This book constitutes the refereed proceedings of the 4th International Workshop on Multiple Access Communications, MACOM 2011, held in Trento, Italy, in September 2011. The 21 full papers presented were carefully reviewed and selected from more than 40 submissions. They are divided in topical sections on cognitive radio; MAC protocols; communications theory; special session on MAC protocols for WSNs; system analysis and scheduling; and queuing systems.
