VDL-2 - It is rather new and the perspective view of aviation telecommunication (ATN). It is very actively introduced in practice. It is provided step-by-step change/move from the previous generation of similar system ACARS, to the new VDL-2, VDL-3. As well as in ACARS, data exchange between aircrafts and the earth occurs by extremely short packages. In average, lenght of the package is about 20-40 мс, but it can be both shorter and longer packages. In comparison with ACARS, the throughput of channel ATN in VDL-2 is essentialy increased from 2400 bps (ACARS) to ~31500 bps.
As a whole, at appropriate quality, the signal is confidently enough analyzed and identified, there are no obvious features detected.
In this update, possibility of resample and shift of the signals on fractional values of frequencies is added.
Perhaps more important part of current updating, is the first stage of integration in SA calculator K.
The first stage doesn't mean the high-grade calculator. At this stage, in SA the mainframe of preliminary processing, so-called preprocessing is integrated. The primary goals of this block, gathering of primary parameters of the signal, and preliminary rough processing of this data.
The list from the most probable values "Magic K" which detailed analysis will be spent in the second part of the calculator which integration is planned further will be result of work the pre-processing block.
Nevertheless, even in such, very strongly simplified kind, it is already possible to receive authentic enough values K on some signals.
PakNet - One of the oldest systems of documentary communication. It was founded in 1985-86 years.
It is necessary to notice that within these years there was very intensive growth and development of various networks, such as Rosnet, Rospak, Sprint, Paknet etc. From that last abundance up to now days not many of them are still "alive" - PakNet one of the such.
The cable network of Russia concerns documentary networks, to the same category belongs PakNet, which is realized on qualitative another high level, than a cable network.
In general PakNet, is not so much name of the protocol or a signal kind, but the name
It's a small article, which dealt with the problem of identifying GMSK and OQPSK. We hope this will be useful...
It's a small fragment...
OQPSK and GMSK are tightly connected, as well as SDPSK and CPFSK, as well as pi/4 DQPSK and C4FM.
Such "dualism" is spread enough, and connected/linked by the fact that often some modes of frequency shift keying at some conditions, smoothly flowing and/or aspire to acquire the shape of phase manipulation.
*** GMSK ***
The general features of GMSK manipulation formation, we had already considered in the article FSK, GFSK, MSK, GMSK and some other modes . Also it was marked, that application of the filter of the Gauss allows to narrow the main spectrum of a signal considerably.
The filter of the Gauss is characterized by parameter BT, interested ones can independently learn this subject, us interested in the practical for the analysis moments.
The value range of parameter BT lies within 1 > BT > 0 limits. The lesser BT value, the more compact spectrum at resultant signal GMSK.
GMSK with the filter of the Gauss with BT = 1, is turning into classical MSK.
For formation of GSM signals the filter of the Gauss with BT = 0.3 is standardly used, and on an example of the synthesized signals it is possible to look as it looks from positions of tasks of the analysis.
Some preliminary remarks.
As, the finished result of concerning of GMSK nuances will be some conclusions about signal TETRAPOL
, then the synthesized signals have the same speed of manipulation equal 8000 Hz.
Besides, sometimes I will add a bit of white noise in the synthesized signals, because ideal signals though look beautifully, nevertheless, having absolute accuracy, in some cases these ideal signals conceal/hide the general details or make these details badly watched. This moment should be well clear from a picture below.
The error, which has been found out by users is fixed: At the opening of stereo files with wav tag, which differs from 1 and 3, the program was going into "deep dream".
Also the displayment of the expanded information about the codec, which is applied in a current wav file is added. I specify, that it is not type of codec which the program supports it, it is the codec title, which is used in the current wav file. Sometimes it allows to communicate with suppliers of records/signals more in detail.
Visual displayment of the constellations and transitions in them is increased in phase viewer , at least visually, the new format looks much more attractive than the old.
Also, as always, the number of minor bugs is fixed.
TETRAPOL - an old enough system of digital trunking communication/connection, which had gotten wide enough spreading. The standard is developed in the mid-eighties the last century. Usage of GMSK modulation with the shaping/forming filter of the Gauss with BT = 0.25 is very interesting. I Will remind, GSM uses the filter of the Gauss with BT = 0.3 and has compact enough spectrum, reduction of this parameter allows to narrow further the spectrum, but as a whole, it does already noticeably reduce interference immunity or restricts/reduces the zone of confident communication. It Was unexpected enough to find out, that on the signals sent by foreign colleagues BT is even less than 0.25, that even more worses interference immunity.
Nevertheless, in TETRAPOL standard it is marked, that it is possible use both channeles as with band 12.5 kHz (most likely it is with BT = 0.25), so in case of need, with a band 10 kHz, and it already implies smaller BT values.
Considering that the standard isn't oriented on commercial networks, and intended for the organization of communication services of public safety, then some lowering of a confident cover zone isn't serious lack according to the developers opinion.
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