Evolution of mobile Communication:

Electromagnetic Rays were discovered as a communication medium in the 19th century. The first telephone systems offering mobile service were introduced in the late 1940s in United States and early 1950’s in Europe. Earlier cell systems were constrained with severe mobility, low capacity, limited service, and poor speech quality. Equipment was heavy, bulky, expensive, and susceptible to interference.

First Generation (1G): Analog Cellular

The introduction of cellular systems in late 1970s and early 1980s represented a quantum leap in mobile communication. 1G cellular systems transmit only analog voice information. Some prominent 1G systems are
· Advanced mobile phone systems (ADPS)
· Nordic mobile telephone (NMT)
· Total Access communication system (TACS)


Second generation (2G): multiple digital systems

The development of 2G cellular systems was driven by the need to improve transmission quality, system capacity, and coverage. Advances in Semiconductor technology brought digital transmission to mobile communication. 2G provided supplementary services apart from speech transmission like fax, short messaging servicing.
2G cellular systems include
· GSM (Global system of mobile communication)
· D-AMPS (Digital Advanced mobile phone system)
· CDMA (Code division multiple access)
· PDC (Personal digital Communication)

Today multiple 1G and 2G standards are used in worldwide mobile communication. Different standards serve levels of mobility, capability, and service area. 2G networks were launched in the early 1990s.




GSM

GSM is the most successful family of cellular standards with GSM900, GSM-R, GSM1800, GSM1900, and GSM400.

1. GSM- 900

· Uplink frequency: 890.2 MHz to 915 MHz (25 MHz)
· Downlink frequency: 935.2 MHz to 960 MHz (25 MHz
· Uplink- downlink distance: 45 MHz

It employes frequency division multiple access and Time Division Multiple Access. In FDMA each channel is 200 KHz wide and accommodates 124 pairs of channels. In TDMA each channel has 8 time slots. Hence theoretically there are 992 channels.

2. GSM –1800

· Uplink frequency: 1725.2 to 1780.4 MHz
· Downlink Frequency: 1820.2 to 1875.4 MHz
· Uplink Downlink Distance: 95 MHz

It has 384 pairs of channels.


The ubiquity of GSM makes international roaming very common between mobile operators, enabling subscribers to use mobile in any part of the world. The key advantage of GSM systems is higher digital voice quality and low cost alternatives like text messaging.
The technical fundamentals of GSM system were defined in 1987.In 1989 ETSI (European telecommunication standards institute) took over; by 1990 the first GSM specification was complete. GSM standards were enhanced in phase 2 in 1995 to incorporate large number of supplementary services. In 1996 ETSI further enhanced in GSM phase 2+ to incorporate 3G capabilities.

2.5 G (2.5 generation)

2.5 is a stepping-stone between 2G and 3G cellular wireless technologies. While 2G and 3G are officially defined, 2.5G is not. It was invented for marketing purposes only. The term "second and a half generation" is used to describe 2G-systems that have implemented a packet switched domain in addition to the circuit switched domain
2.5G provides some of the benefits of 3G (e.g. it is packet-switched) and can use some of the existing 2G infrastructure in GSM and CDMA networks.

GPRS:

Acronym for General Packet radio Service. It is an enhancement over GSM. Provides Packet oriented data service unlike Circuit switched data service in GSM in which data is split into separate but related packets. Allows IP packets to be sent and received across mobile networks.
More efficient for the network operator. Theoretical maximum speed is 171.2 Kbps using all 8-time slots. Some time slots on some frequencies are reserved for packet traffic. Base stations dynamically manage time slots.
However it has few limitations as well. It impacts network’s existing cell capacity, as the use for one purpose simultaneously precludes the use of other service. It has limited bandwidth.


EDGE

Some protocols, such as EDGE (Enhanced Data rates for GSM) and CDMA2000, can qualify as "3G" services (because they have a data rate of above 144 kbit/s), but are considered by most to be 2.5G services (or 2.75G which sounds even more sophisticated) because they are several times slower than "true" 3G services.
Acronym for Enhanced data rate for Global Evolution; it is an enhancement over GSM/GPRS. Has a data rate of 384Kbps or more. It employs FDMA/TDMA like GSM.
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3G (Third Generation)

The services associated with 3G provide the ability to transfer both voice data (a telephone call) and non-voice data (such as downloading information, exchanging email, and instanting messaging).
The first country which introduced 3G on a large commercial scale was Japan. In 2005 about 40% of subscribers use 3G networks only, and 2G is on the way out in Japan. It is expected that during 2006 the transition from 2G to 3G will be largely completed in Japan, and upgrades to the next 3.5G stage with 3 Mbit/s data rates is underway.


IMT –2000
IMT-2000 (International Mobile Teleommunications ) is the global standard for third generation(3G) wireless communication defined by ITU( International Telecommunication Union). The family of compatible standards that have the following charecteristics.
· Used world wide
· Used for all mobile applications
· Support for both Paacet Switched Transmision ans Circuit switched transmission.
· Offers high data rates of upto 2 Mbps.
· Offers high spectrum efficiency.

In the year 1998 3rd generation partenership project was establised. The original scope of 3GPP was to produce globally applicable Technical Specifications and Technical Reports for a 3rd Generation Mobile System based on evolved GSM core networks and the radio access technologies that they support (i.e., Universal Terrestrial Radio Access (UTRA) both Frequency Division Duplex (FDD) and Time Division Duplex (TDD) modes). A cooperation of standard organizations (ARIB, CWTS, ETSI, T1, TTA and TTC) throughout the world that is developing technical specification for IMT-2000.
UMTS is being developed by Third Generation Partnership project (3GPP), a joint venture of several organizations.

· ETSI (European Telecommunication Standard Institute, Europe)

· Association of Radio Industries and Business/Telecommunication Technology Committee (ARIB/TTC) (Japan),

· American National Standards Institute (ANSI) T-1 (USA)

· Telecommunications technology association (TTA) (South Korea)

· Chinese Wireless Telecommunication Standard (CWTS) (China)

To reach global acceptance, 3GPP is introducing UMTS in phases and annual releases.
IMT-2000 represents both the scheduled year for initial trial systems and frequency range of 2000 Mhz. In 1998, 17 different standards were submitted to ITU, 11 for terrestrial systems and 6 for mobile satellite systems. All 17 proposals were accepted as IMT-2000 standards.
The most important IMT-2000 proposals are UMTS (W-CDMA) as the successor of GSM, CDMA2000 and Time-division CDMA (TD-CDMA).