The complexity column is with respect to the techniques
listed within the table. It is the lowest since complete multiple-receiver chains are not required
to accomplish the operations. As far as performance is concerned, it is given a ???good??? status even
though it doesn??™t produce the best performance; it still provides considerable gains over the single
receive antenna case [41??“54].
Now on the other end of the performance spectrum, the discussion becomes more interesting. In
an interference-free environment the performance of the maximal ratio combining (MRC) and
optimal combining (OC) become theoretically equivalent. And special care must be given to the
implementation of the OC since it can perform worse than MRC under certain scenarios and
implementations.
5.2.1 Switch/Selection(SS)
This first technique selects one of M diversity receivers which has the largest SNR and this receiver
is then used in the detection and demodulation process [55]. In order to aid in the derivations characterizing
the signal we assume each diversity receiver is uncorrelated. The multipath channel is
Rayleigh distributed having a mean power, b0, the probability density function (PDF) is given as
(5.85)
where ri is the received signal envelope of the ith antenna.
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