I have just started studying the techniques of digital modulation. The book i am reading only has mentioned the psd of bpsk, bfsk , qpsk and msk. I would like to know, how the psd is actually calculated and I would also like to know, why the angles used in qpsk are (2m+1)pi/4 why cannot be one with a 89 degree and another with 91 degree instead of 90 degree and 90 degree. By these degree I indicate the angle between to signal vectors.
Either a sine or a cosine has a 0 at multiple of pi/4. So one or the other is zero (say I is 0, Q is the one you want. This allows you to just read the value; the one that isn't zero (Q here) is that value.
If you read the value at (say) 89 or 91 degrees, the one (I) wouldn't be quite 0. And the one you wish to read (Q) isn't quite its full value. This makes it harder to get the right values. And this reading isn't easier.