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DVB-S


 DVB-S:    The Digital Video Broadcast-Satellite (DVB-S) operates in the 11/12 GHZ band.  It supports data rates from 23.754 Mbps to 41.570 Mbps.  The modulation is a more complicated version than basic QPSK.  In this case so-called pulse shaping filters are used to compact the signal processing bandwidth.  In particular the root-raised-cosine filter (RRC) with roll of factor 0.35 is employed.  This filter is commonly employed today in a variety of wireless communication systems.  It compacts the signal bandwidth while simultaneously providing for matched filter pairs in the transmitter and receiver without introducing inter-symbol interference (ISI). Figure 6 shows a comparison between the spectra of the standard QPSK and the filtered version. As shown in Figure 6, the spectrum with the RRC filter is much more compact.  This allows for a higher data rate in a fixed operating bandwidth.  The  filtered version in not a constant envelope signal, so careful choice of the transponder backoff via the simulations and analysis described must be performed.

Figure 6.  Frequency power spectra of standard QPSK vs. QPSK with a band limiting rrc filter.

 

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