 - 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.
| LAST UPDATED: |
31 Jul 2001
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