Books like An introduction to signal and system analysis by K. Gopal Gopalan

An essential reference on discrete‑time signal processing, covering theory, filtering, sampling, and Fourier analysis for readers with basic knowledge of signals and systems.

Signals and Systems by Alan V. Oppenheim delivers a concise treatment of signal theory and system analysis essential for electrical engineering and telecommunications.

With the presentation at an introductory level, the third edition of the book (2007 copyright) contains a comprehensive treatment of continuous-time and discrete-time signals and systems, with demos on the textbook website (http://users.ece.gatech.edu/~bonnie/book3), data downloaded from the Web, and illustrations of numerous MATLAB commands for the solution of a wide range of problems arising in engineering and in other fields such as financial data analysis. The book contains a large collection of examples and problems, and practical applications that use actual data dowloaded from the Web. It is shown how data can be downloaded and then imported into MATLAB for analysis by techniques covered in the text. Applications include data analysis in the presense of noise, with the focus on filtering noisy signals and the use of the discrete Fourier transform (DFT) to extract the dominant cyclic components of a signal (time series) from noisy measurements of the signal.

An introductory text that explains the fundamentals of signal processing and linear system analysis, covering concepts such as system stability, frequency response, filtering, and mathematical modelling, aimed at engineers and students.

Signals and Systems is a comprehensive textbook designed for undergraduate students of engineering for a course on signals and systems. Each topic is explained lucidly by introducing the concepts first through abstract mathematical reasoning and illustrations, and then through solved examples- The book provides a simultaneous coverage of continuous-time and discrete-time signals and systems. Beginning with classifying signals, the book sequentially covers important topics such as convolution and correlation of signals, continuous-time Fourier series, discrete-time Fourier series, continuous-time Fourier transform, sampling. Hilbert transform, Laplace transform, and z-transform. A chapter on MATLAB programs presenting the applicability of the software to problems of signals and systems has also been included at the end of the book --Book Jacket.