What this shows is using 2
out of 3 antennas produces results closer to MRC receiver using M 3 antennas.
Next we increase the number of antennas available to M 4 and compare the performance of
MRC, SS, and SC3. This scenario clearly shows the benefits of being able to choose the best 3 out of
4 antennas. One can see the additional gain of using MRC over SC3 is very small, approximately 0.5 dB
(see Fig. 5.63).
274 CHAPTER FIVE
BPSK MRC
1.E??“06
1.E??“05
1.E??“04
1.E??“03
1.E??“02
1.E??“01
0 5 10 15 20
Eb/No (dB)
MRC (M = 1)
MRC (M = 4)
SC (M = 4)
SC3 (M = 4)
BER
FIGURE 5.63 BPSK BER performance for MRC combining.
Next we have taken the above results and plotted them together to emphasize the points made. It
is clear using the best M 1 out of M antennas performs very close to the M antenna MRC diversity
system (see Fig. 5.64).
What we have done in this subsection was to present the theoretical performance of the four diversity
techniques mentioned. The difference in performance between EGC and MRC was shown to be
approximately 1 dB and because their receivers were similar we purposely omitted results for EGC.
Hence comparisons were made between SS and MRC for a variety of antennas. This gap in performance
was filled with the SC2/SC3 techniques which used the best M 1 of M antennas.
Pages:
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450