Our main purpose here is to present the results and provide additional insight.
5.2.2 Equal Gain Combining (EGC)
In this next spatial diversity technique all M antennas will be used to obtain a signal to input into the
baseband for demodulation. Here all M received signals are phase aligned (or co-phased) prior to
being combined. A block diagram emphasizing this is shown in Fig. 5.52.
p(gs)
M
# a1 e
gs
bM1
# e
gs
E5gs6 # aM
k1
1
k
PERFORMANCE IMPROVEMENT TECHNIQUES 265
Receiver
1
Receiver
Receiver
2
M
..
.
Co-
Phase Baseband
Demodulator
C
O
M
B
I
N
E
R
..
.
FIGURE 5.52 Equal gain diversity combining method.
Let us consider QPSK modulation that is transmitted and encounters flat Rayleigh fading channel
with AWGN. Due to uncorrelated fading the constellation on all the M antennas will have various
phase offsets. Co-phasing essentially performs phase derotation and aligns the constellations so that
they can be combined coherently.
The mean SNR of EGC output is given as
(5.93) E5gs6 # c1 (M 1) # p
4 d
When comparing this result to that of the SS equation presented earlier, the EGC performance shows
each additional antenna provides a larger incremental gain for EGC rather over the SS method.
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