GPS/cellular integration

Cellular communication technology is becoming widely accepted throughout the world. Both the number of subscribers and the cellular coverage areas are increasing continuously. In addition, more advanced digital cellular coverage is on the rise, allowing voice and data to be mixed seamlessly. This makes the cellular system very attractive to a number of markets, including emergency 911, AVL, and RTK GPS.

A major limitation with the current cellular system, however, is its ability to precisely determine where a call was originated [11]. Although this limitation is not critical for applications like RTK GPS, it is of utmost importance for other applications such as emergency 911 and AVL. In the United States, for example, about one-third of all emergency 911 calls come from cellular phones. Of these, nearly one-fourth cannot describe their location precisely, which makes it very difficult for an operator to effectively send out assistance. As such, the U.S. Federal Communica-tions Commission (FCC) has made it mandatory that, as of October 2001, wireless emergency 911 callers must be located with an accuracy of 125m (67% probability level) or better [11].

To meet the FCC location requirement, wireless network operators can either use the network-based location or the handset-based location.

Most network-based caller location systems employ either the time-difference of arrival (TDOA) approach or the angle of arrival (AOA) approach to determine the caller’s location. The former measures the dif-ferences in the arrival times of an emergency 911 signal at the cell sites or base stations. The caller’s location can be determined if the signal is received at a minimum of three base stations. Obviously, time synchroni-zation is essential with this technique, which can be ensured by equipping each cell site with a GPS timing receiver. The second technique, the AOA, uses phased-array antennas to compute the angles at which the signal arrives at the base stations. A minimum of two sites is required to compute the caller’s location with this method. As both the TDOA and AOA GPS Integration 125

methods have advantages and drawbacks, some network operators com-bine the two methods [11].

Handset-based location technology integrates GPS with cellular com-munication through the installation of a GPS chipset in the handset of the wireless phone. With selective availability being turned off permanently, this technology would locate the wireless emergency 911 callers with an accuracy that exceeds the FCC requirement by a factor of ten. Unlike network-based technology, handset-based location technology is very sim-ple to imsim-plement and does not require the installation of additional equip-ment at the base stations (e.g., GPS timing receivers). One of the drawbacks of the handset-based location technology, however, is that only new cellu-lar phones can be equipped with GPS. In addition, the GPS signal is very weak to be received inside buildings. This limitation, however, could be efficiently overcome in the near future with the development of integrated GPS/MEMS technology, described in Section 9.3.

In the near future, the development of a new generation of cellular technology, the 3G wideband digital networks, will be completed. The 3G cellular technology supports voice, high-speed data, and multimedia appli-cations. In addition, this technology uses common global standards, which not only reduces the operational cost but also makes the system useable worldwide. Moreover, with this new technology, devices can be turned on all the time for data transmission, as subscribers pay for the packets of data they receive/transmit.

The advances in the wireless communication and caller’s location technologies discussed earlier will greatly impact a number of industries.

The vehicle navigation market, for example, is expected to greatly benefit from the advances in wireless communication, location, and Internet tech-nologies (see Section 10.11 for details about vehicle navigation). Currently, vehicles use complex systems that integrate location technology with in-car computer navigation systems containing electronic digital road maps and other related information. Clearly, the in-car system will not be aware of any real-world changes in the navigation system’s database (e.g., a change in the traffic direction). With the availability of wireless Internet service, however, an up-to-date database residing at a central location could be accessed by drivers, eliminating the need for a complex in-car computer navigation system. Furthermore, with the availability of a precise location system, drivers could customize the information they need according to their locations, such as turn-by-turn navigation, traffic information, and

local weather conditions. This method is simple, cost-effective, and flexi-ble, and has the potential of being the way of the future.

References

[1] Elfick, M., et al.,Elementary Surveying, 8th ed., New York: HarperCollins, 1994.

[2] Ashtech Inc., “Reliance Field Asset Management Tools,” Magellan Corporation, Santa Clara, CA, 2001.

[3] Laser Technology Inc., “Survey Laser For Forestry.” PowerPoint Presentation, accessed July 18, 2001, http://www.losertech.com/

downloads.html.

[4] Madhukar, B. R., et al., “GPS-DR Integration Using Low Cost Sensors,”

Proc. ION GPS-99,12th Intl. Technical Meeting, Satellite Division, Institute of Navigation, Nashville, TN, September 14–17, 1999, pp. 537–544.

[5] Kaplan, E.,Understanding GPS: Principles and Applications,Norwood, MA:

Artech House, 1996.

[6] Schwarz, K. P., and N. El-Sheimy, “Future Positioning and Navigation (POS/NAV) Technologies Technical Study,” Study performed under Scientific Services Agreement with U.S. Topographic Engineering Center, Fort Belvoir, VA, March 1999.

[7] May, M. B., “Inertial Navigation and GPS,”GPS World, Vol. 4, No. 9, September 1993, pp. 56–66.

[8] El-Rabbany, A., “Mining Positioning,”Proc. Smart Systems for Mineral Resources Workshop,Toronto, Ontario, February 14, 2001.

[9] Cobb, S., and M. O’Connor, “Pseudolites: Enhancing GPS with Ground-Based Transmitters,”GPS World, Vol. 9, No. 3, March 1998, pp. 55–60.

[10] Wang, J., et al., “Integrating GPS and Pseudolite Signals for Position and Attitude Determination: Theoretical Analysis and Experiment Results,”

Proc. ION GPS 2000,13th Intl. Technical Meeting, Satellite Division, Institute of Navigation, Salt Lake City, UT, September 19–22, 2000, pp. 2252–2262.

[11] Driscoll, C., “Wireless Caller Location Systems,”GPS World, Vol. 9, No.

10, October 1998, pp. 44–49.

GPS Integration 127

GPS Applications 10

GPS has been available for civil and military use for more than two dec-ades. That period of time has witnessed the creation of numerous new GPS applications. Because it provides high-accuracy positioning in a cost-effective manner, GPS has found its way into many industrial applications, replacing conventional methods in most cases. For example, with GPS, machineries can be automatically guided and controlled. This is especially useful in hazardous areas, where human lives are endangered. Even some species of birds are benefiting from GPS technology, as they are being monitored with GPS during their immigration season. This way, help can be presented as needed. This chapter describes how GPS is being used in land, marine, and airborne applications.