Software Defined Radio

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.

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