GNU Radio Applications

In addition to the examples discussed above, GNU Radio comes with a complete HDTV transmitter and receiver, a spectrum analyzer, an oscilloscope, concurrent multichannel receiver and an ever-growing collection of modulators and demodulators.
Projects under investigation or in progress include:

• A TiVo equivalent for radio, capable of recording multiple stations simultaneously.
• Time Division Multiple Access (TDMA) waveforms.
• A passive radar system that takes advantage of broadcast TV for its signal source. For those of you with old TVs hooked to antennas, think about the flutter you see when airplanes fly over.
• Radio astronomy.
• TETRA transceiver.
• Digital Radio Mundial (DRM).
• Software GPS.
• Distributed sensor networks.
• Distributed measurement of spectrum utilization.
• Amateur radio transceivers.
• Ad hoc mesh networks.
• RFID detector/reader.
• Multiple input multiple output (MIMO) processing.

Politics

Every revolution has its political issues. Free software for building radios is troublesome to some people. In the US, we've run into opposition from the Motion Picture Association of America and its attempt with the Broadcast Flag to restrict the kinds of receivers that can be built for over-the-air digital TV.
The US Federal Communications Commission has issued a Notice of Proposed Rule Making (NPRM) concerning Cognitive Radio Technologies and Software Defined Radios. Several troublesome issues are raised in the NPRM, including restricting the sale of high-speed digital-to-analog converters, requirements for digital signatures or similar methods to keep unauthorized software out of software radio hardware and new restrictions on radios built for the amateur radio market.
Summary

Software radio is an exciting field, and GNU Radio provides the tools to start exploring. A deep understanding of software radio requires knowledge from many domains.