Outros canais de rádio móveis

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 7 Other Mobile Radio Channels
7.1 INTRODUCTION

A great deal of attention has been given to propagation in built-up areas, in particular to the situation where the mobile is located in the streets, i.e. when it is outside the buildings. It is apparent, however, that other important scenarios exist. For example, hand-portable equipment can be taken inside buildings, and in recent years there has been a substantial increase in the use of this type of equipment. As a result, interest in characterising the radio communication channel between a base station and a mobile located inside a building has become a priority. Propagation totally within buildings is also of interest for applications such as cordless telephones, paging, cordless PABX systems and wireless local area networks. In city areas there are tunnels and underpasses in which radio coverage is needed, and away from cities there are suburban and rural areas where the losses due to buildings are not necessarily the dominant feature. Before dealing with such channels, it is worth pausing to clarify a few points and to identify the ways in which the characteristics of the various channels di€er. We wish to distinguish between di€erences which are merely those of scale and more fundamental di€erences of statistical character relating to the signal or the interference. Di€erences of scale are exempli®ed by the urban radio channel. This is characterised by Rayleigh plus lognormal fading and is the same whether the mobile is vehicle-borne or hand-portable. The di€erences are apparent because the fading rate experienced by a moving vehicle is generally much greater than the fading rate experienced by a hand-portable. Although these di€erences do not represent a fundamental change in the statistical nature of the channel, they may not be trivial as