INTRODUCTION
Highly accurate position information is of great importance in many commercial, public safety, and military applications. To this end, the integration of Global Positioning System (GPS) into cellular phones, in conjunction with WiFi localization, is igniting a new era of ubiquitous location-awareness. In the coming years, we will see the emergence of high-definition situation aware (HDSA) applications with capability to operate in harsh propagation environments where GPS typically fails, such as inside buildings and in caves. Such applications require localization systems with submeter accuracy. Reliable localization in such conditions is a key enabler for a diverse set of applications including logistics, security tracking (the localization of authorized persons in high security areas), medical services (the monitoring of patients), search and rescue operations (communications with fire fighters or natural disaster victims), control of home appliances, automotive safety, military systems, and a large set of emerging wireless sensor network (WSN) applications. Other applications include networking protocols taking advantage of position to improve the performance of routing algorithms (georouting), as well as interference avoidance techniques in future cognitive radios. The purpose of localization algorithms is to find the unknown positions of agent nodes given a set of measurements. Localization occurs in two main steps:
(i) selected measurements are performed between nodes;
(ii) these measurements are processed to determine the position of agent nodes.
Further, localization techniques can be classified based on measurements between nodes such as range-based, angle-based, and proximity-based localization. Among them, range-based systems (i.e., based on distance estimates) are more suitable for high definition localization accuracy, especially when low complexity devices are available. We refer the reader to and for insights on the variety of localization techniques. An overview of recent advances in cooperative localization for ultrawide bandwidth (UWB) networks is provided in, which covers Bayesian and non-Bayesian techniques using experimental data.
UWB technology offers the potential of achieving high ranging accuracy through signal TOA measurements, even in harsh environments, due to its ability to resolve multipath and penetrate obstacles. For more information on the fundamentals of UWB, we refer the reader to and references therein. It is expected that the advantages of UWB-based localization will be exploited in future HDSA systems that utilize coexisting networks of sensors, controllers, and peripheral devices. The IEEE 802.15.4a is the first UWB-based standard for low-rate wireless personal-area networks (WPANs) with localization capability ranging accuracy is expected to be one meter or submeter at least 90% of the time. Ranging techniques based on TOA estimation of the first arriving signal path are mainly affected by noise, multipath components, obstacles, interference, and clock drift. In dense multipath channels the first path is often not the strongest, making estimation of the TOA challenging.
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