Week 3 - Lecture 6 - Wireless radio channel characteristics Flashcards
What is LOS
Line of sight
What is OBS
obstructed indoor space
What propagation mechanisms do EM waves exhibit?
Reflection
Diffraction
Scattering
How does signal strength drop in indoor and outdoor radio channels?
Drops logarithmically with distance in both
Pl(d) proportional to (d/d0)^n
Pl(d) = Pl(d0) + 10n log(d/d0)
PL - Path loss
d - distance between transmitter and receiver
d0 - minimum distance from the transmitter that is consideered to be in the far-field of transmitted antenna
n - path loss exponent
What properties should the reference distance have for path loss?
Always be in the far-field of the antenna to avoid near-field effects. Can be found using the free space model or field measurements at the reference distance
path loss exponent (n) values
Free Space 2
Urban area cellular radio 2.7 - 3.5
Shadowed urban cellular radio 3 - 5
Obstructed in building 4 - 6
Obstructed in factories 2 - 3
In building line-of-sight 1.6 - 1.8
How is the far-field of an antenna determined
df = 2D^2 /lambda
Where D is the largest physical dimension of the antenna
What’s the equation for the power recieved at a distance d given a reference distance d0, where d0 is in the far-field distance, all in free space
PRx(d) = PRx(d0) * (d0/d)^2
What is Huygen’s principle?
All points on a wave front can be considered as point sources for the production of secondary wavelets. The sum of these secondary wavelets forms the new wave front.
Fresnel zones exist
Didn’t want to write the card
What effect does scattering have on the power measured at the receiver, versus what was predicted
The actual power received is greater because of scattering
When incident on a “rough” surface, the energy is diffused in all directions, hence the additional energy at the receiver
Reflection coefficients can be modified to consider scattering
