The road ahead for cross-layer design

Of late, there has been an avalanche of cross-layer design proposals for wireless networks. A number of researchers have looked at specific aspects of the network performance and, by approaching cross-layer design as per their interpretation of what it implies, presented several cross-layer design proposals involving different layers of the protocol stack. There have also been works relating to the implementation of cross-layer interactions. It is high time that these various individual efforts be put into perspective and a more holistic view be taken. This paper is a step in that direction. In this paper, we take stock of the existing work in the area of cross-layer design. We do so by suggesting a definition for cross-layer design, by creating a taxonomy of the existing cross-layer design proposals, and by categorizing the initial proposals on how cross-layer interactions can be implemented. We then extract the key insights from the current literature regarding which layers need to be coupled and in what ways. Finally, we highlight some open challenges and new opportunities for cross-layer design that designers can start addressing as they move forward.