Gsm Phones

During the year 1980, analog cellular telephony was gaining momentum of growth in Europe, not only in Scandinavia and the United Kingdom, but also in France and Germany. Each of these countries developed their own system which rendered these technologies incompatible to each other, including the hardware used. This became undesirable owing to the fact that the mobile equipment was not only limited within the national boundaries, but there was also a very limited market for each type of equipment.
Realising this at an early stage, the matter was referred to a study group called Groupe Spécial Mobile, to develop pan-European public land mobile system. The system that would be proposed by the study group needed to meet the following criteria -
· Good quality of speech.
· Low terminal and service cost
· Support for international roaming.
· Ability to support handheld terminals.
· Support for range of new services and facilities.
· Spectral efficiency.
· ISDN compatibility.
This responsibility was transferred from Groupe Spécial Mobile European to Telecommunication Standards Institute (ETSI), and phase one of the project specifications was published in 1990. Global System for Mobile communications (GSM) is an open architecture digital cellular technology having application in transmitting and receiving voice and data. This technology differs from the first generation wireless systems which used analog technology for communication, while GSM uses digital technology and time division multiple Access (TDMA) transmission methods.
GSM technology is a circuit-switched system, and works by dividing each 200 KHz frequency channel into 25 KHz slots and operates on 900MHz and 1.8GHz bands in Europe and the 1.9GHz and 850MHz bands in the US. In Australia, Canada and many South American countries, 850MHz is used for GSM and 3GSM. Data speeds up-to 9.6Kbps is supported by this technology, which allows transmission of basic data services, such as, Short Message Service (SMS). GSM offers a greater facility in international roaming, allowing international travellers to be in touch with the world. GSM satellite services enables users to access the service from areas where terrestrial coverage is not available.
The arrangement of mobile rigs, discussed above, would give way to the development of the generations of mobile phone that we have today. At the very beginning, these so called mobile phones were fixed in the cars, being permanently installed. This contraption gained more mobility when later versions had the equipment fitted with a cigarette lighter plug which would go in the socket for the 12 volts power supply that it needed to operate. This made the unit to be taken out of the car after unplugging it from the cigarette lighter socket.
As time went by, the equipment was modified to be patched with the telephone network, which was tested by the Swedish Police in 1946, for use in the police vehicles. It was observed that car battery would run out after some six to seven calls were made. Radio telephones became available publicly in the United States towards the end of 1940's. Since switching technology was not available those days, these phones had to be manually patched into the telephone network for the purpose of a meaningful communication.
The concept of mobile communication was based on such a network that would bring voice and data communication through-out a wide spread area. The idea was to divide the wide spread area into small sections which would be called a radio cell, which would have a trans-receiver connected to the next cell by switching technology. This concept of dividing the area into cells has given the name - cellular technology. The architecture evolved to provide a system, where seamless communication could be had when moving around from one cell area to the other. As you leave one cell and move to the next, the previous one would hand over the call to the next tower in the area that you are presently in and this way providing you with a seamless connectivity.
As the mobile phone evolved, the first generation systems, 1G, came into commercial operation, based on analog switched circuits. The voice quality was bad and the hands off operation would fail most of the time. These were the two primary disadvantages of the system. The number simultaneous call handling was low and there was no security what-so-ever. The system used a technology called Advanced Mobile Phone Service (AMPS), which operated in the 800MHz band. The system could not be launched commercially before 1983 and was delayed for many reasons, one being the break-up of AT&T. The system was launched in Chicago in the year 1983, with other cities following.
Japan launched AMPS in 1979 and the Europeans had their own technology, which they called Nordic Mobile Telephony (NMT), operating in the 450-MHz band. This was launched in Sweden, Norway, Denmark, and Finland in the year 1981. At a later stage NMT was developed to work on 900MHz bandwidth and came to be known as NMT900. In 1985, the British developed Total Access Communications System (TACS), an entirely different technology of their own. TACS operated on 900MHz and is typically a modified version of AMPS.
This was the big boom in mobile phone technology.
The development of the second generation (2G) system, which is truly the GSM architecture, was started in Europe in the year 1982 and was commercially launched in 1992. The technology is a digital radio system which has been designed on Time Division Multiple Access (TDMA) principle, which enables the subscribers to use the same radio channel simultaneously, in which time-slots are shared. This technology works on full duplex mode, where both, transmit and receive, operate together, considering that in half duplex mode one person can transmit one at a time. Walkie-talkie radios work on half duplex mode and transmission is set by the push of a switch on the body of the radio and with its release, the equipment goes into receive mode.
To this day, more than 700 mobile networks are under operation in the world, across 213 countries or more and consist of 82.5% of all the global mobile connection the world over. There are about 2 million GSM mobile phone users in the world today, with China being the largest user of mobile phones. China has more than 370 million subscribers, with Russia having 145 million. The United States have about 78 million users. GSM phones can be rented and this becomes necessary, especially when you travel outside the United States on a visit, where your GSM phone is not likely to work. The operational frequencies in the North American countries with Canada as well, are different from what the other countries have. GSM operates on the following frequencies -
· 850 MHz (824.2 - 848.8 MHz Tx; 869.2 - 893.8 MHz Rx)
· 900 MHz (880-2 - 914.8 MHz Tx; 925.2 - 959.8 MHz Rx)
· 1800 MHz (1710.2 - 1784.8 MHz Tx; 1805.2 - 1879.8 MH Rx)
· 1900 MHz (1850.2 - 1909.8 MHz Tx; 1930.2 - 1989.8 MHz Rx)
With North America and Canada operating on 850MHz and 1900MHz bands, it sets them apart from the rest of the world, which would mean that incase you are travelling abroad and even if you have a GSM mobile handset, it is likely that you wont be able to operate that handset outside North America and Canada.
If you are a frequent traveller abroad, it is worthwhile to consider buying a quad band GSM mobile phone, so that you are confident of its compatibility with all the GSM frequencies in the world. The quad band mobile handset is compatible with all the frequencies illustrated above. The Tri band phones work operate on 800MHz, 900MHz and 1800MHz frequency bands, which would mean,that it will work in only those countries which operates on those frequency bands. A Dual band mobile operates on 800 MHz and 1900 MHz. Therefore, your choice of the compatible mobile handset will depend upon the countries that you visit frequently.
GSM phones are not only capable of voice transmission, but it allows Short Messaging System (SMS) and also supports General Packet Radio Services (GPRS), which is basically a data service available to GSM phone users. GPRS is a technology in between the second (2G) and the third (3G) generations of mobile telephony. It uses the unused Time Division Multiple Access (TDMA) communication channels in the GSM network to transmit data at a fairly moderate speed. As GSM evolved, it retained the backward compatibility. GPRS is an example, where packet data capabilities were added to the consequent releases of GSM technology. In some countries, GSM offers Enhanced Data rates for GSM Evolution (EDGE). Sometimes it is called Enhanced GPRS (EGPRS). This technology allows the use of enhanced data rates with reliability in transmission. EDGE has been introduced in GSM network since 2003, at first in North America.
GSM phones work with a Subscriber Identity Module (SIM) card. A SIM card is of the size of a postage stamp and is essentially the brain behind all features that are available to a subscriber through the GSM network. The SIM card, as the name implies, holds your personal identification number and identifies you with the network as you switch on your mobile. It is a microprocessor unit with memories, capable of holding your details including your personal data, such as the telephone numbers that you usually use frequently. It is this SIM card that enables the downloading of your favourite picture, MP3 songs, and video from the net into your handset.
GSM mobile phones are at times are SIM locked. This would mean that you cannot operate that handset with any other SIM card other than the one which came along with the handset. When you sign a contract with a service provider for a mobile connectivity, you may have signed that contract with a clause that you agree to stay with the service provider for a period of time, which is usually one year. With such a contract, the service provider gives you a GSM phone free of cost and it is SIM locked. You can only use the SIM card sent by the service provider. With any other SIM card the phone would not work. After the contract is over, the service provider helps you to unlock your phone and you are then at liberty to choose any SIM card for your handset.
GSM offers its subscribers the 'roaming' facility. When you are travelling abroad, you can take your GSM phone with you on roaming mode and you can use your handset to communicate with your business associates, locally and abroad, your friends and your family back home. But you need to know that this roaming feature has an added charge on top of your outgoing call charges. This charge is also levied on your incoming calls when you are on roaming.