Software-defined radio (SDR) is not a new technology anymore; it is a widely adopted, almost mandatory, way to build today’s wireless devices (with an exception made for low-cost, low-power ASIC-based devices like smartphones and tablets). It has been almost 30 years since SDR was first introduced. Here’s a quick summary of landmark events throughout its three decades of evolution.
1984 E-Systems coins “software radio” term
E-Systems, now Raytheon, coined the term “software radio” in a company newsletter. It referred to a prototype digital baseband receiver equipped with an array of processors that performed adaptive filtering for interference cancelation and demodulation of broadband signals.
The first military program that specifically required a radio to have its physical layer components implemented in software was DARPA’s SPEAKeasy. Its primary objective, originating from the U.S. Air Force, was to have a single radio that could support ten different military radio protocols and operate anywhere between 2 MHz and 2 GHz. A secondary goal was the ability to incorporate new protocols and modulations, thereby future-proofing the radio hardware. Taking from DARPA’s description, “SPEAKeasy is an attempt to create the PC of the radio world.”
1992 Joseph Mitola publishes paper about software radio at IEEE
Joe Mitola was the first to publish on the topic of software radio, for the IEEE National Telesystems Conference in 1992, with his paper “Software Radio: Survey, Critical Analysis and Future Directions”. Referred to by many as the godfather of software radio, Mitola is recognized as having coined the term “software radio”, despite E-Systems’ prior use. The E-Systems prototype was a receiver only and therefore not a complete radio. Later, in 1998, Mitola used the term “cognitive radio” to refer to the concept of radios being aware of their spectral environment and having the necessary intelligence to adapt as required.
1996 Creation of the SDR Forum
The first industry association dedicated to SDR was founded in 1996 as “The Modular Multifunction Information Transfer System (MMITS) Forum.” In 1998 it became the SDR Forum, and then in 2010, the Wireless Innovation Forum. The forum consisted of people and organizations from government, industry and academia, all driven by the goal of advancing SDR-related technologies. It formed several working groups and committees to stimulate and steer innovation and standards.
1997 Creation of the JTRS
The Joint Tactical Radio System was created by the U.S. Department of Defense to increase interoperability and waveform portability through the definition and standardization of abstraction layers and interfaces, known as the Software Communication Architecture (SCA). The multi-billion dollar program was very ambitious and experienced difficulties, delays, and cost overruns. It was officially cancelled in 2011 by the U.S Under Secretary of Defense, who stated that the products and technologies resulting from the program were unlikely to meet the established requirements.
Nevertheless, it greatly stimulated advances in SDR development for a decade. SCA-compliant radiosfrom manufacturers like Rohde & Schwarz, Thales, and Harris, have been deployed. Also, the European Defense Agency created the European Secure Software Defined Radio (ESSOR) program, which continues from the work of the JTRS SCA.
1998 Automated code generation for embedded SDR
Nutaq (then Lyrtech) teamed up with MathWorks to create the first development environment that could generate executables directly from a Simulink model for a Texas Instruments DSP and a Xilinx FPGA. This innovation addressed one of the biggest difficulties waveform developers and researchers had to deal with: writing code for embedded processors. The DSP and FPGA were collocated on a board called the SignalMaster. It was interfaced with an A/D and D/A module and was one of the first commercial SDR development platforms for labs and universities to prototype with.
2001 GNU Radio
Evolved from an MIT-originating framework called PSpectra, GNU Radio was founded by Eric Blossom and funded by John Gilmore, employee #5 of Sun Microsystems. GNU Radio is an open-source framework for the development of SDR applications within a PC environment. With more than 5,000 claimed users as of 2012, it is by far the most popular SDR development toolset. Complete waveforms such as P25, 802.11, ZigBee, Bluetooth, RFID, DECT, GSM, and even LTE (still a work in progress) can be downloaded from the repository and run on any x86 system.
2004 FCC first approval of a commercial SDR
Vanu Inc. succeeded in getting their Anywave base station approved by the FCC. The Anywave is a dual-mode base station capable of running GSM and CDMA carriers simultaneously, with all protocols layers being executed on x86 CPUs. Vanu Inc. was founded by Vanu Bose, one of the main contributors to MIT’s PSpectra framework.
2004 PHY processors
Picochip (now Mindspeed Technologies) introduced its PC102, a processor specifically designed for PHY processing (commonly referred to as a baseband processor). The PC102 was aimed for the 3G infrastructure market. It had 308 processing elements, 14 application-specific coprocessors (accelerators), and could handle the MAC layer as well as other protocol elements.
Designed for SDR right from the drawing board, the PC102 (and subsequent members of the PicoArray family) dramatically reduced the size, cost, and power consumption of wireless equipment. Picochip was the instigator behind a new breed of specialized processors. It paved the way for new players like Octasic, with their 24-core OCT2224W, and Coherent Logix, with their HyperX series, and forced traditional vendors to come up with SDR-optimized architectures. This led to the Keystone family from TI and the QorIQ from Freescale.
2006 TI and Xilinx come together to facilitate embedded SDR development
Texas Instruments and Xilinx, usually seen as competitors, joined forces along with Nutaq (then Lyrtech) to create the first completely integrated, stand-alone SDR development platform. It was equipped with an ARM, a DSP, an FPGA, and a front-end tunable from 200 MHz to 1 GHz (other ranges came later). The platform was no bigger than a shoe box and could be battery-powered, which opened up new possibilities for out-of-the-lab applications and experiments. Most notable was Microsoft’s campus-wide whitespace experiments, which were conducted with movable small form-factor (SFF) SDR units onboard campus shuttles.
2009 First commercial single-chip RF front-end
Lime Microsystems unveiled its LMS6002, a radio frequency integrated circuit (RFIC). The LMS6002D shortly followed, which had integrated data converters. The RFIC could tune anywhere between 400 MHz and 4 GHz, supported up to 28 MHz of bandwidth, and provided a selectable 16-position baseband filter bank. Motorola also developed an RFIC (100 MHz to 2.5 GHz) years before but did not widely release it. Since then, other silicon vendors have started offering RFIC solutions. As of this day, RFICs may be sourced from at least five vendors.