Overview

In a centralized wireless network, a central controller has complete network information, e.g. channel states, traffic properties, and queue statuses. The controller determines the resource allocation for each user and the resources can be a set of time slots, codes, frequency bands, power, etc. The allocation can be orthogonal such that different users use resources that do not conflict with each other, e.g. different time slots. The allocation can also be non-orthogonal. In the latter case, different users may use resources that partially overlap with each other and, therefore, the communications of one user will impact those of others.

Many centralized wireless medium access control (MAC) protocols have been designed for use in infrastructure-based networks, where access points or controllers decide access to the channel or perform some other centralized coordination functions. One typical example is a single-cell cellular network where multiple mobile users are communicating simultaneously to a base station. The base station has the channel knowledge of all users as well as the quality of service (QoS) requirements of them. The base station schedules the network resources for both the downlink and uplink transmissions of all users. If the network uses frequency division multiple access (FDMA), the BS divides the system frequency spectrum into several frequency bands, called channels. These channels are separated far enough such that they do not interfere with each other. The BS then assigns each channel to one user exclusively.