11 Excellence Creation by Researcher Students 1 DIGITAL COMMUNICATION WITH CHAOTIC AND IMPULSE WAVELETS Géza Kolumbán 1 , Tamás Krébesz 2 1,2 Department of Measurement and Information Systems, Budapest University of Technology and Economics H-1521 Budapest Pf. 91, Hungary (kolumban@mit.bme.hu ) (tomkrebesz@gmail.com ) Abstract Fourier analyzer concept that generalize the waveform communications to include chaotic carriers can be used to discuss and optimize detection problems. Using this new description it is possible to develop new detector configurations with improved performance for chaotic communications that may be used in ultra-wideband radio (UWB). Radio communications via channels already occupied by traditional telecommunication systems can be achieved by using UWB radio where extremely wideband wavelets are radiated in order to reduce the power spectral density (psd) of transmitted signal. Since the recovery of these UWB carriers is not feasible, noncoherent demodulation techniques have to be used. The paper shows the Fourier analyzer concept then evaluates and compares the noise performances of the feasible noncoherent UWB modulation schemes, namely, that of the noncoherent pulse polarity modulation and the transmitted reference system. Keywords: subspace theory of detection, Fourier analyzer concept, chaotic communications, transmitted reference system, UWB radio 1. INTRODUCTION Digital communications using wideband carriers have been becoming one of the most important applications of radio communications recently [1]. Typical applications are the wireless local area network (WLAN), ultra-wideband radio (UWB) and sensor network. It is not the thermal noise but the multipath propagation that limits the system performance in these, mostly indoor, applications; therefore, the transmitted signal must be a wideband signal. The digital information to be transmitted is mapped into fixed, mostly sinusoidal waveforms in conventional communication systems. These systems are typically narrowband systems, but if it is needed the spectrum of them can be spread by a pseudo- noise sequence [2]. An alternative solution is the application of a wideband carrier, where the digital information to be transmitted is directly mapped into a wideband signal. The carrier can be a fixed waveform in impulse radio [1] or chaotic signal in chaotic UWB radio. The common property of these solutions is that the carrier is a wideband signal; consequently there is no need for an extra spectrum spreading sequence.