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Điện thoại di động vô tuyến điện - Tuyên truyền Channel P11

Planning Radio Networks In earlier chapters we discussed the characteristics of the radio propagation channel in some detail. We introduced methods for predicting the mean signal level within a small area in rural, suburban and urban environments and it became clear that this is a complicated process involving a knowledge of several factors, including the details of the terrain, the building clutter and the extent of foliage along the radio path. Most importantly perhaps, it became apparent that signal strength prediction is not an exact science; the mean signal in a small area can be predicted using any of the methods. | The Mobile Radio Propagation Channel. Second Edition. J. D. Parsons Copyright 2000 John Wiley Sons Ltd Print ISBN 0-471-98857-X Online ISBN 0-470-84152-4 Chapter 11 Planning Radio Networks 11.1 INTRODUCTION In earlier chapters we discussed the characteristics of the radio propagation channel in some detail. We introduced methods for predicting the mean signal level within a small area in rural suburban and urban environments and it became clear that this is a complicated process involving a knowledge of several factors including the details of the terrain the building clutter and the extent of foliage along the radio path. Most importantly perhaps it became apparent that signal strength prediction is not an exact science the mean signal in a small area can be predicted using any of the methods discussed in Chapters 3 and 4 but the prediction is only an estimate. Not only is it inexact in itself there will also be variations about the mean as the mobile moves around within the small area concerned. The variations have lognormal statistics with a standard deviation which depends on the nature of the local environment. Superimposed on these variations in the local mean signal which are known as slow fading are much more rapid and deep variations known as fast fading caused by multipath propagation in the immediate vicinity of the mobile. These follow Rayleigh statistics over fairly short distances. We have also discussed other important characteristics of the channel such as noise mentioned the interference that can affect a given user in a multi-user environment and considered additional parameters that are important in so-called wideband channels where the signal bandwidth is such that frequency-selective fading and intersymbol interference arise. We can now take a look albeit brief at how this information can be brought together in order to plan a radio network for a specific purpose. We will find that some factors are more important than others and that radio .