01-09-2012, 12:36 PM
Diversity Reception
Diversity_Reception.ppt (Size: 48.5 KB / Downloads: 189)
To reduce fading effects, diversity reception techniques are used. Diversity means the provision of two or more uncorrelated (independent) fading paths from transmitter to receiver
These uncorrelated signals are combined in a special way, exploiting the fact that it is unlikely that all the paths are poor at the same time. The probability of outage is thus reduced.
Uncorrelated paths are created using polarization, space, frequency, and time diversity
Space Diversity
A method of transmission or reception, or both, in which the effects of fading are minimized by the simultaneous use of two or more physically separated antennas
Antennas must be spatially distant so that no correlation exists between fading phases (one or more wavelengths).
Polarization Diversity
Diversity transmission and reception wherein the same information signal is transmitted and received simultaneously on orthogonally polarized waves
Frequency Diversity
Transmission and reception in which the same information signal is transmitted and received simultaneously on two or more carrier frequencies.
The frequency difference must be high enough so there no correlation exists between their fading phases
Diversity Combining - Switching
The current branch remains selected until a metric fails a certain threshold, the Received Signal Strength Indicator (RSSI). The next branch is then blindly selected.
An adaptive threshold removes unnecessary switching. When the signal fades relative to the mean, switching occurs
Cheap and simple.