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From hardware to software
In traditional radio communication, a radio signal has to pass through a series of items of hardware equipment in order to pass from the antenna that receives the signal to the point where it takes on a form that is audible by the human ear.
In a software-defined radio (SDR) system, however, it is software rather than hardware that is used for such modulation and demodulation of the radio signals.
The radio waves are normally generated as sampled digital signals, and then converted from digital to analogue form via a wideband digital-to-analogue converter (DAC).
The radio receiver features a wideband analogue-to-digital converter (ADC) that captures all the channels of the software radio node. This receiver then extracts, converts and demodulates the channel waveform, using software that is normally installed in a mass-produced, general-purpose processor.
From rigid to versatile
One of the traditional limitations of radio communication technologies based on hardware is that an extremely wide variety of legacy standards and configurations are used, often with complex geographical, cultural and historical origins that make them a sensitive issue.
Similarly, each equipment configuration is normally limited to specific uses, specific transmission/reception areas and particular equipment configurations with a substantial legacy backlog.
Software-defined radio therefore opens up significant new opportunities in the field of wireless communication. SDR makes it possible to make the transition from dedicated, single-purpose hardware (ASICs, etc.) to highly versatile general-purpose hardware such as FPGAs and DSPs, and even to general-purpose processors whose functionality is defined solely by their software configuration. This in turn paves the way for high-volume/low-cost production, making it financially viable to embed autonomous radio communication devices in a wide range of new kinds of devices and applications.
And once the basic architectures are digitally based, it becomes possible to ensure interoperability between different wireless frequencies, and between different types of applications.
From static to dynamic
Traditional radio communication technologies are, in principle, fixed from the day they leave the factory. Because all the features, functions, and capabilities are embedded in hardware, they cannot normally be updated without direct physical intervention, usually involving new parts.
Any such action has to be undertaken on each particular radio receiver. However, modern cost structures mean this is a time-consuming, impractical process that is prohibitively expensive in relation to the results achieved.
Software-defined radio communication technologies, on the other hand, pave the way for the individual functions being continually updated and improved, and adjusted and reconfigured to meet new and changing needs. Any required fault-finding and error correction can be undertaken automatically using software downloaded from the Internet.
The rapid development of technology turns from being a heritage weakness to a future-oriented strength.
General aims of SDR
In general, the aim of software-defined radio is to move analogue/digital and digital/analogue conversion as close to the antenna as possible, and to move towards substituting software for traditional hardware processing of the radio signal.
However, the specific field known as Software Defined Radio (SDR) is only one component in the overall development of technology in this area. According to the SDR Forum, the stages are
- Software Controlled Radio (SCR), where only limited functions, such as power levels, can be altered using software.
- Software Defined Radio (SDR), where additional functions can be managed via software, but restrictions are still imposed by the RF front end and antenna systems.
- Ideal Software Radio (ISR), where digital hardware and/or software replaces analogue amplification and mixing prior to analogue/digital conversion. This means the only remaining analogue converters are for the antenna, microphone and speaker.
- Ultimate Software Radio (USR), which is the ultimate “all-in-one-box” radio communication device, in which all the different requirements are dealt with digitally, solely via software.
SDR Center @ Aalborg University
The Center for Software Defined Radio is a direct spin-off from the Center for TeleInFrastructure (CTIF) at Aalborg University.
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CTIF is research centre with a staff of more than 130, organised in 10 specialist groups to conduct international-level research to stimulate, support and promote development work within modern wireless communication technologies and telecom infrastructures.
The Center for Software Defined Radio is based on funding from
- the Danish Ministry of Science, Technology and Innovation
- the Danish Ministry for Economic and Business Affairs
along with co-funding from industry and from Aalborg University.
The overall budget for 2006–2009 currently amounts to €6.4 million, with €4.0 million allocated for research, development and dissemination work, and the sum of €2.4 million specifically tagged for commercialising the results of this work.
In addition to Aalborg University, the consortium behind the Center for Software Defined Radio includes
- Danish Technological Institute
- the Engineering College of Copenhagen
- the ITEK trade association (part of Danish Industry)
- the NorCOM Communication Cluster
- industrial partners, such as Rohde & Schwarz, TeleNor and GateHouse A/S.
The scope for SDR research work
The research and development work currently being undertaken at the Center for Software Defined Radio focuses on topics that include
- software test methodologies
- the potential use of software-defined radio in defence applications
- ways to achieve on-line reconfigurability
- context awareness in SDR-based terminals
- the development and setting up of test bed facilities for the Sundance SDR platform, which combines the use of DSP and FPGA processors.
Research domains
Among the initial research domains currently being considered at the Center for Software Defined Radio are
- RF systems and converter technology
- architectures for baseband processing
- methodologies for software testing
- tools and methods for co-designing hardware and software
- tools and methods for designing analogue/digital systems that ensure optimal interaction between algorithms and architectures
- ways of achieving low power consumption
- mathematical descriptions of SDR systems to facilitate the design of optimised software architectures.
Putting know-how into practice
A key part of the work planned at the Center for Software Defined Radio involves passing on the results of the R&D work done here and making sure that these are implemented in commercial contexts with as many industrial partners as possible.
The Center’s methodology encapsulates a structured design flow that ensures that all theoretical work is closely integrated with its practical application in both hardware and software, at the same time as maintaining a cost-effective balance between research work, the training of new researchers and PhD students and the needs of the Center’s commercial partners.
Co-funding cooperation
The Center for Software Defined Radio uses special co-funding frameworks, designed so that companies and research specialists can work together in the most mutually beneficial and commercially fruitful way.
Each company contributes with man-hours rather than money, and two non-competing companies are included in each development project. This helps ensure “cross-pollination” of ideas, as well as the swapping of practical experience in dealing with cutting-edge technical developments in this relatively new and burgeoning R&D field.
Co-existing technologies
The Center for Software Defined Radio is helping to establish a coherent, durable development platform for software-defined radio within the rapidly evolving media and communication landscape.
Once radio has been brought into the digital arena, it will be possible to integrate radio communication seamlessly with all the many other co-existing digital technologies.
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