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10 0
10 *5
FSK
P b 10 *10 OOK
10 *15
DPSK
10 *20
*10 *5 0 5 10 15 20
dd
γ (dB)
Figure 8.28 Error probability of various modulation formats in a direct detection system.
From Eq. (8.96), we have
1 √
PSK
P = erfc( ). (8.326)
b 2
When >> 1,
exp (−)
PSK
P ≅ . (8.327)
b √
2
From Eq. (8.307), we have
DPSK 1
P = exp (−). (8.328)
b 2
10 0
DPSK
10 *5
P b
10 *10
PSK
10 *15
*10 *5 0 5 10 15
dd
γ (dB)
Figure 8.29 Comparison of the performances of homodyne PSK and direct detection DPSK.
