Finding Autocorrelation function with xcorr

I need to find autocorrelation function of a signal. I use xcorr() function. The signal is given as signal.png

I need to use "unbiased" version, specifically xcorr(signal, 'unbiased'). However, when I use this the autocorrelation I observe exhibits an increasing behavior. My result is attached as xcorr-unbiased.png

I know autocorrelation function must be maximum at center. I could not understand why this is happening. Can somebody explain this please?

If I use xcorr(signal, 'coeff') I observe a triangular shape, which I expect. However, my professor says this is not the one I need.

[Image Analyst]

It would be best if you attached the signal as an m-file or something so we have it to experiment with. I don't feel like typing in all those elements by hand.

[Utku]

Thanks for your quick respond. I attached the signal.