Introduction

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Introduction

With the advent of computers the way that we communicate has changed. Initially document file sizes were much smaller and the need to send graphics was not considered necessary, therefore the speed of transmission did not have to be particularly high. Modern computers and software generate much larger files thus the speed of transmission starts to become and important factor especially when considering the cost. Also with business people regularly using portable PC's the need to communicate via e-mail at various time throughout the day when access to a fixed line telephone circuit was not possible, an alternative means of connecting was necessary. This need has driven service providers and thus the telecommunications industry to develop fast, reliable communications has become paramount. Cellular communication has thus become the essential means of providing this connection.

Voice communication should not be forgotten for users require good reliable access and high quality. Also as mobile communications becomes more and more popular the cellular operators are having to find new ways of combating the fraudulent use of their networks and providing secure communications.

Private Mobile Radio (PMR) as the first form of mobile communications. It used VHF frequencies, was based on analogue technology, was easily intercepted, did not provide complete coverage and was limited in capacity. Later PMR systems did provide better coverage but still suffered from all the other drawbacks mentioned earlier. This lead to the development of the Total Access Communication System (TACS) which although was an analogue transmission system based on the Ultra High Frequency (UHF) of 900 MHz did provide users with far greater capacity but suffered from the ability of easy interception and high fraudulent use. To combat these limitations and to provide far greater capacity the telecommunications industry developed the Global System of Mobile communications (GSM). GSM uses encrypted digital transmission that provides a very high degree of security, considerably enhanced anti fraud techniques, greater capacity and the ability to be used in other countries through the use of international roaming agreements. The changing needs of users where data communications is seen as a primary requirement has now forced the telecommunications industry to seek a new system for high speed data transmission. This is the future of digital cellular telecommunications which is known as Universal Mobile Telecoms Services (UMTS) or Third Generation (3G).

The main driver of this communications evolution has been the increasing need for users to have the ability to send data whist mobile. Universal Mobile Telecoms Services (UMTS) will provide users with high-speed data communications and reliable high quality voice communications. The introduction of high-speed data communications has brought about a revolution in the way that the communications networks deal with the traffic. For voice communication it is necessary to provide a continuously connected circuit, but for data communication the introduction of packet switching is seen as the way forward. We have therefore seen the change from permanently connected circuits to packet based systems.

In this dissertation I shall be giving and overview of the earlier analogue systems but going into much greater detail on the modern digital cellular communications systems.

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