Phasor and Carrier Components of Sinusoids
If we restrict in Eq.(4.10) to have unit modulus, then and we obtain a discrete-time complex sinusoid.
where we have defined
PhasorIt is common terminology to call the complex sinusoid's phasor, and its carrier wave.
For a real sinusoid,
When working with complex sinusoids, as in Eq.(4.11), the phasor representation of a sinusoid can be thought of as simply the complex amplitude of the sinusoid. I.e., it is the complex constant that multiplies the carrier term .
Why Phasors are Important
Linear, time-invariant (LTI) systems can be said to perform only four operations on a signal: copying, scaling, delaying, and adding. As a result, each output is always a linear combination of delayed copies of the input signal(s). (A linear combination is simply a weighted sum, as discussed in §5.6.) In any linear combination of delayed copies of a complex sinusoid
The operation of the LTI system on a complex sinusoid is thus reduced to a calculation involving only phasors, which are simply complex numbers.
Since every signal can be expressed as a linear combination of complex sinusoids, this analysis can be applied to any signal by expanding the signal into its weighted sum of complex sinusoids (i.e., by expressing it as an inverse Fourier transform).
Importance of Generalized Complex Sinusoids
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