Cellular radio, isdn networks and satellite communications

Introduction

In describing Cellular Radio, ISDN (Integrated Services Digital Network) and Satellite Communications we must first have a general understanding of the meaning of these forms of Telecommunications. After a brief explanation of the different forms, they will be described in more detail. Then the present and future roles in Irish Telecommunications will be looked at and some examples given. This will then lead to the conclusion.

1. What is Cellular Radio?

Cellular Radio is the use of Technology using low powered radio transmission for transmission and receiving voice or data to a telephone network. Users can be stationary or mobile. It means users are no longer constrained to place to place as it is a 'wireless' system.

2. What is ISDN (Integrated Services Digital Network)?

ISDN is a system which provides digital capacity i.e. voice, video and data transmission in digital form, to be sent and received by a customer. Unlike stand alone services such as telephone, telex, fax and data communications, ISDN is a network which can offer all these services as a package in which a user can talk, exchange data, faxes and other documents at the same time, instead of having to use different networks for these services.

3. What is Satellite Communications?

This is the use of orbiting satellites to relay microwave transmissions from earth stations to the satellite an to re-transmit those signals back down to another earth station by means of microwave transmission.

Cellular Radio

At present there are two types of cellular radio systems in operation in Ireland. These are:

1. TACS

This system is an analogue system in which the voice is transmitted by radio from the telephone to the nearest base station in analogue form. Analogue systems are at present throughout the world but each Country would have different standards. So a user can not use the phone in a different country, also as the signal it transmits is in analogue form the calls can be monitored quite easily with the help of a scanner. America's version of analogue cellular radio is called AMPS (Advanced Mobile Phone System).

2. GSM (Global System for Mobiles)

GSM is a more recent technical standard for cellular mobile phone systems, which was developed in Europe. It is a digital system, which voice and other sounds or data are converted to digital form before they are transmitted between the base station and the mobile phone and then converted back to analogue form.

There are major advantages in using the GSM system as opposed to the TACS system:

a. More complex signaling systems can be used e.g. text messages, fax and e-mail.

b. GSM is an international standard unlike the different analogue systems. GSM is used in most of Europe and parts of Asia. This means a user traveling to another country still has use of their mobile phone.

c. Radio signals carrying digital information are much harder to intercept than radio signals with analogue information. GSM is a more secure transmission.

d. As GSM is a digital system it is more suited to transmit computer data as it's normally in digital form.

e. GSM has higher voice quality in areas where the radio strength is low.

For these reasons the old system (TACS) is slowly on its way out. The new technology is taking over. There are currently two GSM operators in Ireland, ESAT and Telecom, with Meteor starting operations in early 1999.

How does a cellular radio system work?

Mobile telephone networks use a system called the cellular mobile telephone system. The way it works is that the area of coverage, e.g. Ireland would be divided into areas called cells (cellular) each cell would have a low power radio transmitter and receiver. This is called a base station. There is normally one base station in a cell although the cell can be subdivided to give better coverage to a densely populated area, such as Dublin.

When a mobile phone is in a cell it transmits and receives radio signals from the base station in the cell. As the base station is a low power transmitter, the radio signal would be weak. This is so that the radio signals are not picked up if they are out side the area of the cell. Each cell is assigned a set of frequency channels. There is a low range of frequency channels advalibile but it is possible for different cells to use to use the same frequencies. This is as long as they are not attached to another cell with these frequencies or else there would be interference.

Also cells do not have to be the same size. The size of the cell can vary depending on the amount of users in a particular area, for example, in country areas the cells would be quite big whereas in towns they would be smaller. This means more users can make calls in that area at the same time. As ...

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