Wireless communications fundamentals

Communication stack For convenience in design, the operations of radios are often broken into a number of functional layers. The standard version of this stack is referred to as the open systems interconnection (OSI) model [291], as seen in Figure 4.1. The model has two groups of layers: host and media. The host layers are the application, presentation, session, and transport layers. The media layers are the network, data-link, and physical layers. In many radio systems, some of these layers are trivial or the division between the layers may be blurred. The OSI stack is commonly interpreted in terms of wired networks such as the internet. Depending upon the details of an implementation, various tasks may occupy different layers. Nonetheless, the OSI layered architecture is useful as a common reference for discussing radios. In this text, the media layers are of principal importance. The network layer indicates how data are routed from an information source to a sink node, as seen in Figure 4.2. In the case of a network with two nodes, this routing is trivial. In the case of an ad hoc wireless network, the routing may be both complicated and time varying. The network layer may break a data sequence at the source node into smaller blocks and then reassemble the data sequence at the sink node. It also may provide notification of errors to the transport layer.