Software-defined radio (SDR) is a radio communication system where components that conventionally have been implemented in analog hardware (e.g. mixers, filters, amplifiers, modulators/demodulators, detectors, etc.) are instead implemented by means of software on a computer or embedded system.[1] While the concept of SDR is not new, the rapidly evolving capabilities of digital electronics render practical many processes which were once only theoretically possible.
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. Significant amounts of signal processing are handed over to the general-purpose processor, rather than being done in special-purpose hardware (electronic circuits). Such a design produces a radio which can receive and transmit widely different radio protocols (sometimes referred to as waveforms) based solely on the software used.
Software radios have significant utility for the military and cell phone services, both of which must serve a wide variety of changing radio protocols in real time. In the long term, software-defined radios are expected by proponents like the Wireless Innovation Forum to become the dominant technology in radio communications. SDRs, along with software defined antennas are the enablers of cognitive radio.[2]
Real analog-to-digital converters lack the dynamic range to pick up sub-microvolt, nanowatt-power radio signals produced by an antenna. Therefore, a low-noise amplifier must precede the conversion step and this device introduces its own problems. For example, if spurious signals are present (which is typical), these compete with the desired signals within the amplifier's dynamic range. They may introduce distortion in the desired signals, or may block them completely. The standard solution is to put band-pass filters between the antenna and the amplifier, but these reduce the radio's flexibility. Real software radios often have two or three analog channel filters with different bandwidths that are switched in and out.
The flexibility of SDR allows for dynamic spectrum usage, alleviating the need to statically assign the scarce spectral resources to a single fixed service.[3]
History
In 1970, a researcher[who?] 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.[citation needed]
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.[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. 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.[5]
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 InstrumentsTMS320C30 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".[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.[6] 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."[citation needed] 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.[citation needed]
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".[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. 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),[8] 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 frequencybands between 2 and 2000 MHz.[9] 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.[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 RD148.
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 HFSSBteleprinters) and satellites (microwaveQAM). 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 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).[citation needed]
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.[citation needed]
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 4MHz to 400MHz range.[citation needed]
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.[citation needed]
The modules are said to communicate without a central operating system. Instead, they send messages over the PCIcomputer bus to each other with a layered protocol.[citation needed]
As a military project, the radio strongly distinguished "red" (unsecured secret data) and "black" (cryptographically-secured data).[citation needed]
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.[citation needed]
The Joint Tactical Radio System (JTRS) was a program of the US military to produce radios that provide flexible and interoperable communications. Examples of radio terminals that require support include hand-held, vehicular, airborne and dismounted radios, as well as base-stations (fixed and maritime).
This goal is achieved through the use of SDR systems based on an internationally endorsed open Software Communications Architecture (SCA). This standard uses CORBA on POSIX operating systems to coordinate various software modules.
The program is providing a flexible new approach to meet diverse soldier communications needs through software programmable radio technology. All functionality and expandability is built upon the SCA.
The SCA, despite its military origin, is under evaluation by commercial radio vendors for applicability in their domains. 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. Still, software defined radio's inherent flexibility can yield substantial benefits in the longer run, once the fixed costs of implementing it have gone down enough to overtake the cost of iterated redesign of purpose built systems. This then explains the increasing commercial interest in the technology.
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 Wireless Innovation Forum funded the SCA Reference Implementation project, an open source implementation of the SCA specification. (SCARI) can be downloaded for free.
Amateur and home use
Microtelecom Perseus – an HF SDR for the amateur radio market
A typical amateur software radio uses a direct conversion receiver. Unlike direct conversion receivers of the more distant past, the mixer technologies used are based on the quadrature sampling detector and the quadrature sampling exciter.[13][14][15][16]
The receiver performance of this line of SDRs is directly related to the dynamic range of the analog-to-digital converters (ADCs) utilized.[17] Radio frequency signals are down converted to the audio frequency band, which is sampled by a high performance audio frequency ADC. First generation SDRs used a 44kHz PC sound card to provide ADC functionality. The newer software defined radios use embedded high performance ADCs that provide higher dynamic range and are more resistant to noise and RF interference.
A fast PC performs the digital signal processing (DSP) operations using software specific for the radio hardware. Several software radio implementations use the open source SDR library DttSP.[18]
There is a broad range of hardware solutions for radio amateurs and home use. There are professional-grade transceiver solutions, e.g. the Zeus ZS-1[20][21] or FlexRadio,[22] home-brew solutions, e.g. PicAStar transceiver, the SoftRock SDR kit,[23] and starter or professional receiver solutions, e.g. the FiFi SDR[24] for shortwave, or the Quadrus coherent multi-channel SDR receiver[25] for short wave or VHF/UHF in direct digital mode of operation.
RTL-SDR
Internals of a low-cost DVB-T USB dongle that uses Realtek RTL2832U (square IC on the right) as the controller and Rafael Micro R820T (square IC on the left) as the tuner
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 (3MHz) SDR receiver. Experiments proved the capability of this setup to analyze Perseids meteor shower using Graves radar signals.[29] This project is being maintained at Osmocom.
HPSDR
The HPSDR (High Performance Software Defined Radio) project uses a 16-bit 135 MSPS analog-to-digital converter that provides performance over the range 0 to 55 MHz comparable to that of a conventional analogue HF radio. The receiver will also operate in the VHF and UHF range using either mixer image or alias responses. Interface to a PC is provided by a USB 2.0 interface, although Ethernet could be used as well. The project is modular and comprises a backplane onto which other boards plug in. This allows experimentation with new techniques and devices without the need to replace the entire set of boards. An exciter provides 1/2 W of RF over the same range or into the VHF and UHF range using image or alias outputs.[30]
WebSDR
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. De Boer has analyzed Chirp Transmitter signals using the coupled system of receivers.[32]
KiwiSDR
KiwiSDR[33] is also a via-browser SDR like WebSDR. Unlike WebSDR, the frequency is limited to 3 Hz to 30 MHz (ELF to HF)
Other applications
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. SDR is now being used in areas such as wildlife tracking, radio astronomy, medical imaging research, and art.
Amplitude modulation (AM) is a modulation technique used in electronic communication, most commonly for transmitting messages with a radio wave. In amplitude modulation, the amplitude of the wave is varied in proportion to that of the message signal, such as an audio signal. This technique contrasts with angle modulation, in which either the frequency of the carrier wave is varied, as in frequency modulation, or its phase, as in phase modulation.
In electronics and telecommunications, modulation is the process of varying one or more properties of a periodic waveform, called the carrier signal, with a separate signal called the modulation signal that typically contains information to be transmitted. For example, the modulation signal might be an audio signal representing sound from a microphone, a video signal representing moving images from a video camera, or a digital signal representing a sequence of binary digits, a bitstream from a computer.
In electronics, an analog-to-digital converter is a system that converts an analog signal, such as a sound picked up by a microphone or light entering a digital camera, into a digital signal. An ADC may also provide an isolated measurement such as an electronic device that converts an analog input voltage or current to a digital number representing the magnitude of the voltage or current. Typically the digital output is a two's complement binary number that is proportional to the input, but there are other possibilities.
In telecommunications and signal processing, baseband is the range of frequencies occupied by a signal that has not been modulated to higher frequencies. Baseband signals typically originate from transducers, converting some other variable into an electrical signal. For example, the electronic output of a microphone is a baseband signal that is analogous to the applied voice audio. In conventional analog radio broadcasting, the baseband audio signal is used to modulate an RF carrier signal of a much higher frequency.
Composite video is an baseband analog video format that typically carries a 405, 525 or 625 line interlaced black and white or color signal, on a single channel, unlike the higher-quality S-Video and the even higher-quality YPbPr.
A mixed-signal integrated circuit is any integrated circuit that has both analog circuits and digital circuits on a single semiconductor die. Their usage has grown dramatically with the increased use of cell phones, telecommunications, portable electronics, and automobiles with electronics and digital sensors.
Universal Software Radio Peripheral (USRP) is a range of software-defined radios designed and sold by Ettus Research and its parent company, National Instruments. Developed by a team led by Matt Ettus, the USRP product family is commonly used by research labs, universities, and hobbyists.
An S meter is an indicator often provided on communications receivers, such as amateur radio or shortwave broadcast receivers. The scale markings are derived from a system of reporting signal strength from S1 to S9 as part of the R-S-T system. The term S unit refers to the amount of signal strength required to move an S meter indication from one marking to the next.
Analogue electronics are electronic systems with a continuously variable signal, in contrast to digital electronics where signals usually take only two levels. The term analogue describes the proportional relationship between a signal and a voltage or current that represents the signal. The word analogue is derived from the Greek word ανάλογος analogos meaning proportional.
Delta-sigma modulation is an oversampling method for encoding signals into low bit depth digital signals at a very high sample-frequency as part of the process of delta-sigma analog-to-digital converters (ADCs) and digital-to-analog converters (DACs). Delta-sigma modulation achieves high quality by utilizing a negative feedback loop during quantization to the lower bit depth that continuously corrects quantization errors and moves quantization noise to higher frequencies well above the original signal's bandwidth. Subsequent low-pass filtering for demodulation easily removes this high frequency noise and time averages to achieve high accuracy in amplitude which can be ultimately encoded as pulse-code modulation (PCM).
D-STAR is a digital voice and data protocol specification for amateur radio. The system was developed in the late 1990s by the Japan Amateur Radio League and uses minimum-shift keying in its packet-based standard. There are other digital modes that have been adapted for use by amateurs, but D-STAR was the first that was designed specifically for amateur radio.
In digital signal processing, a digital down-converter (DDC) converts a digitized, band-limited signal to a lower frequency signal at a lower sampling rate in order to simplify the subsequent radio stages. The process can preserve all the information in the frequency band of interest of the original signal. The input and output signals can be real or complex samples. Often the DDC converts from the raw radio frequency or intermediate frequency down to a complex baseband signal.
The OpenHPSDR project dates from 2005 when Phil Covington, Phil Harman, and Bill Tracey combined their separate projects to form the HPSDR group. It is built around a modular concept which encourages experimentation with new techniques and devices without the need to replace the entire set of boards. The project has expanded from the original group, and several additional people have been involved in recent HPSDR module designs.
In broadcasting, a transposer or translator is a device in or beyond the service area of a radio or television station transmitter that rebroadcasts signals to receivers which can’t properly receive the signals of the transmitter because of a physical obstruction. A translator receives the signals of the transmitter and rebroadcasts the signals to the area of poor reception. Sometimes the translator is also called a relay transmitter, rebroadcast transmitter or transposer. Since translators are used to cover a small shadowed area, their output powers are usually lower than that of the radio or television station transmitters feeding them.
Red Pitaya is a project intended to be alternative for many expensive laboratory measurement and control instruments. It is known as open-source, though the hardware design is proprietary.
RF CMOS is a metal–oxide–semiconductor (MOS) integrated circuit (IC) technology that integrates radio-frequency (RF), analog and digital electronics on a mixed-signal CMOS RF circuit chip. It is widely used in modern wireless telecommunications, such as cellular networks, Bluetooth, Wi-Fi, GPS receivers, broadcasting, vehicular communication systems, and the radio transceivers in all modern mobile phones and wireless networking devices. RF CMOS technology was pioneered by Pakistani engineer Asad Ali Abidi at UCLA during the late 1980s to early 1990s, and helped bring about the wireless revolution with the introduction of digital signal processing in wireless communications. The development and design of RF CMOS devices was enabled by van der Ziel's FET RF noise model, which was published in the early 1960s and remained largely forgotten until the 1990s.
M17 is a digital radio modulation mode developed by Wojciech Kaczmarski et al. M17 is primarily designed for voice communications on the VHF amateur radio bands, and above. The project received a grant from the Amateur Radio Digital Communications in 2021 and 2022. The protocol has been integrated into several hardware and software projects. In 2021, Kaczmarski received the ARRL Technical Innovation Award for developing an open-source digital radio communication protocol, leading to further advancements in amateur radio.
Time interleaved (TI) ADCs are Analog-to-Digital Converters (ADCs) that involve M converters working in parallel. Each of the M converters is referred to as sub-ADC, channel or slice in the literature. The time interleaving technique, akin to multithreading in computing, involves using multiple converters in parallel to sample the input signal at staggered intervals, increasing the overall sampling rate and improving performance without overburdening the single ADCs.
References
↑ Markus Dillinger; Kambiz Madani; Nancy Alonistioti (2003). Software Defined Radio: Architectures, Systems and Functions. Wiley & Sons. p.xxxiii. ISBN0-470-85164-3.
↑ Mitola III, J. (1992). Software radios-survey, critical evaluation and future directions. National Telesystems Conference. pp.13/15 to 13/23. doi:10.1109/NTC.1992.267870. ISBN0-7803-0554-X.
↑ P. Hoeher and H. Lang, "Coded-8PSK modem for fixed and mobile satellite services based on DSP," in Proc. First Int. Workshop on Digital Signal Processing Techniques Applied to Space Communications, ESA/ ESTEC, Noordwijk, Netherlands, Nov. 1988; ESA WPP-006, Jan. 1990, pp. 117-123.
↑ First International Workshop on Software Radio, Greece 1998
↑ RJ Lackey and DW Upmal contributed the article "Speakeasy: The Military Software Radio" to the IEEE Communications Magazine special issue that Mitola edited and for which Mitola wrote the lead article "Software Radio Architecture", in May 1995.
Rohde, Ulrich L (February 26–28, 1985). "Digital HF Radio: A Sampling of Techniques". Third International Conference on HF Communication Systems and Techniques. London, England.
Software defined radio: architectures, systems, and functions. Dillinger, Madani, Alonistioti. Wiley, 2003. 454 pages. ISBN0-470-85164-3ISBN9780470851647
Software Defined Radio for 3G, Burns. Artech House, 2002. ISBN1-58053-347-7
Software Radio: A Modern Approach to Radio Engineering, Jeffrey H. Reed. Prentice Hall PTR, 2002. ISBN0-13-081158-0
Signal Processing Techniques for Software Radio, Behrouz Farhang-Beroujeny. LuLu Press.
RF and Baseband Techniques for Software Defined Radio, Peter B. Kenington. Artech House, 2005, ISBN1-58053-793-6
The ABC's of Software Defined Radio, Martin Ewing, AA6E. The American Radio Relay League, Inc., 2012, ISBN978-0-87259-632-0
Software Defined Radio using MATLAB & Simulink and the RTL-SDR, R Stewart, K Barlee, D Atkinson, L Crockett, Strathclyde Academic Media, September 2015. ISBN978-0-9929787-2-3
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