Software-defined radio
Encyclopedia
A software-defined radio system, or SDR, is a radio
communication system where components that have been typically implemented in hardware (e.g. mixers, filters, amplifiers, modulators/demodulators, detectors, etc.) are instead implemented by means of software on a personal computer or embedded computing devices. While the concept of SDR is not new, the rapidly evolving capabilities of digital electronics render practical many processes which used to be only theoretically possible.
A basic SDR system may consist of a personal 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. Such a design produces a radio
which can receive and transmit widely different radio protocols (sometimes referred to as a 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 SDRForum (now The Wireless Innovation Forum
) to become the dominant technology
in radio communications. SDRs, along with software defined antenna
s are the enablers of the cognitive radio
.
A software-defined radio can be flexible enough to avoid the "limited spectrum" assumptions of designers of previous kinds of radios, in one or more ways including:
scheme would be to attach an analog-to-digital converter to an antenna. A digital signal processor
would read the converter, and then its software would transform the stream of data from the converter to any other form the application requires.
An ideal transmitter
would be similar. A digital signal processor would generate a stream of numbers. These would be sent to a digital-to-analog converter
connected to a radio antenna.
The ideal scheme is not completely realizable due to the actual limits of the technology. The main problem in both directions is the difficulty of conversion between the digital and the analog domains at a high enough rate and a high enough accuracy at the same time, and without relying upon physical processes like interference and electromagnetic resonance for assistance.
, mixer
, and filter
to tune the desired signal to a common intermediate frequency
or baseband
, where it is then sampled by the analog-to-digital converter. However, in some applications it is not necessary to tune the signal to an intermediate frequency and the radio frequency signal is directly sampled by the analog-to-digital converter (after amplification).
Real analog-to-digital converters lack the dynamic range to pick up sub-microvolt, nanowatt-power radio signals. 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 filter
s between the antenna and the amplifier, but these reduce the radio's flexibility - which some see as the whole point of a software radio. Real software radios often have two or three analog channel filters with different bandwidths that are switched in and out.
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.
Perhaps the first software-defined 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 software-defined radio, and a flexible hardware periphery was proposed.
The term "Software Defined Radio" was coined in 1991 by Joseph Mitola, who published the first paper on the topic in 1992. Though the concept was first proposed in 1991, software-defined radios have their origins in the defense sector since the late 1970s in both the U.S. and Europe (for example, Walter Tuttlebee described a VLF radio
that used an ADC and an 8085 microprocessor
). One of the first public software radio initiatives was a U.S. 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. Further, another 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.
, and SINCGARS
), Air Force radios (VHF AM
), Naval Radios (VHF AM
and HF
SSB
teleprinter
s) 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 met all these goals. There was some discontent with certain unspecified features. 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 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 processor
s (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 wide band software radios.
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 "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.
(JTRS) is 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 warfighter 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 retarded 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) project.
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.
The receiver performance of this line of SDRs is directly related to the dynamic range of the analog-to-digital converters (ADCs) utilized. 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 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 efforts use the open source SDR library DttSP.
The SDR software performs all of the demodulation, filtering (both radio frequency and audio frequency), signal enhancement (equalization and binaural presentation). Uses include every common amateur modulation: morse code
, single sideband modulation, frequency modulation
, amplitude modulation
, and a variety of digital modes such as radioteletype
, slow-scan television
, and packet radio
. Amateurs also experiment with new modulation methods: for instance, the DREAM open-source
project decodes the COFDM technique used by Digital Radio Mondiale
.
More recently, the GNU Radio
using primarily the Universal Software Radio Peripheral
(USRP) uses a USB 2.0 interface, an FPGA, and a high-speed set of analog-to-digital and digital-to-analog converters, combined with reconfigurable free software
. Its sampling and synthesis bandwidth is a thousand times that of PC sound cards, which enables wideband
operation.
The HPSDR
(High Performance Software Defined Radio) project uses a 16-bit analog-to-digital converter that provides performance over the range 0 to 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 though 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 of RF over the same range or into the VHF and UHF range using image or alias outputs.
Radio
Radio is the transmission of signals through free space by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space...
communication system where components that have been typically implemented in hardware (e.g. mixers, filters, amplifiers, modulators/demodulators, detectors, etc.) are instead implemented by means of software on a personal computer or embedded computing devices. While the concept of SDR is not new, the rapidly evolving capabilities of digital electronics render practical many processes which used to be only theoretically possible.
A basic SDR system may consist of a personal computer
Personal computer
A personal computer is any general-purpose computer whose size, capabilities, and original sales price make it useful for individuals, and which is intended to be operated directly by an end-user with no intervening computer operator...
equipped with a sound card
Sound card
A sound card is an internal computer expansion card that facilitates the input and output of audio signals to and from a computer under control of computer programs. The term sound card is also applied to external audio interfaces that use software to generate sound, as opposed to using hardware...
, or other analog-to-digital converter
Analog-to-digital converter
An analog-to-digital converter is a device that converts a continuous quantity to a discrete time digital representation. An ADC may also provide an isolated measurement...
, preceded by some form of RF front end
RF front end
In a radio receiver circuit, the RF front end is a generic term for all the circuitry between the antenna and the first intermediate frequency stage. It consists of all the components in the receiver that process the signal at the original incoming radio frequency , before it is converted to a...
. Significant amounts of signal processing
Signal processing
Signal processing is an area of systems engineering, electrical engineering and applied mathematics that deals with operations on or analysis of signals, in either discrete or continuous time...
are handed over to the general-purpose processor, rather than being done in special-purpose hardware. Such a design produces a radio
Radio
Radio is the transmission of signals through free space by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space...
which can receive and transmit widely different radio protocols (sometimes referred to as a 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 SDRForum (now The Wireless Innovation Forum
Wireless Innovation Forum
The Wireless Innovation Forum is a non-profit "mutual benefit corporation" dedicated to technology innovation in commercial, civil, and defense communications around the world...
) to become the dominant technology
Technology
Technology is the making, usage, and knowledge of tools, machines, techniques, crafts, systems or methods of organization in order to solve a problem or perform a specific function. It can also refer to the collection of such tools, machinery, and procedures. The word technology comes ;...
in radio communications. SDRs, along with software defined antenna
Software defined antenna
SDA - Software Defined Antenna, following and exploiting the concept of Software Defined Radio , is an idea for an antenna system that can be adjusted in such way that similar characteristics can be maintained for any frequency...
s are the enablers of the cognitive radio
Cognitive radio
A cognitive radio is a kind of two-way radio that automatically changes its transmission or reception parameters, in a way where the entire wireless communication network -- of which it is a node -- communicates efficiently, while avoiding interference with licensed or licensed exempt users...
.
A software-defined radio can be flexible enough to avoid the "limited spectrum" assumptions of designers of previous kinds of radios, in one or more ways including:
- spread spectrumSpread spectrumSpread-spectrum techniques are methods by which a signal generated in a particular bandwidth is deliberately spread in the frequency domain, resulting in a signal with a wider bandwidth...
and ultrawideband techniques allow several transmitters to transmit in the same place on the same frequency with very little interference, typically combined with one or more error detection and correctionError detection and correctionIn information theory and coding theory with applications in computer science and telecommunication, error detection and correction or error control are techniques that enable reliable delivery of digital data over unreliable communication channels...
techniques to fix all the errors caused by that interference. - software defined antennaSoftware defined antennaSDA - Software Defined Antenna, following and exploiting the concept of Software Defined Radio , is an idea for an antenna system that can be adjusted in such way that similar characteristics can be maintained for any frequency...
s adaptively "lock onto" a directional signal, so that receivers can better reject interference from other directions, allowing it to detect fainter transmissions. - cognitive radioCognitive radioA cognitive radio is a kind of two-way radio that automatically changes its transmission or reception parameters, in a way where the entire wireless communication network -- of which it is a node -- communicates efficiently, while avoiding interference with licensed or licensed exempt users...
techniques: each radio measures the spectrum in use and communicates that information to other cooperating radios, and then transmitters avoid frequencies currently in use by licensed transmitters or are otherwise unusable, and shift transmissions to "empty" frequencies. - dynamic transmitter power adjustment, based on information communicated from the receivers, lowering transmit power to the minimum necessary, reducing the near-far problemNear-far problemThe near-far problem or hearability problem is a situation that is common in wireless communication systems, in particular, CDMA. In some signal jamming techniques, the near-far problem is exploited to disrupt communications.-Technical explanation:...
and reducing interference to others. - wireless mesh networkWireless mesh networkA wireless mesh network is a communications network made up of radio nodes organized in a mesh topology. Wireless mesh networks often consist of mesh clients, mesh routers and gateways.The mesh clients are often laptops, cell phones and other wireless devices while the mesh routers forward traffic...
where every added radio increases total capacity and reduces the power required at any one node. Each node only transmits loudly enough for the message to hop to the nearest node in that direction, reducing near-far problemNear-far problemThe near-far problem or hearability problem is a situation that is common in wireless communication systems, in particular, CDMA. In some signal jamming techniques, the near-far problem is exploited to disrupt communications.-Technical explanation:...
and reducing interference to others.
Ideal concept
The ideal receiverReceiver (radio)
A radio receiver converts signals from a radio antenna to a usable form. It uses electronic filters to separate a wanted radio frequency signal from all other signals, the electronic amplifier increases the level suitable for further processing, and finally recovers the desired information through...
scheme would be to attach an analog-to-digital converter to an antenna. A digital signal processor
Digital signal processor
A digital signal processor is a specialized microprocessor with an architecture optimized for the fast operational needs of digital signal processing.-Typical characteristics:...
would read the converter, and then its software would transform the stream of data from the converter to any other form the application requires.
An ideal transmitter
Transmitter
In electronics and telecommunications a transmitter or radio transmitter is an electronic device which, with the aid of an antenna, produces radio waves. The transmitter itself generates a radio frequency alternating current, which is applied to the antenna. When excited by this alternating...
would be similar. A digital signal processor would generate a stream of numbers. These would be sent to a digital-to-analog converter
Digital-to-analog converter
In electronics, a digital-to-analog converter is a device that converts a digital code to an analog signal . An analog-to-digital converter performs the reverse operation...
connected to a radio antenna.
The ideal scheme is not completely realizable due to the actual limits of the technology. The main problem in both directions is the difficulty of conversion between the digital and the analog domains at a high enough rate and a high enough accuracy at the same time, and without relying upon physical processes like interference and electromagnetic resonance for assistance.
Receiver architecture
Most receivers use a variable-frequency oscillatorVariable-frequency oscillator
A variable frequency oscillator in electronics is an oscillator whose frequency can be tuned over some range. It is a necessary component in any tunable radio receiver or transmitter that works by the superheterodyne principle, and controls the frequency to which the apparatus is...
, mixer
Frequency mixer
In electronics a mixer or frequency mixer is a nonlinear electrical circuit that creates new frequencies from two signals applied to it. In its most common application, two signals at frequencies f1 and f2 are applied to a mixer, and it produces new signals at the sum f1 + f2 and difference f1 -...
, and filter
Filter (signal processing)
In signal processing, a filter is a device or process that removes from a signal some unwanted component or feature. Filtering is a class of signal processing, the defining feature of filters being the complete or partial suppression of some aspect of the signal...
to tune the desired signal to a common intermediate frequency
Intermediate frequency
In communications and electronic engineering, an intermediate frequency is a frequency to which a carrier frequency is shifted as an intermediate step in transmission or reception. The intermediate frequency is created by mixing the carrier signal with a local oscillator signal in a process called...
or baseband
Baseband
In telecommunications and signal processing, baseband is an adjective that describes signals and systems whose range of frequencies is measured from close to 0 hertz to a cut-off frequency, a maximum bandwidth or highest signal frequency; it is sometimes used as a noun for a band of frequencies...
, where it is then sampled by the analog-to-digital converter. However, in some applications it is not necessary to tune the signal to an intermediate frequency and the radio frequency signal is directly sampled by the analog-to-digital converter (after amplification).
Real analog-to-digital converters lack the dynamic range to pick up sub-microvolt, nanowatt-power radio signals. Therefore a low-noise amplifier
Low-noise amplifier
Low-noise amplifier is an electronic amplifier used to amplify possibly very weak signals . It is usually located very close to the detection device to reduce losses in the feedline. This active antenna arrangement is frequently used in microwave systems like GPS, because coaxial cable feedline is...
must precede the conversion step and this device introduces its own problems. For example, if spurious signals
Spurious emission
A spurious emission is any radio frequency not deliberately created or transmitted, especially in a device which normally does create other frequencies...
are present (which is typical), these compete with the desired signals within the amplifier's dynamic range
Dynamic range
Dynamic range, abbreviated DR or DNR, is the ratio between the largest and smallest possible values of a changeable quantity, such as in sound and light. It is measured as a ratio, or as a base-10 or base-2 logarithmic value.-Dynamic range and human perception:The human senses of sight and...
. They may introduce distortion in the desired signals, or may block them completely. The standard solution is to put band-pass filter
Band-pass filter
A band-pass filter is a device that passes frequencies within a certain range and rejects frequencies outside that range.Optical band-pass filters are of common usage....
s between the antenna and the amplifier, but these reduce the radio's flexibility - which some see as the whole point of a software radio. Real software radios often have two or three analog channel filters with different bandwidths that are switched in and out.
History
The term 'software radio' was coined in 1984 by a team at the Garland Texas Division of E-Systems Inc. (now Raytheon). A classified, yet fairly well known, 'Software Radio Proof-of-Concept' laboratory was developed at E-Systems that popularized Software Radio within various government agencies. This 1984 Software Radio was a digital basebandBaseband
In telecommunications and signal processing, baseband is an adjective that describes signals and systems whose range of frequencies is measured from close to 0 hertz to a cut-off frequency, a maximum bandwidth or highest signal frequency; it is sometimes used as a noun for a band of frequencies...
receiver that provided programmable interference cancellation and demodulation for broadband signals, typically with thousands of adaptive filter
Adaptive filter
An adaptive filter is a filter that self-adjusts its transfer function according to an optimization algorithm driven by an error signal. Because of the complexity of the optimization algorithms, most adaptive filters are digital filters. By way of contrast, a non-adaptive filter has a static...
taps, using multiple array processors accessing shared memory.
Perhaps the first software-defined radio transceiver
Transceiver
A transceiver is a device comprising both a transmitter and a receiver which are combined and share common circuitry or a single housing. When no circuitry is common between transmit and receive functions, the device is a transmitter-receiver. The term originated in the early 1920s...
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 software-defined radio, and a flexible hardware periphery was proposed.
The term "Software Defined Radio" was coined in 1991 by Joseph Mitola, who published the first paper on the topic in 1992. Though the concept was first proposed in 1991, software-defined radios have their origins in the defense sector since the late 1970s in both the U.S. and Europe (for example, Walter Tuttlebee described a VLF radio
Very low frequency
225px|thumb|right|A VLF receiving antenna at [[Palmer Station]], Antarctica, operated by Stanford UniversityVery low frequency or VLF refers to radio frequencies in the range of 3 kHz to 30 kHz. Since there is not much bandwidth in this band of the radio spectrum, only the very simplest signals...
that used an ADC and an 8085 microprocessor
Intel 8085
The Intel 8085 is an 8-bit microprocessor introduced by Intel in 1977. It was binary-compatible with the more-famous Intel 8080 but required less supporting hardware, thus allowing simpler and less expensive microcomputer systems to be built....
). One of the first public software radio initiatives was a U.S. military
Military
A military is an organization authorized by its greater society to use lethal force, usually including use of weapons, in defending its country by combating actual or perceived threats. The military may have additional functions of use to its greater society, such as advancing a political agenda e.g...
project named SpeakEasy
SpeakEasy
SpeakEasy was a United States military project to use software-defined radio technology to make it possible to communicate with over 10 different types of military radios from a single system.-History:...
. The primary goal of the SpeakEasy project was to use programmable processing to emulate more than 10 existing military radios, operating in frequency
Frequency
Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...
bands between 2 and 2000 MHz. Further, another design goal was to be able to easily incorporate new coding
Coding
Coding may refer to:* Channel coding in coding theory* Line coding* Computer programming, the process of designing, writing, testing, debugging / troubleshooting, and maintaining the source code of computer programs...
and modulation standards in the future, so that military communications can keep pace with advances in coding and modulation techniques.
SPEAKeasy phase I
From 1992 to 1995, the goal was to produce a radio for the U.S. Army which could operate from 2 MHz to 2 GHz, and operate with ground force radios (frequency-agile VHF, FMFrequency modulation
In telecommunications and signal processing, frequency modulation conveys information over a carrier wave by varying its instantaneous frequency. This contrasts with amplitude modulation, in which the amplitude of the carrier is varied while its frequency remains constant...
, and SINCGARS
SINCGARS
SINCGARS is a Combat Net Radio currently used by U.S. and allied military forces. The radios, which handle voice and data communications, are designed to be reliable, secure and easily maintained...
), Air Force radios (VHF AM
Amplitude modulation
Amplitude modulation is a technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. AM works by varying the strength of the transmitted signal in relation to the information being sent...
), Naval Radios (VHF AM
Amplitude modulation
Amplitude modulation is a technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. AM works by varying the strength of the transmitted signal in relation to the information being sent...
and HF
High frequency
High frequency radio frequencies are between 3 and 30 MHz. Also known as the decameter band or decameter wave as the wavelengths range from one to ten decameters . Frequencies immediately below HF are denoted Medium-frequency , and the next higher frequencies are known as Very high frequency...
SSB
Single-sideband modulation
Single-sideband modulation or Single-sideband suppressed-carrier is a refinement of amplitude modulation that more efficiently uses electrical power and bandwidth....
teleprinter
Teleprinter
A teleprinter is a electromechanical typewriter that can be used to communicate typed messages from point to point and point to multipoint over a variety of communication channels that range from a simple electrical connection, such as a pair of wires, to the use of radio and microwave as the...
s) and satellites
Communications satellite
A communications satellite is an artificial satellite stationed in space for the purpose of telecommunications...
(microwave
Microwave
Microwaves, a subset of radio waves, have wavelengths ranging from as long as one meter to as short as one millimeter, or equivalently, with frequencies between 300 MHz and 300 GHz. This broad definition includes both UHF and EHF , and various sources use different boundaries...
QAM
Quadrature amplitude modulation
Quadrature amplitude modulation is both an analog and a digital modulation scheme. It conveys two analog message signals, or two digital bit streams, by changing the amplitudes of two carrier waves, using the amplitude-shift keying digital modulation scheme or amplitude modulation analog...
). 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 met all these goals. There was some discontent with certain unspecified features. Its cryptographic
Cryptography
Cryptography is the practice and study of techniques for secure communication in the presence of third parties...
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 basic arrangement of the radio receiver
Receiver (radio)
A radio receiver converts signals from a radio antenna to a usable form. It uses electronic filters to separate a wanted radio frequency signal from all other signals, the electronic amplifier increases the level suitable for further processing, and finally recovers the desired information through...
used an antenna feeding an amplifier
Amplifier
Generally, an amplifier or simply amp, is a device for increasing the power of a signal.In popular use, the term usually describes an electronic amplifier, in which the input "signal" is usually a voltage or a current. In audio applications, amplifiers drive the loudspeakers used in PA systems to...
and down-converter (see Frequency mixer
Frequency mixer
In electronics a mixer or frequency mixer is a nonlinear electrical circuit that creates new frequencies from two signals applied to it. In its most common application, two signals at frequencies f1 and f2 are applied to a mixer, and it produces new signals at the sum f1 + f2 and difference f1 -...
) feeding an automatic gain control
Automatic gain control
Automatic gain control is an adaptive system found in many electronic devices. The average output signal level is fed back to adjust the gain to an appropriate level for a range of input signal levels...
, which fed an analog to digital converter that was on a computer VMEbus
VMEbus
VMEbus is a computer bus standard, originally developed for the Motorola 68000 line of CPUs, but later widely used for many applications and standardized by the IEC as ANSI/IEEE 1014-1987. It is physically based on Eurocard sizes, mechanicals and connectors , but uses its own signalling system,...
with a lot of digital signal processor
Digital signal processor
A digital signal processor is a specialized microprocessor with an architecture optimized for the fast operational needs of digital signal processing.-Typical characteristics:...
s (Texas Instruments
Texas Instruments
Texas Instruments Inc. , widely known as TI, is an American company based in Dallas, Texas, United States, which develops and commercializes semiconductor and computer technology...
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 wide band 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. 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
Modulation
In electronics and telecommunications, modulation is the process of varying one or more properties of a high-frequency periodic waveform, called the carrier signal, with a modulating signal which typically contains information to be transmitted...
and demodulation
Demodulation
Demodulation is the act of extracting the original information-bearing signal from a modulated carrier wave.A demodulator is an electronic circuit that is used to recover the information content from the modulated carrier wave.These terms are traditionally used in connection with radio receivers,...
schemes (FM, AM, SSB, QAM, etc.), "waveform processing" modules actually performed the modem
Modem
A modem is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data...
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
Peripheral Component Interconnect
Conventional PCI is a computer bus for attaching hardware devices in a computer...
computer bus
Computer bus
In computer architecture, a bus is a subsystem that transfers data between components inside a computer, or between computers.Early computer buses were literally parallel electrical wires with multiple connections, but the term is now used for any physical arrangement that provides the same...
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.
Joint Tactical Radio System
The Joint Tactical Radio SystemJoint Tactical Radio System
The Joint Tactical Radio System is planned to be the next-generation voice-and-data radio used by the U.S. military in field operations after 2010...
(JTRS) is 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
Software Communications Architecture
The Software Communications Architecture is an open architecture framework that tells designers how elements of hardware and software are to operate in harmony within a software defined radio. SCA governs the structure and operation of the U.S...
(SCA). This standard uses CORBA
Çorba
Chorba , ciorbă , shurpa , shorpo , or sorpa is one of various kinds of soup or stew found in national cuisines across Middle East...
on POSIX
POSIX
POSIX , an acronym for "Portable Operating System Interface", is a family of standards specified by the IEEE for maintaining compatibility between operating systems...
operating systems to coordinate various software modules.
The program is providing a flexible new approach to meet diverse warfighter 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 retarded 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) project.
Amateur or home use
A typical amateurAmateur radio
Amateur radio is the use of designated radio frequency spectrum for purposes of private recreation, non-commercial exchange of messages, wireless experimentation, self-training, and emergency communication...
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.
The receiver performance of this line of SDRs is directly related to the dynamic range of the analog-to-digital converters (ADCs) utilized. 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 PC sound card to provide ADC
Analog-to-digital converter
An analog-to-digital converter is a device that converts a continuous quantity to a discrete time digital representation. An ADC may also provide an isolated measurement...
functionality. The newer software defined radios use embedded high performance ADCs that provide higher dynamic range
Dynamic range
Dynamic range, abbreviated DR or DNR, is the ratio between the largest and smallest possible values of a changeable quantity, such as in sound and light. It is measured as a ratio, or as a base-10 or base-2 logarithmic value.-Dynamic range and human perception:The human senses of sight and...
and are more resistant to noise and RF interference.
A fast PC performs the digital signal processing
Digital signal processing
Digital signal processing is concerned with the representation of discrete time signals by a sequence of numbers or symbols and the processing of these signals. Digital signal processing and analog signal processing are subfields of signal processing...
(DSP) operations using software specific for the radio hardware. Several software radio efforts use the open source SDR library DttSP.
The SDR software performs all of the demodulation, filtering (both radio frequency and audio frequency), signal enhancement (equalization and binaural presentation). Uses include every common amateur modulation: morse code
Morse code
Morse code is a method of transmitting textual information as a series of on-off tones, lights, or clicks that can be directly understood by a skilled listener or observer without special equipment...
, single sideband modulation, frequency modulation
Frequency modulation
In telecommunications and signal processing, frequency modulation conveys information over a carrier wave by varying its instantaneous frequency. This contrasts with amplitude modulation, in which the amplitude of the carrier is varied while its frequency remains constant...
, amplitude modulation
Amplitude modulation
Amplitude modulation is a technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. AM works by varying the strength of the transmitted signal in relation to the information being sent...
, and a variety of digital modes such as radioteletype
Radioteletype
Radioteletype is a telecommunications system consisting originally of two or more electromechanical teleprinters in different locations, later superseded by personal computers running software to emulate teleprinters, connected by radio rather than a wired link.The term radioteletype is used to...
, slow-scan television
Slow-scan television
Slow-scan television is a picture transmission method used mainly by amateur radio operators, to transmit and receive static pictures via radio in monochrome or color.A technical term for SSTV is narrowband television...
, and packet radio
Packet radio
Packet radio is a form of packet switching technology used to transmit digital data via radio or wireless communications links. It uses the same concepts of data transmission via Datagram that are fundamental to communications via the Internet, as opposed to the older techniques used by dedicated...
. Amateurs also experiment with new modulation methods: for instance, the DREAM open-source
Open source
The term open source describes practices in production and development that promote access to the end product's source materials. Some consider open source a philosophy, others consider it a pragmatic methodology...
project decodes the COFDM technique used by Digital Radio Mondiale
Digital Radio Mondiale
Digital Radio Mondiale is a set of digital audio broadcasting technologies designed to work over the bands currently used for AM broadcasting, particularly shortwave...
.
More recently, the GNU Radio
GNU Radio
GNU Radio is a free software toolkit for learning about, building, and deploying software-defined radio systems. GNU Radio is released under the GPL version 3 license....
using primarily the Universal Software Radio Peripheral
Universal Software Radio Peripheral
The Universal Software Radio Peripheral products are a family of computer-hosted hardware offered by Ettus Research LLC and its parent company, National Instruments, for making software radios. The USRP product is intended to be a comparatively inexpensive hardware device for software radio...
(USRP) uses a USB 2.0 interface, an FPGA, and a high-speed set of analog-to-digital and digital-to-analog converters, combined with reconfigurable free software
Free software
Free software, software libre or libre software is software that can be used, studied, and modified without restriction, and which can be copied and redistributed in modified or unmodified form either without restriction, or with restrictions that only ensure that further recipients can also do...
. Its sampling and synthesis bandwidth is a thousand times that of PC sound cards, which enables wideband
Wideband
In communications, wideband is a relative term used to describe a wide range of frequencies in a spectrum. A system is typically described as wideband if the message bandwidth significantly exceeds the channel's coherence bandwidth....
operation.
The HPSDR
HPSDR
The HPSDR 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 The HPSDR (High Performance Software Defined Radio)...
(High Performance Software Defined Radio) project uses a 16-bit analog-to-digital converter that provides performance over the range 0 to 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
Universal Serial Bus
USB is an industry standard developed in the mid-1990s that defines the cables, connectors and protocols used in a bus for connection, communication and power supply between computers and electronic devices....
2.0 interface though Ethernet
Ethernet
Ethernet is a family of computer networking technologies for local area networks commercially introduced in 1980. Standardized in IEEE 802.3, Ethernet has largely replaced competing wired LAN technologies....
could be used as well. The project is modular and comprises a backplane
Backplane
A backplane is a group of connectors connected in parallel with each other, so that each pin of each connector is linked to the same relative pin of all the other connectors forming a computer bus. It is used as a backbone to connect several printed circuit boards together to make up a complete...
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 of RF over the same range or into the VHF and UHF range using image or alias outputs.
See also
- List of software-defined radios
- Digital radioDigital radioDigital radio has several meanings:1. Today the most common meaning is digital radio broadcasting technologies, such as the digital audio broadcasting system, also known as Eureka 147. In these systems, the analog audio signal is digitized into zeros and ones, compressed using formats such as...
- Digital signal processingDigital signal processingDigital signal processing is concerned with the representation of discrete time signals by a sequence of numbers or symbols and the processing of these signals. Digital signal processing and analog signal processing are subfields of signal processing...
- PACTORPACTORPACTOR is a radio modulation mode used by amateur radio operators, marine radio stations, and radio stations in isolated areas to send and receive digital information via radio. A robust network of PACTOR stations has been established to relay data between radio stations and the Internet,...
- AMTORAMTORAMTOR is a type of telecommunications system that consists of two or more electromechanical teleprinters in different locations that send and receive messages to one another. AMTOR is a specialized form of RTTY protocol...
- Radio Interface LayerRadio Interface LayerA Radio Interface Layer is a layer in an operating system which provides an interfaceto the hardware's radio and modem on e.g. a mobile phone.-Android RIL:The Android Open Source Project provides a Radio Interface Layer between...
- Software GNSS ReceiverSoftware GNSS ReceiverA Software GNSS Receiver is a GNSS receiver that has been designed and implemented following the philosophy of Software-defined radio.A GNSS receiver is an electronic device that receives and digitally processes the signals from a GNSS satellite constellation in order to provide position, velocity...
Further reading
- Software defined radio : architectures, systems, and functions. Dillinger, Madani, Alonistioti. Wiley, 2003. 454 pages. ISBN 0470851643 ISBN 9780470851647
- Cognitive Radio Technology. Bruce Fette. Elsevier Science & Technology Books, 2006. 656 pags. ISBN 0750679522 ISBN 9780750679527
- Software Defined Radio for 3G, Burns. Artech House, 2002. ISBN 1-58053-347-7
- Software Radio: A Modern Approach to Radio Engineering, Jeffrey H. Reed. Prentice Hall PTR, 2002. ISBN 0-13-081158-0
- 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, ISBN 1-58053-793-6
External links
- http://websdr.ewi.utwente.nl:8901/ The world's first web-based software-defined receiver at the university of Twente, the Netherlands.
- http://www.websdr.org/ A list of web-based software-defined receivers.