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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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