On the combining of multipath signals in narrowband Rayleigh fading channels (original) (raw)

A6stracl-This paper deals with the process of constructive and destructive addition of multipath signals in a Rayleigh fading channel. It derives closed formulas associating the number uf multipaths with the Rayleigh statistics of the channel and it displays the accuracy of these formulas by means of simulation. The primary conclusion is that multipaths add constructively with high prohahility, thus the more the multipaths the larger the mean power level experienced at the receiver. In this context, multipath propagation exhibits a beneficial property that could he exploited for designing improved performance receivers. Zrrdex terms-Multipath comhining, Multipath fading, Rayleigh fading, Mobile channels. I. INTIIOLXJCTION IRELESS communication channels are characteri-W zed as multipath propagalion channels because the signal at the rcccivcr is usually composed of several delayed replicas or the transmitted signal. The effects of multipath propagation are hoth detrimental and bcncficial. On tlic one hand, lack of multipath propagation would rcndcr mobile communications almosl impossible in heavily structured cnvironments where line-of-sight (LOS) communication is difficult to achieve. Addilionally, multipath propagation develops a form of time diversity, which in wideband transmission systems can be effectively exploited to provide improved performance. On rhc other hand, multipath propagation introduces severe signal fluctuation, commonly rcfcrrcd to as fading, at a moving receiver in a narrowband transmission system. This fading phcnomenon rcnders mobilc channels particularly hostilc communication cnvironments; it is well known [1,2] that common modulalion schemes p c r h u far worse in a mobilc cnviionmcnt than in a fixed one. The primary source of signal fading is the large variation in relative phase of tlic multipath signals cxpericnccd as the rccciver quickly moves ovcr distances as small as half a wavelength. It is commonly quoted that fading is developed by the constructive and destructivc addition of llie multipath components [ 11. This work has been supported in part by Ihc National Scicnce and Engineering Research Council (NSERC) and the Advanced Systcins lnstitutc (A S) of HC through a Visiting Fellowship Program.