Digital signal processing plays an important role in implementing transceiver functions after a signal has been digitized.
Website with resources for DSP including materials from instructor Rick Lyons.
This applet allows you to experiment with filters. Change filter type, cutoff frequency, and play different sounds through the filter.
A Java applet that let's you experiment with the Fourier series for different wave shapes. You can also listen to the waveforms.
This book by Joe Boccuzzi is the basis of the course Baseband Signal Processing and Wireless Communications.
This is undoubtedly the most accessible book on digital signal processing available to the beginner. Using intuitive explanations and well-chosen examples, this book gives you the tools to develop a fundamental understanding of DSP theory.