The mobile phone as a platform for assisting the independent living ...

However, inside a building, that uncertainty translates into uncertainty in the floor of thebuilding. More generally, topological constraints in indoor environments are much morecomplex than those in outdoor environments. For these and other reasons, prior workon indoor localization has looked to several alternative methods, such as the use of visualmarkers that are detected by ultrasonic signals, RFID, Bluetooth and 802.11.3.2 Applications of indoor localizationWhile the need for estimating the physical position of humans and objects hasaccompanied mankind since its first steps, it becomes apparent that in the future, theimportance of localization will even grow. New breakthroughs, particularly ininformation technology, sensors and micro-electronics, enable ever new applications thatdemand location information at an ever growing accuracy or lower cost. Many of theseapplications are situated indoors.The range of traditional and emerging applications requiring indoor position data ismanifold. A large classic part is in the industrial and logistics sector. Automated or selfguided vehicles and robots are instructed to transport goods in an automated productionfacility or warehouse. In order to navigate autonomously or by remote control, they mustlocalize themselves in their surroundings. Besides these traditional applications, indoorlocalization has experienced additional efforts in recent years with the appearance ofubiquitous computing. In various scenarios objects and goods must be located ortracked, e.g. in an industrial or medical environment. Additionally, people localizationenables a large number of applications and services. Customers and employees can beobserved, intruders detected and patients tracked. In public places like subway stations,safety concerns can be addressed by an emergency guidance system. Another applicationthat has raised much interest in recent years is ad hoc sensor networks. Besidesdistributed sensing it allows for location aware routing which may improve networkefficiency and lower power demands. Some applications of indoor localization aresummarized in the following table (Fig. 2).14