the so-called CIS-20, in its standard format, is an OFDM 20-tone waveform characterised by π/4-DQPSK modulation at 75 symbols per second and 120Hz channel separation, as described here. CIS-20 is supposed to be the successor of CIS-12.
This variant exhibits the same modulation format but speed and channel separation are exactly the half of the ones of the standard version, i.e. 37.5Bd and 60Hz channel step. The signal bandwidth is unchanged (~2800Hz).
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| CIS-20 variant - OFDM parameters | |
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| CIS-20 single channel analysis |
Note, once again, the differences between PSK-8 and π/4-DQPSK constellations (in absolute and relative mode, Diff=0 and Diff=1):
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| in a real PSK-8 the paths cross the origin of axis |
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