November 28, 2018

UMTS

Wireless communication was a magic to our ancestors but Marconi could initiate it with his wireless telegraph in 1895. Wireless Communication can be classified into three eras.

  • Pioneer Era (Till 1920)
  • Pre Cellular Era(1920-1979)
  • Cellular Era (beyond 1979)

The first commercial mobile telephone system was launched by BELL in St. Louis, USA, in 1946. Few lucky customers got the services. Early mobile systems used single high power transmitters with analog Frequency Modulation techniques to give coverage up to about 50 miles and hence only limited customers could get the service due to this severe constraints of bandwidth.

First Car Mounted Telephone

Cellular Era

To overcome the constraints of bandwidth scarcity and to give coverage to larger sections, BELL lab introduced the principle of Cellular concept. By frequency reuse technique this method delivered better coverage, better utility of available frequency spectrum and reduced transmitter power. But the established calls are to be handed over between base stations while the phones are on move.

Even though the US based BELL lab introduced the cellular principle, the Nordic countries were the first to introduce cellular services for commercial use with the introduction of the Nordic Mobile Telephone (NMT) in 1981.

First Generation Systems

All these systems were analog systems, using FDMA technology. They are also known as First Generation (1G) systems. Different systems came into use based on the cellular principle. They are listed below.

Year Mobile System
1981 Nordic Mobile Telephone(NMT)450
1982 American Mobile Phone System(AMPS)
1985 Total Access Communication System(TACS)
1986 Nordic Mobile Telephony(NMT)900

Disadvantages of 1G systems

  • They were analog and hence are were not robust to interference.
  • Different countries followed their own standards, which were incompatible.

To overcome the difficulties of 1G, digital technology was chosen by most of the countries and a new era, called 2G, started.

Advantages of 2G

  • Improved Spectral Utilization achieved by using advanced modulation techniques.
  • Lower bit rate voice coding enabled more users getting the services simultaneously.
  • Reduction of overhead in signaling paved way for capacity enhancement.
  • Good source and channel coding techniques make the signal more robust to Interference.
  • New services like SMS were included.
  • Improved efficiency of access and hand-off control were achieved.
Name of the Systems Country
DAMPS-Digital Advanced Mobile Phone System North America
GSM-Global System for Mobile communication European Countries and International applications
JDC – Japanese Digital Cellular Japan
CT-2 Cordless Telephone–2 UK
DECT-Digital European Cordless Telephone European countries

History of GSM

GSM standard is a European standard, which has addressed many problems related to compatibility, especially with the development of digital radio technology.

Milestones of GSM

  • 1982 – Confederation of European Post and Telegraph (CEPT) establishes Group Special Mobile.
  • 1985 – Adoption of list of recommendation was decided to be generated by the group.
  • 1986 – Different field tests were done for radio technique for the common air interface.
  • 1987 – TDMA was chosen as the Access Standard. MoU was signed between 12 operators.
  • 1988 – Validation of system was done.
  • 1989 – Responsibility was taken up by European Telecommunication Standards Institute (ETSI).
  • 1990 – First GSM specification was released.
  • 1991 – First commercial GSM system was launched.

Frequency Range of GSM

GSM works on four different frequency ranges with FDMA-TDMA and FDD. They are as follows −

System P-GSM (Primary) E-GSM (Extended) GSM 1800 GSM 1900
Freq Uplink 890-915MHz 880-915MHz 1710-1785Mhz 1850-1910MHz
Freq Downlink 935-960MHz 925-960MHz 1805-1880Mhz 1930-1990MHz