Diversity Techniques

Diversity Techniques Diversity is based on the fact hat individual channels
experience independent fading events. We can therefore cor pensate for error effects
by providing multiple logical channels in some sense 1etween transmitter and

receiver and sending part of the signal over each channel. This technique does not
eliminate errors but it does reduce the error rate, since we have spread the transmission
out to avoid being subjected to the highest error rate that might occur. The other
techniques (equalization, forward error correction) can then cope with the reduced
error rate.
Some diversity techniques involve the physical transmission path and are
referred to as space diversity. For example, multiple nearby antennas may be used to
receive the message, with the signals combined in some fashion to reconstruct the
most likely transmitted signal. Another example is the use of collocated multiple
directional antennas, each oriented to a different reception angle with the incoming
signals again combined to reconstitute the transmitted signal.
More commonly, the term diversity refers to frequency diversity or time diversity
techniques. With frequency diversity, the signal is spread out over a larger frequency
bandwidth or carried on multiple frequency carriers. The most important
example of this approach is spread spectrum.