Barbara Hughes

Towards real-time middleware for vehicular ad hoc networks

Applications of inter-vehicle and vehicle-to-roadside communication that make use of vehicular ad hoc networks (VANETs) will often require reliable communication that provides guaranteed real-time message propagation. This paper describes an event-based middleware, called RT-STEAM. Unlike other event systems, RT-STEAM does not rely on a centralized event broker or look-up service while still supporting event channels providing hard real-time event delivery. RT-STEAM event filtering can be based on subject, content and/or proximity. To guarantee real-time communication, we exploit proximity-based event propagation to guarantee real-time constraints within the defined proximities only. The proximity within which real-time guarantees are available is adapted to maintain time bounds while allowing changes to membership and topology, typical of VANETs. This Space-Elastic Model of real-time communication is the first to directly address adaptation in the space domain to guarantee real-time constraints.

Real-time coordination of autonomous vehicles

Autonomous vehicles seem to be a promising approach to both reducing traffic congestion and improving road safety. However, for such vehicles to coexist safely, they need to coordinate their behaviour to ensure that they do not collide with each other. This coordination is typically based on (wireless) communication between vehicles and needs to satisfy stringent real-time constraints. However, realtime message delivery cannot be guaranteed in dynamic wireless networks which means that existing coordination models that rely on continuous connectivity cannot be employed. In this paper, we present a novel coordination model for autonomous vehicles that does not require continuous real-time connectivity between participants in order to ensure that system safety constraints are not violated. This coordination model builds on a real-time communication model for wireless networks that provides feedback to entities about the state of communication. The coordination model uses this feedback to ensure that vehicles always satisfy safety constraints, by adapting their behaviour when communication is degraded. We show that this model can be used to coordinate vehicles crossing an unsignalised junction

Building reliable mobile applications with space-elastic adaptation

Mobile applications, for example mobile robots, are playing an increasingly important role in our everyday lives. Since components of these applications share their environment with each other and with humans, they need to coordinate their behavior to respect strong safety constraints. Unfortunately, they typically make use of wireless networks in which real-time communication is highly unreliable, making coordination particularly challenging. We present a real-time communication model for wireless networks that takes into account that communication might not be reliable. It provides feedback to mobile components about the state of communication, so that they can adapt their behavior accordingly. We show how this model can be used to build reliable mobile applications in wireless networks: this involves specifying the safety constraints that need to be respected, and translating them into constraints on the behavior of individual components. To illustrate our approach, we describe an example from the intelligent transportation systems domain

Using group communication to support mobile augmented reality applications

Augmented reality and group communication in wireless ad-hoc networks form relatively, new fields of research. When using group communication ordering and timeliness requirements are important. Moreover when using wireless ad-hoc networks, the possibility of network partition is a serious consideration. In this paper we explore these three issues in the context of using group communication to support mobile augmented reality applications. We describe a policy that enables its to handle partitions and failures, while allowing the members in a partition to make progress, although limited by the applications consistency requirements. We introduce an approach to determining the message ordering requirements needed to maintain a desired level of consistency and timeliness requirements that should be met in order to have the application state correspond to the sequence of events perceived in the real world.

Providing Hard Real-Time Guarantees in Context-Aware Applications: Challenges and Requirements

Context-aware applications rely on the ability to perceive the state of the surrounding environment. In this paper, we address a class of such applications where real-time guarantees are required on top of mobile ad hoc networks. While guaranteed timeliness is a critical requirement, the unpredictability of dynamic wireless networks adversely impacts such guarantees. Therefore, we identify the challenges and the requirements on different architectural levels in order to provide timeliness guarantees. None of the existing systems have succeeded in providing adequate solutions to all of the identified requirements. Therefore, we describe a cross-layer architecture that supports the development of real-time context-aware applications for wireless networks, in particular, ad hoc networks. This cross-layer architecture is based on three main components. (i) Sentient objects - mobile intelligent software agents that extract, interpret and use context information. (ii) Event-based real-time middleware supports communication between sentient objects and provides hard real-time guarantees within adaptable geographic spaces. (iii) A real-time routing and resource reservation protocol attempts to discover and maintain real-time constrained routes within these proximities in a multi-hop ad hoc network

An event model for real-time systems in mobile environments

We describe an event model that has been designed to address the predictability requirements of applications operating in mobile environments based on hierarchically structured WAN-of-CANs networks. The event model supports an event channel concept for modeling the guarantees provided by the underlying heterogeneous communication infrastructure. The networks that comprise such a WAN-of-CANs may provide fundamentally different degrees of quality of service and as a result can be viewed as zones within which certain guarantees can be enforced. Event channels operating in CAN-based subnetworks typically with strong timing behavior may support hard temporal and reliability attributes whereas channels interconnecting these subnetworks using wireless networks support weaker timing attributes.