Las creencias de causalidad liberales de un gobierno conservador: la

The interaction technique scanning is in principle based on the proximity of mobile device and smart object which can be a real world object as well as a location in general. The mobile device scans the environment for nearby smart objects. This action can be triggered by the user or the environment is permanently scanned by the mobile device. The result is in both cases a list of nearby smart objects. Manually selecting one item of this list represents the selection of an object which may provide several services. On the other hand, the system automatically can monitor the location of a user in relation to several objects. In the case a predefined distance between user and object is sensed, a corresponding service is started which e.g. informs the user about the details of that object. The latter is very intuitive because it corresponds to our everyday behaviour. For example, we approach a person when we intend to talk with her or we approach an object to see it in detail.

The advantage of this interaction technique is the possibility to discover all nearby smart objects and the services they offer. The user does not need to be aware of the augmentation of a real world object nor needs this object be visually changed to draw the attraction of the user. One disadvantage of this interaction technique is that there is no direct link for the user between an item on the list of nearby smart objects and a concrete augmented object in the environment. The items in the list can be textual or visual. Based on this information, for example the word lamp or an image of it, the user has to find the nearby corresponding smart object. This might be simple when thinking about an augmented microwave but might be complicate when a room has for instance several lamps and just one is augmented or controllable.

The idea of using a mobile device for scanning the environment was first seen in the Star Trek television series (1966-1969). The tricorder, a handheld device equipped with several

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sensors, was used for scanning unknown environments, to diagnose a patient or for interactions with smart objects or computers [@WikipediaTricorder].

The usage of Bluetooth functionalities of mobile phones is a very popular implementation of user triggered scanning. Bluetooth [@Bluetooth] is a standard for personal area networks which operates in the unlicensed 2.4 GHz band. The Bluetooth version 1.2 which is currently used in mobile phones offers a maximal data transmission speed of 723 Kbit/s. The achievable ranges between the devices depend on the Bluetooth class whereby class 1 supports distances of up to 100 meters, class 2 which is used in most mobile devices supports distances up to 10 meters and class 3 supports distances up to 1 meter. Bluetooth is the first widely available technology for personal area networks but it has some disadvantages which make it not the perfect implementation of the interaction technique scanning: The paring procedure which consists of device selection, service selection and an optional password exchange is often a time consuming task. Especially the device inquiry and name discovery process which may excess 30 seconds does not support spontaneous interactions [David et al. 2005]. Because of this, several approaches have been developed which bypass this process using infrared [Woodings et al. 2002], RFID [Hall et al. 2002] or visual markers [David et al. 2005] to immediately establish a Bluetooth connection between two devices.

[Tuomisto et al. 2005] used SoapBoxes which communicate with each other via radio communication to implement this interaction technique. In this approach all nearby beacons that are attached to real world object are sensed.

Another widely used communication technique that is used for the implementation of user triggered scanning are wireless local networks (WLAN) such as WI-FI [@802.11]. WI-FI is mostly used for connecting mobile devices with a router to establish a voice or internet connection. It is also possible to connect two devices such as two laptops. But this is rarely used, especially because of the quite complicated pairing process.

In general we currently see a huge interest regarding the provision of location services which provide information about location of the user or any other object. Typical approaches are based on cell identification, the Global Positioning System (GPS), distance to near field networks such a Bluetooth or WLAN, RFID, infrared or ultrasound [Küpper 2005, LaMarca et al. 2005, Rao, Minakakis 2003, Want et al. 1992]. A very comprehensive overview of indoor and outdoor positioning techniques that can be used for user and system triggered scanning can be found in [Küpper 2005].

System triggered scanning is typically used by applications within the fields mobile gaming, mobile tourist guide systems and mobile advertisement. An example for such a system is the Buga Butler which was used during the Bundesgartenschau, the German national garden festival, in 2005 [@BUGAbutler 2005]. The Buga Butler is a PDA with a built-in GPS device. Based on the location of the user, the device presents information about points of interest. NTT DoCoMo launched in 2001 in Japan a location based service which is called i-area [@i-area]. Here cell information is used to get information about the restaurants nearby, about the location of the user on a map, about the local weather and information about the town. The research projects CyberGuide [Abowd et al. 1997] from Georgia Tech and the Lancaster Guide project [Cheverst et al. 2000] went a step further and used the location information for the provision of information about objects in mobile context-aware city or tourist guides.

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