wilamowski-b-m-irwin-j-d-industrial-communication-systems-2011

Media 2-11
uses light backscattering to analyze fibers. OTDR takes a snapshot of the fiber’s optical characteristics.
It sends a high-powered pulse into the fiber and measures the light scattered back toward the
instrument. OTDR can be used to locate fiber breaks, splices, and connectors, as well as to measure
loss. In order to completely specify a fiber-optic cable, four primary performance categories must be
quantified: installation specifications, environmental specifications, fiber specifications, and optical
specifications.
2.4 Wireless Links
Although a wireless radio link has many advantages with respect to mobility, the list of technical
hurdles to be tackled is impressive. The wireless link depends on many parameters like distance,
reflectors, interferers, weather condition, and much more. In order to achieve a desired link quality,
large safety margins are need to be used and suitable modulation formats have to be chosen. A link
will never guarantee 100% perfect transmission of the information; higher BERs than for wired links
have to be expected.
2.4.1 Physical Properties
2.4.1.1 Wavelength
Solving the wave equation (based on Maxwell’s formulas) turns out that electromagnetic waves propagate
with the speed c = 1 µε with μ denoting the permeability and ε denoting the permittivity of the
medium the wave is propagating in. For air, which is the typical transport medium, the free-space permeability
and permittivity μ 0 and ε 0 , respectively, can be used as a first approximation, resulting in a
propagation speed of about the speed of light, c ≈ c 0 (the error due to approximation is