Cognitive Networks: Towards Self-Aware Networks

6.2. Understanding Cross-Layer Design

6.2.1. The Different Interpretations

Cross-layer design is described in the research literature in different ways ^[], ^[]: as a protocol design methodology that exploits the synergy between the layers; as a joint design and optimization across more than one protocol layer; as a protocol design methodology that relies on, and creates, adaptability across the different layers by sharing information between them; and so on. An interpretation of cross-layer design, usually discussed in the context of multimedia transmissions, is that of a design methodology that leverages joint source and channel coding ^[] which creates coupling between the application and the physical layers. Yet another interpretation of cross-layer design, usually discussed in the context of communications over fading channels, is that of a design methodology that takes into account the channel characteristics at the higher layers, and the stochastic arrival of traffic at the lower layers ^[].

6.2.2. A Definition for Cross-Layer Design

In what follows, we present a definition for cross-layer design by viewing it as a violation of a reference layered architecture. Our definition is concise and yet it encompasses the aforementioned notions about cross-layer design. Our definition also draws a clearer contrast between layered protocol design and cross-layer design, regardless of the layered architecture in question.

As noted earlier a layered architecture, like the seven-layer ...