14-11-2012, 05:42 PM
Equalization, Diversity
Equalization.ppt (Size: 859.5 KB / Downloads: 62)
Flat Fading
Flat Fading is caused by absorbers between the two antennae and is countered by antenna placement and transmit power level.
Frequency Selective Fading
Frequency selective fading is caused by reflectors between the transmitter and receiver creating multi-path effects.
Effects of Frequency Selective Fading
The dips or fades in the response due to reflection cause cancellation of certain frequencies at the Receiver.
Reflections off near-by objects (e.g. ground, buildings, trees, etc) can lead to multi-path signals of similar signal power to the direct signal.
This can result in deep nulls in the received signal power due to destructive interference.
Inter Symbol Interference(ISI)
Definition: Delay spread (frequency-selective fading), in which a bit arrives at the receiver at different times because of the different paths taken, causing bits to run into each other and thus cause inter-symbol interference (ISI). This limits the usable digital signaling rate far a given rate. In other words, if the modulation bandwidth exceeds the coherence bandwidth of the radio channel Inter Symbol Interference or ISI occurs. This causes significant error in high bit rate systems.