I wonder why in all spectrum estimation techniques, the analysis depend on the Fourier transform? Why not deal with the signals in time domain?
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$\begingroup$ By definition, a spectrum is a view of a signal in the frequency domain. The Fourier transform maps a time-domain signal to its equivalent in the frequency domain. It's a natural tool for many spectrum estimation problems. $\endgroup$ – Jason R Jun 2 '15 at 13:00
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$\begingroup$ Frequency is the characteristic of a source which is producing the signal.So if we record a complex signal which is due to the effect of 3-4 sources viewing it frequency domain allows us to separate the effect and view the signal as superposition of these individual signals. $\endgroup$ – shrey Jun 3 '15 at 6:43
