Working Passive UHF RFID reader using the LimeSDR

#1

Hi all,

As my final year project at university, I have successfully configured the LimeSDR-USBv1.4 to work as an RFID reader of standard commercial UHF RFID tags. Thanks to all those on this forum who helped me with some of the issues I encountered along the way.

SoapySDR was used with SoapyUHD, in order to use standard UHD blocks in a GNU Radio application. I ended up having to edit the SoapyLMS7 drivers in order to resolve a few problems. I have uploaded my edited version of the drivers to a github repo here, along with my GNU Radio application. Further details of my implementation can be found in the readme.

I wrote up my findings in a final report, which is also included in the repo. The report includes some relevant background, along with a discussion of the problems encountered, the solutions implemented, and an evaluation of the LimeSDR’s performance as an RFID reader. Warning: the report is almost 50 pages long!

I no longer have access to the LimeSDR or any of the relevant equipment so I won’t be able to develop the code further; I am however happy to answer any questions that people may have.

I hope people find the above useful.

Disclaimer: I was (and still am) very much a beginner at SDR in general, let alone the LimeSDR specifically. It is possible that there are therefore mistakes in my implementation, conclusions, and/or analysis - if you spot any, please post them here in order to help others!

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#2

Hello DasSidG

What is the distance of this kind of RFID reader?

Is it possible to add some amplifier, so that this SDR based reader could work in a larger range than a commercial reader?

Thanks.

#3

Hi shao,

In this experiment I did not measure the maximum range. I used a near-field antenna and placed the tag directly on top. I did however estimate the sensitivity of the reader (assuming that the range is reverse-link limited), so if you have a model for the attenuation in air you could probably estimate it from that.

In principle there is no physical reason why you could not add an amplifier to the transmit output to increase the range; however you have to be careful of a couple of things:

  1. Some of the transmitted signal will leak back into the receiver, and this will be increased if the transmitted signal is amplified, which means that more amplification might not actually gain you more range.
  2. If your amplifier is not very linear then you might add a lot of noise.
  3. The transmit power of commercial readers are (I believe) generally limited by regulatory constraints, as opposed to any fundamental physical or electronic limits. Thus, if you intend to use this in a commercial context then you might not be able to do better than a commercial reader in terms of transmit power.
#4

Thanks DasSidG. I am little bit confused. Your project is passive rfid reader, so does it sends out any radio waves before receiving information? Or it’s just receive only?

#5

Hi DasSidG,

What is the power in db whith the frequency 850 / 900 Mhz.

Best regards