gr-rfid — EPC Gen2 UHF RFID Reader for GNU Radio 3.10

Ported from EMDCYY/gr-rfid (itself based on nkargas/Gen2-UHF-RFID-Reader).

What changed from upstream

• GNU Radio 3.10 build system (was 3.8)
• pybind11 bindings replace SWIG
• Headers moved to include/gnuradio/rfid/ (GR 3.10 convention)
• boost::shared_ptr → std::shared_ptr
• GRC YAML files updated for from gnuradio import rfid
• New apps/reader_b210.py — B210 live reader with CLI
• New examples/rfid_test_offline.py — headless offline test

Tested Environment

• Kali Linux (Debian-based), x86_64
• Python 3.13, GNU Radio 3.10.12, UHD 4.9.0
• USRP B210 + Bolton Long Ranger parabolic antenna (600 MHz – 6.5 GHz)
• OTA confirmed: B210 TX+RX at 915 MHz received tag RN16 backscatter

Build & Install

cd gr-rfid
rm -rf build && mkdir build && cd build
cmake -DCMAKE_INSTALL_PREFIX=/usr/local ..
make -j$(nproc)
sudo make install && sudo ldconfig

Verify:

/usr/bin/python3 -c "from gnuradio import rfid; print(dir(rfid))"

Usage

Offline test (no hardware)

/usr/bin/python3 examples/rfid_test_offline.py

Runs the full EPC Gen2 reader pipeline against pre-recorded IQ data in misc/data/file_source_test.

B210 live reader

# Full TX+RX (antenna on TX/RX port)
/usr/bin/python3 apps/reader_b210.py

# Passive eavesdrop (antenna on RX2, near an existing reader)
/usr/bin/python3 apps/reader_b210.py --rx-only

# Custom parameters
/usr/bin/python3 apps/reader_b210.py --freq 910e6 --rx-gain 50 --tx-gain 60 --ampl 0.5

Press Ctrl+C to stop and print results.

Known Issues

• B210 TX underruns: The feedback loop (reader → gate) generates TX samples on-the-fly. The B210's USB transport introduces latency that causes TX underruns (U warnings), corrupting query waveforms. The N210's Ethernet transport handles this better. A fix would pre-buffer query waveforms instead of generating them sample-by-sample.
• Offline test CRC: The included test recording has marginal signal quality — the pipeline decodes RN16 and EPC bits but CRC-16 fails. This is a signal quality issue, not a code bug.
• B210 USB firmware: The B210 sometimes fails to load FX3 firmware on connect (stays at VID 2500 PID 0020). Power-cycling the USB port via sysfs authorized attribute resolves this:

  echo 0 | sudo tee /sys/bus/usb/devices/<port>/authorized
  sleep 5
  echo 1 | sudo tee /sys/bus/usb/devices/<port>/authorized

Architecture

Three C++ blocks communicating via global singleton state:

• gate — pulse detection, gates tag responses based on Gen2 timing
• tag_decoder — FM0 differential decode, CRC-16 validation
• reader — Gen2 QUERY/ACK/QueryRep generation, inventory state machine

Flowgraph topology (feedback loop):

usrp_source → fir_filter(decim=5) → gate → tag_decoder → reader → amp → usrp_sink
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Original Authors

• Nikos Kargas ([email protected]) — original Gen2-UHF-RFID-Reader
• Xin Liu — EMDCYY/gr-rfid fork (GR 3.8 updates, debug output)