Parameters used for modulation techniques detection

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Shruti01

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Hello,


Can anyone tell me on what parameters can one detect the modulation techniques used in the system...

Thanx...
 

Shruti01

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I am talking about digital communication system.... On basis of what parameters one can detect the modulation techniques used in digital communication system....


thanx....
 

majoco

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Which digital communication system?
There are many 'systems' - most not involving radio. Or are you wanting to break into the many types of secure government, military and police radio data links. Watch out for the men in dark suits and sunglasses.:)
 

Shruti01

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My received signal contains a set of sample points... How do I detect which modulation technique is being used....For ex- how to detect whether the modulation technique used is BPSK or QPSK..... On basis of what parameters can I detect the modulation technique used....
 

Shruti01

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Is eye pattern useful in determining the modulation technique used............ If the number of eye opening is 1 then it means the modulation technique is BPSK. If the number of eye opening is 3 then it means it is QPSK.... Am I correct......What will be number of eye openings for binary amplitude shift keying (BASK) and binary frequency shift keying (BFSK)....


Thanx...
 

MattSR

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My received signal contains a set of sample points... How do I detect which modulation technique is being used....For ex- how to detect whether the modulation technique used is BPSK or QPSK..... On basis of what parameters can I detect the modulation technique used....
I have a friend that does exactly this. Balint, VK2FUNK presented this at a computer security conference in Melbourne last year:-

Ruxcon 2011: Hacking the wireless world with Software Defined Radio - YouTube

His website is at:- Software Defined Radio | spench.net


Typically you us a variety of tools, including I/Q quadrature plots to determine the modulation type, however the real tricks and funky maths come out when you start trying to determine symbol rates etc. Thats when it gets HARD.

Have a watch of the video - it describes the techniques and thought processes that he uses when reverse engineering an unknown RF data protocol.

Cheers,
Matt
 

MattSR

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Another point - GNUradio is a great way to do that. The inbuilt GNUradio Companion lets you use a GUI to connect up different modulation/demodulation blocks and experiment around with different things until you figure out whats going on with a specific protocol.
 

KA1RBI

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Another point - GNUradio is a great way to do that. The inbuilt GNUradio Companion lets you use a GUI to connect up different modulation/demodulation blocks and experiment around with different things until you figure out whats going on with a specific protocol.
One old simple trick for determining baud rate was to pass the signal through a band-pass filter whose BW is equal to that of the unknown signal. That is then fed into an envelope (AM style) detector. The result is then plotted using an FFT. There will be a peak at the baud rate of the signal (of course this doesn't work for all classes of digitally modulated signals; I've used it on m-PSK though). [It may be interesting to note that the resulting signal is often in the audio range]...

Another possibility for gaining insight on unknown signals is to use a software tool such as
SignalScopePage

Best Regards

Max
 
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