Larger beam divergence and FoV are not
highly desirable, as discussed in the preceding sections. On the other hand, the complexity
of tracking required to compensate for all types of mispointing may make it impractical
for certain applications. The right solution is often a combination of both methods.
Movements that produce large magnitude mispointing, such as building expansion,
happen at much slower speeds, in the order of several minutes to a few hours.
Compensation for such a large mispointing solely by passive means would require a
relatively large divergence and FoV. However, such slow movements are suited to being
corrected by means of active tracking using much simpler mechanisms than would be
required to compensate for fast movements. On the other hand, movements that are
fast (in the order of milliseconds such as the ones produced by vibrations) cause much
smaller magnitude mispointings. Compensation for such fast and small mispointings
solely by means of active tracking may not be commercially viable for certain applications.
However, they can be compensated for much more reliably by passive means
Optical Wireless Mesh Networks 243
without having to use too large a divergence and FoV.
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