The software defined by the radio is exactly what its name suggests: a radio device whose operating characteristics are determined by the software, not the hardware. Components in hardware, such as filters, sensors, modulators / demodulators, are usually implemented by software for general purpose processors that can be executed on most personal computers. This provides the SDR with enormous flexibility in operating frequencies, supported protocols, waveforms, and so on. In terms of virtually anything that can be practiced. The practical implementation of such tools has only recently become feasible because of the rapid advances in electronics. SDRs are said to be the future of telecommunications, as most devices are expected to be SDRs in the near future.
Current applications include the United States Army's Common Tactical Radio System (JTRS), as well as numerous amateur radio or home-use applications instead of previously used, much slower computer sound cards. Certain implementations, such as the USRP, discussed below, are also widely used in academic and industrial research programs, as they provide flexibility in contrast to hardware vendors.
Universal Radio Peripheral Radio (USRP)
USRP generates relatively inexpensive hardware for software radio equipment. Open design, sketches and train drivers are freely available. The GNU radio software project uses a number of well-known analogue and digital radio protocols, such as FM radio and digital television receivers. For hardware, the USRP includes some high-speed 14-bit digital-to-analog (DAC) and 12-bit analogue-to-digital (ADC) converter, an Altera Cyclone FPGA, a USB 2.0 interface, and 4 slots for the boards. These boards have particular demands. For example, radio transmitters with frequency ranges from DC (0 Hz) to 4 GHz are available, covering almost all the radio spectrum used. This board features Xilinx Spartan 3 FPGA, gigabit ethernet, higher resolution and faster DAC and ADC modules. The disadvantage of Xilinx software tools that are compatible with Spartan FPGA is not available for free. It's important to note that this platform is not intended to replace the original USRP, but is sold in parallel. HPSDR (High Performance Software Defined Radio) is a project that uses a 16-bit 135MSPS analog-to-digital converter (USRP2 instead of 14-bit @ 100MSPS), which provides a standard analog HF radio, similar to the 0-55 MHz range.
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