New article: "GMSK and OQPSK"

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 full description here.

SA update to version v 6.2.6.4: Visualization improvement.

SA Update to version v 6.2.6.4.

The planned SA update.

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.

PSK: TETRAPOL

TETRAPOL

The trunking system for VHF, Br - 8000, mode GMSK

Author: SergUA6 

Band Width ~9000-1000 Hz

Baud Rate 8000 Hz

n-Ary (PSK/MPSK) GMSK

ACF  20 ms

RX mode  source I/Q record

Perfect by the quality example of TETRAPOL. Sent by foregin collegues.

An example of TETRAPOL (two channeles). Sent by foregin collegues.

Sonograms:

pic.1 General view

pic.2 Manipulation speed

Diagrams:

pic.3 The graphical spectrum

pic.4 Allocation of the channeles

 Pictures:

pic. 5 Phase constellation

 pic.6  Transitions in the constellation

pic.7 The signal's ACF

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.

CROWD-36 (SERDOLIK) - OFDM mode

CROWD-36(SERDOLIK) - OFDM mode

Ch-34, Br-40, Sh-40, PSK-4, The OFDM without CP

Author: SergUA6 

Band Width ~1400 Hz

Baud Rate 40 Hz

n-Ary (PSK/MPSK) PSK-4

Count of Carriers 34

Step between carriers 40 Hz

Pilot tone(s) 393 Hz, this tone or pilot, or continue transmit data of zero in PSK-4 mode

RX mode SSB

The example of CROWD-36 (SERDOLIK) OFDM MODE

Sonograms:

pic.1 General view

pic.2 Manipulation speed

pic.3 Detalization of the second channel

 Diagrams:

pic.4 The first channel in the fourth degree

 pic.5 Constellation of the first channel

CROWD-36 (SERDOLIK) - OFDM mode - is curious enough signal, where the principles of OFDM technologies usage  for formation of a various type of manipulations/modulations are perfectly shown. 


MFSK and OFDM segments are generated/formed absolutely equally, the difference is only in the form of used modulation, besides this OFDM signal has no cyclical prefix. Speed of manipulation is precisely equal to frequency space (step between frequencies) - that is the big rarity, and it is possibly linked with the fact, that initial synchronization is provided on the operation stage in MFSK a mode. 


The presence of pilot-tone or the continuous transmission of zero in PSK-4 mode is viewed In the second channel of OFDM segment, alghough i can't say definitely.


Though OFDM signals without CP  are very difficult for the analysis, in this record  it is even possible to define a manipulation mode in the first (lower) channel thus this channel is rather easily possible to select/mark this channel confidently enough, thanking presence of the pilot-tone in the second channel. 


Absence of the prefix allows to use as much as possible densely all the spectrum, with the maximum real speed that in this signal makes 34*40*2=2720 bps. If the second channel is really the pilot, then the maximum technical speed is slightly less - 2640 bps.

MFSK: CROWD-36 (SERDOLIK)

CROWD-36(SERDOLIK)

MFSK-34, Br-40, Sh-40, Ch-34

Author: SergUA6 

Band Width ~1400 Hz

Baud Rate 40 Hz

Count of Carriers 34 manipulation frequency

Step between carriers 40 Hz

RX mode SSB

An excellent example of CROWD36 (SERDOLIK) MFSK. Send by Ware.

Sonograms:

pic.1 General view at the different spectrum resolution.

pic.2 Manipulation speed

Diagrams:

pic.3 Allocation and quantity of the frequencies

pic.4 demodulation in SA

CROWD-36(SERDOLIK) MFSK From the different sources, it is used by various diplomatic services of the CIS countries, Russia is defined in general easily enough. Spacing is 40, speed 40, frequencies 34.Alghough it is necessary to manage to count the frequencies, because to do it on the spectrum it not so that easy. ;) The number "36" in the name of the signal is the mystery for me. I haven't ever seen 36 frequencies, so I may suppose that 36 frequencies are very seldom used or quantity of frequencies does not play a role in the name of the signal. 
Speed of manipulation in chat-mode makes 10 hertz.  Mazielka 2 tone and it is possible Mazielka 6 tones are Very closely connected with Crowd-36.

OFDM, COFDM: DRM+ (DRM-E)

DRM+ (DRM-E)

Ch - 213, PSK-4, Br - 400 Hz, Sh - 444.4(4) Hz, k = 1/9

Author: SergUA6 

Band Width ~95500 Hz

Baud Rate 400 Hz

n-Ary (PSK/MPSK) PSK-4

Count of Carriers 213

Step between carriers 444.4(4) Hz

ACF      100 ms

RX mode Source I/Q record

The excellent example of DRM+. Thanks to IK1YDE.

Sonograms:

pic.1 General view

pic.2 The main signal's parameters.

Diagrams:

pic.3 The constellation in the channel

pic.4 Detalization

Pictures:

pic.5 ACF of the signal.

DRM+(DRM-E) - DRM format for VHF broadcasting, it is intended to extrude the analogue decisions in this sphere. It posseses range of attractive advantages: the necessary band is about 95-96 kHz on the broadcast channel, the transmission till 4 of independed programs is possible in one channel.


The signal itself is the typical representative of OFDM tecnology. All the parameters are defined in SA easyly enough. The maximum technical speed for PSK-4 and 213 channeles is 170 kbit/sec. In reality, the real speed of data transmission is a bit lower (about 130-150 kbit/sec), at the expencse of usage of part of the channels and symbols as the pilot/service.


As far as i know, the prespective of this standard in Russia are *foggy* enough, this record sent by collegues from Europe.

SA update to versionv 6.2.6.3

SA update to version v 6.2.6.3 

This is the planned SA update.

In this version support of Drag-and-Drop function is added.

The function of detection/determinition of the offset modes of the phase manipulation is introduced in the Phase viewer. 

It is necessary to show certain care, as any automatic system of identification, this function can be mistaken, especially on the signals, which are damaged by various distortions. Nevertheless in some cases, the presence of this automatization is justified. 


Also a number of minor errors found out by users is corrected.

~ Good Luck