Chapter 4 begins a discussion of sensor network protocols. We address physical
layer issues such as channel-related concerns, radio-frequency bands, bandwidth,
propagation modes (ground wave, sky wave, line of sight), and channel impairments (e.g., refraction, atmospheric absorption, fading, multipath, free space,
Gaussian noise, Rayleigh fading, Rician fading). Reference is made to the gamut
of off-the-shelf radio technologies that can be used for WSNs.