Both the two signals A and B have the same duration and both have a long preamble-segment followed by the data-segment. The signals spread ~3KHz bandwidth and consist of a 1800Hz carrier with PSK-8 modulation at 2400 symbols/sec.
![]()
synchronization preamble segment
From MS188-110C App.D "The synchronization preamble is used for rapid initial synchronization and provides time and frequency alignment. The synchronization preamble shall consist of two main sections, a transmitter level control (TLC) settling time section, and a synchronization section containing a repeated preamble super-frame. The preamble super-frame consists of three distinct subsections, one with a fixed (known) modulation, one to convey a downcount, and one to convey waveform identification." The superframe shall be repeated M times. The Synchronization section shall be immediately followed by the modulated data (pic 1).
 |
| Pic. 1 |
Both the two sync preamble segments have the same lenght (~ 5 seconds) and the same ACF structure: 239.98 ms frame that makes 576 symbols or 1728 bits.
From the 188-110C App.D documentation, the orthogonal Walsh modulation is used in the synchronization section of the preamble and the length of the super-frame is 18 channel-symbols, ie:
9 (fixed) + 4 (downcount) + 5 (waveform identification)
Since in 3KHz bandwidth waveforms the preamble channel-symbol is 32 symbol length (pic. 2), the length of each repeated superframe is: 18 (channel-symbols) x 32 (length of one channel-symbol) that makes the measured 576 symbols or 1728 bits (pic. 3).
 |
| Pic. 2 |
 |
| Pic. 3 |
That's ok in pic.4, where the synchronizationsection of the two preambles exhibits a clear 1728 bit period length.
 |
| Pic. 4 |
data segment
The data segments have the same lenghts but different frame structures (pic. 5).
The frame structure for the signal-A waveform is the one shown in figure D-7 of Appendix D: the initial synchronization preamble is followed by frames of alternating data (unknown-data) and probe symbols (known-data):
The data segments have the same lenghts but different frame structures (pic. 5).
 |
| Pic. 5 - over-the-air bitstreams after removed the sync preamble |
The frame structure for the signal-A waveform is the one shown in figure D-7 of Appendix D: the initial synchronization preamble is followed by frames of alternating data (unknown-data) and probe symbols (known-data):
 |
| Pic. 6a - WID-7 frame structure |
 |
| Pic. 6b - WID-7 32 known-data (96 bits probe) |
The signal-B waveform does not exhibit a data+probe structure but rather strong 853.4ms ACF spikes (pic. 7) that makes 2048 symbols/sec at 2400Bd speed or 6144 bits. The signal B is the waveform ID-0, using a different structure after the synchronization preamble: data “frames” are 32-symbol Walsh sequences (channel symbols), each corresponding to a single unknown (data) bit.
As shown in pic. 8 (after demodulating the signal-B) mini-probes are not sent in waveform 0, Walsh-coded data symbols are sent continuously after the initial synchronization preamble and the 2048 symbols (6144 bit) period is due to the scrambler lenght. For waveform 0 the data scrambling implementation just generates 256 x 8 or 2048 values and the scrambling sequences are continuously wrapped around the 2048 symbol boundary. Athough data are modulated using Walsh ortogonal modulation, they are scrambled to appear, on-air, as an 8PSK constellation.
 |
| Pic. 7 - 2048 symbols ACF (~853.4ms) for the signal B |
As shown in pic. 8 (after demodulating the signal-B) mini-probes are not sent in waveform 0, Walsh-coded data symbols are sent continuously after the initial synchronization preamble and the 2048 symbols (6144 bit) period is due to the scrambler lenght. For waveform 0 the data scrambling implementation just generates 256 x 8 or 2048 values and the scrambling sequences are continuously wrapped around the 2048 symbol boundary. Athough data are modulated using Walsh ortogonal modulation, they are scrambled to appear, on-air, as an 8PSK constellation.
 |
| Pic. 8 - WID-0 6144 bit period caused by the scrambler lenght |