SPEAKeasy Phase II
The goals were to get a more quickly reconfigurable architecture (i.e. several conversations at once), in an open software architecture, with cross-channel connectivity (the radio can "bridge" different radio protocols). The secondary goals were to make it smaller, weigh less and cheaper.
The project produced a demonstration radio only fifteen months into a three year research project. The demonstration was so successful that further development was halted, and the radio went into production with only a 4 MHz to 400 MHz range.
The software architecture identified standard interfaces for different modules of the radio: "Radio Frequency Control" to manage the analog parts of the radio, "Modem Control" managed resources for modulation and demodulation schemes (FM, AM, SSB, QAM, etc), "Waveform Processing" modules actually performed the modem functions, "Key processing" and "Crytographic processing" managed the cryptographic functions, a "multimedia" module did voice processing, a "Human Interface" provided local or remote controls, there was a "Routing" module for network services, and a "control" module to keep it all straight.
The modules are said to communicate without a central operating system. Instead, they send messages over the PCI (computer) bus to each other with a layered protocol.
As a military project, the radio strongly distinguished "red" (unsecured secret data) and "black" (cryptographically secured data).
The project was the first known to use FPGAs (field programmable gate arrays) for digital processing of radio data. The time to reprogram these is an issue limiting application of the radio.
Joint Tactical Radio System (JTRS)
JTRS is a U.S. and allied program (NATO participates) to produce a family of software radios for different military domains. For example, hand-held, vehicular, base-stations (fixed and maritime), airborne and dismounted.
The radio uses CORBA on POSIX operating systems to coordinate the different modules. A software architecture is published on the web.
Software-Defined Radio (SDR)
The software configuration architecture (SCA) is the SDR Forum's industrial version of JTRS, adapted to cellular base stations and other practical commercial applications. The SCA is described at the SDR Forum'd web site.
Amateur software radios
The typical amateur software radio (see amateur radio) uses a direct conversion receiver (see the ARRL Handbook, 1999 for a suitable dual mixer design). The conversion is to an audio frequency, 0 to 20 kHz. A fast PC operates custom (amateur-written) software as the signal processor. A commercial high-quality stereo-input audio card operates as the analog-to-digital converter.
The typical transmission set-up feeds the audio output of the PC to a microphone input of a commercial AM shortwave transmitter. Flexible digital transmission chains are an area of active research among amateurs, with much interest in predistortion and direct digital amplification.
The above set of equipment is adequate to let amateurs operate within their limited radio bands.
Uses include every common amateur modulation: morse code, single sideband, frequency modulation, radioteletype, slow-scan TV and packet radio. Amatuers also experiment with new modulation methods.
See also digital radio