Standard Signals or Basic Signals

The standard signals or basic signals are generated in Labs for analyzing the system response.
1. Impulse Signals.
2. Step Signals.
3. Ramp Signals
4. Parabolic Signals
5. Rectangular (Gate) Signals.
6. Triangular Signals
7. Signum Signals
8. Sinc Signals
9. Sinusoidal Signals
10. Exponential Signals

Continuous Time and Discrete Time signals

Signal specified for every value of time 't' is called continuous time signal and is denoted by x(t)

Signal represented for discrete value of time is discrete time signals and is denoted by x[n]

Signals

1. Signal is a physical phenomenon that carries information
2. A function of one or more independent variables which contains some information is called a signal
3. A signal is formally defined as a function of one or more variables that conveys information on the nature of a physical phenomenon

NPTEL Lecture series

This link contains useful lecture series.
http://nptel.iitm.ac.in/courses.php