Nicos Gollan

Energy-Efficent TDMA Design Under Real-Time Constraints in Wireless Sensor Networks

Many wireless sensor networks (WSNs) are used to collect and aggregate data from potentially hostile environments. Catering to this, early application scenarios did not put tight constraints on performance properties like delay, but rather focused on ruggedness and energy conservation. Yet, there is a growing number of sceanarios like e.g. production monitoring, intrusion detection, or health care systems which depend on the sensor network to provide performance guarantees in order to be able to act upon the phenomena being sensed in a timely fashion. Nevertheless, these applications still face the traditional issue of energy-efficiency. In this paper, we present means to find energy-efficient medium assignments in time-slotted multi-hop networks that satisfy given real-time constraints. Specifically, we present a way to find the optimal length of time slots and periods in TDMA schemes. We also present a software to compute those values for typical sink-tree WSNs.

Pay bursts only once holds for (some) non-FIFO systems

Non-FIFO processing of flows by network nodes is not a rare phenomenon. Unfortunately, the state-of-the-art analytical tool for the computation of performance bounds in packet-switched networks, network calculus, cannot deal well with non-FIFO systems. The problem lies in its conventional service curve definitions. Either the definition is too strict to allow for a concatenation and consequent beneficial end-to-end analysis, or it is too loose and results in infinite delay bounds. Hence, in this paper, we propose a new service curve definition and demonstrate its strength with respect to achieving both finite delay bounds and a concatenation of systems resulting in a favorable end-to-end delay analysis. In particular, we show that the celebrated pay bursts only once phenomenon is retained even without any assumptions on the processing order of packets. This seems to contradict previous work [15]; the reasons for this are discussed.

Searching for tight performance bounds in feed-forward networks

Computing tight performance bounds in feed-forward networks under general assumptions about arrival and server models has turned out to be a challenging problem. Recently it was even shown to be NP-hard [1]. We now address this problem in a heuristic fashion, building on a procedure for computing provably tight bounds under simple traffic and server models. We use a decomposition of a complex problem with more general traffic and server models into a set of simpler problems with simple traffic and server models. This set of problems can become prohibitively large, and we therefore resort to heuristic methods such as Monte Carlo. This shows interesting tradeoffs between performance bound quality and computational effort.

Firewalling wireless sensor networks: Security by wireless

Networked sensors and actuators for purposes from production monitoring and control to home automation are in increasing demand. Until recently, the main focus laid on wired systems, although their deployment requires careful planning and expensive infrastructure that may be difficult to install or modify. Hence, solutions based on wireless sensor networks (WSNs) are gaining popularity to reduce cost and simplify installation. Clearly, one of the key issues rising from the switch to wireless communication lies in security; while an air gap is among the most effective security measures in wired networks, wireless communication is not as easy to isolate from attack. In this paper, we propose a system leveraging the peculiarities of the wireless medium, such as the broadcast nature of wireless communication and the unpredictability of indoor signal propagation to achieve effective protection against attacks based on the injection of fake data. Using a real-world WSN deployment and a realistic implementation of an attacker, we analyze this protection scheme and demonstrate that neither position change, transmission power manipulation, nor complete knowledge of wireless parameters can help an attacker to successfully attack the network. As a result, this work demonstrates how the chaotic nature of radio communication, which is often considered a disadvantage in regard to security objectives, can be used to enhance protection and support implementation of lightweight security mechanisms.

Dimensioning of Time-Critical WSNs -- Theory, Implementation and Evaluation

It is difficult to design and operate a Wireless Sensor Network (WSN) that ensures timely data delivery. Hence, few time-critical WSNs are nowadays in operation despite numerous application scenarios that would benefit from such a system. This paper presents a novel dimensioning framework that can be used to efficiently construct WSNs for time-critical applications. The framework employs the Sensor Network Calculus (SNC) as an analytical method for network dimensioning. A medium access control (MAC) protocol called SNC-MAC is used to ensure that this dimensioning process is reflected accurately in a subsequent deployment. The proposed framework is evaluated using both simulations and measurements in an experimental WSN deployment. The evaluation shows that observed message transfer delays in the deployment never exceed delay bounds determined during network dimensioning. Therefore, the framework can be used to implement WSNs requiring transmission delay guarantees.

Chaotic Communication Improves Authentication: Protecting WSNs Against Injection Attacks

In this paper, we propose a system leveraging peculiarities of the wireless medium, such as the broadcast nature of wireless communication and the unpredictability of indoor signal propagation to achieve effective protection against attacks based on the injection of fake data. Using a real-world WSN deployment and a realistic implementation of an attacker, we analyze this protection scheme and demonstrate that neither position change, transmission power manipulation, nor complete knowledge of wireless parameters can help an attacker to successfully attack the network. As a result, this work demonstrates how the chaotic nature of radio communication, which is often considered a disadvantage in regard to security objectives, can be exploited to enhance protection and support implementation of lightweight security mechanisms. Copyright

A New Service Curve Model to Deal with Non-FIFO Systems

In this paper, delay bounds in data flow systems with non-FIFO service disciplines are explored. It is shown that conventional network calculus definitions of a service curve are not satisfying under the assumption of non-FIFO service. Either the definition is too strict to allow for a concatenation and consequent beneficial end-to-end analysis, or it is too loose and thus results in infinite delay bounds. Hence, a new definition is proposed and demonstrated to achieve both finite delay bounds and a concatenation of systems resulting in a favourable end-to-end analysis. In particular, we show that the celebrated pay bursts only once phenomenon is retained under non-FIFO service.