2.3.2 Second Generation 2G:
The second generation mobile standards are
based on digital technology. Digital technology utilizes the transmission
resources in an efficient way, both due to advances in audio compression
standards and also due to advances in digital modulation technologies.
Another important characteristic of the 2G
mobile is the less fragmented mobile market. This is particularly due to
Europe’s decision to use a common standard and the creation of a single mobile
market, but also because the European standard, GSM, has had enormous success
beyond Europe and is used in a number of other countries.
However, there are a number of competing standards to GSM,
mainly:
·
TDMA
IS-136 is the digital enhancement of the analogue AMPS technology. It was
called D-AMPS when it was fist introduced in late 1991 and its main objective
was to protect the substantial investment that service providers had made in
AMPS technology. It is mainly used in North America.
·
CDMA
IS-95 increases capacity by using the entire radio band, each using a unique
code (CDMA or Code Division Multiple Access). It is a family of digital
communication techniques and South Korea is the largest single CDMA IS-95
market in the world.
·
Personal
Digital Cellular (PDC) is the second largest digital mobile standard
although it is exclusively used in Japan, where it was introduced in
1994. Like GSM, it is based on the TDMA access technology.
2.3.2.1 Group Special Mobile (GSM):
Group
Special Mobile within the CEPT started to develop GSM in 1982. Later it was
standardized by the ETSI and branded as a Global System for Mobile (GSM). One
of the most important conclusions from the early tests of the new GSM
technology was that the new standard should employ Time Division Multiple
Access (TDMA) technology. This ensured the support of major corporate
players like Nokia, Ericsson and Siemens, and the flexibility of having access
to a broad range of suppliers as well as the potential to get product into the
marketplace faster. After a series of tests, the GSM digital standard was
proven to work in 1988.
GSM operates mainly on 900 and 1800 frequency bands.
However, in North America it operates on 1900 MHz. There is also a version
which uses the 450 MHz band (GSM400), which can be used in the less populated
areas, and can be relevant for the less populated rural areas in the developing
countries. In the transition from 2G to 3G a number of standards have been
developed, which are categorized as 2.5G. These are add-ons to the 2G standards
and mainly focus on deployment of efficient IP connectivity
within the mobile networks.
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