1. Field of the Invention
The present invention relates to use of the Global Positioning System (GPS) and other location based resources in mobile devices such as cellular phones and handheld devices. More specifically, the present invention relates to intelligent utilization of GPS and location based resources in a mobile device in order to preserve battery life of the mobile device and minimize network bandwidth resources accessed by the mobile device.
2. Description of the Related Art
Operation of the GPS
The GPS is a series of twenty-four space-based satellites transmitting signals to a GPS receiver on the ground. Each GPS satellite transmits data that indicates that particular satellite's location and the current time. All GPS satellites synchronize operations so that these repeated signals are transmitted at the same instant as provided by atomic clocks at the U.S. Naval Observatory and an atomic clock on board each GPS satellite.
Signals emitted by GPS satellites arrive at a GPS receiver at different times because some GPS satellites are farther away than other GPS satellites in relation to the GPS receiver; information relating to the location of each GPS satellite is included in GPS satellite transmissions. The distance to a GPS satellite from a GPS receiver can be determined by the time it takes for a GPS satellite signal to reach a GPS receiver. The GPS receiver can calculate its location in relation to these GPS satellite transmissions through a process known as trilateration. Through trilateration, a GPS receiver measures the distance from the GPS satellite using travel time of the GPS satellite signals.
For example, the distance between a GPS receiver and a GPS satellite might be 10,000 miles. The location of the receiver relative to the particular GPS satellite is limited to a sphere with a radius of 10,000 miles, the GPS satellite serving as the center point as shown in FIG. 1A. The distance between the same GPS receiver and a second GPS satellite might be 11,000 miles. As was the case with the first GPS satellite, the location of the receiver relative to the second satellite is limited to a sphere with a radius of 11,000, the second GPS satellite serving as the center point as shown in FIG. 1B. Combining the information from these two GPS satellites relative to the GPS receiver, we can determine that the GPS receiver is located “somewhere” where the two spheres intersect. By obtaining a relative measurement from a third GPS satellite (e.g., 12,000 miles), the location of the GPS receiver is further narrowed to a point where the 10,000 miles and 11,000 mile spheres intersect with the 12,000 mile sphere as shown in FIG. 1C.
Mobile Devices and the GPS
With the proliferation of mobile devices such as cellular phones—over 150,000,000 cellular phones are presently in service—the mobile device handset has become increasingly functional beyond that of a mere telephonic device. Many cellular phones are now integrated with other mobile features such as a Personal Digital Assistant (PDA), camera, instant messaging and electronic-mail. The Federal Communications Commission, too, recognized this proliferation and the possible safety advantages of equipping mobile devices with GPS tracking under its E911 mandate.
While a 911 emergency phone call placed from a land-line is associated with a phone number assigned to a physical address, a 911 emergency phone call placed from a cellular phone can originate from the user's home but also from, for example, the user's office, while on vacation, or even while stranded in a remote location. Sending an emergency response team to the user's home address when the call was placed in one of these latter locations fails to provide the necessary emergency services where needed but also distracts those services from other possible emergencies. GPS tracking solves this conundrum by associating a phone number with actual physical location. In this regard, GPS technology in cellular handsets and other mobile devices also offers additional commercial advantages such as the user determining their location or obtaining turn-by-turn directions to a particular destination.
Receipt of GPS satellite signals is not a simple feat, however, especially for a mobile device with less power than a conventional GPS receiver that is designed for—and only for—receipt of GPS signals. Mobile devices such as cellular phones are, obviously, phones first and foremost. Additional features such as electronic mail and GPS functionality require additional processing power in the mobile device that represents an additional strain on battery availability in addition to another strain on outside resources such as a GSM (Global System for Mobile Communications) network that allows a user to connect to a proprietary cellular network via local base stations.
Representing a further strain on battery and network resources is the fact that GPS signals shift in frequency due to the relative motion between, for example, a handset GPS receiver and the constant motion of GPS satellites. This Doppler frequency shift requires the GPS receiver to, first, find the frequency of the signal before the GPS receiver can lock onto the signal and make a determination of location. As such, prior knowledge of a GPS satellite's position and velocity data and the initial handset receiver position can reduce the number of frequencies to be searched because the GPS receiver directly computes the Doppler frequency shift instead of searching over a whole possible frequency range.
Many GPS equipped cellular phones are also equipped with technology known as the Assisted Global Positioning System (“A-GPS”). A-GPS uses a combination of GPS satellites and cellular phone base stations to pinpoint location of the mobile device and its GPS receiver and to offer a determination of location that is more accurate than GPS alone. Mobile device GPS receivers, in correlation with an estimate of the mobile handset's location as determined by a cell-sector, can predict with greater accuracy the GPS signal the handset will receive and send that information to the mobile device handset. With this assistance, the size of the frequency search space is reduced and the time-to-first-fix (TTFF) of the signal is reduced from minutes to seconds. A-GPS handset receivers can also detect and demodulate signals that are weaker in magnitude than those required by a traditional GPS receiver.
A-GPS requires precise timing information to perform satellite signal processing. A-GPS can utilize precise time from a synchronized network, which provides optimized TTFF and sensitivity, or derive it on either a synchronized or an asynchronous network from aiding data received from an assistance server. The assistance server communicates with the GPS receiver via a wireless network link. The assistance server, generally, provides three types of data to the GPS receiver: GPS satellite orbit and clock information; initial position and time estimate; and for A-GPS-only receivers, satellite selection, range, and range-rate information. The assistance server is also able to compute position solutions, leaving the GPS receiver with the sole job of collecting range measurements. With assistance from the network, the receiver can operate more quickly and efficiently than it would unassisted, because a set of tasks that it would normally handle is shared with the server. The architecture of conventional GPS receiver implementation compared to that of an A-GPS implementation is reflected in FIGS. 2A and 2B, respectively.
A-GPS operates on any air interface network, synchronized or not, without requiring any costly equipment to derive time, and will operate with enhanced efficiency and performance on precisely synchronized networks. The A-GPS architecture, in and of itself, helps increase capabilities on the cellular phone with regard to battery conservation. Nevertheless, constantly querying the GSM Network and/or GPS satellite network represents an ongoing drain on battery power in addition to a strain on requisite networks. Therefore, there is a need in the art for a GPS handset solution that incorporates A-GPS architecture with an intelligent system for making queries of location on an as-needed basis.