Software-defined radio
A software defined radio (SDR) system is a radio communication system which uses software for the modulation and demodulation of radio signals.
The hardware of a software defined radio typically consists of a superheterodyne RF front end which converts RF signals from and to analog IF signals, and analog to digital converter and digital to analog converters which are used to convert a digitised IF signal to and from analog form.
GNU Radio is a project to implement software defined radio as free software.
Software defined radio can currently be used to implement simple radio modem technologies.
In the long run, software defined radio is expected by its proponents to become the dominant technology in radio communications.
One of the first software radios was a militar project named SpeakEasy. The primary goal of the SpeakEasy project is to utilize programmable processing to emulate more than 10 existing military radios, operating in frequency bands between 2 and 200 MHz . Further, another design goal was to be able to easily incorporated new coding and modulation standards can in the future, so that military communications can keep pace with advances in coding and modulation techniques.