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Many measures, functions and protocols in digital mobile radio networks are based on the properties of the radio channel and its speci®c qualities in contrast to information transmission through guided media. For the understanding of digital mobile radio networks it is therefore absolutely necessary to know a few related basic principles. For this reason, the most important fundamentals of the radio channel and of cellular and transmission technology will be presented and brie¯y explained in the following. For a more detailed treatment, see the extensive literature [4,42,50,64]. . | GSM Switching Services and Protocols . Second Edition. Jörg Eberspächer Hans-Jörg Vögel and Christian Bettstetter Copyright 2001 John Wiley Sons Ltd Print ISBN 0-471-49903-X Online ISBN 0-470-84174-5 2 The Mobile Radio Channel and the Cellular Principle Many measures functions and protocols in digital mobile radio networks are based on the properties of the radio channel and its specific qualities in contrast to information transmission through guided media. For the understanding of digital mobile radio networks it is therefore absolutely necessary to know a few related basic principles. For this reason the most important fundamentals of the radio channel and of cellular and transmission technology will be presented and briefly explained in the following. For a more detailed treatment see the extensive literature 4 42 50 64 . 2.1 Characteristics of the Mobile Radio Channel The electromagnetic wave of the radio signal propagates under ideal conditions in free space in a radial-symmetric pattern i.e. the received power PEf decreases with the square of the distance L from the transmitter P L2 These idealized conditions do not apply in terrestrial mobile radio. The signal is scattered and reflected for example at natural obstacles like mountains vegetation or water surfaces. The direct and reflected signal components are then superimposed at the receiver. This multipath propagation can already be explained quite well with a simple two-path model Figure 2.1 . With this model one can show that the received power decreases much Figure 2.1 Simplified two-path model of radio propagation 10 2 The Mobile Radio Channel and the Cellular Principle more than with the square of the distance from the transmitter. We can approximate the received power by considering the direct path and only one reflected path two-path propagation 42 Pe p 4 2 r h2 2_ p h-h. 0 4nL X 2 XL J 0 L2 and we obtain under the simplified assumptions of the two-path propagation model from Figure 2.1 a .
