path: root/scenarios.tex
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authorMatthias P. Braendli <matthias.braendli@mpb.li>2018-01-22 02:27:57 +0100
committerMatthias P. Braendli <matthias.braendli@mpb.li>2018-01-22 02:27:57 +0100
commitf99b0216576436a3191c06426120661839db7b13 (patch)
treeea53eb162b50a5511ba012fcb70d721ceceac2ce /scenarios.tex
parent6ffd038e7f32bac67ce52e8ae66182d0db54a7d8 (diff)
Explain OFDM windowing
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diff --git a/scenarios.tex b/scenarios.tex
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@@ -222,7 +222,7 @@ it helps to produce a cleaner spectral output. At higher rates one needs to
ensure that samples are not being dropped on the USB and that CPU resources are
not being contended.
-The shoulder performance has been measured with shoulder performance at a little
+The shoulder performance has been measured with a value at a little
better than $35$dB, which is roughly equivalent to that obtained from first
generation commercial modulator equipment. This can be increased to a relatively
respectable $\approx 40$dB by enabling the FIR baseband filter in ODR-DabMod.
@@ -265,6 +265,24 @@ into a circle of radius proportional to the error clipping value.
Settings and some statistics are available through the remote control.
+\subsubsection{OFDM Symbol Windowing}
+One technique to improve the shoulder performance is to avoid generating abrupt
+transitions between the OFDM symbols, but apply cross-fading from one symbol to
+the next using a windowing function.\footnote{As of ODR-DabMod v1.0.1, this feature is
+still in the \texttt{next} development branch, and not part of a released
+This feature can be enabled by setting the number of samples to use for
+overlapping one symbol with the next one, the default value is $10$ (out of a
+total symbol length of $2552$ samples in Transmission Mode I). Refer to the
+parameter \verb+ofdmwindowing+ in the file \verb+doc/example.ini+ for
+As this windowing feature modifies samples that are in the guard interval, the
+trade-off is reduced resilience against delayed reflections, reduced maximum
+transmitter delay difference in an SFN scenario, and potentially diminished
+robustness against Doppler spread.
\subsubsection{Digital Pre-Distortion}
An ongoing activity is the development of a method to characterise a power
amplifier and predistort the I/Q samples to invert the distortion behaviour of