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Điện thoại di động vô tuyến điện - Tuyên truyền Channel P8

Sounding, Sampling and Simulation In the earlier chapters we discussed the characteristics of mobile radio channels in some detail. It emerged that there are certain parameters which provide an adequate description of the channel and it remains now to describe measuring equipment (channel sounders) that can be used to obtain experimental data from which these parameters can be derived. It is often of interest to make measurements which shed some light on the propagation mechanisms that exist in the radio channel but engineers are usually more interested in obtaining parameters that can be used to predict the performance, or the. | 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 8 Sounding Sampling and Simulation 8.1 CHANNEL SOUNDING In the earlier chapters we discussed the characteristics of mobile radio channels in some detail. It emerged that there are certain parameters which provide an adequate description of the channel and it remains now to describe measuring equipment channel sounders that can be used to obtain experimental data from which these parameters can be derived. It is often of interest to make measurements which shed some light on the propagation mechanisms that exist in the radio channel but engineers are usually more interested in obtaining parameters that can be used to predict the performance or the performance limits of communication systems intended to operate in the channel. The choice of channel sounding technique will usually depend on the application foreseen for the propagation data. Basically a choice has to be made between using narrowband or wideband transmissions and whether a time or frequency domain characterisation is required. In what follows we will briefly describe both narrowband and wideband systems and provide an indication of how relevant data can be extracted from measurements. We make only a brief reference to the data processing techniques particularly in the case of wideband channels for details the interested reader will need to consult the literature 1-4 . 8.2 NARROWBAND CHANNEL SOUNDING It is clear from the earlier discussion that when the mobile radio channel is excited by an unmodulated CW carrier i.e. a single tone large variations are observed in the amplitude and phase of the signal received by a moving antenna. These variations are apparent over quite small distances. A considerable number of mobile radio propagation studies have been undertaken by transmitting an unmodulated carrier from a fixed base station receiving the .