Etude d'application d'un convertisseur analogique a numerique a la reception directe des radiofrequences.

摘要

The next generation of software radios, cognitive radios, needs a flexibility that current software radios do not possess. This work's objective is to improve this flexibility by establishing how an analog-to-digital converter can be used as a direct radiofrequency receiver.;A software receiver, composed of an interconnection board between the converter and a logic analyzer and a Matlab signal processing unit, is designed. Signal integrity on the board and software unit's functionality are then confirmed.;The selected converter is then characterized. Results are compared to manufacturer's data. Except for maximum operating frequency, which is way below expectations, the measurements are similar to those anticipated.;The converter is finally used in a direct radiofrequency receiver. Results show that conversion deteriorations are not important enough to prevent the demodulation of the received signal. However, a more important limitative factor is highlighted: dynamic range allocated to the main signal. Since a large bandwidth is instantly digitalized, the dynamic range is divided between all signals in this bandwidth. The power of those signals alters the signal to noise ratio at reception.;A review of conversion techniques proposed in the literature shows that direct conversion is the best way to achieve such a receiver. The analog to digital converter AT84AS004, made by e2v, is identified as the best suited, commercially available converter, for the present application.;Keywords: Analog-to-digital conversion, cognitive radio, direct radiofrequency receiver, software defined radio.