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Oct 31, 2016

RAIN RFID Tag Read Range: Opinion or Fact?

中文版 Chinese version

Creating a tagging solution for passive RAIN RFID tags to a particular application starts with understanding the application specific requirements. That involves plenty of process engineering, but also typically discussions around the expected read range between tagged items and reader antennas. The read range is impacted by several factors and many start the cooking process by looking at the properties of RAIN RFID tags.

Tag datasheets carry plenty of information: protocol, operating frequency, chip type, memory utilization, physical size and much more. Amongst all information on datasheet, I reckon tag dimensions and read range are typically the first ones checked. Both are relatively easy values to understand, although the first one is a fact, and the second more an opinion. In the following I explain how to interpret the tag read range right.

Classic Approach: Take a Tag and Walk Away

The simplest way to get an idea of the read range is to place a reader to the end of a hall, take a tag and walk away from the reader antenna to see how far the tag can still be successfully read. In this kind of empirical test the result is not a fixed distance under which the reading would always be successful, but instead the result typically varies as below:

Result of a “walk away” read range measurement using a lower end RFID reader. What would you choose for a read range value?

Obviously such a result leaves a problem: how to interpret the results? What in fact is the read range in this case? A bigger problem is that the result is actually a synthesis of so many factors, such as reader properties, tag alignment, other objects in the environment, illumination in the hall, settings in the reader… So, what was it again you wanted to see?

Very few halls, office spaces or basements are stable enough to reproduce the test from day to another with the same test result. Therefore, key delivered value of this approach is merely the physical exercise, and most vendors don’t use these results in their tag datasheets.

Laboratory vs. Real Life Performance

RFID measurement systems characterize tags at high precision after which read range is calculated based on a few assumptions. Laboratory measurements themselves are often performed in shielded and anechoic chambers to remove other variables from the test results, which greatly improves the value of the data and the repeatability of the test process.

Theoretical read range of two RAIN RFID tags designed for different applications. Tag 2 shows better max read range at the FCC band, but is too highly tuned to efficiently cover the whole band. Despite of its shorter read range, Tag 1 as a broadband design seems like a more reliable choice.

This kind of measurement does not emulate effects of environment where tags are used. Experts talk of multipath propagation and path loss, and some others may talk of reflections, shadowing and interior design. No matter which definition is used, the environment is the grand source of differences between laboratory and real life performance.

Practical Difference of ERP and EIRP

Theoretical read range values plotted by the Tagformance system are based on the Tag Performance Parameters and Test Methods Version 1.1.2, 2008, EPCGlobal Inc. For the read range standard specifies 35dBm EIRP transmit power to be used in the calculation. 35dBm EIRP transmit power equals 33dBm ERP power. 33dBm ERP equals 2W and 35dBm EIRP equals 3.28W. If maximum power 4W EIRP is allowed, as in the FCC band, theoretical read range results can be obtained by adding 11% on the figures shown in the Tagformance software.

Forward Limited Read Range Is Not a Safe Assumption Anymore

As tag dimensions shrink and tag ICs become more sensitive, readers often become the limiting factor of read range. A reader with more sensitive receiver is able to pick up a tag’s reply from greater distance. When read range is analyzed it is typical to separate read range to forward (up) and reverse (down) links.

Picture below shows forward and reverse read range curves, which are calculated using 1W ERP transmit power, 2dBi antenna gain and -65dBm receiver sensitivity.

Separated forward, reverse and resulting read range curves. For ETSI range forward and reverse curves are equal, but for FCC range read range is reverse link limited – a reader with more sensitive receiver would improve read range on FCC band.

Tag Close Coupling Issues to Be Addressed by TIPP

As tagging spreads to new product categories in the retail industry, small tagged items are often brought into close proximity to each other. Just think about items boxed for transport. Especially when the distance between tags is less than 3 cm, the tags start to couple with each other.

The close coupling effects will be considered in the upcoming GS1 TIPP global standard. Stay put for Juho Partanen’s upcoming blog post regarding these issues!

From Opinions Back to the Facts

As you saw from the above, the read range is a factor of many issues. As you work yourself through the tag and reader datasheets with the aid of expert tools and good standards, you can connect the dots with relative ease. This process transforms opinions into facts.

I’d appreciate your comments and suggestions around these topics. New perspectives are always welcome.

Learn How to Test the Read Range with Tagformance

Download our application note “Read Range Test with Voyantic Tagformance” to learn how easy it is to test the read range!

Dec 11, 2015

This Doesn’t Look Right – Should I Contact Technical Support?

What do you do if, one morning, a new light with some strange symbol is suddenly lit on your car’s dashboard? You probably pull over and start browsing the car owner manual. You may be a little worried. Did I do something wrong? Can I fix this myself, or does the car need to be serviced? How long will I need to survive without my car?
In the same way, your Tagformance, the RFID test system that you typically use every day may have a problem you need to solve. You may already be an experienced user, or maybe you have just recently started to work with the system. When a new error message pops up or you get unexpected measurement results, it’s just like with your car. What’s wrong? Should I contact Voyantic Technical Support?

The answer to the last question is yes. You should.

*‘No such thing as a stupid question’ is a common phrase with a long history, and it makes perfect sense to me. *

If you have a problem with anything, and there is a possibility to get it solved quickly by asking someone who can help you, why shouldn’t you? The one who asks the “stupid question” may be doing a service to everyone, including the vendor, by pointing out a visible improvement to the product.

Here are some more or less typical situations where you might wonder if you should contact the vendor or just carry on. Uncertainty: You are performing measurements that look nice and smooth, but deep down, you are still wondering whether the results are correct? Is there some bias in the device? Am I measuring the right way? By contacting Voyantic Technical Support, we can verify if the device is OK by comparing the reference tag measurement results with the same measurement setup. We can also measure your sample tags and give a second opinion of the results and maybe give pointers on what else you can measure from your tags.

Differences between sites: You may have a colleague in the next room or on the other side of the globe doing the same measurements that you are. The equipment may be the same, the setup may be identical, but still, your results don’t match completely. For example, you get a theoretical read range value of 11 meters, and your colleague measures 10 meters. One meter sounds like a lot, but is it after all? By looking at the measurement data, we can verify whether the difference is something to worry about, or if it fits into production variation and typical measurement accuracy. Other factors, such as temperature, may cause a difference. The effect of temperature is described in more detail in an Application Note, which can be downloaded here. While visiting the site, you may find other Application Notes worth reading too.

Missing features: Different Tagformance measurement options are enabled with the license file. We can create license files where any measurement option can be enabled for a given time. So, if you think that one or more options could be useful for your work, we can enable the option for a trial period. To name a few;

  • Scripter is a great tool to automate your daily measurement routines and reduce the human error from the results.
  • The Tagformance has two Application Programming Interfaces, APIs, that enable you to write your software that uses the Tagformance device. The LabVIEW API is a perfect match for LabVIEW users, and the DLL API serves users of other programming languages.
  • Memory management is a brand new tool for one of the hot topics, sensor tags, for example. With Memory management, it is possible to verify changes of any memory address content within seconds.

Memory Management

All this said, do not hesitate to contact us! In most cases, it is a win-win situation where you will get your problem solved or a question answered, and we get valuable feedback, which will help us in making our products even better. We are here to help you – send us a message!