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Essential Factors in Evaluating and Purchasing RFID Readers

Lastly, note the sponsored column today from Sirit, which discusses the role and importance of the RFID reader to overall system performance. The article explains the key performance characteristics end users should consider when evaluating readers for purchase: tag singulation, tag read sensitivity, and interference tolerance.
Sep 02, 2008This article was originally published by RFID Update.

September 2, 2008—Within an RFID system, there are initial costs associated with hardware, such as readers, antennas, and network infrastructure installation, in addition to the costs related to middleware products and data management. As a critical system component, the RFID reader can have a major impact on overall system effectiveness. If a reader is unable to perform reliably, there is a cascading effect that is detrimental to the entire system. Investing in a high performance reader may cost slightly more in the short-term, but the decision to invest in a better reader could have a tremendous long-term effect throughout the life-cycle of an RFID system.

Performance Does Matter

RFID reader performance does make a difference in the overall success of a RFID implementation. Better accuracy in reading tags leads to more reliable data, fewer exceptions that must be managed, and ultimately lowers the total cost of ownership. As potential users of RFID make their purchasing decisions with regard to which reader to buy, reader performance should certainly be at the top of the list of considerations.

There are three key components in evaluating readers: tag singulation performance, tag receive sensitivity, and tolerance to interference.

Tag Singulation

The ability of a RFID reader to reliably read (or singulate) tens, hundreds or even a thousand tags and their data quickly and accurately is critical in a real world application environment.

High tag read rates are important in case level applications because of line production speeds and the speed at which forklifts travel through a portal. High tag read rates are also important in item-level applications due to the high concentration of tags also read at high line speeds.

The ability of a reader to "saturate" a read field at the allowable frequency and power level has a big impact on read rate. Being able to fully manage and optimize the available frequency bandwidth is also critical. A software radio powered reader has an advantage in being able to dynamically respond and manipulate performance in tag singulation, and Sirit has developed proprietary algorithms that set the INfinity 510 UHF reader apart when it comes to tag singulation.

Another important aspect is the "forward link rate", defined as the rate or clock speed at which the reader is able to transmit data. This is similar to a baud rate that is a familiar term in data transmission. Having the highest forward link rate is advantageous, but this needs to be combined with the ability to execute the necessary anti-collision algorithms at these high data rates. So, a close examination of this aspect is also necessary.

As an RFID user, care should be taken when evaluating reader tag singulation. Users should test read rates at their usual production line speeds and under their normal working conditions. Having a reader that can perform beyond read rate expectations can make a big difference in overall system performance, while marginal performance can be detrimental in achieving the goals of an RFID implementation.

Tag Receive Sensitivity

Like RFID readers, not all tags perform the same, although tag manufacturers have made tremendous strides in improving tag performance consistency. The reader and its tag receive sensitivity can play a significant role in ensuring that tag data is reliably received and interpolated. The amount of RF energy required to energize a tag is far stronger than is required to receive the data from the tag to the reader, which is why receive sensitivity is so essential.

As the RF signal is broadcast and effectively fills the space of the read field, tags are energized and they respond with a return signal containing their data that essentially rides on top of the RF signal (modulation). The challenge for a reader is to not only receive and process the data from "strong" tags, but to also dig deep into the RF field where some tags may not be "talking" as loudly as others. These hard-to-reach tags pose a challenge to readers because only pieces of the data may be received. Readers must be designed in such a way that they maximize the RF read zone to be able to pick up even the faint signal of weak tags.

Having a reader that is sensitive to these "quieter" tags and being able to reach and extract their data is a performance differentiator and should be a key aspect of reader evaluation and selection. Sirit's IN510 has been tested by numerous customers and has differentiated itself because of its ability to achieve high tag receive sensitivity through a unique design approach that maximizes receive signal strength.

Interference Tolerance

In many of today's RFID implementations, multiple readers are often in close proximity to each other. This is especially true in a warehouse environment where there are a number of dock doors with readers and antennas that make up portals through which forklifts may travel. These adjacent portals can cause each reader to interfere with the performance of the others. In this configuration, a reader must operate as if it had blinders on. The ability to perform this task is vital and is measured in how much external, extraneous interference can be tolerated without it affecting tag read performance. This is an important consideration when deploying readers to be used immediately, but should also be a consideration for future deployments, as the problem of interference can be further exacerbated when more readers are brought on-line.

From a RFID reader's perspective, everything outside of the frequency on which the reader is broadcasting is noise, whether it's from other readers or other RF sources. Excessive amounts of noise or interference will cause false data to be read by the reader and can substantially curtail performance. In addition, two or more adjacent readers trying to read the same data from the same tag will create havoc and decrease system performance. This is one of the areas where a high performance reader like the IN510 with a reliable scheme for noise rejection will make a difference.

In Conclusion

Initial cost of an RFID reader is an obvious consideration and typically correlates with performance. There are a variety of low and mid-priced readers on the market that are sufficient for some applications, but in most cases, having a reader that is just adequate can be detrimental to overall system effectiveness. Selecting the right reader should never be based strictly on price.

Comparison testing of readers in an environment that is close to real world conditions is important because readers can behave differently under certain application conditions. Also, testing readers with various tag types should be brought into the equation since all tags do not behave the same when placed on objects. The initial evaluation of a reader can be complex, but the selection of the best performing, most reliable reader will easily contribute to a lower total cost of ownership because of reduced maintenance costs, in addition to better, more reliable data. This will ultimately lead to the goal of a fast recovery of a user's return on investment from their RFID system. Reader performance does matter.

For questions or additional information please contact Tawnya Clark, tclark@sirit.com.
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