GNU Radio is a free software development toolkit that provides signal processing blocks to implement software-defined radios and signal-processing systems. It can be used with external RF hardware to create software-defined radios, or without hardware in a simulation-like environment. It is widely used in hobbyist, academic, and commercial environments to support both wireless communications research and real-world radio systems. Overview The GNU Radio software provides the framework and tools to build and run software radio or just general signal-processing applications. The GNU Radio applications themselves are generally known as "flowgraphs", which are a series of signal processing blocks connected together, thus describing a data flow. As with all software-defined radio systems, reconfigurability is a key feature. Instead of using different radios designed for specific but disparate purposes, a single, general-purpose, radio can be used as the radio front-end, and the signal-processing software (here, GNU Radio), handles the processing specific to the radio application. These flowgraphs can be written in either C++ or Python. The GNU Radio infrastructure is written entirely in C++, and many of the user tools (such as GNU Radio Companion) are written in Python. GNU Radio is a signal-processing package and part of the GNU Project. It is distributed under the terms of the GNU General Public License (GPL), and most of the project code is copyrighted by the Free Software Foundation. History First published in 2001, GNU Radio is an official GNU package. Philanthropist John Gilmore initiated GNU Radio with the funding of $320,000 (US) to Eric Blossom for code creation and project-management duties. GNU Radio began as a fork of the Pspectra code that was developed by the SpectrumWare project at the Massachusetts Institute of Technology (MIT). In 2004, a complete rewrite of GNU Radio was completed, so today GNU Radio no longer has any original Pspectra code. Matt Ettus joined the project as one of the first developers, and created the Universal Software Radio Peripheral (USRP) to provide a hardware platform for use with the GNU Radio software. In 2004, Matt founded Ettus Research LLC and began selling USRPs that worked with GNU Radio. In September 2010, Eric Blossom stepped down as Project Lead and was replaced by Tom Rondeau. Early in the project, the core developers began holding semi-annual Hackfests. In 2011, the GNU Radio project began holding a yearly conference, called "GRCon", which generally has a Hackfest on the last day of