June 1, 2010 by Isybel Harto
At the beginning of the 1980s it was realized that the European countries were using many different, incompatible mobile phone systems. At the same time, the needs for telecommunication services were remarkably increased. /due to this, CEPT (Conference Europeenne des Postes et Telecommunications) founded a group to specify a common mobile system for Western Europe. This group was named “ Groupe Speciale Mobile” and the system name GSM arose. This abbreviation has since been interpreted in other ways, but the most common expression nowadays is Global System for Mobile (GSM) communications. As shown in Fig.1.1
1.1 (a) History:
Mobile phones have gone through three distinct generations, with different technology.
• Analog voice
• Digital voice
• Digital voice and data
1. First Generation: Analog Voice: –
Mobile radiotelephones were used sporadically for maritime and military communication during the early decades of the 20th century. In 1946, the first system for car-based telephones was setup in St. Louis. This system used a single large transmitter on top of a tall building and had a single channel, used for both sending and receiving. To talk, the user had to push a button that enabled the transmitter and disabled the receiver. Such system, known as push to talk system, was installed in several cities beginning in the late 1950s.
In 1960s, IMTS-improved mobile telephone system- was installed. It used a high- powered (200 watts) transmitter, on the top of a hill. But it used two different frequencies for sending and receiving. IMTS supported 23 channels spread out from 150MHz to 450MHz. Due to the small no of channels; user often had to wait a long time before getting a dial tone. Also due to the large power of hill-top transmitter adjacent system had to be several hundred kilometers apart to avoid interference.
In 1982, AMPS- Advance mobile phone system- was invented by Bell Labs and first installed in U.S. It was also used in England, where it was called TACS and in Japan, where it was called MSC-L1.
2. Second Generation: Digital Voice:-
The first generation of mobile phones was analog; the second generation was digital. Four systems of second generation are in use now.
D-AMPS was carefully designed to co-exist with AMPS, so that both first and second-generation mobile phones could operate simultaneously in the same cell. D-AMPS uses the same channels, which are used by AMPS also. So that one channel can be analog and the adjacent ones can be digital in one cell.
It is used only in Japan and is basically D-AMPS modified for compatibility with the first generation Japanese analog system.
3. CDMA: Code Division Multiple Access
D-AMPS and GSM use FDMA and TDMA. While CDMA is completely different. Instead of dividing the all9owed freq. range into a few hundred narrow channels, CDMA allows each station to transmit over the entire frequency spectrum all the time. The multiple simultaneous transmissions are separated using coding theory. CDMA also relaxes the assumptions that colliding frames are totally garbled.
4. GSM: Global System For Mobile Communication
GSM is a globally accepted standard for digital cellular system. It is established in 1982 to create a common European mobile telephone standard which provides full duplex data traffic to any device fitted with GSM capability, such as a phone, fax, or pager at a rate of 9600 bps using the TDMA communications scheme.
Since GSM is purely digital, it can easily interface with other digital communications systems, such as ISDN, and digital devices. Unlike any other services, GSM products such as cellular phones, require the use of a Subscriber Identity Modules, or SIM card.
These small electronic devices are approximately the size of credit card and record all of the user information. This includes data such as programmed telephone numbers and network security features which identify the user. Without this module, the device will not function. Some of the milestones for communication through GSM are as shown.
1982 GSM formed
1986 field test
1987 TDMA chosen as access method
1988 memorandum of understanding signed
1989 validation of GSM system
1990 Pre operation system
1991 commercial system start-up
1992 coverage of larger cities/airports
1993 coverage of main roads
1995 coverage of rural areas
3. Third Generation: Digital Voice And Data: –
Digital voice and data like Internet access and other video and multimedia applications.
Year Mobile System
1981 Nordic Mobile Telephone (NMT) 450
1983 American Mobile Phone System (AMPS)
1985 Total Access Communication System (TACS)
1986 Nordic Mobile Telephony (NMT) 900
1991 American Digital Cellular (ADC)
1991 Global System for Mobile Communication (GSM)
1992 Digital Cellular System (DCS) 1800
1994 Personal Digital Cellular (PDC)
1995 PCS 1900—Canada
1996 PCS—United States
In the beginnings of cellular systems, each country developed its own system, which was an undesirable situation for the following reasons:
The equipment was limited to operate only within the boundaries of each country.
The market for each mobile equipment was limited.
In order to overcome these problems, cept formed GSM in 1982.
• Good subjective speech quality.
• 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.
1.1 (c)FREQUENCY ALLOCATION:
GSM network presently operate in three different frequency ranges.
GSM 900 (also called GSM): operates in the 900 MHz frequency range and is the most common in Europe and the world.
GSM 1800 (also called PCN and DCS 1800): operates in the 1800 MHz frequency range and is found in a rapidly-increasing number of countries including France, Germany, Switzerland, UK and Russia.
GSM 1900 (also called PCS 1900 and DCS 1900): The only frequency used in the United States and Canada for GSM
Key points of G.S.M describe below:
The system must be Pan European.
The system must maintain a good speech quality.
The system must use radio frequencies as efficiently as possible.
The system must have high\ adequate capacity.
The system must be compatible with the ISDN (Integrated /services Digital Network).
The system must be compatible with other data communication specifications.
The system must maintain good security concerning both subscriber and transmitted information.
1.1 (d) Advantages of GSM
Due to the requirements set for the GSM system, many advantages will be achieved. These advantages can be summarized as follows:
• GSM uses radio frequencies efficiently, and due to the digital radio path, the system tolerates more intercell disturbance.
• The average quality of speech achieved is better than in analogue cellular systems.
• Data transmission is supported throughout the GSM system.
• Speech is encrypted and subscriber information security is guaranteed.
• Due to the ISDN compatibility, new services are offered compared to the analogue systems.
• International roaming is technically possible within all countries using the GSM system.
• The large market increases competition and lowers the prices both for investments and usage.