Cramer-Rao bounds for the estimation of multipath parameters and mobiles' positions in asynchronous DS-CDMA systems

Commercial applications for the location of subscribers of wireless services continue to expand. Consequently, finding the Cramer-Rao lower bound (CRLB), which serves as an optimality criterion for the location estimation problem, is of interest. In this paper, we derive the deterministic CRLBs for the estimation of the specular multipath parameters and the positions of the mobiles in an asynchronous direct sequence code division multiple access (DS-CDMA) system operating over specular multipath fading channels. We assume a multilateral radio location system where the location estimates are obtained from some or all of the estimated signal parameters at different clusters of antennas of arbitrary geometry. Extension for unilateral and composite radio location techniques is also discussed. As an application example, we use numerical simulations to investigate the effects of specular multipath and multiple access interference (MAI) on the positioning accuracy for different radio location techniques.     

A technique for measurement of the extent of spatial organizationof atrial activation during atrial fibrillation in the intact humanheart

Atrial fibrillation (AF) is a common clinical problem, associated with considerable morbidity and motility, for which effective management strategies have yet to be devised. The absence of objective measures to guide selection of antiarrhythmic drug therapy for maintenance of sinus rhythm leaves only clinical endpoints (either beneficial or detrimental) for assessment of drug action, with occasional catastrophic consequences. As part of an attempt to provide an objective framework for the assessment of antiarrhythmic drug action on the electrophysiologic determinants of atrial fibrillation, the authors have developed a measure of the spatial organization of atrial activation processes during atrial fibrillation. By recording activation sequences at multiple equally spaced locations on the endocardial surface of the atrial during atrial fibrillation in humans and determining the degree of correlation between these activation sequences as a function of distance, the authors have been able to construct spatial correlation functions for atrial activation. They have found that atrial activation remains well-correlated, independent of distance during normal sinus rhythm and atrial flutter. During atrial fibrillation, correlation decays monotonically with distance and the space-constant for this decay may be used to describe the relative spatial organization of atrial fibrillation. The authors provide examples of the impact of antiarrhythmic agents on the space-constant and suggest that assessment of the relative spatial organization of atrial activation using this methodology may potentially provide an objective framework to guide therapy in patients with AF     

Bulk-source-coupled CMOS quadrature oscillators

A quadrature oscillator based on a coupling between the bulk and the source of MOS transistors is proposed. Since the resonator load is not directly involved in the coupling process, the oscillation frequency is very close to the resonant frequency, hence a good phase noise characteristic. The developed theory matches very well to the simulations.     

Effects of system and environment parameters on the performance of network-based mobile station position estimators

This paper provides an asymptotic performance evaluation of network-based or multilateral positioning systems, where the times and/or angles of arrival of the signals traveling from a mobile station (MS) to a set of fixed stations (FSs) are used to estimate the MS's position. The effects of the various system-design parameters as well as the effects of biased bearing and time measurements are analyzed, and explicit formulas are derived. Biased measurements can result, for example, from hardware calibration errors or multipath effects, including the lack of line of sight (LoS). Among other results, it is shown that only a few system and cellular parameters can be used to minimize their nuisance effects. The mathematical analysis is based on the Cramer-Rao lower bound (CRLB) and the maximum likelihood theory. It is completed with numerical simulations and a discussion of the positioning performance for two important second-generation cellular systems, GSM and IS-95.