Digital Signal Processing Reference
In-Depth Information
thor. The residual-carrier problem can only be verified at the center carrier
(3408 or 852, resp.) in the center of the band and only causes interference
there or in the areas around the center carrier. A lack of carrier suppression
can be detected right away as a dip in the display of the modulation error
ratio over the range of DVB-T subcarriers in the center of the band and an
expert in DVB-T measuring techniques can immediately tell that there is a
DVB-T modulator operating in direct modulation mode.
Fig. 21.11.
Effect of residual carrier
DC
I Gain
I
Re(f)
re(t)
+
IFFT
cofdm(t)
Q Gain
im(t)
Im(f)
Q
DC
Phase
90°
Fig. 21.12.
COFDM modulator with I/Q errors
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