GNU Radio Drives Oscilloscope



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Improving WiFi Throughput with FM Radio

WiFi networking is one of those things that is reasonably simple to use, but has a lot of complex hidden features (dare we say, hacks) that make it work, or work better. For example, consider the Distributed Coordination Function (DCF) specified in the standard. Before a station can send, it has to listen for a certain time period. If the channel is clear, the station sends. If not, it has to delay a random amount of time before trying again. This is a form of Carrier Sense Multiple Access (CSMA) channel management.

Unfortunately, listening time is dead time when–at least potentially–there is no data transmitted on the network. DCF allows you to use various handshaking packets to do virtual carrier detection and ready/clear to send, but these are also less efficient use of bandwidth. There are other optional coordination functions available in the WiFi standard, but they all have their drawbacks.

[Aleksandar Kuzmanovic] at Northwestern University and two of his students have recently published a paper with a new way to coordinate multiple unrelated wireless networks using ubiquitous FM broadcast radio signals called WiFM. Instead of trying to synchronize to the WiFi data channel, this new scheme selects a strong FM radio station that broadcasts Radio Data Service (RDS) data (the data that populates the song titles and other information on modern radios).

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Getting Started with GNU Radio






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Mid-Priced Hardware Gets Serious About Software Defined Radio




[Balint]’s GNU Radio Tutorials






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Hacking Rolling Code Keyfobs

Most keyfobs out there that open cars, garage doors, and gates use a rolling code for security. This works by transmitting a different key every time you press the button. If the keys line up, the signal is considered legitimate and the door opens.

[Spencer] took a look into hacking rolling code keyfobs using low cost software-defined radio equipment. There’s two pars of this attack. The first involves jamming the frequency the keyfob transmits on while recording using a RTL-SDR dongle. The jamming signal prevents the receiver from acknowledging the request, but it can be filtered out using GNU Radio to recover the key.

Since the receiver hasn’t seen this key yet, it will still be valid. By replaying the key, the receiver can be tricked. To pull off the replay, GNU Radio was used to demodulate the amplitude shift keying (ASK) signal used by the transmitter. This was played out of a computer sound card into a ASK transmitter module, which sent out a valid key.

Audio Networking With GNU Radio






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