Exploiting space/time trade-offs in real-time mobile ad hoc networks

The unpredictability of mobile ad hoc networks (MANETs) characterised by dynamic membership, host mobility and time-varying connectivity, poses significant challenges to achieving real-time communication guarantees. In this paper we describe both a new communication model, the space-elastic model, that provides timely communication in a desired geographical area and a new real-time ad hoc routing protocol, the space-elastic adaptive routing (SEAR) protocol, that supports the space-elastic model. In a MANET, timeliness guarantees may not always be achievable within the complete desired network topology. The space-elastic model makes use of a trade-off between time and space to provide timely communication in an adaptable geographical area. In addition, the model guarantees timely notification of adaptations to this area to applications, which may then be used by them as the basis for behavioural changes. We have experimentally validated the model's guarantees of both timely message transmission and adaptation notification in the real world. Our results show that both low-jitter message transmission (e.g., worst case jitter of only 163 μs over three hops regardless of receiver mobility) and notification of adaptations within known time bounds are achieved, thereby demonstrating the feasibility of the model.