Narrowband Multipath Fading: A Simple Model

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But the signal amplitude uctuates due to multipath according toi.e., with frequency SW (t) = x(1 , cos );2f SW = V 2(1 , cos ):Examples: If = 0 then both waves are arriving from the samedirection, and f SW =0. If = (opposite directions) f SW = V .Interpretation: as mobile moves with constant velocity in a xedmultipath environment, amplitude of the received signal uctuateswith frequency f SW . This is sometimes called the \amplitudestanding wave pattern" due to motion. Notice that as V increases,so does f SW :EEL 6593/Fall '95/Paul Flikkema/USF 6
RemarksThis scenario illustrates two key properties of wireless multipathchannels:1. The fade level (amplitude) varies as a function of position. Inthe general case when a large and random number of pathsexist, the resulting amplitude (envelope) is modeled as arandom variable (e.g., a Rayleigh r.v.).2. The rate of fading uctuations depends on velocity. A roughmeasure of the fading rate is the Doppler spread.Finally, note that channel variations (both level and rate of change)can be caused by objects (i.e., those that reect or absorb thetransmitted energy) other than the transmitter and receiver.EEL 6593/Fall '95/Paul Flikkema/USF 7
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Narrowband Multipath Fading: A Simple Model

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