Browsing by Author "Haller, Bruno"

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    Effcient Implementation of Rotation Operations for High Performance QRD-RLS Filtering
    (1997-07-20) Haller, Bruno; Gӧtze, Jürgen; Cavallaro, Joseph R.; Center for Multimedia Communications (http://cmc.rice.edu/)
    In this contribution we present practical techniques for implementing Givens rotations based on the well-known CORDIC algorithm. Rotations are the basic operation in many high performance adaptive filtering schemes as well as numerous other advanced signal processing algorithms relying on matrix decompositions. To improve the effciency of these methods, we propose to use "approximate rotations", whreby only a few (i.e. r << b, whre b is the operand word length) elementary angles of the original CORDIC sequence are applied, so as to reduce the total number of required shift-add operations. This seemingly rather ad hoc and heuristic procedure constitutes a representative example of a very useful design concept termed "approximate signal processing" recently introduced and formally exposed by Nawab et al. in [1]. concerning the trade-off between system performance and implementation comlexity, i.e. between accuracy and resources. This is a subject of increasing importance with respect to the efficient realization of demanding signal processing tasks. We pressent the application of the described rotation, schemes to QRD-RLS filtering in wireless communications, specifically high speed channel equalization and beamforming, i.e. for intersymbol and co-channel/interuser interference suppression, respectively. It is shown via computer simulations that the convergence behavior of the scheme using approximate Givens rotations is insensitive to the value of r, and that the misadjustment error decreases as r is increased, opening up possibilities of "incremental refinement" strategies.
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    Near-Far Resistant Code Synchronization For CDMA systems - An Implementation Perspective
    (1996-04-20) Haller, Bruno; Cavallaro, Joseph R.; Aazhang, Behnaam; Center for Multimedia Communications (http://cmc.rice.edu/)
    In this paper we evaluate and compare several algorithms based on eigenanalysis techniques for near-far resistant code acquisition and tracking, i.e., delay estimation in multiuser CDMA communication systems under different operating conditions. We show how the algorithms derived for the static case can easily be adapted to cope with time-varying situations. The proposed schemes are applicable to single-user as well as multiuser CDMA receivers and require neither a preamble nor decision feedback during initial acquisition and subsequent tracking.