Just to point out some differences bewteen these two types of CIS bursts (figure 1) :
* the ones sent in group or in front of the OFDM-121
* the ones sent individually or before Serdolik MFSK/OFDM
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| Fig. 1 |
Both the bursts are 2400 Baud keyed and have the same 20ms ACF value as well as - likely - the used modulation, although their constellations and state transitions are not much help in identifying the type of modulation (figure 2): most likely PSK2 in preambles and reinserted probes. The number of the transmitted frames is different, 33 Vs 22, but since they have the same 48-symbol length framing (same ACF) their duration differs (about 760 and 476 ms).
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| Fig. 2 |
For what concerns the structure of the frames, the classical method can be misleading, showing two different structures consisting of 33 unknown symbols + 15 known symbols for a type of burst and 32 unknown symbols + 16 known symbols for the other (figure 3a); the plain raster method anyway shows the same 32 + 16 framing for both the burst (figure 3b).
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| Fig. 3a |
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| Fig. 3b |
Given the different systems in which these bursts are used, and also the modalities of their transmission (isolated, in group or in front of OFDM), I think they also have different purposes and functionalities.
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