An Application of Secure RFID Network Tracking
Logan Isch
Kevin Lane
12/4/2006
Radio Frequency Identification, or RFID, is a rising technology in today’s electronic world. The usefulness of RFID is becoming more apparent as humans move to become detached from the world of wired electronics. One of the latest trends in “wireless” technologies is the use of Global Positioning Systems, or GPS, in automobiles. Systems like these allow the driver to easily navigate roads to reach their destination. However, services like those rely on good satellite communications and cost a daily fee. Our proposal is the establishment of a roadside system based on RFID technology that will allow drivers the same services that a GPS system can provide in a much cheaper and efficient approach. Before the details of the proposal are discussed, the functionality and usefulness of RFID will be examined.
RFID consists of a system of small chips and wireless radio antennas that are placed on or in certain objects for various purposes. Some of these purposes include inventory tracking, object positioning, and passive toll booth payment. RFID systems contain two major components; the interrogator and the tag.
The tag component contains an antenna and a small circuit, which usually contains an integrated circuit chip. There is a multitude of tag types used in commercial applications. One type is called the disk or coin tag. These are small, round, plastic-encased tags with a central hole for fastening to objects. Another format is the smart label tag. This tag consists of a paper-thin tag with a coiled antenna of foil printed onto the back of a plastic sticker. This format is widely used in department stores for security detector systems. One more type of tag is the contactless smart card. It is very similar to a credit card, only it contains a tag system with a coiled antenna. This is a very current application that allows people to simply wave their card in front of an interrogator sensor to pay for merchandise directly from their accounts without actually swiping a credit card or paying with check or cash. Two kinds of tags are used; passive tags and active tags.
Figure 1: An example of a smart label tag.
Passive tags are simple and contain no internal power supply. The antenna’s electrical current from receiving a signal produces enough power to run the integrated circuit and transmit a return response. Most passive tags use a principle called backscatter to return the signal back to the sender. Because there is no power supply in these tags, their size can be very small and used in commercial products as security tags. Usually the tag is only bigger due to the size of the antenna to increase range. Passive tags have a varying maximum read distance from 10 centimeters to 6 meters depending on the size of the tag used.
Figure 2: An example of a passive tag.
Active RFID tags have their own power source used to power the integrated chip and any transmitting done through the antenna. These types of tags are larger than passive tags because of the power source, but are considered much more reliable. The power source allows the active tag to communicate with the interrogator without the interrogator sending a signal first. Because of the power source, active tags also have a better chance of transmitting through mediums that decrease the propagation speed of the signal. This also drastically increases the range of the tag over the passive types. Distances can reach from 300 feet to hundreds of meters, allowing for tag reading from far away. Many tags have very long battery lives, spanning up to ten years. The battery can either run all the time or be activated only when a “wake-up” signal is received, much like a passive tag’s operation. One of the only major drawbacks to active tags is the high cost. They are only cost-effective when used in systems that require long distances between the tag and the interrogator.
Figure 3: An example of an active RFID tag.
Tag memory is usually one of three types; Read-Only (RO), Write Once Read Many (WORM), and Read-Write (RW). Read-Write is more complex to produce and thusly costs more than a Read-Only chip. Read-Only chips are also more secure than Read-Write chips, as they cannot be corrupted by electromagnetic interference. Memory capacity for passive tags varies. The smallest tags can use 1-bit of memory while larger and newer passive tags can use up to 2 kilobytes. Active tags can have a much larger capacity of memory because they have their own power source.
The interrogator is the device which sends a signal out in order to read the data stored on a tag. An interrogator sends out an RF signal to the tag. The amount of power the signal has in transmission has a direct influence on a passive tag’s ability to return a signal to the interrogator. When the signal is sent, it travels as far as it can. It will only receive a reply signal if the tag is within the range of transmission. However, because the interrogator is usually a stationary device, it may have the benefit of a larger power source for long-distance transmissions. No matter how far the interrogator can transmit, though, the tag must be able to transmit a signal back along the same distance.
Figure 4: An example of a store’s RFID reader (interrogator).
RFID systems use the electric principle of coupling though components called inductors. Inductors are simple coils of wire that create magnetic fields from the flow of electrons inside them. When two inductors are coupled, the magnetic fields overlap and energy is transferred between the two inductors. This principle allows for the contactless transfer of energy between the interrogator and the tag in an RF system. The transfer of energy, however, is only useful when the signal flowing through the circuit is below a frequency of 27 megahertz. For systems that operate above 27 megahertz, backscatter is used. Backscatter is the reflection of waves or signals back to the direction of their origin. This occurs in RFID systems by resonance. The antenna length of the tag must be at least one-fourth of the size of the signal wavelength to resonant correctly.
Figure 5: Inductive coupling.
When a tag receives power from the interrogator’s signal, it is activated and starts to operate. During the activation, the previously mentioned concepts of inductive coupling and backscatter will have occurred. If the tag is passive, it will continue receiving the signal from the interrogator until is has retained enough power to carry out its function and return a signal. After a signal is generated by a tag, it is transmitted through the antenna to the interrogator. The interrogator then takes the received signal and extracts the data from it using a demodulating technique. The information is then sent to the appropriate destination to be used for one of many purposes.
In the RFID industry, there are no organizations that regulate the standards of transmission frequencies. Thusly, a number of countries established their own regulations to reduce the number of interferences between RF systems. The Federal Communications Commission (FCC) has set up frequency band specifications for RFID devices in the Ultra High Frequency (UHF) range. These frequencies are from ranges of 902 – 928 megahertz, 2400 – 2483.5 gigahertz, and 5725 – 5850 gigahertz. The FCC recommends that the systems used should use frequency hopping spread spectrum modulation techniques. These techniques maximize the power allowance for interrogator-transmitted frequencies. Standards issued by other countries can be found in the following table:
Frequency / Region/Country125-134 kHz / United States, Canada, Japan, Europe
13.56 MHz / United States, Canada, Japan, Europe
433.05-434.79 MHz / United States, most of Europe, under consideration in Japan
865-868 MHz / Europe
866-869 MHz / South Korea
923-925 MHz / South Korea
902-928 MHz / United States
952-954 MHz / Japan
2400-2500 GHz / United States, Canada, Japan, Europe
5.725-5.875 GHz / United States, Canada, Japan, Europe
Table 1: Range of Frequency by Country.
A few practical RFID applications were mentioned earlier. Many more applications are used using RFID technology. One of the major applications in Europe and Asia is the use of the Smart Card for currency transaction systems. Rather than using the old magnetic strip technology, the Smart Card sends the same data with an RF signal to pay for items. The Smart Card doesn’t even have to be taken out to be used; it only needs to be moved within the range of the interrogator. A similar application is the use of the toll payment tag in automobiles. Using these tags, a driver can simply drive under a sensor that deducts the toll from their account rather than stop to waste time searching for spare change to drop in a basket.
Figure 6: An example of a toll payment tag.
The most common application of RFID technology is the use of security scanners in retail stores. Hidden in many products are small smart labels that contain Write Once Read Many memory. To prevent the tag from setting off the alarm in the interrogator, the tag must be disabled with a special proximity signal. This is apparent when the store clerk moves the item back and forth over a special pad on the checkout counter.
One more application is used in industrial settings for the tracking of item progression in an assembly line. The tag allows for the inventory system to keep track of parts as they move along the line. It also serves for post-production uses to authenticate the part as being made from the correct manufacturer. This concept of item positioning is very important for the use of RFID monitoring of real world traffic.
A practical use of RFID is help with monitoring traffic. An RFID system would be more accurate than a radar system or even the hose-connected-to-a-box system. With a radar system, vehicles are easily missed as the radar picks up on the most reflective and/or largest surface. This means if a semi-trailer that is all metal on the outside is going to be picked up and anything thing beside it missed.
The hose-connected-to-a-box system relies on counting on the number of times a tire runs over the hose. If two vehicles run over the hose at the same time, then it will only be counted as a single vehicle. Also, there must be some type of algorithm used to average out between motorcycles, four-wheeled vehicles (cars, trucks, SUV’s) and vehicles with trailers attached to them. Since the counting box has no optical perception it only records each time the hose is run over.
Using the RFID tracking system could be done in a similar fashion to the tracking of items on a manufacturing line and traffic across the internet. All it would take are RFID readers (interrogators), RFID tags and powerful servers to track and process the traffic flows. These items are currently available today without much modification needed for the purpose of traffic monitoring.
To monitor traffic in specific areas, readers would have to be placed along the roadways. This could be done for interstates, freeways, city roads and even small county roads. Since the readers are more expensive to replace than road signs, the readers would need to be placed at least the same distance off the road as street lights and the posts for exit signs. These readers would need to be enclosed in some type of weather and tamper proofing system in order to maximize the length of time the units will last.
Figure 7: Example of possible reader mounting locations.
The height of the reader would be set low enough to pick up on a sports car’s tag. This could be set on its own stand or to save on costs, be mounted existing light poles. By mounting on the light poles, the reader can be tied into the electrical power already going to the pole and thus save on the cost of running electricity to the readers. Some type of networking would also need to be tied into the readers so they can report their data back to the server. Fiber optic cable would be best because of the high speed of the data communication and the large amount of data that could be transferred from each reader.
Each vehicle on the road would need to have a tag on them. In order to make sure the data from the tag would reach the readers, these would be active tags. With the tags needing to be active, they could not just be the window tags like the tags used for toll booths. The best way of adding these tags to vehicles on the road would be to have them put on during regular service at no charge to the vehicle owner. New vehicles would have them put in the vehicle before being sold.
As these tags could also be changed or added to vehicles by individuals or corporations, there is not really anyway to make sure a specific RFID tag is assigned to a specific vehicle or person. Therefore, the “owner” of the tag would not need to be recorded or tracked. With a little bit of work, I’m sure someone would come up with a method so tags could randomly pick a new number each time the vehicle is started. As such, this system would not be designed to actually track where someone goes, but to track or monitor the traffic occurring. The system could be programmed to track a specific tag when it has been “noticed” for specific problems. If the monitoring system picks up on a vehicle traveling at high rates of speed, authorities could be notified and informed where the vehicle is currently located and what direction it is traveling. This could help prevent high speed chases on busy roadways.