Besser Associates offers training courses on Digital Signal Processing. These courses develop the student's fundamental understanding of DSP theory. The practical aspects of signal processing techniques are stressed allowing DSP professionals to make their processing algorithms more efficient.
Charan Langton has a unique gift for creating tutorials on complex topics that are easy to read and understand. (She has also been known to attend a Besser Associates course from time to time!) She lists recommended books on her Complex to Real website.
Instructor Rick Lyons posted his list of free DSP books that are available for downloading in electronic format. The list is posted as an entry on his blog at DSPRelated.com.
Over forty books are listed and categorized by application.
This site is full of well-written tutorials on wireless communications and DSP topics.
Communications is not an easy science. The math is heavy, and intuition is slow to develop. To complicate things further, the field does not stay put. New concepts are always coming to the fore.
This website offers tutorials I have written on various topics in analog and digital communications that will help you cut through this complexity. I keep adding to this collection, albeit very slowly.