software-defined radio (SDR)

Software-defined radio (SDR), sometimes shortened to software radio (SR), refers to wireless communication in which the transmitter modulation is generated or defined by a computer, and the receiver uses a computer to recover the signal intelligence.? To select the desired modulation type, the proper programs must be run by microcomputers that control the transmitter and receiver.

A typical voice SDR transmitter, such as might be used in mobile two-way radio or cellular telephone communication, consists of the following stages.? Items with asterisks represent computer-controlled circuits whose parameters are determined by the programming (software).

  • Microphone

  • Audio amplifier

  • Analog-to-digital converter (ADC) that converts the voice audio to ASCII data

  • Modulator that impresses the ASCII intelligence onto a radio-frequency (RF) carrier

  • Series of amplifiers that boosts the RF carrier to the power level necessary for transmission

  • Transmitting antenna

A typical receiver designed to intercept the above-described voice SDR signal would employ the following stages, essentially reversing the transmitter's action. Again, items followed by asterisks represent programmable circuits.

  • Receiving antenna

  • Superheterodyne system that boosts incoming RF signal strength and converts it to a constant frequency

  • Demodulator that separates the ASCII intelligence from the RF carrier

  • Digital-to-analog converter (DAC) that generates a voice waveform from the ASCII data

  • Audio amplifier

  • Speaker, earphone, or headset

The most significant asset of SDR is versatility. Wireless systems employ protocols that vary from one service to another. Even in the same type of service, for example wireless fax, the protocol often differs from country to country. A single SDR set with an all-inclusive software repertoire can be used in any mode,anywhere in the world. Changing the service type, the mode, and/or the modulation protocol involves simply selecting and launching the requisite computer program, and making sure the batteries are adequately charged if portable operation is contemplated.

The ultimate goal of SDR engineers is to provide a single radio transceiver capable of playing the roles of cordless telephone, cell phone, wireless fax,wireless e-mail system, pager, wireless videoconferencing unit, wireless Web browser, Global Positioning System (GPS) unit, and other functions still in the realm of science fiction, operable from any location on the surface of the earth, and perhaps in space as well.

This was last updated in November 2010

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