The convolution sum for discrete-time linear time-invariant (LTI) systems is given by the equation:
\[
y[n] = \sum_{k=-\infty}^{\infty} x[k] \cdot h[n - k]
\]
where:
- \( y[n] \) is the output signal,
- \( x[k] \) is the input signal,
- \( h[n - k] \) is the impulse response of the system,
- \( n \) and \( k \) are integer indices representing time steps.
In simpler terms, the convolution sum expresses how the output \( y[n] \) of an LTI system depends on the input signal \( x \) and the system's impulse response \( h \). It’s a fundamental concept for analyzing the behavior of LTI systems in the time domain.