Thursday, December 19, 2013

Combining RFID and GPS technologies Part II

Last week we looked at how GPS and RFID work, today we'll compare and contrast the two technologies and see how the strengths of each can be used to compensate for the limitations of the other.

The global range of the global positioning system is its greatest strength. GPS enabled devices can be tracked all over the world with no additional equipment necessary as the GPS satellites are already positioned overhead. However, reliance upon satellites yields the system's greatest weakness - inaccuracies or failure to determine position due to obstacles or signal reflections. The presence of buildings, mountains, or dense foliage can serve to block GPS satellite signals; operating in canyons or indoors can be very difficult or impossible. Signals can also reflect off of nearby surfaces causing the GPS device to receive too many mixed signals resulting in inaccurate locations or failures.

One of the biggest strengths of RFID is its customize-ability and flexibility. The different types of tags can address nearly all necessary purposes. Lower-cost passive tags require closer read ranges but can be teamed with readers positioned at entry points or along conveyor belts to log the tag's movement, while higher cost, "always on", active tags can be placed on items throughout a warehouse or stockyard for constant monitoring. The weakness in RFID is the reliance upon a reader. While there are handheld readers available, meaning the position of the reader is not required to be fixed in space, the overall scale of an RFID operation, due to it's reliance upon readers and limited tag read-ranges, is very much "local".

The other major difference between RFID and GPS is that an RFID tag transmits to the reader information stored on its chip. RFID tags have been combined with other monitoring equipment such as thermometers or medical equipment in order to transmit not only the tag's location, but various characteristics of the tracked item (such as temperature or vital signs).

By creating tags with combinations of RFID and GPS chips users are able to get the global tracking ability of GPS while outside the local zine then utilizing RFID for indoor or local position tracking possibly combined with other status measurements.
There are many unique ways in which this combination may manifest itself. There are combination tags developed where the tag is set to operate as RFID by default, switching to GPS once the item has left the facility "exit point". One company has a system where GPS is used to monitor an item's location in an open air stock yard. When an item needs to be moved a reader mounted on the forklift collects data on the item's exact contents. Then there is the unique example we cited in the opening of Part I, where Macy's is testing a system where GPS detects a user's approach (via smartphone) and then launches an app with advertisements to entice the customer to enter the store. Once in the store RFID systems detect customer's locations and provide promotions specific to the customer's immediate vicinity.

There are many possibilities for these relatively new GPS and RFID combined tags. With the way these two technologies uniquely balance each other there are surely many more applications to come.

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.