Having selected the platform for the client device, the most difficult part is how to include the LAS bit. Mobile phone LAS available are:
LAS for Mobile Phones:
LAS can be classified depending on the position techniques they implement to resolve device’s location.
• Absolute LAS
Absolute LAS determine actual location globally. These systems have wide area coverage and position is determined based on coordinates that have been used to map the area. Global Positioning System (GPS) and the Global System for Mobile Communication (GSM) implement this technique.
GPS
The Global Positioning System covers the whole Earth surface. It was designed and is controlled by the USA Department Of Defence. It is available to use free of charge. It’s a satellite navigation system that uses at least 24 satellites that are on low-orbit. In order to implement it is necessary a receiver that works in conjunction with the satellites. The receiver calculates its position on the Earth by a method of triangulation using four of the satellites. The information received is expressed inlatitude, longitude and elevation. The basic GPS schema has a median accuracy of 10 meters.
Despite of its wide coverage, it has some limitations. Weather conditions may affect reliability. The signals emitted by satellites are not strong enough to reach receivers inside of buildings; in addition, in highly dense urban areas like cities, the urban canyon effect causes GPS to lose functionality.
Next generation GPSs are currently being developed to overcome these deficiencies. The European Union has created the Galileo project, which implements stronger radio signals, promising greater accuracy and functionality outdoors as well as indoors.
GSM Localization
Mobile phone network providers can determine the absolute position of mobile devices subscribed to their networks. They use different techniques like cell ID, enhanced CELL ID, Time of Arrival (TOA), Angle of Arrival (AOA). Its accuracy varies from 50 to 200 meters. Network providers charge for providing this information, and they have already developed different Location Based Services (LBS) over cellular networks.
Assisted GPS
This system combines GPS with GSM localization. It overcomes the urban canyon effect associated to normal GPS, and provides greater efficiency. Mobile phones handsets have to include GPS receivers. Assisted GPS is being encouraged by USA and European laws to enhance emergency services. They have mandated that mobile network providers have to be able to locate users within 100 meters.
• Relative LAS
Relative LAS determine the location by relating device’s position to other objects in the environment. To accomplish that, device and objects have to share common communication protocols. Objects in this sense can be wireless 802.11 networks, GSM cell towers or Bluetooth devices. Those communication protocols identify objects with a unique ID. When the device is in range to communicate with them, the device “listen” to those objects and send the ID to a central database where information on the location of those objects is stored. The location of the device is obtained by triangulation, in a similar way as GPS does.