Bardia Alavi

Modeling of the TOA-based distance measurement error using UWB indoor radio measurements

Time of arrival (TOA) estimation used with ultra wideband (UWB) transmission is currently the most popular technique for accurate indoor geolocation. Due to severe indoor multipath conditions, these techniques often suffer from significant inaccuracy in location estimation. In this paper, we introduce a model for the error in estimated distance as measured from the estimated TOA of the direct path (DP) in a typical multipath indoor environment. The TOA estimation error has two components, (1) the errors caused by the multipath dispersion affecting any signal path and (2) the errors caused by undetected direct path (UDP) conditions. The statistical behavior of this error is also a function of the system bandwidth. The empirical data from UWB indoor measurements in an office building are used to design a model for the distance measurement error. This model relates the behavior of the two components of the TOA estimation error to the bandwidth of the system.

Modeling of the distance error for indoor geolocation

This paper uses the results of a calibrated ray tracing software in a sample office environment to analyze and model the distance error measured from the estimated time of arrival (TOA) of the direct line-of-sight (LOS) path in a typical indoor environment. First, we analyze the effect of bandwidth on the measured distance error using TOA and then, we propose a model for simulation of the distance error in LOS and OLOS indoor areas.

Bandwidth effect on distance error modeling for indoor geolocation

In this paper we introduce a model for the distance error measured from the estimated time of arrival (TOA) of the direct path (DP) between the transmitter and the receiver in a typical multipath indoor environment. We use the results of a calibrated Ray tracing software in a sample office environment. First we divide the whole floor plan into LOS and Obstructed LOS (OLOS), and then we model the distance error in each environment considering the variation of bandwidth of the system. We show that the behavior of the distance error in LOS environment can be modeled as Gaussian, while behavior of the OLOS is a mixture of Gaussian and exponential distribution. We also related the statistics of the distributions to the bandwidth of the system.

A Novel Cooperative Localization Algorithm for Indoor Sensor Networks

Recently, node localization for multi-hop sensor networks has attracted considerable attention. In these networks, error propagation provides a serious challenge to algorithm development and accuracy of final location estimates. In this paper we introduce a novel computationally efficient distributed algorithm, cooperative localization with optimum quality of estimate (CEOQ) which takes advantage of the behavior of the channel to provide accurate indoor positioning. This algorithm uses the quality of ranging and positioning estimates to provide practical and accurate results and more importantly reduce error propagation substantially. Using UWB measurements and modeling of the ranging error in a typical office building we compare the performance of this cooperative localization algorithm with a non-channel based algorithm for indoor ad-hoc sensor environments

Analysis of undetected direct path in time of arrival based UWB indoor geolocation

Accurate indoor geolocation using time-of-arrival (TOA) is seriously challenged with the occurrence of undetected direct path (UDP) conditions caused by severe multipath in indoor areas. As a result, analysis of the occurrence of UDP in indoor areas is extremely important for design and performance evaluation of the emerging indoor geolocation systems. A UDP occurs when the received signal strength of the direct path (DP) between the transmitter and the receiver falls below the detection threshold of the receiver, but the total received signal power is still above the threshold. This paper provides a novel analysis for modeling the behavior of the DP and the total received power and uses the model to calculate the probability of UDP occurrence. To verify the accuracy of the analytical model, the results are compared with the empirical UWB measurements in typical indoor areas. the UDP conditions. There is nothing available in the literature to address this issue. The only available analysis is the results of empirical measurements reported in (4), in which occasional occurrence of UDP in a typical building using a system with a bandwidth of 200MHz is studied. In this paper based on the analysis of the total received signal power described in (5) and a novel analysis for calculation of the received signal in the direct path, we show that the occurrence of UDP is inevitable. In addition, using a partitioning technique, we determine the probability of occurrence of this condition in an indoor area. We validate the results of our analysis with the empirical UWB channel measurements with 3GHz bandwidth performed in a typical indoor office area. The structure of the sections of this paper is as follows: Section I introduces the importance of UDP in indoor geolocation. Section II is about the measurement system and scenario. Section III describes the concept of UDP and its different definitions. Section IV introduces a channel model that helps calculation of probability of UDP and compares the results of the model with the UWB channel measurements. Finally section V is the conclusion. II. THE CONCEPT AND DEFINITIONS OF UDP A. Existing reports of UDP

UWB Channel Measurements for Accurate Indoor Localization

Recently, indoor localization has attracted considerable attention. More importantly, indoor channel measurements and models are very essential to accurate characterization of the ranging error for military applications. This paper provides the results of UWB measurements and modeling performed for indoor geolocation applications. The measurement campaign took place in the Worcester, MA in a modern office building, a manufacturing floor, a residential house, and an old office building. A total of 2934 wideband measurements at frequency band of 3-8 GHz were collected in the four sites. Measurements were divided into indoor-to-indoor, outdoor-to-indoor, and roof-to-indoor conditions with two different polarity of the mobile antenna representing an upright soldier and a soldier lying on the ground. The models developed from the measurements represent a number of propagation scenarios for different areas in each set of measurements. In this paper we provide novel path-loss models of the first-detected path (FDP) and the total power which is essential for localization applications. In addition ranging error models are also provided which characterizes the behavior of the direct-path (DP) and its relationship to the error. All the models are presented for two different bandwidths of 500 MHz and 3 GHz.

Indoor Geolocation Distance Error Modeling using UWB Channel Measurements

In this paper we introduce a model for the distance error measured from the estimated time of arrival (TOA) of the direct path (DP) in a typical multipath indoor environment. We use the results of our ultra-wideband (UWB) measurement database in a sample office environment. To begin modeling, first we separate the causes of the error into multipath and undetected direct path (UDP), and then we model them separately considering the variation of bandwidth of the system. We show that the behavior of the distance error consists of two parts; one that is from multipath, and the other one from UDP. Both errors can be modeled as Gaussian, so the final distance error is a mixture of two Gaussian distributions. We also related the statistics of the distributions to the bandwidth of the system

An Error Propagation Aware Algorithm for Precise Cooperative Indoor Localization

Recently, node localization for sensor networks has attracted considerable attention for military application. Despite the recent proposals, the relationship between the channel behavior and the performance analysis of cooperative algorithms has not been addressed. The assumptions about the statistics of the ranging error used in the literature are either too general or overly optimistic. Additionally when sensors collaborate to localize each other, there is no attempt to characterize the error in the position of the nodes. This lack of error propagation-awareness can degrade the performance of an algorithm and create divergence problems. In this paper we first introduce detailed modeling of channel propagation in indoor environments in the form of novel empirical path loss (PL) and distance measurement error (DME) models developed from the results of UWB channel measurements. Then we integrate these models in developing error propagation aware (EPA) precise cooperative localization algorithm that tracks the extent of the position error in each sensor node and its overall effect on subsequent multi-laterations. Finally we compare the algorithm against the Cramer-Rao lower bound (CRLB)

Studying the effect of bandwidth on performance of uwb positioning systems

In this paper we study the effect of bandwidth on performance of positioning systems. We introduce a benchmark for performance evaluation, distance measurement error (DME). We analyze DME and introduce a model for it. We show that there are two causes for DME, multipath dispersion and undetected direct path (UDP), and we study the effect of bandwidth on each of these components in DME. We show that increasing the bandwidth can decrease the multipath DME, but for the UDP effect, beyond a certain point it increases the DME. Thus there is an optimum bandwidth for minimizing overall error. The results were obtained using a database of UWB measurements conducted in an indoor propagation environment

Spatial Characteristics of UWB TOA-based Ranging in Indoor Multipath Environments

This paper provides the results of comprehensive measurement and modelling of time of arrival (TOA) based UWB ranging in different indoor environments and ranging scenarios. We show that ranging accuracy of UWB systems is directly related to the physical constraints of the environment and system bandwidth. In addition we show through empirical measurement and modelling that the spatial characteristics of the ranging error depend on the presence and absence of the Direct Path (DP). In the former, the spatial error follow a normal distribution, while in the latter, the error behaviour is best modelled as lognormal.