A low-power impulse radio ultra-wideband CMOS radio-frequency transceiver

Abstract

Ultra-Wideband (UWB) is a promising technology for short-range and low-power indoor data communications. The recent interest in this technology was initiated in February 2002 in the United States. The amendment of the spectrum policies by the Federal Communication Commission (FCC) allowed the use of a radio signal occupying a bandwidth in excess of 500 MHz within the frequency range between 3.1 and 10.6 GHz. This opened the way to two main classes of wireless applications: 1) high-speed wireless aiming at transmission rates above 100 Mb/s for multimedia applications, and 2) low-complexity radio systems with high integration level intended for low-power applications such as wireless sensor networks (WSN). This work focuses on the second class of applications. Ultra-Wideband has been recognized as an interesting candidate for small portable devices transmitting data at faster rates and lower power consumption than the existing short-range wireless Standards such as Bluetooth or ZigBee. Following the United States, the Electronic Communications Committee (ECC) in Europe finalized a decision in February 2007, which clearly states that the 68.5 GHz frequency range is the preferred band for long-term operation of FCC-like UWB devices. The goal of this project was the development of a standalone wireless integrated transceiver using the promising Impulse-Radio UltraWideband (IR-UWB) technology. The benefits and the limitations of this technology were first thoroughly investigated. We specified a transceiver that could easily be implemented with the minimum loss of performance with respect to an optimum transceiver. Investigations showed that the main limitation comes from the characteristics of the indoor channel. The latter suffers from the multipath effect that induces fading and inter-symbol interferences. In low-complexity transceivers, where no extensive signal processing can be applied, there is an interest to use the multipath rather than to mitigate it. The principle of “energy-collection” is thus applied to the proposed receiver. The second principle of diversity is based on the use of frequency multiple access (carrier-based IR-UWB). For the class of devices targeted in this work (single antenna), the frequency diversity is also the only diversity strategy for enabling a reliable communication link. If the wireless devices are stationary or seldom moving, time diversity is not a reliable option, while small size rules out spatial diversity (eg. multiple antennas).