D11.2: Mobility and LBS

Title: NETWORK-EXTERNAL SOURCE OF LOCATION-INFORMATION

Network-external source of location-information

Network-external means that the positioning system is outside the control of the Network Operator and provided by a third party / third system. Common external sources of positioning information are user input, satellite based positioning systems, such as the widely used Global Positioning System (GPS) or the newly emerging Galileo positioning system, position senders, such as radio or infrared beacons, Wireless LAN positioning and peer-to-peer positioning.

“User” as source of positioning information

Having the user as source of location information for the provision of location based services is a “double-edged sword”. One of the key advantages is that the user keeps the positioning process under his control. That means that he can decide whether he wants to provide positioning-information, when he wants to provide positioning information (so there is no automatic tracking possible) and what kind information concerning the degree of precision of the positioning information he wants to provide to the LBS-provider. The degree of precision can vary from general information (country, city) to more concrete information like e.g. ZIP-code or address. Additionally, the provision of positioning information via the user is possible using almost every kind of terminal or medium.

In contrast to automatically derived and processed positioning information, the “manual” way to provide the current position is much more inconvenient and time consuming. Additionally, the user can only provide positioning information if he is able to localise himself in the area (familiarity with the location). That might be no problem for more general location information like country or area, but it gets gradually difficult with a rising degree of required precision for the provision of location information. The most precise way to locate someone may be to provide an address. However, this is only possible in more densely populated areas.  

Satellite based positioning information

Theoretically, the determination of someone’s position using satellites can be carried out all over the world. Satellite based positioning is characterised by a unilateral way of communication, as the mobile device only passively receives location information. The accuracy of satellite based positioning is between 1 and 15 meters depending on the used service / technology (c.f. Chapter ).

Figure : Satellite based location tracking needs at least 3 satellites to triangulate the position of a device or person.

The position of the user can be determined by using the position signals of at least 3 satellites that move on fixed orbits (cf. ). Satellite based positioning systems have the following (dis-)advantages:

1. (+) High availability

2. (+) High precision

3. (+) Relatively low cost for chipsets that can be embedded in terminals.

4. (-) High time needed for the initialization of the positioning process

5. (-) High-power consumption especially in the non-stop-positioning mode.

6. (-) Signal strength: It is mostly used outside as the signals are generally too weak to be received inside buildings.

The world-wide standard for satellite based positioning still is the Global Positioning System (GPS), established and controlled by the USA. The accuracy of the GPS can be altered in case of military emergency. The forthcoming European satellite positioning system Galileo is planned to be implemented by 2011-12 and should obtain a higher accuracy than GPS.

Figure : Positioning satellites orbiting the earth.

Further external information sources

Another method to allow positioning is the usage of position transmitters that communicate their location to a user’s device via e.g. radio or infrared signals submitted by a beacon within a given area (cf. D11.5 and D7.7 for example applications). The accuracy of the location information thereby depends on the size of this area and can vary from 10 centimetres to several meters. Common usage scenarios for position transmitters are exhibition information systems, museum guides, tourist guides or promotion activities.  

Figure : Peer to peer versus stationary transmitter positioning (e.g. by radio or infrared beacons).

W-LAN Access Points (esp. relevant in urban areas), peer-to-peer positioning or Radio Frequency Identification (RFID) are further relevant technologies / methods to determine users’ location.