Hard real-time communication for mobile ad hoc networks

Abstract

The increasing availability of wireless local area networking, particularly ad hoc networking, has lead to the evolution of new application domains, such as inter-vehicle communication and communication between autonomous mobile robots. Real-time communication is essential to allow applications in these domains to be realised. The characteristics of a mobile ad hoc network, typified by host mobility, unpredictable resource availability and time-varying connectivity, pose challenges for providing hard real-time communication guarantees in this domain. An approach adopted by previous real-time communication models is to adapt the communication time bounds to reflect the dynamics of the network. However, allowing time-bound adaptation implies that only soft real-time communication is available and, critically, that hard real-time communication is not. This thesis describes a new communication model, the space-elastic model, to provide hard realtime communication for applications with guaranteed response-time requirements in wireless networks in general, and ad hoc networks in particular. In addition, a new real-time ad hoc routing protocol, the Space-Elastic Adaptive Routing (SEAR) protocol, is described, which provides the basis of a real-world implementation of the space-elastic model. The contributions of this thesis are two-fold. Firstly, the space-elastic model is proposed to enable hard real-time communication by using specified geographical bounds to scope the area within which timely communication must be guaranteed in a wireless network. Due to network dynamics the space or actual coverage within which timely communication is guaranteed may be adapted over time with timely adaption notification to higher layers when a space adaptation occurs. No change is made to the specified communication time-bounds within the actual coverage. Secondly, a new location-aware real-time ad hoc routing protocol, SEAR, coupling time-bounded route discovery and maintenance with dynamic resource reservation has been designed and implemented. An evaluation of the spaceelastic model, using SEAR, shows that time-bounded communication is possible within the actual coverage and that time-bounded notification can be provided if adaptation occurs.