Where the NLOS
cases have the larger values shown in the group and the LOS cases have the smaller values. Note an
overlap in the measurements. Now that we have zoomed in, we can see there are more data points
available in this region than at the higher frequency regions. Lastly, recall the above data points have
been made in different buildings, made up of different construction material and in different countries
(i.e., USA, Canada, Netherlands, Sweden, China, UK, etc.).
It should be mentioned that there exists a range of RMS delay spread measurements that exist in the
literature. One example is some measurements published RMS 30 nsec while others publish values
greater than 100 nsec. The first explanation is that the actual environment will vary (residential, factory,
office building) not to mention factors such as indoor furniture, wall and floor construction, and so on.
For those measurements with very large values of delay spread then special attention should be given to
the outside surrounding buildings (possibly mountains). In other words, outside buildings and mountains
can act as reflectors and thus increasing the multipath arrival time and in turn increasing RMS.
Another rather interesting question is how does the delay spread vary as a function of distance or
antenna separation.
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