8 March 2016

About CIS-3000, possibly a counterpart of NATO ALE ?


The so-called CIS-3000 is a single 8-ary PSK-modulated 2000 Hz carrier (pic. 1) and it's nick name is just due to its constant 3000 symbols/sec waveform. This single-tone signal provides a teoric limit of max 9000 bit/sec and neeeds about 3300 Hz bandwidth.

pic.1 - main characteristics of CIS-3000
CIS-3000 is allegedly almost 100% of Russian origin and possibly used by Intel/Diplo agencies. It can be seen either as a continuous stream and as bursts,  and very often used before MFSK-68 and OFDM-128 "Corvette" modem transmissions (pic. 2).


pic. 2
The burst waveform has been analyzed by radioscanner.ru friends and in this blog too; it is worth noting that in the analysis the radioscanner guys, mostly SergUA6, often use the terms "in this example only!" perhaps to draw attention to the existence of different CIS-3000 modes as, for example, the stream mode I heard and that is illustrated below in picture 3.
The first thing that strikes the eye is a sort of well-defined structure consisting of a preamble and data (say a superblock) that is repeated each ~3456 ms and indicated as "A" in pic. 3; in that same picture is also visible the repetition of the same structure "B" along the superblocks.

pic.3 - super-blocks and blocks repetitions

A more refined measurement of the length of the superblock "A" is obtained by the demodulation of the signal and analyzing the resulting bistream: the length is 31104 bits or 10368 PSK-8 symbols (exactly 3456 ms, as a confirm of the precision of SA), as shown below in pic.4 where the number of the lines just match the number of the superblocks (unless the initial sync and the final trailer).

pic.4 - the same signal seen by the bitstream analyzer
Processing the CIS-3000 bistream returns a characteristic period of 5760 bits length, or 1920 PSK-8 symbols. Besides the period,  another interesting characteristic are the sequences of repeated data: as shown in pics. 5-6, the same sequences are repeated either along "B" blocks and "A" superblocks. This means that the system transmits contiguous redundant informations (source and destination adresses?, commands?, controls?, ...), most likely to combat and reduce the effects of fading, interference, and noise.

pic.5
pic.6

Back to the burst mode, it's interesting to observe that this mode too has both the same 5760 bits length structure and redundancy feature (pic. 7),  although the repetitions in this sample seem to be limited to 3 times and then less "aggressive". So, the 5760 bits period length and the redundancy are certain characterstics of CIS-3000, regardless the stream or the burst mode.

pic.7 - structure and redundancy of a CIS-3000 burst
By the way, since the lengths of a single burst and a superblock are pretty the same (pic. 8), the stream waveform could be thinked as a sequel of burst sent side by side (preambles included), but it's only a my speculation.

pic.8
The substantial redundant format adopted by the system, like MS188-141 or CODAN PSK-8 selcall, and its use before MFSK-68 and OFDM-128 modems, leads to think that the CIS-3000 could be used  as a selcall or a sort of CIS counterpart of the NATO ALE.

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