Ce texte exceptionnellement en Anglais est issu d’un de mes travaux pour un de mes anciens cours d’Ubiquitous Computing à l’Information & Communication University. La prochaine étape des Smartphones étant certainement de recevoir des puces GPS, il serait bon avant de s’attaquer aux nouvelles possibilités de ce service de localisation. Mais avant de se lancer à corps perdu, essayons de voir quelles sont les différentes technologies.
Avec la plateforme Google Android (plateforme mobile basée su Java), obtenir la position géographique de l’appareil sera aussi simple que ca:
Location locationManager =
Location location = locationManager.getCurrentLocation("gps");
The geolocalisation is a process allowing a system to know the position on Earth of a terminal’s user. This process is useful for providing services in function of your position like tourist information, security, road navigation or weather. This tool for the moment is asking to be developed more and more in mobile computing.
I- The different ways to be localised with its mobile terminal
Many systems exist for locating a mobile device. We’ll see the main technologies: the mobile phone technologies and Satellite technologies.
1- With a cell phone (GSM or CDMA)
CDMA is a mobile phone norm used mainly in America and Asia. GSM is another norm, for the same use, mainly deployed in Europe. With those technical norms, a mobile operator can get your position by three ways.
- Cell ID
The system of the identification by cell is certainly the simplest technique of geolocalisation and the least expensive. When the user is in a zone covered by the network, it is localised by the identification of the cell to which the transmission antenna belongs. This localization is fast and obtained into two or three seconds. It is not very precise: it locates a person at more or less 250 meters in urban zone where the network is dense against ten kilometres in rural medium.
Geolocalisation with Cell ID technology
- Enhanced Observed Time Difference
The mobile telephone emits a signal towards the surrounding mobile stations. The closest returns this signal to it. The elapsed time between the emission and the reception of this wave will be analyzed by an external server which will calculate the localization of the portable telephone in the network.
Enhanced Observed Time Difference technology
The system of the triangulation rests on the cross treatment of information coming permanently from 3 transmitting relays and receivers.
This system requires the installation of an application on chart SIM of the portable telephone. The time of localization is a little longer than with technologies Cell ID, approximately 5 seconds, but the precision is better, from 125 meters in urban environment and 4 kilometres in rural medium.
2- By satellite (Galileo or GPS)
The localization by GPS, “Global Positioning System” is a satellite technology created by the Defence Department of the United States. Its use is free, which implies that the reception of information does not require the payment of any royalty. The European countries initiated a similar system named Galileo which will be more precise than GPS. Several countries like China or maybe South Korea are going to cooperate to that project.
Those systems are composed of 20 to 30 satellites emitting signals which are collected by the mobile telephones. Consequently it calculates its position. This technique allows a very precise localization of the individual: from 3 to 20 meters.
Localisation by Satellite is similar to triangulation
Since 2000, mobile phones in Japan are more and more equipped of GPS. However this system does not function any more since the telephone does not receive the waves emitted by the satellites. It occurs when the user is inside a building and even in a very dense urban zone. Basically, this system has been designed for aviation.
The time of localization is rather long since it can reach 15 minutes time that the terminal hangs the satellites which will allow the calculation of its position, after a loss of reception for example. Moreover the use of this technology supposes the integration of a chip GPS within each terminal of electronic communication in addition to chart SIM, which makes it more expensive.
3- By IP
Some organisations collect IP and localisation for producing translation tables: IP band to Country or even City. For example, somebody who has an IP between 126.96.36.199 and 188.8.131.52 means that he is in South Korea.
This technology is more dedicated to regular home computer and its better precision is at the level of a town. The technology works fine if you have are not collected to gateways which supply several terminals in different places. Some networks like AOL can’t have their users localizeefficiently.
In modern mobile computing, the connection throw a gateway (like the unsuccessful WAP) is going to be deprecated. With new norms and IPv6, all the mobile terminals should have their own IP on the Internet.
Connect you at http://www.maxmind.com/app/locate_my_ip and you’ll know where you are!
II – Using the data issued from the Geolocalisation
As we have seen, the actual networks are not really designed for geolocalisation. The actual solution looks like a way of doing “our best with what we have”. But no protocol like TCP/IP wich transmits your IP address or HTTP which transmits information about your browser, transmit your position.
1- Partner of the mobile communication network
Several mobile companies have their own geolocalisation system using their established network of antennas, like Cell-ID.
Anyway, actually they don’t supply those data outside of their internal network. If a company would like to supply service using geolocalisation, its apps will have to be hosted by the mobile phone company itself.
This restriction is essentially due to the law, promoting the right to the private life.
Simplified view of a mobile phone company network supplying applications based on geolocalisation
2- With any internet applications.
Actually the best way to get your precise localisation is to fill manually your position to your mobile application. The IP of your mobile phone or of its gateway could only supply your country.
If you are in the street of a big town, you have few chances to get your localisation. And that’s surely the place that the geolocalisation will have the most of success, for finding local services.
If you’re not partner of a mobile communication, you can’t have access to its geolocalisation system. The consequences are that few application servers can use efficiently geolocalisation.
III- Some ways for improving geolocalisation for mobile computing
Anyway, two ways could be developed for obtaining a better localisation. First, all the positioning systems have weakness, and we’ll give some ideas to reduce them. Secondly, we’ll see how to get your position efficiently.
1- Improving the geolocalisation: get a better position
The mobile companies divert their communication infrastructure for localisation. They use non adapted stuff and even with triangulation localisation, they don’t have good results. A way to improve GPS is doing like the Europeans do with the European Geostationary Navigation Overlay System (aka EGNOS). They use network of 40 ground stations covering Europe and correcting GPS system (and sonly Galileo). In practice, the horizontal position accuracy is at the meter level (5m approx.) and it avoids bad communications throw atmosphere. Anyway, it can’t be enough in some buildings.
Another way could be deploying the same idea, more locally and with less expensive ground station.
The last years, we have seen more and more mobile phones with Bluetooth on the market. Recently, commercial Bluetooth spot appeared in some bus stations. It consists in a Bluetooth emitter, broadcasting advertisements to the closest mobile phones. Why can’t we imagine, Bluetooth spots broadcasting its position to the mobile phones? A kind of Bluetooh Positioning System (or BPS)!
Those BPS spots will send only and always the same datas: its position and why not some information about its sponsors. Those kinds of BPS spots won’t be expensive (maybe less $200 per unit), but we’ll need a lot in a city for getting a good localisation. For being interesting, the position supplied has to be really inferior to 150m (better than the triangulation with GSM or CDMA).
A method between switching GPS/Galileo mode and BPS where satellite communication doesn’t work, could be envisaged in some cities for a better positioning system.
2- Supplying its position to server applications
Actually there’s not uniformed way for sending in positioning formations to a web applications. Actually, the user has to input manually its position.
The thing that we can propose is to use a positioning server. The mobile device puts on this positioning server, its position and the datas about services who can access to its position. After the server application will introduce itself to the positioning server and will get the position of the mobile device.
This server can be positioned in two places:
- the terminal itself, if its IP address is reachable
- a dedicated server permanently connected to the web by wire, if the IP of the mobile terminal is unreachable
To conclude, this survey, geolocalisation is on good way and not at its beginning. That’s used, since the 70s in aviation, but the geolocalisation for all has 15 years. Anyway, actually we are at time 0 for the exploitation of those geographic positions.