Here we compare the performance gain of MRC over that
of EGC and plot this improvement factor. We also consider the improvement of MRC over SS as the
number of antennas increases. Figure 5.56 clearly shows the gain of MRC over EGC starts at approximately
0.5 dB and then increases to 1 dB for the number of antennas shown. In fact, it can be looked
at as a constant gain relatively insensitive to the number of antennas used in the receiver.
268 CHAPTER FIVE
Relative SNR Improvement Factor
0
1
2
3
4
5
6
7
8
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Number of Antennas (M)
Improvement Factor
Gain of MRC over EGC
Gain of MRC over SS
FIGURE 5.56 Relative performance improvement of MRC.
Diversity Performance Summary. Let us take a moment to recall the above results have assumed
uncorrelated signals, 0, on each antenna. Here is the magnitude of the complex crosscovariance
function of two faded Gaussian signals. Here we fix M 2 and compare the SS to the
MRC for various values of the correlation present across the antennas.
For the SS diversity the CDF can be rewritten as
(5.98)
where the following definitions have been used.
(5.99)
and (5.100)
For MRC diversity the CDF can be written as
(5.
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