Location Systems: An Introduction to the Technology Behind Location Awareness

Anthony LaMarca, Eyal de Lara
2008 Synthesis Lectures on Mobile and Pervasive Computing  
Editor Mahadev Satyanarayanan, Carnegie Mellon University Mobile computing and pervasive computing represent major evolutionary steps in distributed systems, a line of research and development that dates back to the mid-1970s. Although many basic principles of distributed system design continue to apply, four key constraints of mobility have forced the development of specialized techniques. These include unpredictable variation in network quality, lowered trust and robustness of mobile
more » ... limitations on local resources imposed by weight and size constraints, and concern for battery power consumption. Beyond mobile computing lies pervasive (or ubiquitous) computing, whose essence is the creation of environments saturated with computing and communication yet gracefully integrated with human users. A rich collection of topics lies at the intersections of mobile and pervasive computing with many other areas of computer science. ABSTRACT Advances in electronic location technology and the coming of age of mobile computing have opened the door for location-aware applications to permeate all aspects of everyday life. Location is at the core of a large number of high-value applications ranging from the life-and-death context of emergency response to serendipitous social meet-ups. For example, the market for GPS products and services alone is expected to grow to US$200 billion by 2015. Unfortunately, there is no single location technology that is good for every situation and exhibits high accuracy, low cost, and universal coverage. In fact, high accuracy and good coverage seldom coexist, and when they do, it comes at an extreme cost. Instead, the modern localization landscape is a kaleidoscope of location systems based on a multitude of different technologies including satellite, mobile telephony, 802.11, ultrasound, and infrared among others. This lecture introduces researchers and developers to the most popular technologies and systems for location estimation and the challenges and opportunities that accompany their use. For each technology, we discuss the history of its development, the various systems that are based on it, and their trade-offs and their effects on cost and performance. We also describe technology-independent algorithms that are commonly used to smooth streams of location estimates and improve the accuracy of object tracking. Finally, we provide an overview of the wide variety of application domains where location plays a key role, and discuss opportunities and new technologies on the horizon. Fifty years of developments in electronic location technology, coupled with the advent of mobile computing, fueled by smaller, less expensive, and more capable devices, have opened the door for location-aware applications to permeate all aspects of everyday life. Location is at the core of a number of high-value applications including emergency response, navigation, asset tracking, ground surveying, and many others. The market for GPS products and services alone is expected to grow to US$200 billion by 2015 [141] . Location is also commonly used to infer other contexts. For example, symbolic location is often a good proxy for activity (e.g., grocery store is indicative of shopping). Similarly, social roles and interactions can be learned from patterns of colocation [39] , and physical activities and modes of transportation can often be inferred from the changes in coordinate-based location [129, 157] . Unfortunately, there is no single location technology that is good for every situation and exhibits high accuracy, low cost, and universal coverage. In fact, high accuracy and good coverage seldom coexist, and when they do, it comes at an extreme cost. The modern localization landscape is thus populated by a kaleidoscope of location systems based on a multitude of different technologies including satellite, mobile telephony, 802.11, ultrasound, and infrared among others. The aim of this lecture is to inform researchers and developers about the most popular technologies and systems for location estimation, and the challenges and opportunities that accompany their use. Throughout this lecture, we will illustrate the trade-offs made by various systems and describe the effect on cost and performance. For each technology, we introduce the history of its development, the various systems that are based on it, and the performance characteristics of those systems. We characterize each of the technologies we discuss across the following dimensions: Accuracy: This is the most often-cited metric of location systems and refers to the correctness of a system's location estimates. For coordinate-based location systems, accuracy is expressed as an error distribution, typically in centimeters or meters. It is most common for location accuracy to be expressed as a "median error" which indicates that 50% of the location estimates are at least that accurate. Systems that exhibit normally distributed error often have their error expressed in meters at 1 (or 2) sigma, meaning that 66% (or 95%) of •
doi:10.2200/s00115ed1v01y200804mpc004 fatcat:cbvw7weeibhxjnbwnp4y4mat3m