In 1970, a researcher at a
United States Department of Defense laboratory coined the term "digital receiver". A laboratory called the Gold Room at
TRW in California created a software baseband analysis tool called Midas, which had its operation defined in software. In 1982, while working under a US Department of Defense contract at
RCA,
Ulrich L. Rohde's department developed the first SDR, which used the
COSMAC (Complementary Symmetry Monolithic Array Computer) chip. Rohde was the first to present on this topic with his February 1984 talk, "Digital HF Radio: A Sampling of Techniques" at the Third International Conference on HF Communication Systems and Techniques in London. In 1984, a team at the
Garland, Texas, Division of
E-Systems Inc. (now
Raytheon) coined the term "software radio" to refer to a digital baseband receiver, as published in their E-Team company newsletter. A 'Software Radio Proof-of-Concept' laboratory was developed by the E-Systems team that popularized Software Radio within various government agencies. This 1984 Software Radio was a digital
baseband receiver that provided programmable interference cancellation and demodulation for broadband signals, typically with thousands of
adaptive filter taps, using multiple
array processors accessing shared memory. In 1991, Joe Mitola independently reinvented the term software radio for a plan to build a
GSM base station that would combine Ferdensi's digital receiver with E-Systems Melpar's digitally controlled communications jammers for a true software-based transceiver. E-Systems Melpar sold the software radio idea to the US Air Force. Melpar built a prototype commanders' tactical terminal in 1990–1991 that employed
Texas Instruments TMS320C30 processors and
Harris Corporation digital receiver chip sets with digitally synthesized transmission. The Melpar prototype didn't last long because when E-Systems ECI Division manufactured the first limited production units, they decided to "throw out those useless C30 boards", replacing them with conventional RF filtering on transmit and receive and reverting to a digital baseband radio instead of the SpeakEasy like IF ADC/DACs of Mitola's prototype. The Air Force would not let Mitola publish the technical details of that prototype, nor would they let Diane Wasserman publish related software life cycle lessons learned because they regarded it as a "USAF competitive advantage". So instead, with USAF permission, in 1991, Mitola described the architecture principles without implementation details in a paper, "Software Radio: Survey, Critical Analysis and Future Directions" which became the first
IEEE publication to employ the term in 1992. When Mitola presented the paper at the conference, Bob Prill of
GEC Marconi began his presentation following Mitola with: "Joe is absolutely right about the theory of a software radio and we are building one." Prill gave a GEC Marconi paper on PAVE PILLAR, a SpeakEasy precursor. SpeakEasy, the military software radio was formulated by Wayne Bonser, then of
Rome Air Development Center (RADC), now Rome Labs; by Alan Margulies of
MITRE Rome, NY; and then Lt Beth Kaspar, the original DARPA SpeakEasy project manager and by others at Rome including Don Upmal. Although Mitola's IEEE publications resulted in the largest global footprint for software radio, Mitola privately credits that DoD lab of the 1970s with its leaders Carl, Dave, and John with inventing the digital receiver technology on which he based software radio once it was possible to transmit via software. A few months after the National Telesystems Conference 1992, in an E-Systems corporate program review, a vice-president of E-Systems Garland Division objected to Melpar's (Mitola's) use of the term "software radio" without credit to Garland. Alan Jackson, Melpar VP of marketing at that time, asked the Garland VP if their laboratory or devices included transmitters. The Garland VP said: "No, of course not — ours is a software radio receiver." Al replied: "Then it's a digital receiver but without a transmitter, it's not a software radio." Corporate leadership agreed with Al, so the publication stood. Many amateur radio operators and HF radio engineers had realized the value of digitizing HF at RF and of processing it with Texas Instruments TI C30
digital signal processors (DSPs) and their precursors during the 1980s and early 1990s. Radio engineers at
Roke Manor in the UK and at an organization in Germany had recognized the benefits of ADC at the RF in parallel. Mitola's publication of software radio in the IEEE opened the concept to the broad community of radio engineers. His May 1995 special issue of the
IEEE Communications Magazine with the cover "Software Radio" was regarded as a watershed event with thousands of academic citations. Mitola was introduced by Joao da Silva in 1997 at the First International Conference on Software Radio as "godfather" of software radio in no small part for his willingness to share such a valuable technology "in the public interest". Perhaps the first software-based radio
transceiver was designed and implemented by Peter Hoeher and Helmuth Lang at the German Aerospace Research Establishment (
DLR, formerly
DFVLR) in
Oberpfaffenhofen, Germany, in 1988. Both transmitter and receiver of an adaptive digital satellite modem were implemented according to the principles of a software radio, and a flexible hardware periphery was proposed. In 1995, Stephen Blust coined the term "software defined radio", publishing a request for information from Bell South Wireless at the first meeting of the Modular Multifunction Information Transfer Systems (MMITS) forum in 1996 (in 1998 the name was changed to the Software Defined Radio Forum), organized by the USAF and DARPA around the commercialization of their SpeakEasy II program. Mitola objected to Blust's term, but finally accepted it as a pragmatic pathway towards the ideal software radio. Although the concept was first implemented with an IF ADC in the early 1990s, software-defined radios have their origins in the U.S. and European defense sectors of the late 1970s (for example, Walter Tuttlebee described a
VLF radio that used an ADC and an
8085 microprocessor), about a year after the First International Conference in Brussels. One of the first public software radio initiatives was the U.S. DARPA-Air Force
military project named
SpeakEasy. The primary goal of the SpeakEasy project was to use programmable processing to emulate more than 10 existing military radios, operating in
frequency bands between 2 and 2000
MHz. Another SpeakEasy design goal was to be able to easily incorporate new
coding and modulation standards in the future, so that military communications can keep pace with advances in coding and modulation techniques. In 1997,
Blaupunkt introduced the term "DigiCeiver" for their new range of DSP-based tuners with
Sharx in
car radios such as the Modena & Lausanne RD 148.
SpeakEasy phase I From 1990 to 1995, the goal of the
SpeakEasy program was to demonstrate a radio for the
U.S. Air Force tactical ground air control party that could operate from 2
MHz to 2
GHz, and thus could interoperate with ground force radios (frequency-agile
VHF,
FM, and
SINCGARS), Air Force radios (VHF
AM), Naval Radios (VHF
AM and
HF SSB teleprinters) and
satellites (
microwave QAM). Some particular goals were to provide a new signal format in two weeks from a standing start, and demonstrate a radio into which multiple contractors could plug parts and software. The project was demonstrated at
TF-XXI Advanced Warfighting Exercise, and demonstrated all of these goals in a non-production radio. There was some discontent with failure of these early software radios to adequately filter out of band emissions, to employ more than the simplest of interoperable modes of the existing radios, and to lose connectivity or crash unexpectedly. Its
cryptographic processor could not change context fast enough to keep several radio conversations on the air at once. Its software architecture, though practical enough, bore no resemblance to any other. The SpeakEasy architecture was refined at the MMITS Forum between 1996 and 1999 and inspired the DoD integrated process team (IPT) for programmable modular communications systems (PMCS) to proceed with what became the Joint Tactical Radio System (JTRS). The basic arrangement of the radio
receiver used an
antenna feeding an
amplifier and down-converter (see
Frequency mixer) feeding an
automatic gain control, which fed an
analog-to-digital converter that was on a computer
VMEbus with a lot of
digital signal processors (
Texas Instruments C40s). The transmitter had
digital-to-analog converters on the
PCI bus feeding an up converter (mixer) that led to a power amplifier and antenna. The very wide frequency range was divided into a few sub-bands with different analog radio technologies feeding the same analog to digital converters. This has since become a standard design scheme for wideband software radios.
SpeakEasy phase II The goal was 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, cheaper, and weigh less. The project produced a demonstration radio only fifteen months into a three-year research project. This 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 "cryptographic 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 was an issue limiting application of the radio. Today, the time to write a program for an FPGA is still significant, but the time to download a stored FPGA program is around 20 milliseconds. This means an SDR could change transmission protocols and frequencies in one fiftieth of a second, probably not an intolerable interruption for that task.
2000s The SpeakEasy SDR system in the 1994 uses a
Texas Instruments TMS320C30 CMOS digital signal processor (DSP), along with several hundred
integrated circuit chips, with the radio filling the back of a truck. By the late 2000s, the emergence of
RF CMOS technology made it practical to scale down an entire SDR system onto a single
mixed-signal system-on-a-chip, which
Broadcom demonstrated with the BCM21551 processor in 2007. The Broadcom BCM21551 has practical commercial applications, for use in
3G mobile phones. == Military usage ==