Ans :
Cellular Mobile System has come a long way as at present scenario, every person
carries a cellular phone in his/her hand. This tremendous growth has established the
growth of cellular technology. From a cordless phone which gave mobility to users
but only of short distance in meters to a basic phone which has overcome the
disadvantage of short range cordless phone. And now today, a basic cellular phone is
converted to a smart multimedia cellular phone which is used not only for making
calls but is used to click pictures, listen songs, record voice, checking mails etc. In this
section, we will draw your attention towards the emerging generations of a wireless
cellular phone.
Before starting with generations, we will discuss the two channel access technologies
Time Division Multiple Access (TDMA) and Frequency Division Multiple Access
(FDMA) which are used in these generations.
Frequency Division Multiple Access (FDMA) allocates individual frequency channel
to an individual user at a time. Each user gets a frequency channel whenever the user
demands for it. Any other user cannot use the same frequency channel until the
assigned channel is given back by the user to the pool of freely available frequency
channel.
Time Division Multiple Access (TDMA) divides an individual frequency channel into
number of time slots. These time slots are then allocated to users on demand. Unlike
FDMA, one or more user can share the same frequency channel. Each slot is used
either for transmitting or receiving signals. Therefore, the data transmission is noncontinuous in nature which makes the hand-off simpler. Consecutive slots are used to
transmit the data.
First Generation (1G) –
First Generation also called 1G is based on analog Frequency Modulation (FM) and
Frequency Division Multiple Access (FDMA). 1G uses circuit switched technology
and came in 1980. According to this generation, each user has allocated with a
dedicated frequency channel. Moreover, this generation made solely to provide voice
services to its users. It was not intended for any data services. These lacked features in
1G were the biggest reason behind the rise of Second Generation (2G).
Second Generation (2G) –
Second Generation provides the voice as well as data services to its users. Unlike 1G,
no user has allocated dedicated frequency channel. 2G uses digital modulation
technique and multiple access techniques like Time Division Multiple Access
(TDMA) and Code Division Multiple Access (CDMA). 2G came in 1990 and uses
circuit switched technology. Every user in 2G uses a time-sharing frequency channel.
In this generation, there are 3 TDMA standards which are – Global System Mobile
(GSM), Interim Standard 136 (IS 136) and Pacific Digital Cellular (PDC) and one
CDMA standard called 2G CDMA or Interim Standard 95 (IS 95) CDMA.
• Global System Mobile (GSM) – For every 200 KHz radio channel, there are 8
times slotted users. 2G TDMA standard GSM is used in countries like Europe,
Australia, Asia and South America. It is also used in India
• Interim Standard 136 (IS 136) – For every 30 KHz radio channel, there are 3
times slotted users. 2G TDMA standard IS 136 is used in countries like
Australia, North America and South America. IS 136 is also known as US
Digital Cellular (USDC) or North American Digital Cellular (NADC).
• Pacific Digital Cellular (PDC) – This is a Japanese standard and is very similar
to IS 136 with around 50 million users
• 2G CDMA or Interim Standard 95 (IS 95) CDMA – For every 1.25 MHz
channel, there are up to 64 users which are orthogonally coded. This standard is
also known as CDMAOne and is used in Australia, Korea North America,
Japan, China and South America.
Evolution to Mid of Second Generation (2.5G) –
After the second generation comes 2.5G and introduced in the year 2000. 2.5G is
intended for faster data rates which are required for supporting modern internet
applications. Existing 2G equipment is modified (both hardware and software) to
support 2.5G services for enhanced data rates. Enhanced rata rates are provided for
services such as web browsing, mobile commerce, e-mail services and location based
mobile services. 2.5G also supports web browsing technology like Wireless
Application Protocol (WAP).
• High Speed Circuit Switched Data (HSCSD) – As the name suggests, this
TDMA upgrade is a circuit switched technology and provides higher data speed
rates as compared to 2G. This technology upgrade is the first attempt to provide
better data rates for GSM. Rather than allocating a single time slot to a single
user, the higher data rates are provided to users by providing consecutive time
slots. This technology also takes care of error control coding algorithm.
• General packet Radio Service (GPRS) – Unlike HSCSD, this TDMA upgrade is
a packet based technology. GPRS supports more users as compared to HSCSD.
It uses 2G TDMA modulation format but redefines air interface for better
packet data access. It is more suitable for non real time applications like
retrieval of email, faxes and asymmetric web browsing. Installation of internet
gateway and new routers at base station is mandatory for using this technology.
• Enhanced Data rates for GSM Evolution (EDGE) – EDGE provides better data
rates than GPRS by using new digital modulation technique called 8-PSK
(Phase Shift Keying).This is implemented by upgrading hardware and software
at base station. This technology is also called as Enhanced GPRS. Nine
different air interface formats are defined by EDGE known as Multiple
modulation and Coding Schemes (MCS) with error control protection.
Third Generation (3G) –
3G is designed to provide higher data rates with much available wider bandwidth. It
uses packet switched technology and users uses smaller bandwidth. This generation
allows the identification of user’s location. The 3G technology provides the services
like transparent roaming, communication using Voice Over Internet Protocol (VOIP),
receives live music, interactive live web sessions, better network capacity, multi
mega-bit internet access, readily available internet access and simultaneous exchange
of voice and data packets using a single cellular mobile.
