Voxtel VS600, Service Manual

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VS600 Service Manual
VOXTEL Technical Documentation 6
2 Overview of GSM Operation
2.1 Cellular Phone Concept
The cellular system was first used to provide radiotelephone service in the frequency
range 890-960 MHz. A cellular system provides higher call handling capacity and system
availability than would be possible with conventional radiotelephone systems (those
which require total system area coverage on every operating channel) by dividing the
system coverage area into several adjoining sub-areas or cells.
Each cell contains a base station (cell site) that provides transmitting and receiving
facilities, for an allocated set of duplex frequency pairs (channels). Since each cell is a
relatively small area, both the cell site and the radiotelephone that it supports can
operate at lower power levels than would be used in conventional systems.
Using this technique, radiation on a given channel is virtually contained in the cell
operating on that channel and, to some extent, those cells directly adjacent to that cell.
Since the coverage area of a cell on a given channel is limited to a small area
(relative to the total system coverage area), a channel may be reused in another cell
outside the coverage area of the first. By this means, several subscribers may operate
within the same geographic area, without interference with each other, on a single
channel.
2.2 GSM-Global System for Mobile communications
Unlike former cellular systems, GSM uses digital radio techniques. The GSM system
has the following advantages over previous analogue systems:
International Roaming - Due to international harmonization and standardization, it will be
possible to make and receive calls in any country, which supports a GSM system.
Digital Air Interface - The GSM phone will provide an entirely digital link between the
telephone and the base station, which is, in turn, digitally linked into the switching
subsystems and on into the PSTN.
ISDN Compatibility - ISDN is a digital communications standard that many countries are
committed to implementing. It is designed to carry digital voice and data over existing
copper telephone cables. The GSM phone will be able to offer similar features to the
ISDN telephone.
Security and Confidentiality – Telephone calls on analogue systems can very easily be