Advanced Modulation And Coding Schemes 12121 Two Approaches

There are two approaches to the transmission of binary message traffic or data on a conventional HF link: serial tone transmission and parallel tone transmission. Today it is still probably more common to encounter links using binary FSK on a single channel or multiple channels in the 3-kHz passband with VFCT. (See Table 12.4.) On single-channel systems, when transmitting 150 bps or less, the center tone frequency is at 1275 Hz with a frequency shift of ± 42.5 Hz (Refs. 24 and 25). For 600-bps operation the center frequency is at 1500 Hz with a frequency shift of ± 200 Hz; for 1200 bps, the center tone frequency is at 1700 Hz shifted ± 400 Hz.

We will briefly describe two parallel tone systems and two serial tone systems. The first parallel tone system transmits 16 simultaneous tones and each tone is differentially phase shifted. The second method uses 39 tones. In either case these tones are contained in the nominal 3-kHz passband envelope. Of the two serial tone techniques, one uses 8-ary PSK and the other 8-ary FSK modulation.

For a good introductory text on data transmission, see Ref. 20.

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