Digital Signal Processing Reference
In-Depth Information
1
frequency axis
R 2 = 500
kHz
-R 2 =-500
kHz
Figure 17.5. Modulated signal frequency width.
of T seconds, and decays slowly. A very long filter is needed to
approximate the sinc response. The impulse response of the
symbols immediately preceding and following the center symbol
are in
Figure 17.6
shown below. The signal transmitted will be the
sum of all the symbols' impulse response (we are just showing
three symbols here). If the I or Q sample has a negative value for
a particular symbol, then the impulse response for that symbol
will be inverted from what is shown below.
The receiver is sampling the signal at T intervals in time to
detect the symbol values. It must sample at the T intervals shown
on the time axis above (leave aside for now the question of how
Following
symbol
Preceding
symbol
F
cutoff
= R/2 = 1/2T
time axis
-4T
-3T
-2T
-T
T
2T
3T
4T
Figure 17.6. Sinc impulse response.
