This introduction describes our motivation for building a transceiver based on software-radio, hereafter called software-radio testbed, and gives an overview of the general philosophy.

Why Software-Radio?

We talk about Software Radio when the map between the data (sending and receiving) and the data-carrying antenna signal are completely (within hardware limits) specified by the software. Any map that conforms with the hardware limitations (power, bandwith, hardware imperfections) may be implemented by means of an appropriate code. (B.Rimoldi, 2003)
If you like the idea of a flexible transceiver and are not too concerned with size and energy consumption, then you want your transceiver to be software-radio based. For instance, let us say that you have a software radio mobile phone. This mobile phone is a general purpose communication device with a piece of software that makes it behave like a mobile phone. You can turn your mobile phone into a GPS receiver, or a TV receiver, or a Wi-Fi interface, just by down-loading a piece of software (assuming there is a server that has the software you need).

For the technically oriented person: in a software-based transmitter, the software creates the samples corresponding to the signal to be transmitted. A general purpose hardware converts these samples into the signal that will be sent to the antenna. Similarly, in a software-based receiver, the general purpose hardware takes the signal captured by the antenna and produces the corresponding samples. The software does the rest. The hardware is not aware of the standard you are using: it just converts back and forth between samples and waveforms.

Fig.[*] shows the two main components of a software-defined transceiver. The hardware implements a two-way mapping between waveforms and samples. Except for the possibility of controlling the power of the transmitted signal, the amplification of the received signal, as well as some other parameters that are not relevant for this discussion, this mapper performs the same operation regardless of the standard implemented by the transceiver.

Figure 2.1: Dumb hardware and intelligent software

Linus Gasser 2004-04-14