How to measure the RSSI value between an RF tag and a reader?

[VSoni.1]

Hello, I am fairly new to the field of RF communication. I am working on a project wherein I have to communicate with RF tags using RF readers. The RF tag IC I am planning to use belongs to the ST25TV series. Since I'm planning to use multiple RF tags in my project which will be moving, I wanted to know how could I measure the RSSI value for each tag? Would that value be measured by STmicroelectronic's reader ICs and any particular software offered by you for the same? Please suggest if there are any specific ST25 RFID readers which might measure RSSI or any third-party products/software which might be capable of that. Thank you very much!

[Travis Palmer]

Hello VSoni,

yes the ST35R3911B and ST25R3916 and their derivates support have a dedicated register to display the "Received Signal Strength" as an indicator (RSSI).

For example looking at the ST25R3911B:

Looking at Figure 4 of the datasheet, you can see that at the end of the receiver chain, the received signal strength is being measured. Since the signal travels through the whole receiver chain, the gains of the first, second and third gain stage have to be taken into account, as well as the attenuation of demodulator and individual attenuation of the gain stages. (details can be found in chapter 1.2.3 Receiver - "demodulator stage" and "Filtering and gain stages".

The RFAL already provides some API for getting the RSSI value of a received frame and calculating the signal strength based on the gain stages.

There is also a dedicated section in chapter 1.2.3 about the RSSI measurement.

The ST25R3916 offers a similar functionality. due to the advanced receiver, I would recommend to use this device.

You can explore the the RSSI feature on our ST25R3916-DISCO board.

After connecting the board via µUSB you have to select R/W mode and reading the card. Once clicking on the UID, the "Tag Info" tab opens.

The bar on the bottom indicates the RSSI value. By moving the card closer or further away from the antenna, you should see how the bar changes.

If RSSI indicates "Link lost" the card is out of the reading range of the reader.

It would be great, if you could share a bit more information about your application and what you want to achieve with it.

BR Travis

[VSoni.1]

Thanks a lot, Travis! The ST25R3916-DISCO board looks pretty good and we are planning to consider that. Unfortunately, I cannot reveal too much about our application. I also checked that ST has an NFC sensor app for both Android and iOS which has a bunch of variables that it outputs even as a .csv file. Could you tell me if this app would provide the RSSI value as an output or if it can be accessed as a variable in the app's source code? If we can access the measured RSSI value using the app itself, that would be great as we would minimize an extra device in our system.

[Brian TIDAL]

Hi,

in addition to the previous post, the API provided in our library is rfalGetTransceiveRSSI().

rgds

BT

[VSoni.1]

Thanks a lot, Brian!