Thursday, December 12, 2013

Combining RFID and GPS technologies Part I - The Basics

Imagine you are walking through a busy downtown street, surrounded by businesses each seeking to stand out from the rest, gain your attention and entice you to enter their store. As the GPS chip in your smartphone detects that it has approached within a certain range of one of these businesses and app launches showing you discounts and coupons available at a store nearby. When you enter the store and RFID reader detects your phone, and therefore your entry into the business. As you browse the stores shelves RFID technology follows your exact location inside the store and provides ads for products within your immediate vicinity. 

This combination of GPS and RFID technologies is already in use, being tested in places like a Macy's store in New York. This week and next week we will look at the similarities and differences between RFID and GPS technologies and look at how they can be effectively combined.

The Global Positioning System (GPS)
GPS stands for global positioning system. According to, the GPS is a network of 24 satellites spaced around Earth orbit in such a way that at any given time at nearly any given location on Earth, at least 4 satellites should be positioned somewhere overhead. These satellites are equipped with very accurate atomic clocks and broadcast a signal indicating their exact location, their status and a very accurate measure of their internal time. 

GPS devices contain a chip capable of picking up these signals. Upon reading the signal from a satellite the GPS device notes the time indicated in the signal and compares it to its own internal time, using the (very small) difference between the two times along with the knowledge that the signal traveled at the constant speed of light (186,000 miles per second) to calculate its exact distance from that particular satellite. 

As seen in the image below from, knowing your distance from one satellite indicates a range of possible locations, you could be at any point on a circle with your distance to that satellite the radius. More information is needed to identify your exact location. Utilizing the signal from 3 (or more) satellites allows a "triangulation" calculation (depicted in the image)  and your device is now able to determine your exact location. The more satellite signals the device can detect, the more accurate the determined location.  
We've exlpored RFID related topics numberous times over the past few years (articles sorted for you here) so many of our readers are probably quite familiar with what makes an RFID system. In summary, an RFID system consists of two parts: a reader and a tag. An RFID tag can be as simple as a microchip and an antenna. The tag transmits information to the reader via radio waves and the reader intercepts and interprets the information or the reader sends out a signal "interrogating" the tag and the tag responds with information.

RFID tags are generally classified by power type, passive tags are the basic chip and antenna. When the reader sends a signal, that signal "wakes" the tag and the data stored on the chip is reflected back to the reader. Active tags contain batteries and are always "on", always transmitting their signals for nearby readers to pick up and the battery power boosts the strength and read-range of the signal. Battery-Assisted Passive (BAP) tags are the hybrid, a tag that "wakes up" when the reader's signal is detected (like a passive tag) and transmits the information contained in the chip, but like active tags, BAP tags use the battery to boost read range. The BAP tag is not always "on" and therefore batteries can last longer (or smaller batteries can be used). 

There are a wide variety of uses for RFID, and they make use of all the different RFID tag configurations. Small, inexpensive and simple Passive RFID tags can be printed out in large quantities and used to help track large volume, but relatively low cost items such as garments for Wal-Mart, low read range is not an issue reading items running through a conveyor belt or checkpoint. BAP or Active tags, while more expensive, provide options for tracking large items, perhaps even in real-time, in large fields like containers in a dockyard, automobiles in a parking lot, or pallets in a warehouse.

Next week we will look at the similarities and differences between GPS and RFID and how integrating the two can balance the weaknesses of each to create unprecedented tracking possibilities. 

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