Saturday, October 6, 2018

Is there a way to obtain the impulse response of a discrete system by just knowing it's response to the discrete unit step function?


In continuous time it was possible;



u(t)systemy(t)δ(t)=du(t)dtsystemdy(t)dt=h(t)


Does the same apply for discrete time system i.e.
δ[t]=du[t]dtwhere:{δ[t]is the discrete time deltau[t]is the discrete time unit step function


Is there a way to obtain the impulse response of a discrete system by just knowing the response of the discrete unit step?



Answer



A simpler version of Phonon's answer is as follows.


Suppose that y denotes the response of the system to the unit step function. Then, as discussed in this answer, in general, y is the sum of scaled and time-delayed copies of the impulse response, and in this particular case, no scaling is required; only time delays. Thus, y[0]=h[0]y[1]=h[1]+h[0]y[2]=h[2]+h[1]+h[0]y[3]=h[3]+h[2]+h[1]+h[0] = 

where each column on the right is a (unscaled and) time-delayed impulse response. Thus, we easily get that h[0]=y[0]h[1]=y[1]y[0]h[2]=y[2]y[1] = h[n] =y[n]y[n1] = 
with nary a mention of filters, inverses, convolutions, integration, operators and the like, just simple consequences of the definition of linear time-invariant system.


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