error while using comm.QPSKModulator object

I am working on simulation a Tx-Rx system with BPSK and QBPSK. Input is a .wav file of a 3 musical notes for a duration of 6 minutes.

No problem getting it to work for BPSK (using pskmod function).

However, I am struggling with QBPSK using the comm.QPSKModulator object.

The error message I'm getting is not descriptive so it's not helpful. It simply says: "Error in transmitter (line 56) modData = step(hModulator, adjustedIndex);"

I suspect it is related to the coded signal format.

Attached are all files used (program is ran from main.m, comm.QPSKModulator is in transmitter.m file).

Any assistance will be greatly appreciated.

[Geoff Hayes]

Franklin - your attached files didn't come through. Once you choose the file, you have to press the Attach File button.

[Franklin]

Ooops. Good catch, Geoff.

Did not see your comment until today. Trying again. Let me know if they don't come thru again.

Answer 1

[Geoff Hayes]

Franklin - I suspect a problem with the line 56 of transmitter.m

 modData = step(hModulator, adjustedIndex);

is that you are trying to use the step function in the same body of code where there is a global variable declared as step

 global step;

This appears to be a scalar based on how it is initialized (assuming that maxValue, minValue, and quantBits are all scalars) and so is probably creating a conflict between it and the function that you want to call. It is unfortunate that the more of the error message isn't provided as that might give more of a clue (I can't run your code since I don't have the Communications System Toolbox).

I recommend that you rename the global variable step to something that won't conflict with this function, and then try again. As an aside, is there a reason why so many global variables are used? An alternative might be to create a struct with fields matching these global variables, initializing it, and then passing around between the functions.

[Franklin]

Yep, that was it.

Made the QPSK modulator and awgn channel to work. Haven't tested the receiver side yet, but making progress.

Thanks for your help.