floor of a multi-story building. An embodiment of the method of the invention includes establishing a database that associates transmission metrics with altitudes of x-y coordinate locations having more than one altitude at which the mobile wireless device could be located, receiving a communication from the mobile wireless device, determining an x-y coordinate location of the mobile wireless device, measuring a transmission metric of the mobile wireless device, and consulting the database to determine the altitude from the x-y coordinate location and the measured transmission metric. The transmission metric could be, for example, the transmission time or angle of arrival of a wireless signal received from the mobile wireless device.

BACKGROUND

1. Field of the Invention

The present invention relates generally to determining the location of a mobile wireless device, and more particularly, to determining the altitude of a wireless telephone caller with respect to a particular x-y coordinate location.

2. Background of the Invention

When a 911 emergency center receives a call, the ability to accurately locate the caller can dramatically affect the degree of success emergency personnel have in responding to the need for help. Dispatching the emergency personnel to the correct location is crucial to administering help as quickly as possible. When a person dials 911 from a traditional wireline telephone, the emergency center identifies the number of the wireline telephone and cross-references that number with an address database to determine the location of the wireline telephone, and thus the location of the caller.

Wireless telephones, however, are not fixed in a single location and therefore are not associated with any particular address. Thus, without a means for determining the location of the mobile wireless telephone, the emergency center must rely on the caller's knowledge and communication of her location, which often leads to errors. The inability to determine the location of a wireless caller is compounded by the fact that an increasing number of 911 calls are coming from wireless telephones. Indeed, studies indicate that approximately 45 million Americans made 911 calls from wireless telephones in the year 2000. In some areas, wireless 911 telephone calls account for fifty to seventy percent of the call volume coming into public centers.

Recognizing the need to automatically determine the location of wireless telephone callers, in 1996, the Federal Communications Commission required wireless network operators to have the ability to determine the location of wireless 911 callers by October 2001. As a result, wireless operators have developed what are generally referred to as enhanced 911, or E911, services. These services typically identify the latitude and longitude (i.e., x and y coordinates) of a wireless device that is making a 911 call.

E911 services help ensure that wireless telephones provide 911 call centers, or Public Safety Answering Points (PSAPs), with the vital information necessary to locate and identify a caller in an emergency. The E911 standards promulgated by the Federal Communications Commission (FCC) require wireless network providers to track the location and identity information of all wireless callers, with the purpose of providing such information to emergency personnel when a caller dials 911 from a wireless telephone.

Under the FCC rules, wireless networks and the corresponding wireless handheld devices, such as cellular telephones, will provide both the identity and location of the caller to a 911 dispatcher. To provide a caller's identity, the wireless handheld device will furnish a device identification, e.g., a mobile identification number (MIN), indicating in most instances the telephone number of the device. The wireless network and wireless handheld devices will provide the location of callers using a network-based location system (e.g., triangulation), global positioning systems (GPSs) within the handheld devices, or a combination of the two systems.

When conventional E911 systems provide only a longitude and latitude for a wireless device, the systems assume that a device could be found at only one possible altitude of that location. Thus, for example, given x-y coordinates corresponding to a soccer field, emergency responders can assume that the wireless device is on the soccer field at the reported x-y coordinates. As another example, given x-y coordinates corresponding to a single-level highway, emergency responders can assume that the wireless device is on the highway at the reported x-y coordinates.

In many situations, however, buildings and irregular topography provide several different altitudes or elevations at which the wireless device could be located on the same x-y coordinates. For example, in a skyscraper, the same x-y coordinates could correspond to a device located on the first floor or the eightieth floor. An emergency responder arriving at the skyscraper, knowing only the x-y coordinates, would therefore be unable to quickly determine on which floor the emergency is occurring.

FIG. 1illustrates this skyscraper problem, in which a coordinate X,Y within the footprint of building100is reported by the E911 location service. That particular coordinate X,Y could correspond to a device anywhere along the axis Z for the entire height H of building100. Thus, the taller building100is, the more difficult it is to determine the exact location (i.e., altitude) of the calling wireless device.

As another example, on an interchange between major highways, several roads and ramps may pass under and over each other. The same x-y coordinates could correspond to a device located, for example, on the lowest road or a bridge passing high above. Knowing only the x-y coordinates, an emergency responder would have to guess on which road the emergency is occurring.

FIG. 2illustrates this situation, in which a first road200passes underneath a second road202. A particular coordinate X1,Y1 is reported by the E911 location service. However, as shown, that particular coordinate X1,Y1 could correspond to a point on road200at a first altitude A1 or to a point on road202above at a second altitude A2. Thus, knowing only the coordinate X1,Y1, an emergency dispatcher does not know whether to send responders to road200or road202.

SUMMARY OF THE INVENTION

The present invention provides a method and system for determining the three-dimensional location of a mobile wireless device. Given an x-y coordinate location of a mobile wireless device, the present invention determines the altitude at which the mobile wireless device is located. In this manner, the present invention provides a more accurate location determination in situations in which a mobile wireless device could be found at different altitudes on the same x-y coordinates. This enhanced location method can therefore significantly improve the ability of emergency personnel to quickly locate and reach wireless telephone callers in need of help.

An embodiment of the present invention provides a method for determining the altitude of a mobile wireless device that includes establishing a database that associates transmission metrics with altitudes of x-y coordinate locations having more than one altitude at which the mobile wireless device could be located, receiving a communication from the mobile wireless device, determining an x-y coordinate location of the mobile wireless device, measuring a transmission metric of the mobile wireless device, and consulting the database to determine the altitude from the x-y coordinate location and the measured transmission metric. The x-y coordinate location can be determined by, for example, a global positioning system, signal attenuation, angle of arrival (AOA), time of arrival (TOA), time difference of arrival (TDOA), enhanced observed time of arrival (E-OTD), time advance (TA), or a combination of any of the foregoing. The transmission metric could be, for example, the time a wireless signal takes to travel from the mobile wireless device to a fixed wireless signal receiver and/or the angle of arrival of a wireless signal from the mobile wireless device. Optionally, the transmission metric is measured from more than one wireless signal receiver.

Another embodiment of the present invention provides a system for determining the altitude of a mobile wireless device that includes a wireless signal receiver, a location system, a database, and a processor. The wireless signal receiver is in communication with the mobile wireless device. The location system is adapted to determine an x-y coordinate location of the mobile wireless device. The database contains x-y coordinates at which the mobile wireless device could be located at more than one altitude. The database also associates possible altitudes with each x-y coordinate location and associates a value of a transmission metric with each possible altitude. The transmission metric relates to a wireless signal received by the wireless signal receiver from the mobile wireless device. The processor is adapted to receive a current x-y coordinate location of the mobile wireless device from the location system, to measure a current value of the transmission metric, and to retrieve an altitude associated with the current x-y coordinate location and the current value from the database.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides the three-dimensional location of a mobile wireless device. Given a particular x-y coordinate location from which a mobile wireless device is transmitting, the present invention provides the altitude of the device. Optionally, the present invention also provides a description that correlates the altitude with the physical structure or topography of the x-y coordinate location.

FIG. 3illustrates an exemplary system300for determining the three-dimensional location of a wireless device, according to an embodiment of the present invention. As shown, system300includes a plurality of mobile wireless devices302, a wireless service provider304, and a location requestor306.

Mobile wireless devices302include any communication device supported by wireless service provider304. Common examples of wireless devices include cellular telephones, cellular telephones with text messaging capabilities, wireless personal digital assistants (PDAs), and interactive text pagers. A mobile wireless device302can include a mobile location system308, which determines the x-y coordinates of the device302. As an example, mobile location system308could be a global positioning system.

Wireless service provider304provides the communications network that supports the plurality of mobile wireless devices302. In this embodiment, wireless service provider304also includes one or more network-based location systems310and an altitude processor312. Network-based location systems310provide the x-y coordinates of mobile wireless devices302, and can use technologies such as signal attenuation, angle of arrival, time of arrival, time difference of arrival, enhanced observed time of arrival, time advance, and global positioning systems (e.g., GPS systems in which network components receive raw GPS data from mobile devices and calculate exact locations from the data). Altitude processor312determines the altitude or elevation of a mobile wireless device302, given the x-y coordinates of the device. This determination is based on the time it takes for a wireless signal to travel from the wireless device302to a wireless signal receiver of wireless service provider302and/or on the angle at which the signal arrives at the wireless signal receiver. Knowing the time or angle, altitude processor312consults an altitude database314to retrieve an associated altitude and, optionally, a description of the altitude.

AlthoughFIG. 3shows network-based location systems310and altitude processor312as part of wireless service provider304, one of ordinary skill in the art would appreciate that these components could be separate from wireless service provider304, for example, as a part of a location service provider.

Location requester306is the entity that is requesting the three-dimensional location of a wireless device. For example, in an emergency, location requestor306would be a 911 emergency call center, also known as a Public Safety Answering Point (PSAP). As another example, location requester306could be a retail store that occupies several floors of a building and desires the ability to track the location of customers among the several floors.

When a mobile wireless device302is in operation, wireless service provider304tracks the location and identity of the device. Each of the plurality of mobile wireless devices302provides wireless service provider304with its identities, typically as a mobile identification number (MIN). For tracking location and providing x-y coordinates, system300could have individual location systems308in mobile wireless devices302, could have a network-based location system310as part of wireless service provider304, or could use a combination of both systems308and310. As an example, a typical network-based location system would be a system that calculates triangulation across cell sites or cell sectors. A typical example of a suitable individual location system would be a global positioning system.

With continuing reference toFIG. 3,FIG. 4illustrates an exemplary method for determining the altitude of a mobile wireless device, according to an embodiment of the present invention. This exemplary method encompasses two phases: an altitude database creation phase400and an altitude determination phase402. In the altitude database creation phase400, transmission metric data is collected for x-y coordinate locations having more than one possible altitude and is stored in a database that correlates the transmission metric data to the different altitudes of the x-y coordinate locations. As an example, this phase could involve a technician visiting a multi-story building, collecting transmission metric data for each level of the building, and entering the data in a database. In the altitude determination phase402, a wireless service provider receives the x-y coordinate location of a communicating mobile wireless device, measures a transmission metric of the communicating mobile wireless device, and consults the database to determine the altitude of the device.

As shown inFIG. 4, the method begins at step410of altitude database creation phase400with the identification of x-y coordinates that have more than one possible altitude at which a wireless device could be located. Such x-y coordinates could correspond to, for example, multi-story buildings, highway interchanges, stadiums, and multi-level parking garages.

Having identified x-y coordinates with multiple possible altitudes, the method continues in step412by determining a wireless signal transmission metric associated with each possible altitude (i.e., each possible z coordinate). In one embodiment, this transmission metric is the time that a wireless signal takes to travel from the mobile wireless device302at the x-y-z location to the wireless signal receiver of the network of wireless service provider304. In another embodiment, this transmission metric is the angle of arrival of the wireless signal at the wireless signal receiver.

FIG. 5illustrates the measurement of transmission time for different possible altitudes. As shown, this example includes a wireless signal receiver500on a cellular tower502. Wireless signal receiver500is in communication with an altitude database504, which corresponds to database314ofFIG. 3. Altitude database504could reside in a mobile switching center of the network of wireless service provider304.

FIG. 5illustrates two examples of x-y coordinates from which a mobile wireless device could transmit from different altitudes. In the first example, the intersection of highways506and508at coordinates X2,Y2 shows two altitudes Z2 and Z2′ at which a mobile wireless device could be located. Altitude Z2 corresponds to highway506, while altitude Z2′ corresponds to highway508. Because the distance between wireless signal receiver500and altitude Z2 differs from the distance between wireless signal receiver500and Z2′, the measured transmission times also differ, as represented by time T2and T2′. In other words, a wireless signal from a mobile wireless device302located on highway506at coordinates X2,Y2,Z2 takes time T2to travel to wireless signal receiver500. A mobile wireless device302located on highway508at coordinates X2,Y2,Z2′ takes time T2′ to travel to wireless signal receiver500.

In the second example, a multi-story building510is located at coordinates X3,Y3, which includes several floors on which a mobile wireless device could be located. Altitude Z3 corresponds to the second floor, while altitude Z3′ corresponds to the eightieth floor. Again, because the distance between wireless signal receiver500and altitude Z3 differs from the distance between wireless signal receiver500and altitude Z3′, the measured transmission times also differ, as represented by time T3and T3′. Thus, a wireless signal from a mobile wireless device302located on the second floor of building510at coordinates X2,Y2,Z3 takes time T3to travel to wireless signal receiver500. A wireless signal from a mobile wireless device302located on the eightieth floor of building510at coordinates X2,Y2,Z3′ takes time T3′ to travel to wireless signal receiver500.

To measure transmission time, a preferred embodiment of the present invention uses the time-division multiple access (TDMA) digital cellular system. This system tracks the time that wireless signals take in traveling from handsets to mobile stations. As another option, the TDMA-based Global System for Mobile Communications (GSM) digital cellular system could be used, which also tracks transmission times between handsets and mobile stations.

As another example of a transmission metric,FIG. 6illustrates the measurement of transmission angle of arrival for two different possible altitudes Z4 and Z4′ at a building600located at coordinates X4,Y4. Altitude Z4 corresponds to the fifth floor of building600, while altitude Z4′ corresponds to the fortieth floor. As shown, this example includes a wireless signal receiver600on a cellular tower602. To measure signal angles, wireless signal receiver600includes a directional antenna, such as a phased array of two or more antenna elements. Wireless signal receiver600is in communication with an altitude database604, which corresponds to database314ofFIG. 3. Altitude database604could reside in a mobile switching center of the network of wireless service provider304.

As shown inFIG. 6, the measured angle of arrival differs for each altitude Z4 and Z4′. Thus, wireless signal receiver600receives a signal from a mobile wireless device302located at X4,Y4,Z4 at an angle θ, and receives a signal from a mobile wireless device302located at X4,Y4,Z4′ at an angle θ′. In this example, the angle of arrival is measured with respect to a horizontal axis606.

As with transmission times, the TDMA and GSM digital cellular systems can also be used to measure angle of arrival. Indeed, using TDMA and GSM systems to determine both transmission times and also angles of arrival enables more accurate altitude determinations, as described in more detail below in reference toFIG. 8.

Returning toFIG. 4, with the transmission metric measured, the method continues in step414by storing the altitudes and metrics associated with each x-y coordinate location. These associations are stored in altitude database314. Specifically, each x-y coordinate location is associated with all of its possible altitudes, and with a transmission metric for each of the possible altitudes. Thus, for the highway example ofFIG. 5, coordinate X2,Y2 would be associated with altitudes Z2 and Z2′. In turn, altitude Z2 would be associated with T2and altitude Z2′ would be associated with T2′.

Optionally, altitude database314could also include a description of the altitude that would help a person understand the location. For example, the description “Interstate 95” could be associated with altitude Z2 to describe highway506.

FIG. 7illustrates an example table700of the associations stored in altitude database314. In column702, the x-y coordinate entries (X2,Y2), (X3,Y3), and (X4,Y4) correspond to the examples shown inFIGS. 5 and 6. Column704lists the possible altitudes at which a mobile wireless device302could be found at each of these locations. Column706lists the transmission metric associated with each altitude, such as a time of transmission of a wireless signal or an angle of arrival of a wireless signal. Finally, column708lists a common name or description that gives an ordinary meaning to the altitude. For example, altitude Z3 at coordinates X3,Y3 is described as the second floor of the building.

With altitude database314populated, the altitude database creation phase400is complete, as shown inFIG. 4. The exemplary method continues in the altitude determination phase402. In this phase, wireless signal provider304receives a communication from a mobile wireless device302and determines the three-dimensional location of the mobile wireless device302based on the altitude data collected in phase400.

The altitude determination phase402begins in step416when a communication is received from a mobile wireless device302for which three-dimensional location information is desired. In this example, location requestor306is the entity that desires the location information. As an example, the communication could be a 911 call from a wireless telephone (mobile wireless device302), and location requester306could be a Public Safety Answering Point.

Once the communication is in progress, the method continues by determining the x-y coordinates of the mobile wireless device302. This location determination is accomplished by mobile location system308, network-based location systems310, or some combination thereof. The location determination can also include the retrieval of a description associated with the x-y coordinates, such as a building name, street address, or highway interchange number. Thus, at the end of step418, wireless service provider304knows the x-y coordinate location of the mobile wireless device302, along with a description of the x-y coordinate location, if applicable.

Given the x-y coordinates, in step420, altitude processor312of wireless service provider304measures a transmission metric associated with the mobile wireless device302. In a first embodiment, this transmission metric is the time that a wireless signal takes to travel from mobile wireless device302to a wireless signal receiver of wireless service provider304. Taking the skyscraper example ofFIG. 5, the time for a wireless signal to travel from a mobile wireless device302located on the eightieth floor of building510to wireless signal receiver500would be measured as T3′.

In a second embodiment, the transmission metric is the angle of arrival of a wireless signal from the mobile wireless device302. Considering the example ofFIG. 6, the angle at which a wireless signal is received from a mobile wireless device302on the fortieth floor of building600would be measured as θ′.

Thus, at the end of step420, wireless service provider304has the x-y coordinates of the mobile wireless device302, as well as a measured transmission metric associated with the mobile wireless device302. In step422, altitude processor312looks up the given x-y coordinates in altitude database314. In the exemplary table700ofFIG. 7, altitude processor312would search the x-y coordinate column702.

After locating the appropriate x-y coordinate entry in altitude database314, in step424, altitude processor312looks in the entry for the transmission metric that was measured in step420(or a value that is substantial equivalent to the measured transmission metric, e.g., within some acceptable range of measuring error). After locating the metric, in step426, altitude processor312retrieves the altitude associated with the metric. Thus, for example, referring toFIG. 7, given coordinate X2,Y2 and metric T2′, altitude processor312would retrieve the altitude Z2′.

Optionally, in step426, if a description has been associated with the retrieved altitude in altitude database314, then altitude processor312retrieves that description as well. Continuing the previous example, altitude processor312would retrieve the description “Route 1,” which is associated with altitude Z2′. This description correlates the altitude to the actual physical structure or topography located at the given x-y coordinates. For example, a person trying to find a mobile wireless device that is located in a building would understand the description “10th floor” better than the altitude of one hundred feet.

As the final step of altitude determination phase402, wireless service provider304reports the three-dimensional location of the mobile wireless device302to location requestor306in step428. This three-dimensional location includes the x-y coordinates, the altitude, and descriptions of the x-y coordinates and altitude, if applicable.

As one of ordinary skill in the art would appreciate, implementations of the present invention must take into consideration the resolution capabilities of the systems and equipment used to determine the x-y coordinate location and the transmission metric of the mobile wireless device. Ideally, location systems308and310would be able to determine x-y coordinates with an error of less than one foot in either the x or y direction. This level of accuracy would ensure that a measured difference in transmission metric (e.g., time) is attributable to a change in altitude, rather than an error in the x-y coordinates (i.e., an error range in the x-y plane). For example, if, because of the limited accuracy of the location systems308and310, the mobile wireless device could be found anywhere within a 4000 square foot area of the reported x-y coordinates, then the measured transmission metric (e.g., time or angle of arrival) could vary over the 4000 square foot area even though the altitude is the same. The difference in the measured transmission metric could therefore be mistaken for a different altitude. Thus, location systems308and310preferably have accuracies that minimize this effect.

Similarly, one of ordinary skill in the art would also appreciate that the equipment used to measure the transmission metric should be sensitive enough to measure differences between mobile wireless devices transmitting at different altitudes. For example, measuring equipment located at a base station one mile away from the x-y coordinates should be sensitive enough to distinguish between the differences in transmission time or angle between two different altitudes. In this way, for example, the equipment would be able to measure the time of transmission from one floor of a building as different duration (e.g., one nanosecond longer) than the transmission time from the next floor up. Of course, the desired accuracy of the altitude determination is also a factor. If a user merely needs to know whether a mobile wireless device is located in the bottom half or top half of a tall building, then a greater error factor in the measured transmission metric could be tolerated.

To compensate for limited accuracy of x-y coordinate determinations and to resolve ambiguities in measured transmission metrics, an embodiment of the present invention determines altitude using more than one transmission metric. For example, both transmission time and angle of arrival could be measured and cross-referenced to an altitude in an x-y coordinate entry of the altitude database.

FIG. 8illustrates this method of error correction. As shown, a wireless signal receiver800is measuring transmission metrics for a first floor802and a second floor804of a building806. Area808represents the error range of the x-y coordinate location system. In other words, when the location system reports x-y coordinates corresponding to building806, a mobile wireless device could be located anywhere within area808(which is, for example, a 4000 square foot area). Likewise, the location system would report the x-y coordinates responding to building806for a mobile wireless device transmitting from floor802or804anywhere within the areas812and814, respectively.

Therefore, as shown inFIG. 8, if time of transmission is used as the transmission metric, then it is possible to measure the same time for mobile wireless devices that are on different floors (i.e., at different altitudes). For example, relative to wireless signal receiver800, a point816on near side of floor802might be the same distance away as a point818on the far side of floor804. Therefore, the time of transmission T would be the same at these two different altitudes (i.e., floors). However, measuring the angle of arrival in addition to the transmission time solves this problem. For example, if the angle of arrival is determined to be angle α, then it could be determined that the mobile wireless device is located on floor802at point816, and not on floor804at point818.

As another way to compensate for limited x-y coordinate accuracy and to resolve ambiguities in measured transmission metrics, another embodiment of the present invention determines altitude using more than one wireless signal receiver. In other words, a first transmission metric is measured between the mobile wireless device and a first wireless signal receiver, and a second transmission metric is measured between the mobile wireless device and a second wireless signal receiver.

FIG. 9illustrates this method for increasing accuracy. As shown, this example assumes that a reported x-y coordinate location has a resolution equal to the footprint of building900. That is, a mobile wireless device determined to be at the x-y coordinates of building900could be located anywhere within the footprint of building900. Measuring a transmission time T9from a first wireless signal receiver902would therefore reveal that the mobile wireless device could be anywhere along arc904over the footprint of building900. Measuring another transmission time T9′ from a second wireless signal receiver906dramatically reduces the number of possible locations of the mobile wireless device, by showing that the mobile wireless device must be along another arc908. The intersections910of arcs904and908represent the possible altitudes of the mobile wireless device. Introducing additional measured transmission times from other wireless signal receivers would further reduce the number of possible altitudes of mobile wireless device and further increase accuracy.

Although, for clarity,FIG. 9illustrates the wireless transmissions in two dimensions, it should be understood that the described concepts can be extrapolated to three dimensional implementations, e.g., instead of arc904, the possible locations of the mobile wireless device would be anywhere along the portion of the surface of a sphere that is over the footprint of building900. The intersection of two spheres would be a circle or a portion of a circle along which the mobile wireless device could be located.

In an alternative embodiment of the present invention, instead of receiving only an x-y coordinate location, altitude processor312(seeFIG. 3) receives a complete x-y-z coordinate location. Some global positioning systems provide this capability. Thus, it is unnecessary for altitude processor312to measure a transmission metric to determine the altitude of a wireless mobile device. However, in most instances, the z-coordinate (altitude) reported by the location system will not be easily comprehendible to users such as emergency dispatchers. Thus, in this alternative embodiment, although altitude processor312does not measure transmission metrics, altitude processor312still looks up the reported altitude in the altitude database314to find a corresponding ordinary description such as “second floor.” Altitude database314associates x-y coordinates with altitudes and descriptions.