Real software radios often have two or three analog channel filters with different bandwidths that are switched in and out. The standard solution is to put band-pass filters between the antenna and the amplifier, but these reduce the radio's flexibility. They may introduce distortion in the desired signals, or may block them completely. For example, if spurious signals are present (which is typical), these compete with the desired signals within the amplifier's dynamic range. Therefore, a low-noise amplifier must precede the conversion step and this device introduces its own problems. Real analog-to-digital converters lack the dynamic range to pick up sub-microvolt, nanowatt-power radio signals produced by an antenna. However, in some applications it is not necessary to tune the signal to an intermediate frequency and the radio frequency signal is directly sampled by the analog-to-digital converter (after amplification). Typically in SDR, this signal is then sampled by the analog-to-digital converter. Superheterodyne receivers use a VFO ( variable-frequency oscillator), mixer, and filter to tune the desired signal to a common IF ( intermediate frequency) or baseband. Each node transmits using only enough power needed for the message to hop to the nearest node in that direction, reducing the near–far problem and reducing interference to others.
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. Such a design produces a radio which can receive and transmit widely different radio protocols (sometimes referred to as waveforms) based solely on the software used.
Significant amounts of signal processing are handed over to the general-purpose processor, rather than being done in special-purpose hardware ( electronic circuits). While the concept of SDR is not new, the rapidly evolving capabilities of digital electronics render practical many processes which were once only theoretically possible.Ī 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.
mixers, filters, amplifiers, modulators/ demodulators, detectors, etc.) are instead implemented by means of software on a personal computer or embedded system. Software-defined radio ( SDR) is a radio communication system where components that have been traditionally implemented in hardware (e.g.