Wireless Communications Systems by Randy L. Haupt

Author:Randy L. Haupt
Language: eng
Format: epub
ISBN: 9781119419167
Publisher: Wiley
Published: 2019-11-25T00:00:00+00:00

Figure 5.34 Frequency selective fading.

5.7.1 Small‐Scale Fading Models

Small‐scale fading has fast variations in the signal over wavelength‐size distances. Signal levels appear to be random and are very difficult to precisely predict. Experimental measurements under various practical conditions produced data bases that have resulted in statistical models that have proved extremely useful in system design.

5.7.1.1 Rayleigh Fading

Consider the case of many signals arriving in a region via different paths. Each signal has a different amplitude and phase at the receiver due to the differences in path lengths as well as the diversity of reflections, diffractions, and refractions encountered. If the 2 GHz signals in Table 5.3 converge over a 6λ × 6λ area, they form an interference pattern. Figure 5.35a,b show the real and imaginary parts of the total electric field due to these multipath signals. Converting the real and imaginary parts of the total field to amplitude and phase produces the plots in Figure 5.35c,d. These plots clearly indicate that the signal over this small area dramatically oscillates. A mobile wireless user passing through this area of interference encounters large signal variations and fading.

Table 5.3 Ten 2 GHz multipath signals at a receiver.

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