Collision Avoidance, Contention Control and Power Saving in IEEE 802.11 Wireless LANs

In recent years the proliferation of portable and laptop computers required LAN technology to support wireless connectivity. Mobile and wireless solutions for communication have been designed to allowmobile users to access information anywhere and at anytime. A variety of networking solutions, services, protocols, standards, technologies, and new applications have been proposed to meet the wireless Internet goals. One of the most successful technologies in recent years is based on the IEEE 802.11 Standard. The IEEE 802.11 Standard defines the Physical, the medium access control (MAC), and link layer control (LLC) sub-layers of the wireless technology that is widely deployed in today’s wireless LANs. The aim of this chapter is to illustrate the evolution in the design and the main issues originating and characterizing the protocols as the basis of the distributed, random-access implementation of the IEEE 802.11 DCF MAC protocol. In general, it is interesting to determine the motivations for a consistent redesign work and the leading role of protocols in the resolution of many peculiar issues for the wireless scenario. Basically, this chapter will introduce and analyze the problems considered in the protocol design that are determined by the wireless scenarios and, more specifically, the evolution of protocols that inherited most of the design concepts from their wired counterpart. The chapter describes the new protocol-adaptation solutions proposed to control new critical system factors and limitations such as time- and space-contention under distributed control, channel bandwidth limitation, host mobility and variable hosts density, battery energy limitation, and power control.