This frequency offset, colloquially named the Doppler shift, is caused by several factors, chief among them: When observing Wi-Fi packets in the wild, we can notice that each packet has a slightly different carrier frequency. Test setup for demonstrating GNU Radio Wi-Fi transceiverĭon’t have the required hardware? Try the RFtap RDS tutorial instead, using the low-cost RTL-SDR receiver. Presentation about GNU Radio IEEE 802.11a/g/p OFDM Receiver You can verify that Wireshark supports RFtap by loading this sample RFtap pcap file. See gr-ieee802-11 README for troubleshooting.
Verify that you can receive Wi-Fi packets from nearby 5GHz access points by running: gnuradio-companion gr-ieee-80211/examples/wifi_rx.grc.
Install GNU Radio from source (I followed these instructions), install GNU Radio’s Wi-Fi IEEE 802.11 a/g/p transceiver. Plenty! You will need a fast Mac or Linux computer (I use Ubuntu 16.04 on Intel i5), a SDR receiver capable of receiving 20MHz bandwidth at a center frequency of ~5GHz such as Ettus N210 or B200. The RFtap protocol is designed to encapsulate any type of packet: Wi-Fi, Bluetooth, or packets from any proprietary protocol. You can think of RFtap as the “glue” between GNU Radio and Wireshark, allowing access to RF metadata from Wireshark or Scapy.