Signal-adapted Multiresolution Transform for Image-coding

Wavelet-type multiresolution transforms have recently been introduced in digital image coding, and have been shown to offer some advantages over classical block transform techniques such as the discrete cosine transform (DCT). This correspondence is mainly concerned with the problem of designing suitable multiresolution transforms that are adapted to the given image signal, in the sense that they maximize the coding gain at each resolution level. A simple alternating optimization algorithm is derived for solving this problem in the framework of the lattice realization of para-unitary quadrature mirror filters (QMF). The resulting image coding scheme is discussed in some detail, and its performance is compared with the DCT (JPEG) technique and with some non-adapted multiresolution transforms

Fast Parallel Self-tuning Controllers

Fast self-tuning discrete-time control algorithms based on 'recursive least squares' parameter estimation and 'generalized minimum-variance' (GMV) control design are presented both in lattice and transversal forms. This derivation relies both on the linear prediction interpretation of GMV control and on the embedding of the pole-zero predictive model (for the system output) into a multichannel all-pole model for the joint system input-output process. The proposed multichannel algorithms are simplified via a modular decomposition principle which converts all matrix recursions into coupled scalar recursions. The resulting control algorithms require 0(n) computations per time instant, where n denotes the controller order. Furthermore, we present parallel implementations of such fast 'self-tuning controllers' (STCs) in O(n) processor arrays. Several structures, obtained for different implementations of the controller and of the identifier, are devised to this end but, as far as we are concerned with an 'ideal' STC (i.e. one which generates the control signal at each time instant with the best and most recent currently available parameter estimates), none of them can lead to a pipelined STC. We show that a pipelined STC can be obtained by implementing the controller in transversal form and introducing an O(n) 'lag' in the transfer of parameters from the identifier to the controller. This amounts to using delayed parameter estimates in the control computation which. for slowly time-varying systems, could be a viable solution in order to increase the sampling rate

Областная газета. Новая Эра. 2004. № 153

International audienceWe describe the design steps and final implementation of a MIMO OFDM prototype platform developed to enhance the performance of wireless LAN standards such as HiperLAN/2 and 802.11, using multiple transmit and multiple receive antennas. We first describe the channel measurement campaign used to characterize the indoor operational propagation environment, and analyze the influence of the channel on code design through a ray-tracing channel simulator. We also comment on some antenna and RF issues which are of importance for the final realization of the testbed. Multiple coding, decoding, and channel estimation strategies are discussed and their respective performance-complexity trade-offs are evaluated over the realistic channel obtained from the propagation studies. Finally, we present the design methodology, including cross-validation of the Matlab, C++, and VHDL components, and the final demonstrator architecture. We highlight the increased measured performance of the MIMO testbed over the single-antenna system