The previous chapters primarily address the link-level issues between a transmitter and a receiver. In a multiuser environment, the radio resource must be shared among multiple users. In addition, to support bandwidth-demanding multimedia traffics, a wireless network must be able to serve a diverse set of users in highly dynamic, resource constrained and data intensive environments.
This chapter discusses the multiple access control/medium access control (MAC) related issues in OFDM-based broadband wireless networks. In a large scale wireless system, users' channel characteristics, mutual interference patterns, as well as traffic requirements are largely diverse. Therefore, each radio resource unit in the time-frequency-space dimension is likely to bear high utility value to certain users. Consequently, the total channel capacity or spectral efficiency of the network can be significantly increased through judicious resource allocation in MAC layer. This motivates the design of highly adaptive MAC layer protocols and algorithms that can cope with the channel and traffic dynamics.
There are two basic types of MAC protocols that are commonly used in modern wireless communication systems: contention based and non-contention based MAC protocols.
In a contention based MAC protocol, each terminal transmits in a decentralized way. There is no central controller, e.g., a ...