Software-defined radio
A basic SDR system may consist of a computer equipped with a sound card, or other analog-to-digital converter, preceded by some form of RF front end.
[2] Superheterodyne receivers use a VFO (variable-frequency oscillator), mixer, and filter to tune the desired signal to a common IF (intermediate frequency) or baseband.
Real analog-to-digital converters lack the dynamic range to pick up sub-microvolt, nanowatt-power radio signals produced by an antenna.
The flexibility of SDR allows for dynamic spectrum usage, alleviating the need to statically assign the scarce spectral resources to a single fixed service.
[4] 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.
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.
[citation needed] 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.
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.
[citation needed] 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.
[7] 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.
[citation needed] 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.
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.
[citation needed] 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.
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.
[citation needed] 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 program is providing a flexible new approach to meet diverse soldier communications needs through software programmable radio technology.
The adoption of general-purpose SDR frameworks outside of military, intelligence, experimental and amateur uses, however, is inherently hampered by the fact that civilian users can more easily settle with a fixed architecture, optimized for a specific function, and as such more economical in mass market applications.
SCA-based infrastructure software and rapid development tools for SDR education and research are provided by the Open Source SCA Implementation – Embedded (OSSIE[12]) project.
The newer software defined radios use embedded high performance ADCs that provide higher dynamic range and are more resistant to noise and RF interference.
[19] Amateurs also experiment with new modulation methods: for instance, the DREAM open-source project decodes the COFDM technique used by Digital Radio Mondiale.
Eric Fry discovered that some common low-cost DVB-T USB dongles with the Realtek RTL2832U[26][27] controller and tuner, e.g. the Elonics E4000 or the Rafael Micro R820T,[28] can be used as a wide-band (3 MHz) SDR receiver.
[30] WebSDR[31] is a project initiated by Pieter-Tjerk de Boer providing access via browser to multiple SDR receivers worldwide covering the complete shortwave spectrum.
Unlike WebSDR, the frequency is limited to 3 Hz to 30 MHz (ELF to HF) On account of its increasing accessibility, with lower cost hardware, more software tools and documentation, the applications of SDR have expanded past their primary and historic use cases.
