books of digital communication
If you are new to digital communications, contrary to many people's opinion, Proakis is not a good book for the beginners. Don't get me wrong. Proakis is an excellent reference book and it always sits by my desk where I can easily reach.
If you are new to digital communications, perhaps, Sklar is perhaps more friendly and the author writes the text in tutorial fashion. However, many detailed derivations are (intentionally) missing in Skalar's book.
Digital communication is quite a difficult subject to study. Many people spend years and still not entering the door. I would recommend following books & chapters if you want to become a serious student.
Proakis: Chapters on bandlimited communication and equalization, also chapter on communication over fading channel is very good.
Wozencraft and Jacobs: Chapters 4 & 5 worths the price of the book.
Van Tree: Detection & estimation, vol. 1
Verdu: Multiuser detection
Tse: Wireless communication theory,
Stuber: good and practical book on mobile communications.
Lin & Constello: error control coding.
There are other good digital communications books. Above list is an essential.