Software-defined radio

A radio system in which software performs much of the signal processing traditionally handled by dedicated hardware, allowing functions such as modulation and filtering to change through reprogramming.

Radio frequency front end: The analog circuitry that connects an antenna to a radio’s conversion and processing stages. It handles amplification and frequency selection before signals reach programmable processing.
Nyquist–Shannon sampling theorem: A theorem stating the conditions under which a band-limited signal can be reconstructed from its samples. It sets a fundamental sampling constraint for digitizing radio signals.
Cognitive radio: A radio system that senses its environment and adapts its operation to use available spectrum or meet changing conditions. It builds on software radio’s reconfigurability to make spectrum-aware choices.
Hardware radio: A radio system whose key signal-processing functions are implemented in fixed-function electronic circuits. It represents the fixed-function architecture that software-defined radio makes more adaptable.
Analog-to-digital converter: An electronic circuit that converts a continuous analog signal into digital samples. Its sampling rate and resolution constrain which radio signals software can process.
Complex number: A number with real and imaginary components, commonly used to represent magnitude and phase together. Complex samples compactly encode the in-phase and quadrature components used in radio processing.
Amateur radio: A radio service in which licensed operators communicate and experiment for personal, technical, and public-service purposes. Software radios let operators experiment with modes and protocols on shared hardware.
System on a chip: An integrated circuit that combines a processor and other system components on one chip. Its integration can reduce size and power, while a software radio emphasizes reconfigurable signal functions.
Digital downconverter: A signal-processing unit that shifts a sampled band to a lower frequency and reduces its sampling rate. It isolates and efficiently represents a selected channel after digitization.
In-phase and quadrature components: Two signal components separated by 90 degrees in phase, used to represent a modulated carrier. Their digital representation lets software manipulate carrier amplitude and phase.

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