Chapter List

3.1 Introduction

This chapter takes a qualitative look at several aspects of thetransmission channel generated by multipath. Among other things, it reviewsstatistical distributions normally used to describe the signal envelopevariations; these distributions are used to evaluate the fade margins requiredfor both the uplink and downlink budgets. In addition, this chapter reviews thetwo types of channels frequency- and time-dispersive and thephenomena that cause them. Finally, the chapter summarizes some of thetechniques used to measure channel characteristics under both narrowband andwideband conditions.

3.2 Angle of Incidence and Spectrum of the Received Signal

This chapter starts by reviewing the mechanisms that give rise tothe received signal time/location variations presented in Chapter 1. Time/locationvariations are mainly related to the motion of the mobile receiver as ittraverses a standing wave pattern created by a number of multipath echoes. Time(or space) selectivity of the channel is closely related to frequencydispersion (Doppler shift) caused by the time variation, due to the mobiledisplacement, of the propagation channel. The velocity of change in the signalphase translates into a Doppler shift in the received RF carrier.

To illustrate this phenomenon, consider the situation illustratedin Figure 3.1(a) where the mobile runs ata constant speed V along a path between Aand A?. Considering only the direct signal (similar arguments may beapplied to the different multipath echoes), the increment in traveled distance? d is given...