MSK constellation

[mstaylor97]

The modulation toolbox examples for MSK (Mod-Demod) and any MSK constellation plots I've seen show more distinct symbols than I expect from MSK.  Or maybe they'd be better described as sub-symbols.  MSK should have 4 phase locations around the circle, while the example shows 4 "areas", with each area having 2 distinct states associated, each just slightly rotated around the circle from the other but with the same vector magnitude.  Even when I adjust the the Eb/N0 to allow the highest signal quality (in case the 2nd sub-symbol of the area was caused by phase skew due to noise)... the sub-symbol remains.  Does anyone know the cause of this phenomenon?  I can't attach a screen grab due to internal networking policies.

Here's a text translation (hope the spacing holds up after post):

Expected Constellation:

        |

  x     |     x

        |    

 ---------------

        |

  x     |     x

        |

Observed Constellation:

        |

  x     |     x

 x      |      x   

        |

-----------------

        |

 x      |      x

  x     |     x

        |

[JÞB]

If you look into "mod_Create Continuous MSK.vi" you'll see this:

See That "TRUE" constant?

That beast causes a reset of an IIR filter down deep in the guts of the TK where someone anticipated using the TK in a continuous loop where the impulse on the filter caused by a reset to rho = 0 (where the ideal initial assumpotion would be rho=1) would stabilize before you would ever see its effects.  Wrap the sub-vi with a for loop and toss out the first iteration data like so:

Its not really "Elegant" but it lets the darned filter stabilize

[JÞB]

Dup post

[mstaylor97]

thanks for the quick response. 

So I took a look through the VI heirarchy of the "MT MSK Mod-Demod.vi" that I was working with and didn't see a call to the "mod_Create Continuous MSK.vi" you referenced.  However, just in case I might have missed it, I did locate the vi you referenced and made the prescribed change.  I then re-opened "MT MSK Mod-Demod.vi" and it still does the same thing.

Taking a look at what you did, it appears the same thing is sort of already handled in the "MT MSK Mod-Demod.vi" at the top level call to "MT Modulate MSK.vi".    The "MT MSK Mod-Demod.vi" front panel has a T/F reset switch (which I have set to false).  On the block diagram, the FP-T/F switch is OR'd with a First Call function, all inside a while loop that is only stopped by an error or the FP-stop button.  The output of the OR gate feeds all the reset inputs to each of the various VI's inside "MT MSK Mod-Demod.vi"  (ie generate filter coefficients, MSK system parameters, etc).  So it appears on the first iteration everything will get a reset, and all subsequent iterations will have reset = FALSE.  Of course this is how I interpreted the change you referenced, so if that's not what was intended please advise.

Playing around with it some more, I did notice the symbol filtering options on the FP changed the number of sub-symbols and their spacing, but none of the filter choices (including "none") made the sub-symbols combine to a single symbol. 

[mstaylor97]

BTW, I'm working on LabVIEW 2012 - SP1, MT 4.3.3

[JÞB]

Thanks for pointing me to the correct example. 

Phase Increments In is an array of 0.100 values.  0.100 cannot be exactly represented as a DBL in IEEE 754
  this may be the cause of what you see here:

The example has a few other problems that the MTK team should address.

[HARSHsmit]

Hello

I am trying to make program for 8 PSK but not able to make it. Can you please help me with the program for 8 PSK

Harsh

[Case_in_Point]

Hi Harsh,

This thread you replied to is several years old and also dealing with a specific example for MSK modulation, as opposed to PSK modulation. If you need some help with PSK, there are both generation and acquisition examples for PSK that have 8-PSK as an option included with the Modulation Toolkit. They're titled MT niRFSA PSK Demod.vi and MT RFSG Generate PSK.vi.

If you have more questions about using the examples, I'd suggest making a new thread instead of replying on this several year old one. That'll make it easier for people to actually see your post and know it's dealing with PSK.

Regards,

Cason

NI AE, CLD

[Sravani27]

Can u pls send me that vi i.e., vi for gmsk constellation, modulation and demodulation. Please

[Aht22]

In MT MSK Transceiver example, the the transmitted bits are 1000 and received bit are 989,the 11 bits are missing the the example show BER of 0.000,whats the issue behind this how to recover complete bits message.the block diagram and front panel pictures are attached.

thanks in advance