Cramer-Rao bounds in the estimation of time of arrival in fading channels

This paper computes the Cramer-Rao bounds for the time of arrival estimation in a multipath Rice and Rayleigh fading scenario, conditioned to the previous estimation of a set of propagation channels, since these channel estimates (correlation between received signal and the pilot sequence) are sufficient statistics in the estimation of delays. Furthermore, channel estimation is a constitutive block in receivers, so we can take advantage of this information to improve timing estimation by using time and space diversity. The received signal is modeled as coming from a scattering environment that disperses the signal both in space and time. Spatial scattering is modeled with a Gaussian distribution and temporal dispersion as an exponential random variable. The impact of the sampling rate, the roll-off factor, the spatial and temporal correlation among channel estimates, the number of channel estimates, and the use of multiple sensors in the antenna at the receiver is studied and related to the mobile subscriber positioning issue. To our knowledge, this model is the only one of its kind as a result of the relationship between the space-time diversity and the accuracy of the timing estimation.Peer ReviewedPostprint (published version

Space-Time diversity for NLOS mitigation in TDOA-based positioning systems

This paper studies the potential impact of using space-Time information in the mitigation of the Non-LineOf-Sight condition in mobile subscriber's positioning systems. First of all, this work discusses the positioning problem based on measures of Time Differences Of Arrival departing from a more exact characterization of the signal statistics and including some geometrical restrictions to achieve an improved accurate. Furthermore, a novel approach that integrates signal propagation characteristics to information provided by a suitable timing estimation model based on Cramer Rao Bound for a Rayleigh-fading channel, when antenna arrays are used at the receiver and when a set ofchannel vector estimates are available, has been introduced to study the positive benefits of space-Time diversity. These approaches are evaluated within a realistic simulation scenario.Peer ReviewedPostprint (published version

Coarse First Arriving Path Detection for Subscriber Location in Mobile Communication Systems

The objective of this paper is to determine the potentialities of a detection scheme within the framework of subscriber location. Usually, it is the first arrival that bears the necessary information for user location. In NLOS situations, this first arrival is very much attenuated with respect to the RAKE synchronisation time instant, and it is placed well before this point. The determination of a window comprising this point is a must for a later use of a high resolution technique. Using a Generalized Likelihood Ratio Test (GLRT), an improved coarse first arriving path detector from propagation channel estimates is derived. Furthermore, an expression for false alarm probability is provided and detector performance is evaluated for different receiver configurations and signal propagation conditions

NLOS mitigation based on TOA for mobile subscriber positioning systems by weighting measures and geometrical restrictions

This paper studies the Non-Line-Of-Sight condition mitigation issue in mobile subscriber positioning systems by weighting Time-Of-Arrival measures and applying geometrical estrictions. Particularly, this work departs from a more exact characterization of the signal statistics to achieve weighting factors able to reach a more effective mitigation, and consequently a more accurate mobile subscriber positioning. In addition, restrictions based on the cell geometry are incorporated as a complementary refinement method. Therefore, three new methods with better properties than those taken from the literature and used as reference are introduced. These approaches are evaluated within a realistic simulation scenario.Peer ReviewedPostprint (published version

Cramer-Rao bounds in the estimation of time of arrival in fading channels

This paper computes the Cramer-Rao bounds for the time of arrival estimation in a multipath Rice and Rayleigh fading scenario, conditioned to the previous estimation of a set of propagation channels, since these channel estimates (correlation between received signal and the pilot sequence) are sufficient statistics in the estimation of delays. Furthermore, channel estimation is a constitutive block in receivers, so we can take advantage of this information to improve timing estimation by using time and space diversity. The received signal is modeled as coming from a scattering environment that disperses the signal both in space and time. Spatial scattering is modeled with a Gaussian distribution and temporal dispersion as an exponential random variable. The impact of the sampling rate, the roll-off factor, the spatial and temporal correlation among channel estimates, the number of channel estimates, and the use of multiple sensors in the antenna at the receiver is studied and related to the mobile subscriber positioning issue. To our knowledge, this model is the only one of its kind as a result of the relationship between the space-time diversity and the accuracy of the timing estimation.Peer Reviewe

Space-Time diversity for NLOS mitigation in TDOA-based positioning systems

This paper studies the potential impact of using space-Time information in the mitigation of the Non-LineOf-Sight condition in mobile subscriber's positioning systems. First of all, this work discusses the positioning problem based on measures of Time Differences Of Arrival departing from a more exact characterization of the signal statistics and including some geometrical restrictions to achieve an improved accurate. Furthermore, a novel approach that integrates signal propagation characteristics to information provided by a suitable timing estimation model based on Cramer Rao Bound for a Rayleigh-fading channel, when antenna arrays are used at the receiver and when a set ofchannel vector estimates are available, has been introduced to study the positive benefits of space-Time diversity. These approaches are evaluated within a realistic simulation scenario.Peer Reviewe

NLOS mitigation based on TOA for mobile subscriber positioning systems by weighting measures and geometrical restrictions

This paper studies the Non-Line-Of-Sight condition mitigation issue in mobile subscriber positioning systems by weighting Time-Of-Arrival measures and applying geometrical estrictions. Particularly, this work departs from a more exact characterization of the signal statistics to achieve weighting factors able to reach a more effective mitigation, and consequently a more accurate mobile subscriber positioning. In addition, restrictions based on the cell geometry are incorporated as a complementary refinement method. Therefore, three new methods with better properties than those taken from the literature and used as reference are introduced. These approaches are evaluated within a realistic simulation scenario.Peer Reviewe

Fast computation of Cramer-Rao Bounds for TOA – An application to network-based positioning simulations

As part of a larger scope work that studies network-based positioning, that employs timing measures, this article proposes a methodology to add Cramer-Rao Bounds (CRBs) information to the propagation model. Moreover, it enables a very quick computation of CRBs for timing, avoiding the growing computational effort resulting from Fisher’s matrix formulation and its inversion for each required position at the simulation stage, assuring at the same time the reliability of the required data in the study of positioning using space-time diversity. This methodology considers the variability of the propagation conditions in terms of delay spread (DS) and Signal-to-Noise ratio (SNR) in a realistic scenario. It also coordinates the operation of concurrent models within simulation, and finally performs bi-exponential regression and interpolation procedures on pertinent operational regions for CRBs. Properly validated models provide simple closed expressions that ease the operational region discrimination and its integration to the positioning simulation platform.Peer ReviewedPostprint (published version

Selection of the reference anchor node by using SNR in TDOA-based positioning

This article studies the positioning problem for wireless networks when TDOA measures are used and the reference anchor node is not previously known. We carried out various experiments to show the impact on accuracy when a poor selection of this reference is achieved. Furthermore, we study the use of SNR at receivers as a mean to proper select the closest node as the reference anchor, previously to perform mobile positioning. An appropriate mechanism to perform this selection is provided within a simulation platform built to study network-based positioning using space-time diversity in realistic conditions. This approach shows that the use of a signal that measures or estimates the received power is a viable mechanism for the proper selection of the anchor node even in a shadowed environment, avoiding the severe degradation that involves a poor selection.Peer ReviewedPostprint (published version