Software Defined Radio

By | November 1, 2015

A software defined radio (SDR) is a radio communication system where components are software applications and are used to handle hardware based radio devices. Software Defined Radio attempts to place much or most of the complex signal handling involved in  communications receivers and transmitters into the digital (DSP) style. In its purest form, SDR receiver might consist simply of an analog-to-digital convert chip connected to an antenna. All the filtering and signal detection can take place in the digital domain, perhaps  in an ordinary personal computer. While there are still good reasons to use some analog components in high-performance gear, the SDR  approach is becoming more common in Amateur Radio.

However, software defined radios or SDRs, do have characteristics that make them unique from  other types of radios. As the name implies, an SDR is a radio that has the ability to be transformed through the use of software or re-definable logic. Quite often this is done with general purpose DSPs or FPGAs as discussed later in the chapter.  In order to take advantage of such digital processing, traditional analog signals must be converted  to  and from the digital domain. This is accomplished using analog-to-digital(ADC) and digital-to-analog converters(DAC). To take full advantage of digital processing, SDRs keep the signal in the digital domain for as much of the signal chain as possible, digitizing  and  reconstructing as close to the antenna as possible, which allows digital techniques to perform functions traditionally done by analog components as well as others not possible in the analog domain.

A software-defined radio system 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. i.e. A software defined radio system is a radio communication system where components software applications are used to handle hardware based radio devices. 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  communication. SDRs,  along  with  software defined antennas are the enablers of the cognitive radio.

DESIGN CONSIDERATIONS
Software-defined radio (SDR) is a radio communication technology that is based on software defined wireless communication protocols instead of hardwired implementations. In other words, frequency band, air interface protocol and functionality can be upgraded with software download and update instead of a complete hardware replacement. SDR provides an efficient and secure solution to the problem of building multi-mode, multi-band and multifunctional wireless communication devices.

What does the hardware involve?

Radio Frequency Unit
Analog to Digital / Digital to Analog Converter
Baseband Unit
An audio amp / filter
A sound card
A PC with some clever DSP software

BENEFITS OF USING SDR

There are a few things that software radios can do that haven’t been possible before:

They can be reconfigured “on-the-fly”. That is, depending on what you need, your universal communication device would reconfigure itself appropriately for your environment. It could be a cordless phones one minute, a cell phone the next, a wireless internet gadget the next, and a GPS receiver another.

They can be quickly and easily upgraded with enhanced features. In fact, the upgrade could be delivered over-the-air.

They can talk and listen to multiple channels at the same. OK, so what do I care? Imagine you’re a cop, or a fire fighter, or an ambulance driver. Today there are many places where public safety people from one organization can’t talk to another. The locals can’t talk to the emergency crew from the next town because they’ve got different kinds of radios. Software radio solves this problem.

We can build new kinds of radios that have never before existed. Smart radios or cognitive radios can look at the utilization of the RF spectrum in their immediate neighborhood, and configure themselves for best performance.

GNU Radio is a free software toolkit for learning about, building and deploying software radios. Being free software, it comes with complete source code so anyone can look and see how the system is built.

APPLICATIONS

1) SDR is underlying technology behind Joint Tactical Radio System (JTRS) initiative to develop software programmable Radios that can enable seamless, real time communication across U.S military services and with coalition and allies.

2)The functionality and expandability of the JTRS is built upon an open architecture framework called the Software Communications Architecture. The JTRS terminals must support dynamic loading of any one of over 30 specified air interfaces or waveforms that are typically more complex than those used in the civilian sector.

3) On the commercial side, wireless providers are attracted to SDR technology because it enables remote upgrading and reconfiguration of handset and base station software with new features and patches, as well as potential interoperability across multiple networks. SDR provides a solution for a broad range of communications and devices used in: cellular base station and handsets, commercial and military satellites, military radios, public safety, wireless LAN/WAN, aerospace, automotive

 ADVANTAGES OF SDR

  • Flexibility:

The idea of a more flexible radio has already been mentioned throughout this discussion, but it becomes the most obvious and important advantage over classic radio systems. The ability to upgrade your system not only for better performance, but also for new performance means endless possibilities for software radios as they are developed.

  • Cheaper RF Front End design:

One problem with classic RF design is the complexity and the labor in developing a reliable design. With the design of a reliable SDR, the quality and performance of the SDR can be enhanced by the digital hardware (Digital Signal Processor (DSP), Field Programmable Gate-Array (FPGA), or General Purpose Processor (GPP)) in order to reduce the complexity (and therefore the cost) of the RF front-end.

  • Smaller list of components:

Another related benefit to SDR is that by making a less complicated RF front-end, the total parts needed (theoretically) become much more simplified. With digital components like the DSP and FPGA taking the place of many passive and active components the list is smaller and hopefully cheaper in the long run.

  • Faster time to market:

With the ease of porting software to the SDR in order to upgrade the system less time can be spent on manufacturing which will eventually bring the product to market faster than classic designs.

LIMITATIONS OF SDR

The limitations of SDR still relatively few, but there are some very foreseeable obstacles that must be overcome in order to create a functional SDR mainstream.

  • Software Reliability:

If the SDR is sending a signal at 2 Watts in a particular band when FCC regulations say its max output can only be 1 Watt, then there is a serious issue. Although these are certainly obstacles they are not deterrents from using SDR. Software development has been available for years for communication systems in more specific applications (cell phones, Wi-Fi, etc.). The problem is controlling and monitoring multiple waveforms, regulations, and rules that have yet to be fully developed.

  • Security:

One great benefit of SDR is that it provides flexibility to reconfigure new waveforms, but it does not allow to access certain waveforms. Some precautions have to be made to allow different levels of access to waveforms and spectrum as determined by local and federal regulations.

  • Cost:

One limitation, at present, that will always be improving is cost. As of todays available technology, the SDR technology is either too monstrous (for example the DMR covers a huge spectrum but weighs 210lbs which is certainly an indication that it is not cheap) or on the other end, some SDRs are still limited in its capabilities (for example, the USRP is around $500 but is limited to 128MS/s transmit and 64MS/s receiving). So as technology develops more and more options will be opening to the radio community.

  • Power consumption:

One ever improving and constant battle in communications devices is power. One problem with SDR?s at present is the computationally heavy applications are not able to run at high speed unless they are using large quantities of power. As battery and chip technology improves, the consumer market will converge on reasonable power restrained SDR for everyday use.

CONCLUSION

SDR is an emerging technology that spans all radio network topologies in the commercial, military and civil government sectors, and enables flexible solutions. SDR technology provides software control of a variety of modulation, interference management and capacity enhancement techniques over a broad frequency spectrum while ensuring secure communications management. Within this Report, the aspects of Software Defined Radio have been addressed.

This comprises definition of Software Defined Radio as well as its working and its implementation. Potential impact of SDR technology on the Systems also has been made. As one major topic technical aspects such as the principal system overview as well as some latest areas of research and the state of technology development has been briefly described.

Since SDR comprises many different and evolving technical aspects, this report should be seen as an initial technical report. The report also addresses issues like market development and external bodies that are working on SDR related topics. Further this report is a preliminary review of the potential for SDR to facilitate regional and global harmonization aswell as the technical considerations necessary to ensure conformance with ITU-R recommendations.Technical implementations are being developed by the industry.

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