Wireless Medium Access Control Protocols General Network Concepts Duplexing Choices Network Architecture Slotted Systems Wireless Mac Issues

he ability to communicate with anyone on the planet from anywhere on the planet has been mankind’s dream for a long time. Wireless is the only medium that can enable such untethered communication. With the recent advances in VLSI and wireless technologies, it is now possible to build high-speed wireless systems that are cheap as well as easy to install and operate. However, the wireless medium is a broadcast medium, and therefore multiple devices can access the medium at the same time. Multiple simultaneous transmissions can result in garbled data, making communication impossible. A medium access control (MAC) protocol moderates access to the shared medium by defining rules that allow these devices to communicate with each other in an orderly and efficient manner. MAC protocols therefore play a crucial role in enabling this paradigm by ensuring efficient and fair sharing of the scare wireless bandwidth. Wireless MAC protocols have been studied extensively since the 1970s. The initial protocols were developed for data and satellite communications. We are now witnessing a convergence of the telephone, cable and data networks into a single unified network that supports multimedia and real-time applications like voice and video in addition to data. The multimedia applications require delay and jitter guarantees from the network. This demand of the network is known as the Quality of Service (QoS) guarantee. These requirements have led to novel and complex MAC protocols that can support multimedia traffic. This article surveys the various MAC protocols that have been proposed in the literature and compares them based on architecture (MAC co-ordination, duplexing), performance (throughput, delay, stability, contention resolution algorithms and fairness) and multimedia support (scheduling, access priorities). We confine our study to systems that span relatively small areas. The article is organized as follows. First we contrast different wireless network architectures. We then bring out the issues unique to wireless MAC protocols. The performance metrics used to compare different MAC protocols are discussed later. We then present a classification of the protocols. We will present the different classes of proposed MAC protocols and compare the pros and cons of the proposed protocols.