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| author | Matthias P. Braendli <matthias.braendli@mpb.li> | 2018-01-22 02:27:57 +0100 |
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| committer | Matthias P. Braendli <matthias.braendli@mpb.li> | 2018-01-22 02:27:57 +0100 |
| commit | f99b0216576436a3191c06426120661839db7b13 (patch) | |
| tree | ea53eb162b50a5511ba012fcb70d721ceceac2ce | |
| parent | 6ffd038e7f32bac67ce52e8ae66182d0db54a7d8 (diff) | |
| download | mmbtools-doc-f99b0216576436a3191c06426120661839db7b13.tar.gz mmbtools-doc-f99b0216576436a3191c06426120661839db7b13.tar.bz2 mmbtools-doc-f99b0216576436a3191c06426120661839db7b13.zip | |
Explain OFDM windowing
| -rw-r--r-- | scenarios.tex | 20 |
1 files changed, 19 insertions, 1 deletions
diff --git a/scenarios.tex b/scenarios.tex index 308d50e..7d3d006 100644 --- a/scenarios.tex +++ b/scenarios.tex @@ -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 +version.} + +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 +instructions. + +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 |