Vaidhyanathan Mayilrangam Gopalan
Founder
FolkMaps.com
Email: vaidhy@folkmaps.com
Abstract
One of the basic necessities for most civilian GIS applications like location based services or routing is the identification of current location. There are various known ways of identifying one’s location, varying widely in the cost and accuracy. This paper presents one more way, using RFID to determine a location and also discusses various other possibilities.
RFID
Radio Frequency IDentification (RFID) is automatic identification method. The system consists of a transponder (RFID tag) and a receiver or reader. There are various types of tags, but in general, transponders respond to a signal from the reader. Depending on the type of tag, it may also send additional information.
Types of RFID Tags
There are primarily three types of RFID tags, passive, semi-active and active.
Passive tags contain no power supply. When a reader sends a signal, passive tags use the energy of the signal to send back a response in the same direction the request signal came from. Passive tags have a range of about couple of meters. Since they have no power requirements, they have an unlimited lifespan and are very cheap to produce.
Semi-active (or semi-passive tags) have a small battery used for powering the transponders. They have a similar range as passive tags, but their response times are faster and they can project back their response more accurately.
Active tags have their own power supply and for powering the transponders and for generating the signals. They have a much larger range, usually in tens to hundreds of meters, depending on the radio frequency used.
Current Uses of RFID
RFID tags find many uses, primarily in tracking materials and other shipment items. It is also used for animal identification, truck and container tracking, electronic toll collection, sensor identification, electronic cards and keys etc. The common usage pattern in that, the RFID tags move from place to place while the reader is stationary.
Location identification with RFID
It is possible to place RFID tags in roads, intersections, landmarks and other “interesting places” so that a vehicle equipped with a reader can identify its location accurately. However there are other location identification methodologies available and the next section will describe some of the more popular ones.
Other providers of location information
Cell phone Identification
This is based on cell phone network. The transmitting tower is deemed to location of the user. The advantages to using tower of transmission are very fast response time, already built network and there is no need to have new devices. On the other hand, the accuracy is very poor, usually off by few meters to few kilometers and data consistency is very poor.
Time Difference of Arrival
This is also based on cell phone network. The cell phone service provider looks the time difference at the arrival of signal from a cell phone at three or more towers to find the location of the user. This system provides better accuracy than tower identification and fast response time. However, this requires the service providers to have additional infrastructure, and there are very few providers of TDOA service.
Enhanced Observed Time Difference
This is based cell phone network too. Instead of the provider finding the time difference, the cell phone is modified so that it can compute the time difference between signals from multiple towers. This system also provides better accuracy than tower identification and fast response time. However, the cell phone handsets need to be modified and the cost of additional infrastructure is also quite high. There are only a few providers of EOTD service.
GPS
GPS is the most well known of all location identification services. It is based on a set of 27 satellites orbiting earth twice each day. Each satellite emits radio waves and a GPS receiver uses triangulation from three or more satellites to position a user accurately in three dimensions. The accuracy of positioning is very accurate in the range of 5 to 50 meters. However, depending on the location and time, the response time can vary widely. It is also very expensive to build, deploy, monitor and maintain the network of satellites.
RFID based location identification is intended to be a replacement for these services.
RFID
As mentioned before, RFID based location identification is based on the multiple RFID tags that are placed at various “interesting” locations. This has many advantages over other location identification services.
- Very low implementation cost – RFID cost about 10 cents for each tag (about Rs. 4.60)
- Fast implementation – RFID can be placed pretty fast.
- Low power requirements – Active RFID tags can be run off solar cells leading to long life with low maintenance
- Vandalism proof – RFID tags are hard to break.
- Rugged – RFID tags are weather proof and also work in all kinds of weather
- Works everywhere – It can work inside tunnels, in middle of high rise buildings etc
- Allow public private partnership – RFID tags can be placed by government on roads, private institutions and individuals can also sponsor placing the tags on certain locations.
Potential Cost
Assuming Bangalore to be a typical city, its size is 1400 sq. km. If we want to place one tag every 200 meters, or 5 tags per kilometer, we would need 25 tags per sq. kilometer or about 35000 tags. Each tag is about a dollar each USD which makes the cost of RFID enabling a city less than $40000.
There are 35 cities with a population of more than a million in India. So RFID enabling all these cities would cost $1.4 million, a fraction of cost of setting up GPS infrastructure.
Other advantages
There are various other advantages of using RFID tags
- Business can advertise their location using RFID tags.
- Checking for routes becomes trivially simple since the user only has to follow the trail of RFID tags.
- Other information like the name of intersecting road, traffic information like one-way or two-way etc can also be broadcasted by RFID tags.
- If each RFID tag has a web presence, people can share useful information on the areas around the RFID tags.
- Since RFID tags are language neutral, the readers can be used to show the information in the language most familiar with the user rather than a device broadcasting the same information in multiple languages.
- Police can analyze traffic patterns easily by looking for number of “reads” on a particular tag.
Conclusion
Given these advantages, we believe that RFID can be considered as a potential location identifier for the following reasons: it can be installed with minimal expense; the cost of readers are very low; there is no dependence on large scale deployment and finally, it would help immensely in gathering and distributing GIS data which is not possible now. Further, there are also enough incentives for individuals or business to contribute to the process that acceptance should be much simpler than GPS.