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Welcome to the new home of the Celtnet Mobiles in formation site. This page is the sixth in a series of eight articles that takes you through how mobile phones work. You can either page through the aritcles, below, or you can use the navigation menu on the left to find the page you want.
In part 3 of this introduction to mobile phones and mobile phone technology the history of GSM technology and how it works was introduced.
GSM was a revolutionary standard that brought about the current mobile phone revolution and which also introduced interoperability between networks and country. Indeed, without GSM it would not be possible to buy a mobile telephone that works in most countries of the world. GSM networks are also allowing parts of the world, such as Africa where landline networks are often primitive and of low coverage to become integrated parts of the modern digital world. Indeed, without this revolution I would find if very difficult to communicate with my wife in Senegal, West Africa.
The Limitations of GSM
However, GSM is a technology of the mid 1980s where the only usage envisaged for a mobile phone is that of transmitting and receiving voice data. In fact, basic GSM phones only send and receive data at an apalling transmission rate of 9.6 kbps (kilobits per second). However, as mobile phones have grown into multimedia devices and text messaging has proved to be the 'killer app' — the one usage that brought mass appeal to mobile phones — then the data throughput limit has proved to be a real bottleneck. It's even possible to access the text content of web pages that have been converted to WAP (Wireless Access Point) format with a GSM phone. Unfortunately, due to the slow data transfer of GSM phones it can actually take several minutes to download even a WAP-converted page to your phone.
In Japan this limitation was overcome by the DoCoMo company with their extremely successful I-mode range of mobile phones which can transfer data at ten times the speed of standard GSM. Standard GSM uses circuit switching as a means of data transfer. This means that the phone must make a dedicated connection with the base station thus tying-up the channel completely for that phone. In contrast, I-mode uses technology borrowed from the Internet, called packet switching where the transferred data is broken up into blocks called 'packets'. Each packet is labelled with the address of the final destination and any packet can be transferred on any available channel and no channel is dedicated to any telephone. Because of this data transfer proceeds at a much, much, higher rate. Not only are downloads quicker, but as the phone is only connected to the network when a package of information is being sent users pay for the amount of data they have sent rather than for the total time they remain connected.
It is planned that all GSM networks will move to packet switching technology, which can only be of benefit to customers and it envisaged that data transfer rates will reach up to 171 kbps with the introduction of a system called GPRS (General Packet Radio Service) which not only splits the mobile phone call into packets but also allows each phone to use several channels which are shared amongst many users. Thus not only is data transfer speed increased but overall throughput is also increased.
Beyond GSM — 3G
3G, which stands for 'Third Generation' is the great white hope of many mobile operators. The International Telecommunication Union (ITU) has defined the demands for third generation mobile networks with the IMT-2000 standard. An organisation called 3GPP has continued that work by defining a mobile system that fulfils the IMT-2000 standard. This system is called Universal Mobile Telecommunications System (UMTS). The first stage in the evolution of GSM to UTMS is the introduction of GPRS to all GSM services.
Another advance in 3G systems is CDMA (Code Division Multiple Access) which allows a single 'burst' of data to carry several signals simultaneously. This further compresses the amount of data that can be sent in a single data burst and, theoretically at least, allows for a maximum data transfer rate of up to 2 Mbps (megabits per second).
It is this increased data transfer rates that allows 3G services to deliver video to its subscribers and which should also allow video messaging between 3G mobile phones. It is the hope of the nascent 3G providers that this video communication will be 'killer application' that drive through the sales of 3G phones and systems (just as texting did for GSM).
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