|Subject:||Re: [Discuss-gnuradio] CPM timing recovery|
|Date:||Wed, 6 Jun 2007 19:43:56 -0400|
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Nothing that modulates data has constant envelope. Plot the amplitude of
a BPSK or GMSK signal (after transmission, not simulation) sometime.
Achilleas Anastasopoulos wrote:
> this is not correct.
> The CPM signal is by definition constant envelope.
> It is defined as
> s(t)=exp(j phi(t))
> phi(t)= 2 pi int_0^t f(t') dt'
> f(t)= h sum_k a_k p(t-kT).
> Selecting the approprate pulse shape p(t) shapes the spectrum of CPM,
> but regardless of the selection it has continuous phase
> (not abrupt transitions) as the name suggests ;-) and constant envelope.
> Thus the method you suggested (looking at the envelope variations)
> will not work.
> Since the signal will not really have infinite bandwidth (instantaneous
> transitions from one state to the next), the envelope will not be of
> constant modulus. The signal will be amplitude modulated with a
> component due to the data transitions. Looking at the modulus or
> modulus squared will reveal a line in the fft due to this amplitude
> Discuss-gnuradio mailing list
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