Location-aware technologies will revolutionize many aspects of commercial, public service, and military sectors, and are expected to spawn numerous unforeseen applications. A new era of highly accurate ubiquitous location-awareness is on the horizon, enabled by a paradigm of cooperation between nodes. In this paper, we give an overview of cooperative localization approaches and apply them to ultrawide bandwidth (UWB) wireless networks. UWB transmission technology is particularly attractive for short- to medium-range localization, especially in GPS-denied environments: wide transmission bandwidths enable robust communication in dense multipath scenarios, and the ability to resolve subnanosecond delays results in centimeter-level distance resolution. We will describe several cooperative localization algorithms and quantify their performance, based on realistic UWB ranging models developed through an extensive measurement campaign using FCC-compliant UWB radios. We will also present a powerful localization algorithm by mapping a graphical model for statistical inference onto the network topology, which results in a net-factor graph, and by developing a suitable net-message passing schedule. The resulting algorithm (SPAWN) is fully distributed, can cope with a wide variety of scenarios, and requires little communication overhead to achieve accurate and robust localization.

Cooperative Localization in Wireless Networks

Over the coming decades, high-definition situationally-aware networks have the potential to create revolutionary applications in the social, scientific, commercial, and military sectors Ultrawide bandwidth (UWB) technology is a viable candidate for enabling accurate localization capabilities through time-of-arrival (TOA)-based ranging techniques These techniques exploit the fine delay resolution property of UWB signals by estimating the TOA of the first signal path Exploiting the full capabilities of UWB TOA estimation can be challenging, especially when operating in harsh propagation environments, since the direct path may not exist or it may not be the strongest In this paper, we first give an overview of ranging techniques together with the primary sources of TOA error (including propagation effects, clock drift, and interference) We then describe fundamental TOA bounds (such as the Cramer-Rao bound and the tighter Ziv-Zakai bound) in both ideal and multipath environments These bounds serve as useful benchmarks in assessing the performance of TOA estimation techniques We also explore practical low-complexity TOA estimation techniques and analyze their performance in the presence of multipath and interference using IEEE 802154a channel models as well as experimental data measured in indoor residential environments

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Ranging With Ultrawide Bandwidth Signals in Multipath Environments

The availability of position information is of great importance in many commercial, public safety, and military applications. The coming years will see the emergence of location-aware networks with submeter accuracy, relying on accurate range measurements provided by wide bandwidth transmissions. In this two-part paper, we determine the fundamental limits of localization accuracy of wideband wireless networks in harsh multipath environments. We first develop a general framework to characterize the localization accuracy of a given node here and then extend our analysis to cooperative location-aware networks in Part II. In this paper, we characterize localization accuracy in terms of a performance measure called the squared position error bound (SPEB), and introduce the notion of equivalent Fisher information (EFI) to derive the SPEB in a succinct expression. This methodology provides insights into the essence of the localization problem by unifying localization information from individual anchors and that from a priori knowledge of the agent's position in a canonical form. Our analysis begins with the received waveforms themselves rather than utilizing only the signal metrics extracted from these waveforms, such as time-of-arrival and received signal strength. Hence, our framework exploits all the information inherent in the received waveforms, and the resulting SPEB serves as a fundamental limit of localization accuracy.

Fundamental Limits of Wideband Localization— Part I: A General Framework

The availability of position information is of great importance in many commercial, governmental, and military applications Localization is commonly accomplished through the use of radio communication between mobile devices (agents) and fixed infrastructure (anchors) However, precise determination of agent positions is a challenging task, especially in harsh environments due to radio blockage or limited anchor deployment In these situations, cooperation among agents can significantly improve localization accuracy and reduce localization outage probabilities A general framework of analyzing the fundamental limits of wideband localization has been developed in Part I of the paper Here, we build on this framework and establish the fundamental limits of wideband cooperative location-aware networks Our analysis is based on the waveforms received at the nodes, in conjunction with Fisher information inequality We provide a geometrical interpretation of equivalent Fisher information (EFI) for cooperative networks This approach allows us to succinctly derive fundamental performance limits and their scaling behaviors, and to treat anchors and agents in a unified way from the perspective of localization accuracy Our results yield important insights into how and when cooperation is beneficial

http://publications.lib.chalmers.se/records/fulltext/local_133941.pdf

Fundamental Limits of Wideband Localization— Part II: Cooperative Networks

Ultra Wideband Signals and Systems in Communication Engineering

This paper investigates time of arrival (ToA) estimation methods for ultra-wide bandwidth (UWB) propagation signals. Different algorithms are implemented in order to detect the direct path in a dense multipath environment. Different suboptimal, low-complex techniques based on peak detection are used to deal with partial overlap of signal paths. A comparison in terms of ranging accuracy, complexity, and parameters sensitivity to propagation conditions is carried out also considering a conventional technique based on threshold detection. In particular, the algorithms are tested on experimental data collected from a measurement campaign performed in a typical office building.

/pdf/time-of-arrival-estimation-for-uwb-localizers-in-realistic-4g8xafw2yx.pdf

Time of arrival estimation for UWB localizers in realistic environments

This paper investigates time of arrival (ToA) estimation methods for ultra-wide bandwidth (UWB) propagation signals. Different algorithms are implemented in order to detect the direct path in a dense multipath environment. In particular, suboptimal low-complex techniques based on peak detection are used to deal with partial overlap of signal paths. A comparison in terms of ranging accuracy, complexity, and parameters sensitivity to propagation conditions is carried out also considering a conventional technique based on threshold detection. The algorithms are tested on experimental data collected from a measurement campaign performed in a typical office building.

Range Estimation in UWB Realistic Environments

This paper investigates channel parameters estimation methods for ultra-wide bandwidth (UWB) propagation signals. Different algorithms are implemented in order to detect the multipath components (MPCs) in a dense multipath environment. Different suboptimal, low-complex techniques based on peak detection are used to solve the ambiguities due to partial overlapping of signal paths. In particular, the algorithms are tested on experimental data collected from a measurement ent campaign performed in a typical office building. The distribution functions of delays and amplitudes of different paths are analyzed in order to characterize the propagation channel. Once the relevant channel parameters have been estimated, the performance of Rake receivers is evaluated as well.

Chiara Falsi

Papers

Time of arrival estimation for UWB localizers in realistic environments

Range Estimation in UWB Realistic Environments

Channel Parameters Estimation for UWB Realistic Environments