by Phavanhna Douangboupha
This blog contains information about some of the current practices in location tracking technologies. It mainly discusses the three common methodologies – GPS, Cell Towers, and Wi-Fi positioning service. The blog is a part of the ongoing investigation for the proposed capstone project on Web-based resource tracking during a disaster or crisis situation.
In general, there are four geo-location methods including triangulate, associate, geo term extraction, and data entry or geo-coding. The Global Positioning System (GPS), Cell Towers, and Wi-Fi positioning service (WPS) are the three well known triangulation techniques to identify a mobile device geo-location. GPS and Cell Towers are based on triangulation to identify an object position by using the location of known objects.
To put a location on a map, the geo-coding position technology relies on getting a location of an object via a meaningful X, Y coordinate or a latitude and longitude coordinate. In fact any available mapping tool such as Microsoft live search maps, Google maps, and Yahoo maps use the coordinate system to identify a requested location.
GPS relies on satellites that send microwave signals information back to the earth. The information is a navigation message of each satellite’s position and time. An object location is calculated by GPS receivers by the use of triangulation and the signal information provided by at least three satellites in order to determine an object’s location and four satellites for greater accuracy. The use of fourth satellite enhances the accuracy in the order of nanoseconds. GPS receivers compare the time difference between the arrival of satellite signals to tell the position. At least three satellites are needed in the calculation for an accuracy result. The first satellite provides a possible location of an object narrowed down to the surface of a sphere. The position is recorded as a radius equal to range 1. On the same token, satellite number two provides confirmation that the object is located within the first sphere (as located by the first satellite). Satellite number two provides an additional position circle of a radius range 2. The first and second satellite indicate that the object is positioned between the intersection between their two spheres – sphere one and sphere two. Finally, the third satellite shows a third sphere of radius range 3 for the positions. The object position is the intersect location of the three spheres. Finally, the fourth satellite is used to confirm the location and hence provides the time reference.
A GPS-enabled device provides geo-code location accuracy about 1 to 5 meters. Despite the fact that GPS system is widely used with many position tracking systems, it does come with some drawbacks. GPS does not work within indoor environment positioning and it requires costly power-consumption on mobile devices. In addition, not all mobile devices are GPS-enabled.
Another solution for location finding is the Cell Tower technique. Similar to GPS system, it requires at least three different cell towers within range of the device to calculate an object location for a high accuracy result. Otherwise, at least two cell towers are required. Each cell tower ,with a unique cell identifier, returns a positioning data to a requested mobile phone. Each mobile phone constantly pings a signal to nearby cell towers to get the cellular radio signal and hence some mobile phones also require costly power-consumption just like in the GPS positioning techniuqe. Having data from all the cell towers, an algorithm can be used to calculate a final location of the mobile phone which lies in the middle. The advantage of cell tower triangulation technique is that is available for all mobile phones that have registered service providers . In addition, cell towers can be set up to send signal to mobile devices. Unlike GPS, cell towers will work in both indoor and outdoor environment. The accuracy of a position allocation depends on the density of cell towers in the area.
Wi-Fi Positioning Service (WPS) is the least accurate technique for location finding among the three techniques (GPS, Cell Towers, and WPS). IP address from a mobile device Wi-Fi connection is used to get a guessed location back from a service provider database such as Google map using API. Some of the available and well known mobile device location locator technologies are Google gear (Google map version for a mobile device), iPhone Core Location, and Navizon. Google mobile map and Navizon peer-to-peer wireless positioning tools make the use of their massive data collection to provide a best guessed location for a device without GPS-enabled and for thoser devices that can not communicate with cell towers.
Google gear uses all three triangulation technologies to get the best accurate result. Google gear is compatible with many mobile devices including Windows Mobile, and Android. On the other hand, Core Location is another tool specifically programmed for iPhone. Apart from Google gear and iPhone Core Location, Navizon is another map locator tool. Navizon is free for a cellular enabled device, with some limitations, using cell ID positioning. However, it is not free for a Wi-Fi or cellular enable device using cellular and Wi-Fi triangulation. Navizon database collects geo-coding data from registered users or devices with GPS-enabled. These data is collected and used as a virtual GPS. The tool uses the bank of data as a reference positioning point to locate a mobile device geo-location.
Another alternative technology is a tool so called PhoneGap that utilizes web application technology and Objective-C core features available on three mobile devices – iPhone, Android, and Blackberry.
References
- Bellavista, P., & Corradi, A. (2007). Mobile Middleware for Location-Dependent Services. In The Handbook of Mobile Middleware. USA: Auerbach Publications
- Berka, J. (2008, January 22). PhoneGa tool provides JavaScript access to iPhone features. In PhoneGap tool provides JavaScript access to iPhone features - Ars Technica [Internet Article]. Retrieved January 31, 2009, from
http://arstechnica.com/apple/news/2008/10/
PhoneGap-tool-provides-javascript-access-to-iphone-features.
- B’Far, R. (2005). Mobile Computing Principles: Designing and Developing Mobile Applications with UML and XML. United Kingdom: Cambridge University Press.
- Google. (2008). Services – Google Maps API – Google Code. In Google Maps API [Google Maps API Reference]. Retrieved November 9, 2008, from Google Web site: http://code.google.com/apis/maps/documentation/
services.html#XML_Requests
- Google. (2009). Geolocation API. In Geolocation API – Gears API – Google Code [documentation]. Retrieved January 31, 2009, from Google Web site: http://code.google.com/apis/gears/api_geolocation.html#getCurrent
- Katsaros, D., Nanopoulos, A., & Manolopoulos (eds), Y. (2005). Location-Based Services. In Wireless Information Highways (section iv – location-based
services). United States of America: Idea Group Publishing . Retrieved
November 6, 2008
- Mallick, M. (2003). Mobile and Wireless Design Essentials. Indianapolis,
Indiana, USA: Wiley Publishing. Retrieved November 8, 2008
- Mark, D., & LaMarche, J. (2009). Where Am I? Finding Your Way with Core
Location. In Beginning iPhone Development: Exploring the iPhone SDK (pp. 429-439). USA: Apress
- Mexens. (2005-2008). How it works. In Peer-to-peer wireless positionin [product description]. Retrieved January 31, 2009, from http://www.navizon.com
- Olla, P. (2008). Global Navigation and Satellite Systems and Services. In
Commerce in Space: Infrastructures, Technologies, and Applications
(chapter v). USA: IGI Publishing. Retrieved November 8, 2008
- Wu, S.-L., & Tseng, Y.-C. (2007). Wireless Ad Hoc Networking-Personal-Area, Local-Area, and the Sensory-Area Networks (S.-L. Wu & Y.-C. Tseng, Eds.). USA: Auerbach Publications. Retrieved January 30, 2009
Links to other blogs in this project