TABLE OF CONTENTS There are many different cellular radio or cellular telecommunications systems in use around the world. Naturally, they have many differences in the way they operate. Not only are there different implementations of similar technologies, but over the years there have also been developments in the technologies that are used. The first analogue systems gave way to digital systems, and in turn these are being migrated to technologies that are able to carry much higher data-rate signals to cope with the new applications that are being found. Yet despite these differences there are some fundamental concepts that are at the core of cellular telecommunications technology.
One of the key requirements for any radio-based telecommunications system is the efficient use of the frequencies that are available. Early schemes for radio telephones used a single central transmitter to cover a wide area. These suffered from the limited number of channels that were available, with waiting lists for connection being many times greater than the number of people that were actually connected. This arose from the way the system was operated.
Take, for example, a system where each user is allocated a channel. Using a typical analogue system, each channel needs to have a bandwidth of around 25 kHz to enable sufficient audio quality to be carried, as well as allowing for a guard band between adjacent signals to ensure there are no undue levels of interference. Using this concept, it is possible to accommodate only forty users in a frequency band...
