Understanding RFID Performance Drivers

Troubleshooting a faulty RFID portal or a poorly performing reader will require you to become the Sherlock Holmes of RFID. You'll need to have a basic understanding of what could go wrong with the various components of an RFID system to qualify as a supersleuth. There is a saying pilots use to determine whether they have their head in the right place while they are flying: "Being ahead of the airplane." This means always anticipating what needs to happen to make a desired change, or how the pilot would react when a certain event happens-for example, an engine falling off. The same attitude can help an RFID technician as you go about initially deploying an RFID network, and it can really come in handy when you need to determine what is causing problems with the interrogation zone. If you are ahead of the RFID system, you are always thinking about what might go wrong and how to deal with it. With that in mind, I'm going to review the basics of the interrogation zone in terms of what could go wrong.

Reader Functionality

The reader controls the foundation of the interrogation zone. Remember that the power level is the biggest variable in how an RFID reader performs. Don't get hung up on power, though; many other components depend on the reader, from retry rates to antenna cycling order. A lot of people also tend to overlook the fact that the reader has to send its data someplace to be effective. The communication method can be broken when the reader is working perfectly, and thus give the impression that everything is broken.

The RFID industry is relatively new; consequently, manufacturing consistency and quality are all over the map. One thing we discovered at ODIN Technologies, doing thousands of tests before deploying readers from all the major manufacturers, is that there is a significant variability in the power output at each port. The Federal Communications Commission (FCC) allows 1 watt of effective radiated power (ERP) for UHF RFID in the United States with at least 50 channels hopping. Some reader manufacturers interpret this FCC rule as being the power level after it's attached to the reader, so they account for cable loss (more on that later) and check power at the antenna. Almost all the reader manufacturers have variability in power output at each port, and some ports just plain don't work. Remember that power is the big daddy of the interrogation zone. If you want to read at a farther distance, you need more power; conversely, if you don't want to read at another location, such as a dock door adjacent to the interrogation zone you're working on, power needs to be contained.

Another interesting consideration is operating temperature of the reader. This is a doubleedged sword like many other components of RFID-if the reader is too hot, the performance drops off precipitously, and if it is too cold, the performance will be subpar. This should also be an important consideration when setting up your RFID system, and another thing to look at when you're troubleshooting.

Tip 

As you become more and more involved in the RFID world, one of the best things you can do is keep a journal. When you go on-site, if you are doing tag testing, or if you are prebuilding an RFID rack, you should write down metrics. The metrics can provide key insights into being successful going forward. Some of the metrics you should track when you are keeping a journal are the length of time that a particular action took, the issues you ran into, the temperature when you deployed, and the humidity. If you are a big quantitative analysis (QA) fan, you can dump all of this data into a spreadsheet and figure out what levers really move performance and pricing.

Antenna Options

Antennas are how the reader gets its signal out to the tags coming through the interrogation zone. The antenna is responsible for shaping the RF pattern, and can be wildly variable depending on the need. Think of an RFID antenna as you'd think of a cutting instrument-one requirement may call for a Swiss Army knife, another may call for a meat cleaver, and still another for a chain saw. To make matters worse, if the blade is dull (even if it is the right kind for the job), it will not work well. Antennas can create various shapes or radiation patterns and be sending a suboptimal amount of power to the tag. The antenna can take a perfect RF signal that would ideally provide a great read back from the tag, and if the antenna is improperly tuned or is the wrong design, it can distort that perfect reader signal to the point where nothing will be read.

Tag Impact

The tag is the third critical aspect in the RFID system. It's important to remember that for a passive ultra-high-frequency (UHF) RFID tag in the United States, the antenna is specifically tuned with a resonant frequency around 915 MHz, and designed to cover a broad band of communication. Because the passive tags are so sensitive, they can easily be detuned by material in close proximity to the tag. This means that metal inside a box, liquid in a container, and other objects hidden inside a box being tagged can change the nature of how the tag is likely to communicate with a reader. The RFID reader and antenna can be putting out just the right amount of RF energy in just the right form, but a bad tag will keep you from getting any accurate read results. The largest two variables in tag performance are manufacturing quality and trial-and-error placement. Other factors that can have an impact on performance are environmental issues such as humidity or damage from a direct blow.

Other frequencies are equally important to know about-13.56 MHz or high frequency is very common, particularly at the item level in pharmaceuticals. Also, 433 MHz is very common for active tags worldwide because the U.S. Department of Defense has standardized an active tag from Lockheed Martin (formerly Savi Technology). The active tag can be the critical factor if there is a battery failure. Active tags do not function without a battery on board. The battery life is driven by how often the tag is broadcasting its signal.

Middleware

In truth, middleware cannot by itself affect the performance of an RFID interrogation zone. However, what it can do is change the setting of the RFID reader, which in turn can wreak havoc on the well-tuned RFID reader that you spent hours getting right. To make sure that you are not setting yourself up for certain disaster, it's critical to know what functionality the middleware controls and how it speaks to the reader. Some middleware can control only one or two parameters of a reader, such as power level or retry rate, when in fact a reader may have a dozen or more different parameters that can be finely tuned. From a communication perspective, it is important to find out whether a reader is constantly sending information to the middleware or if the middleware is asking for information only at certain instances. Finally, you need to determine how much filtering is being done at the reader level so you know how hard the middleware server is going to have to work.

Note 

Don't confuse the firmware with the middleware. The firmware sits natively on every reader and needs to be changed if you are upgrading a reader to read different tags-for instance, changing from Generation 1 to Generation 2, which affects whether or not they can read the latest version of tags.