Often, you want to lowpass filter your speech waveform before you attempt to extract the fundamental frequency.
Have you seen these two examples in the Signal Processing Toolbox documentation:
As far your questions:
"If my speech file's fundamental frequency is about 200 Hz, then it's fundamental period is 1/200 sec?
And the file's sampling rate is 44100 Hz, so I need to set the frame larger then 1/200*2*44100=441?"
A 200 Hz oscillation sampled at 44.1 kHz has a period of 220.5 samples.
dt = 1/44100;
T = 1/200;
N = T/dt
So 2 periods would be 441 samples as you state. However, in my experience you need more than 2 periods to make accurate estimates, so I would consider increasing that length if you can. 441 samples is only 0.01 seconds, or 10 milliseconds. You should be able to find vowel sounds in the speech signal longer than that in duration.
