Digital Signal Processing Reference
In-Depth Information
Case 2: multipath components are spread over only a few symbol periods (T
s
)
receiver
transmitter
channel
both intra-symbol and
intersymbol interference
T
s
T
s
T
s
time
time
considerable
fading remains
frequency-selective
channel
|H(f,t
i
)|
2
|H(f,t)|
2
df
∫
t
1
+
t
2
t
3
t
1
t
2
t
3
frequency
time
Figure 4.3.
If the channel response is only slightly longer than the symbol pe-
riod, this results in a frequency-selective channel. However, the received
power still has a considerable level of fading.
Case 3: multipath components are spread over multiple symbol periods (T
s
)
channel
receiver
transmitter
heavy multipath
environment
T
s
T
s
T
s
T
s
T
s
T
s
time
time
reduction of fading
due to frequency
diversity
frequency-selective
channel
|H(f,t
i
)|
2
∫
|H(f,t)|
2
df
t
t
t
3
+
t
1
t
2
t
3
frequency
time
Figure 4.4.
A heavy multipath environment causes a lot of intersymbol
interference, but also results in a more reliable channel as a
result of frequency diversity.
