Diversity Methods
The replica of the transmitted signal can be sent through
different means [99]. For example, it can be transmitted in a different time
slot, a different frequency, a different polarization, or a different antenna.
The goal is to send two or more copies of the signal through independent fades.
Then, since it is less likely to have all the independent paths in deep fades,
using appropriate combining methods, the probability of error will be lower.
For the current project only the Spatial Diversity is taken
into consideration, hence from now on the discussion will be based on this
topic only.
When multiple antennas are present at the receiver, two
forms of gain are available: diversity gain and array gain. Diversity gain results from the creation of multiple
independent channels between the transmitter and the receiver and is a product
of the statistical richness of those channels. Array gain, on the other hand,
does not rely on statistical diversity between the channels and instead
achieves its performance enhancement by coherently combining the energy
received by each of the antennas. Even if the channels are completely
correlated, as might happen in a line-of-sight system, the received SNR
increases linearly with the number of receive antennas, Nr, owing to the array
gain.
In : Theory