What is Cross-Layer Algorithms

Real-time systems have undergone an evolution in the last several years in terms of their number and variety of applications, as well as in complexity. A natural result of these advances, coupled with those in sensor techniques and networking, have led to the rise of a new class of applications that fall into the distributed real-time embedded systems category (Loyall, Schantz, Corman, Paunicka, & Fernandez, 2005; Report, 2006). Recent technological advancements in device scaling have been instrumental in enabling the mass production of such devices at reduced costs. As a result, applications with a number of internetworked embedded systems have become prominent. At the same time, there has been a need to move from stand-alone real-time unit into a network of units that collaborate to achieve a real-time functionality. Extensive research has been carried out to achieve real-time guarantees over a set of nodes distributed over wired networks (Siva Ram Murthy & Manimaran, 2001). However, there exist a number of realtime applications in domains, such as industrial processing, military, robotics and tracking, that require the nodes to communicate over the wireless medium where the application dynamics prevent the existence of a wired communication infrastructure. These applications present challenges beyond those of traditional embedded or networked systems, since they involve many heterogeneous nodes and links, shared and constrained resources, and are deployed in dynamic environments where resource contention is dynamic and communication channel is noisy (Report, 2006, Loyall et al., 2005). Hence, resource management in embedded realtime networks requires efficient algorithms and strategies that achieve competing requirements, such as time sensitive energy-efficient reliable message delivery. In what follows, we discuss some applications in this category, and discuss their requirements and the research challenges.