Filling the Spectral Holes: Novel\/Future Wireless Communications and Radar Receiver Architectures

The requirement of wireless access by novel telecommunications and remote-sensing applications, such as Internet-in-mobile services and ultrawideband (UWB) radar systems, is continuously growing in western society but also in countries with big and emerging economies such as China, Brazil, India, and even some African nations. As a consequence, the radiofrequency (RF) spectrum is becoming a very valuable but scarce natural resource. In relation to this, it is well known that some portions of the RF spectrum, such as those assigned to military and emergency services, remain underutilized. These spectral holes, usually referred as "white spaces," then become excellent opportunities for new wireless communications and radar systems to operate. Nevertheless, the necessary dynamic access to properly exploit these free spectral holes can only be performed through very sophisticated and reliable receiver architectures. They must be capable of sensing very broad spectrum ranges while assuring a minimum quality for the received signals. This article addresses modern RF receiver schemes for sensing widebands in communications and radar scenarios.