High-Frequency Propagation Conditions; Interference Factors - Aastra Messkoffer Bedienungsanleitung

Basics

High-Frequency Propagation Conditions

For a better understanding of the explanations on physical conditions given in the following sec-
tions, we first need to take a look at the basic principles of high-frequency propagation.
The method under discussion here is DECT standard. This one operates in the 1880 ... 1900 MHz fre-
quency range and provides 120 communication channels.
All cordless telephony systems are subject in principle to the following explanations. The experience
gained in planning any system will be very useful when it comes to planning DECT systems.

Interference factors

The knowledge of potential reasons for interference can raise the project engineer's awareness to
such an extent that many critical points can be avoided already at the design stage of the DECT sys-
tem by using the appropriate measures. In radio technology there are many interference factors that
affect mainly the range and quality of the transmission.
In principle we need to differentiate between two types of interference factors:
• Interference by obstacles that attenuate and/or reflect radio propagation, causing dead spots
• Interference due to other radio signals (e.g. other non-synchronous DECT systems) which lead to
transmission errors.
The receive power of DECT signals can fluctuate a great deal, locally, within only a few centimetres.
This means that signal interference can be reduced or eliminated simply by altering the position of
the base station.
Obstacles may include:
• Moving metal objects such as lifts, cranes, carriages, escalators, blinds, especially ones that are
actuated automatically (the influence of such obstacles varies and is therefore difficult to assess)
• Metal-panelled rooms and large metal-clad objects such as air conditioners, computer rooms,
metallized glassed areas (mirrored), fire protection walls, storage tank installations, refrigerating
units, boilers, pipes.
• Building structures and installations such as steel-reinforced concrete ceilings and walls, stair-
ways, long corridors, rising mains, cable ducts.
• Room furnishings such as metal shelves, file cabinets.
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