Week 2.2 Flashcards
Ground Wave Propagation?
Follows contour of the earth
Can propagate considerable distances
Frequencies up to 2MHz4\
Sky Wave Propagation?
Signal reflected from ionized layer of atmosphere back down to earth
Signal can travel a number of hops, back and forth between ionospehere
LOS Propagation?
Line Of Sight
Transmitting and receiving antennas must be within line of sight.
Refraction - bending of microwaves by the atmosphere
2 types of communication for LOS?
Satellite Communication
Ground Communication
LOS wireless transmission impairments?
Attenuation and attenuation distortion Free space loss Noise Atmospheric absorption Multipath Refraction Thermal noise
Attenuation?
Strength of signal falls off with distance over transmission medium.
Shadowing?
Shadowing is the effect that the received signal power fluctuates due to objects obstructing the propagation path between transmitter and receiver.
Popular models for outdoor environment?
Okumura Model
Hata Model
Hata Model?
It is an empirical formulation of the graphical path loss data provided by Okumura model
Valid for 150~1500 Mhz
Small Scale Propagation Model?
Describes the rapid fluctuations of amplitude or phase and/or multipath delays of a radio signal over short travel distance and/or short period of time
Flat Fading?
The channel has a constant gain and linear phase over a bandwidth which is greater than the bandwidth of the transmitted signal.
Frequency Selective Fading?
The channel has a constant gain and linear phase over a bandwitdth.
Thermal Noise?
Noise arising for the movement of electron in the devices.
Intermodulation Noise?
Occurs if signals with different frequencies share the same medium
Crosstalk?
Unwanted coupling between signal paths
