Oversampling factor parameter for fsk modulation with gaussian shaping filter

Hello,

I have been playing around with fskmod with gaussdesign (e.g., fsk modulation and filtering with a gaussian shaping filter) where both functions requires oversampling factor, i.e., nsamp for fskmod and sps for gaussdesign. I wonder what am I supposed to set if I only need oversampling by 2? What am I supposed to do if I want to set the oversampling in gaussdesign not in fskmod?

JK

Answer 1

[Pooja Kumari]

Dear Jay,

It is my understanding that you wanted to learn about oversampling factor parameters to be chosen to have oversampling by a factor of 2 in FSK modulation and gaussian shaping filter.

If you only want to achieve oversampling by a factor of 2 in “fskmod” function, you can set the ‘nsamp’ parameter to 2. This means that each input symbol will be represented by two samples in the output waveform. You can refer to the below documentation for more information on “fskmod” function:

https://www.mathworks.com/help/comm/ref/fskmod.html

If you want to set the oversampling factor specifically in “gaussdesign” function and not in “fskmod”, you can use the ‘sps’ parameter in “gaussdesign” which determines the oversampling factor for the Gaussian shaping filter.

To achieve the same oversampling factor of 2, you can set the ‘sps’ parameter to 2 in “gaussdesign”. This will result in the shaping filter generating two samples for each input symbol. Additionally, ensure that the ‘nsamp’ parameter in “fskmod” is set to 1 when using “gaussdesign” to control the oversampling factor. You can refer to the documentation below for more information on “gaussdesign” function:

https://www.mathworks.com/help/signal/ref/gaussdesign.html

I hope this helps you in achieving oversampling by a factor of 2.

Regards,

Pooja Kumari

[Jay]

Thanks Pooja for the reply!

What I was trying to do was FSK modulation with Gaussian filtering with overall oversampling factor of 2. As you explained that threre are parameters sps and nsamp in "gaussiandesign" and "fskmod", respectively. Indeed, I tried to enforce 'nsamp' in "fskmod" to be 1 but MATLAB returned an error saying it is supposed to larger than 1 and 2 is default value. Same for sps in "gaussdesign". So I had to set oversamping factor of 2 for nsamp in "fskmod" and another oversampling factor of 2 for sps in "gaussdesign" to make the code works, which makes overall oversampling factor of 4. Am I missing something?

Thank you again for your reply.

[Pooja Kumari]

Hello Jay,

One possible solution is to perform oversampling by a factor of 2 in "fskmod" by setting "nsamp" to 2. Then, you can apply a downsampling operation after the FSK modulation to achieve the desired overall oversampling factor of 2.

You can use a downsampling factor of 2 to reduce the number of samples in the waveform generated by "fskmod" by half. This downsampling operation will effectively achieve the desired overall oversampling factor of 2.

[Jay]

Thanks Pooja for provding additional thought. It helps.