Digital Signal Processing Reference
In-Depth Information
in addition, pauses could be inserted between the symbols, so-called guard
intervals.
Symbol
n
Symbol
n+1
Symbol
n+2
Symbol
n+3
Symbol
n+4
Symbol
n+5
Path 1
+
Symbol
n
Symbol
n+1
Symbol
n+2
Symbol
n+3
Symbol
n+4
Symbol
n+5
Path 2
t
=
Path 1+2
t = echo delay time
Intersymbol interference
Fig. 19.3.
Inter-symbol interference / intersymbol crosstalk with multipath recep-
tion
A(f)
f
Fig. 19.4.
COFDM: multicarrier in radio channel with fading
However, there is still the problem of the location- and frequency-
selective fading phenomena. If then the information is not transmitted via a
single carrier but is distributed over many, up to thousands of subcarriers
and a corresponding overall error protection is built in, the available chan-
nel bandwidth remaining constant, individual carriers or carrier bands will
be affected by the fading, but not all of them.
At the receiving end, sufficient error-free information could then be re-
covered from the relatively undisturbed carriers to be able to reconstruct an
error-free output data stream by means of the error protection measures
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