CIS-45 π/4-DQPSK "special" transitions

During these days there are a large variety of signals on the air, mostly on 14MHz and 17MHz bands; among these signals there is the OFDM 45-tone HDR modem (aka CIS-45), running in both the two waveforms: 40Bd π/4-DQPSK and 33.33Bd BPSK.
And just one of them, tuned on 17434.0 KHz USB, caught my attention because of a certain shapes in its spectrum (pic. 1). Apparently it looks like a version 2 modem (pic. 2), ie 40Bd and 62.5Hz step, but the relative constellations in the channels do not exhibit the expected π/4-DQPSK but rather an odd 3-ary constellation in some channels (in blue colour) and an unplanned BPSK in others (red color), as arranged in picture 3 related to the segments "A".

About the segments "A", by isolating the 44th (apparently 2-ary) and the 45th channel (app. 3-ary) you can get the used modulation and then the real constellations: as it is clearly visible in pictures 4 and 5, all the channels have π/4-DQPSK modulation (see Diff.0 constellation), as it should be, BUT with the special transitions 3-of-4 and 2-of-4 of the possible states.
The same results are obtained by analyzing the segments "B" (Pic. 7) and "C" (Pic. 8), with the presence of two 3-ary transitions. It's interesting to notice that the BPSK-like transitions occupy always the same channels along all (at least) this sample: 2,5,8,11,14,17,20,23,26,29,32,35,38,41 and 44.

Given the position of these segments along the signal, they could act as service or sync tones for the receiver modems, anyway in my little experience I never seen this arrangement before in CIS-45 signals.
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Pic. 1

Pic. 2 - OFDM parameters

Pic. 3 - carriers arrangement

Pic. 4 - 44th channel, π/4-DQPSK with special transitions

Pic. 5 - 45th channel, π/4-DQPSK with special transitions

Pic. 6 - demod

Pic. 7 - transitions and their arrangement in segments "B"

Pic. 8 - transitions and their arrangement in segments "C"

CISwitching...

September, 30 at 0711z on 15812.0 KHz on USB: on-the-fly switch from CIS-45 to CIS-60, both belonging to HDR (High Data Rate) family modem. Maybe tests or fast (auto) adatpion to the channel conditions ?

CIS-45 v2 HDR modem 40 Bd π/4 DQPSK

This is another variant of the CIS-45 v2 waveform exhibiting the π/4 DQPSK manipulation in the channels and 40 symbols baudrate: this way the operating speed is increased to 3600 bps.

CIS-45 v2 HDR modem: modulation switching

16230.0 --- Russian Mil, RUS:

   1412 USB OFDM 45-tone HDR Modem v1, 33.33Bd 62.5Hz DBPSK bursts
   1410 USB OFDM 45-tone HDR Modem v2, 40Bd 62.5Hz pi/4 DQPSK then BPSK stream

Today I heard the CIS-45 OFDM HDR modem running on 16230.0 KHz on USB around 1410z. More precisely, the heard signals were the two well known CIS-45 waveforms: the 33.33 Baud version (v1) in burst mode and the 40 Baud version (v2) in bistream. The v2 modem came with a discrete signal so I decided to record it for later analysis. The signal clearly exhibits the CIS-45 v2 features: baudrate = 40, Sh = 62.5 and BPSK modulation in the channels as in:

http://signals.radioscanner.ru/base/signal230/

http://i56578-swl.blogspot.it/search/label/CIS-45_v2 

I was surprised by analyzing another segment of that signal: the modulation in the channels is no more the expected BPSK but pi/4 DQPSK and still running at 40 Baud. So, it seems that the system has the capability to change the modulation mode (from pi/4 DQPSK to BPSK) on-the-fly, mantaining the same baudrate:

I do not know the reasons of such behavior, possibly an adaptive feature? I searched the web to get some other informations and found that KarapuZ too recently noticed this beahavior: http://www.radioscanner.ru/forum/topic36750-153.html#msg1183165

As the others, this signal is available on request: just email me.

CIS-45 v1 HDR modem 33.33 Bd BPSK bursts

CIS-45 Ch, Russian 45 tones HDR modem, version 1 http://signals.radioscanner.ru/base/signal46/
This is a Russian 45 tones HDR modem, version 1, formed using the principles of OFDM and here running in burst-mode. Most likely it is a lightweight version of the Russian 93 tone modem. The HDR name is just an abbreviation of High Data Rate.

The transmission heard on 15812.0 KHz USB at 0705z, is composed of two bursts, sent at irregular intervals. Looking at its features it corresponds to the version 1 of the well known Russian 45-tones PSK-2 OFDM modem (also known as CIS-45), here running in burst mode at 33.33 Baud.

The pilot tone also acts as a sync tone at the beginning of each burst. The 45 sub-carriers in the trailer are un-modulated and followed by a PSK-2 modulated segmen. The data-block after the preamble shows a PSK-2 modulation in the channels at the speed of  33.33 baud.

Bandwidth: ~ 3000 Hz
Number of channels: 45 + 1 pilot tone (~ 3350 Hertz)
Manipulation in the channels: 2-PSK
Step between channels (frequency net/grid): 62.5 Hz
Manipulation speed (Baud rate): 33.33(aggregate 1800)

CIS-45 v2 HDR modem 40 Bd BPSK

CIS-45 Ch, Russian 45 tones HDR modem, version 2 http://signals.radioscanner.ru/base/signal230/

CIS-45 version 2 shows a reduced CP and manipulation speed increased to 40 Hz so the maximum operating speed is increased to 1800 bps. In general, the signal is the same as CIS-45 HDR modem version 1.

Bandwidth: ~ 3200 Hz
Number of channels: 45 + 1 pilot tone (~ 3350 Hertz)
Manipulation in the channels: 2-PSK
Step between channels (frequency net/grid): 62.5 Hz
Manipulation speed (Baud rate): 40

45 tone and pilot tone (spectrum)

Here is another CIS-45 reception (25 mar) that shows a better signal quality in the upper channels:

CIS-45 v1 HDR modem 33.33 Bd BPSK stream

Number of channels: 45 + 1 pilot tone (~ 3300 Hertz)
Manipulation in the channels: 2-PSK
Step between channels (frequency net/grid): 62.5 Hz
Manipulation speed (Baud rate): 33.33

The signal has the same features of CIS-45 Version 1 burst-mode, but here it is used in stream-mode. This is the third variant I have seen of CIS-45 modem other than CIS-45 v2 (40 Bd stream) and CIS-45 v1 (33.33 Bd burst)