The mobile radio propagation environment clearly places fundamental limitations on the performance of radio communication systems. Signals arrive at a receiver via a scattering mechanism, and the existence of multiple propagation paths (multipath) with di erent time delays, attenuations and phases gives rise to a highly complex, time-varying transmission channel. In order for systems engineers to determine optimum methods of mitigating the impairments caused by multipath propagation, it is essential that the transmission channel be properly characterised. . | 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 6 Wideband Channel Characterisation INTRODUCTION The mobile radio propagation environment clearly places fundamental limitations on the performance of radio communication systems. Signals arrive at a receiver via a scattering mechanism and the existence of multiple propagation paths multipath with different time delays attenuations and phases gives rise to a highly complex time-varying transmission channel. In order for systems engineers to determine optimum methods of mitigating the impairments caused by multipath propagation it is essential that the transmission channel be properly characterised. Previously we dealt with narrowband characterisation which is appropriate for transmissions where the inverse of the signal bandwidth is very much greater than the spread in propagation path delays. For narrowband transmissions in a mobile environment the multipath then results in rapid fading of the received signal envelope and an associated Doppler spread is apparent in the received spectrum. The signal statistics appropriate to narrowband transmissions are usually determined from measurements carried out at a single frequency and as we have seen the Rayleigh distribution is usually a good approximation for the envelope statistics. However the distribution departs significantly from Rayleigh when a strong direct path is present and in that case the envelope statistics are better described by a Rician distribution. Even so it is the areas of low signal strength where multipath dominates that are of the greatest importance in determining the limits on mobile radio system performance and departures from the Rayleigh model in areas of high signal strength do not detract from its usefulness for most system analysis applications. The slower variation in the average signal strength caused by gross changes along .
