edit psk parameters

[jstarustka]

I am working with a DQPSK signal where the state transition table is computed using the following equation. 

Iout=(Complement(Iin xor Qin))(Iin xor Iout1)+(Iin xor Qin)(Qin xor Qout1)

Qout=(Complement(Iin xor Qin))(Qin xor Qout1)+(Iin xor Qin)(Iin xor Iout1)

Where

Iin and Qin are the current input bits

Iout1 and Qout1 are the previous output bits

Iout and Qout are the current output bits

The phase of the QPSK symbol states relative to the carrier phase should be:

00  0degrees

01  -90 degrees

10  +90 degrees

11  180 degrees

I have the modulation toolkit and was wondering if it is possible to edit one of the VI's to produce this type of signal.  If so which one.

Thanks

Joe

[David S.]

Hi Joe -

Actually, the Modulation Toolkit only has functions to create a PRBS of the message signal you want to transmit.  So it's entirely up to you to create whatever DQPSK message you desire, then input that bit stream to toolkit functions that will package it.

If you want to see an example of this, there's an example program called MT DQPSK (pi over 4) Tranceiver.vi that ships with the latest version of the toolkit.  There's a subVI in it called mod_PSK Transmitter.vi that creates the message signal and packages it with a shaping filter. 

On its block diagram is another subVI called mod_Create Tx Sequence.vi that generates a PRBS message and outputs it in chunks.  This is the function that you'll want to replace with your own.

Message Edited by David S. on 07-11-2007 03:46 PM

Message Edited by David S. on 07-11-2007 03:46 PM

Message Edited by David S. on 07-11-2007 03:47 PM

[jstarustka]

Thanks for the help,  I am planning to send signals to a device so I was planning on using the RFSG.  I found the MT RFSG Generate PSK.vi and then inside the Cont. BB-PSK Gen.vi there are tabs where you can define a bitstream pattern.  I was planning on modifying that so that I create and encode the bitstream using the formulas in my previous post.  Do you see any issues with that?

Thanks

Joe

[David S.]

Hi Joe -

That's the VI that generates the baseband pattern, so it's the one you'll want to modify.  I don't foresee any issues per se, but there will be considerations like waveform resampling and shaping filters to consider.  Be sure to study the example programs and read the literature on the Modulation Toolkit before you start.