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

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Fig. 2: Applications of indoor localization 2Nowadays there is an immense interest in the field of Location-based services (LBS).Location-based services make use of location information about an entity to offerservices based on this information. For example, services can use either the location ofthe user and offer certain services to the user based on the user’s location, or they canuse the location of one entity and offer services to another entity. An example of the firstcase could be a Personal Digital Assistant (PDA)-based tour guide that gives informationabout the sights in the user’s current location. An example of the other case could be asystem that keeps track of where your co-workers are, so that they can be easily located,should you need to meet them.3.3 Indoor localization choicesLocalization process involves several issues and characteristics that need to be defined inorder to develop a localization system. Each choice on these issues delivers certainstrengths and weaknesses and thus, it may be suitable in one application over the other.3.3.1 Physical position and symbolic locationPhysical position is the position obtained from the system using physical co-ordinatessuch as those obtained from a GPS device. The GPS device usually provides the user2 Image courtesy of Holger Linde - On aspects of Indoor Localization [39]15
with co-ordinates in the form of lateral and longitudinal degrees as well as altitude withrespect to the sea. On the other hand, a symbolic location is a location that has ameaning in its context. For example, a symbolic location system could inform users thatthey are in the living room instead of giving them co-ordinates. Usually, a physicalpositioning system can provide the co-ordinates to another interface that would query adatabase of symbolic locations in order to emulate a symbolic location system.3.3.2 Absolute and relative positioningIn an absolute positioning system, if two mobile devices are located at the same spot,their position will be the same (for example, in a GPS system). On the other hand, if arelative positioning system is used, the device will report its location with respect to aspecific reference point or in case of locating other devices, with respect to itself. As thecase with physical position and symbolic location, either systems; absolute or relative, canbe augmented to simulate the other, though with limited success. In case of an absolutepositioning system, the system could emulate relative positioning by searching for areference point and modifying the reported location to be with respect to that referencepoint. In case of relative positioning, one could use the knowledge of the position ofother reference points in order to determine the absolute location.3.3.3 Location ComputationThe location computation parameters define whether the client is the one that calculatesthe location using a specific algorithm or that it is a centralized server that manages thiscalculation. This choice would depend upon the size as well as the designated powerconsumption of the client. If the client computes its location (for example usingtriangulation from GPS signals), it would need to have sufficient computational power inorder to calculate its position in adequate time. This computational power wouldtranslate as more electronic power consumption. On the other hand, a device that relieson an external server to locate it by broadcasting a beacon signal or receiving thelocations directly from the server would not need much computational power but wouldmean that the server would have to undertake more responsibilities which might affectthe number of clients that could be served simultaneously. On another note, having theserver compute the clients' locations and possibly saving them raises privacy concerns.16
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Page 5 and 6: AbstractMobile phones or Personal D
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Page 13 and 14: Chapter 2Smart Homes2.1 Smart Homes
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Page 21 and 22: The Amigo project [10] is a joint e
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Page 63: [65] X. Chen and A.L. Yuille, “A

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