3.29. The measured distances were larger in the residential results.
Generally speaking, we can prepare a simplified model that relates RMS delay spread to distance,
with the use of Eqs. (3.52) and (3.53).
(3.52)
(3.53)
Combining these equations gives us the following relationship
(3.54)
where one can curve fit the above equations to come up with close approximations to the variables
used within.
The last point we want the reader to be aware of is the actual procedure or methodology used in
obtaining the RMS results. Also we will neglect the differences in multipath arrival time bin widths and
focus more on the threshold value used to consider if multipaths are valid to be used in the RMS calculation.
The typical range has been 10 dB to 20??“30 dB below the main path power. In the next figure
we present more results showing the effects of the choice/value of threshold on the RMS calculated.
These measured results were taken in Canada. It is expected as the multipath threshold increases, more
multipaths will be used in the calculation of RMS and thus increasing the value (see Fig. 3.30).
tRMS X # eY5AB # log(d)6
PL A B # log (d)
tRMS X # eY # PL
140 CHAPTER THREE
Threshold Effects on RMS Delay Spread
5
15
25
35
45
0 10 20 30 40
Tx-Rx Distance (meters) RMS Delay Spread
10 dB Threshold
20 dB Threshold
30 dB Threshold
FIGURE 3.
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