DEFERRARI: FIXED-SYSTEM MEASUREMENTS OF TIME- VARYING MULTIPATH 

 AND DOPPLER SPREADING 



Histograms for each of the above time series are shown in Figure 9. 

 They are all about the same with a standard deviation of about 5.5 dB. 

 The essential difference in the three cases is the autocorrelation 

 function. In Figure 10 it is seen that the Bermuda series decorrelates 

 more rapidly than the other two. It appears more noiselike. If we 

 take the decorrelation time to be that value at which the normalized 

 autocorrelation function falls to 1/e , then we get about 4-1/2 minutes 

 for the Bermuda range, 8-1/2 for Eleuthera and 18 in the Florida Straits, 



Another measure is the mean square bandwidth (defined at the top 

 of Figure 11) of the power spectrum of the transmission-loss time 

 series. Figure 11 shows that the more noiselike Beirmuda time series 

 has a broader bandwidth. 



Now, the characteristics that we have looked at so far are ones 

 which are really consistent from day to day over long periods. But we 

 must be able to differentiate between the fast fading events and the 

 intermediate ones. Figure 12 is a sequence of histograms for a time 

 series of 63 days. Each time series is high pass filtered with a 

 cutoff of 4 cycles/day so the periods of variation are less than 6 

 hours. All the longer periodicities are removed. Note the spectra 

 day after day are consistent and formally speaking appear to be 

 wide-sense stationary. Figure 13 shows the corresponding autocorrela- 

 tion functions, again for 63 days. Again these are consistent one 

 after another. 



In the above figures, the longer term trends were filtered out. 

 Figure 14 shows variations for periods longer than 5 hours which are 

 significant and I don't think are related to multipath. I can't think 

 of any mechanism for them offhand other than it may just be a complete 

 change in the whole propagation regime . It appears that there are 



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