Emilio Ancillotti

Review: The role of communication systems in smart grids: Architectures, technical solutions and research challenges

The purpose of this survey is to present a critical overview of smart grid concepts, with a special focus on the role that communication, networking and middleware technologies will have in the transformation of existing electric power systems into smart grids. First of all we elaborate on the key technological, economical and societal drivers for the development of smart grids. By adopting a data-centric perspective we present a conceptual model of communication systems for smart grids, and we identify functional components, technologies, network topologies and communication services that are needed to support smart grid communications. Then, we introduce the fundamental research challenges in this field including communication reliability and timeliness, QoS support, data management services, and autonomic behaviors. Finally, we discuss the main solutions proposed in the literature for each of them, and we identify possible future research directions.

The role of the RPL routing protocol for smart grid communications

Advanced communication/networking technologies should be integrated in next-generation power systems (a.k.a. smart grids) to improve their resilience, efficiency, adaptability, and sustainability. Many believe that the smart grid communication infrastructure will emerge from the interconnection of a large number of small-scale networks organized into a hierarchical architecture covering larger geographic areas. In this article, first we carry out a thorough analysis of the key components of the smart grid communication architecture, discussing the different network topologies and communication technologies that could be employed. Special emphasis is given to the advanced metering infrastructure, which will be used to interconnect the smart meters deployed at customers premises with data aggregators and control centers. The design of scalable, reliable, and efficient networking solutions for AMI systems is an important research problem because these networks are composed of thousands of resource-constrained embedded devices usually interconnected with communication technologies that can provide only low-bandwidth and unreliable links. The IPv6 Routing Protocol for Low Power and Lossy Networks was recently standardized by the IETF to specifically meet the requirements of typical AMI applications. In this article we present a thorough overview of the protocol, and we critically analyze its advantages and potential limits in AMI applications. We also conduct a performance evaluation of RPL using a Contiki-based prototype of the RPL standard and a network emulator. Our results indicate that although average performance may appear reasonable for AMI networks, a few RPL nodes may suffer from severe unreliability issues and experience high packet loss rates due to the selection of suboptimal paths with highly unreliable links.

Reliable Data Delivery With the IETF Routing Protocol for Low-Power and Lossy Networks

The IPv6 routing protocol for low-power and lossy networks (RPL) has been recently standardized by the Internet Engineering Task Force (IETF) routing protocol for low-power and lossy networks (ROLL) working group to support IPv6 routing for resource-constrained devices in industrial, home, and urban environments. However, several studies have shown that RPL may experience (very) low delivery rates, particularly in large-scale deployments. In this paper, we provide an in-depth analysis of the protocol attributes and design choices that generate such unreliability issues. Then, we describe and evaluate a new implementation of the RPL standard for the Contiki operating system (OS) to improve data delivery reliability. The salient feature of our RPL implementation is to adopt a flexible cross-layering design that provides simple routing optimizations, enhanced link estimation capabilities, and efficient management of neighbor tables. In order to verify the effectiveness of our RPL implementation, we use an advanced metering infrastructure (AMI) as a case study. Results obtained using Cooja emulator in two sets of experiments, differentiated by the presence or lack of duty cycling, indicate that our RPL implementation outperforms the one provided in Contiki in terms of average packet delivery rates by up to 200% in networks with 100 nodes.

Experimentation and performance evaluation of rate adaptation algorithms in wireless mesh networks

In this paper we present an experimental study conducted in 802.11-based mesh networks of three existing rate adaptation algorithms. The aim of this study is twofold. On the one hand, we explore the ability of these algorithms to cope with moderate to high medium contention levels. On the other hand, we investigate their performance on medium-distance 802.11 links. Our study indicates that, in congested networks, the network throughput can degrade up to ten times with respect to the best performance if the rate decision process is based solely on frame loss rates, without differentiating between the various causes of losses (i.e., channel errors or collisions). In addition, we have shown that these rate adaptation strategies perform reasonably well when the time correlation between channel errors is at least of the order of the sampling period used to estimate the channel dynamics. We believe that this study can be useful to derive correct guidelines for the design of new optimized rate adaptation algorithms taking into consideration the above factors.

Fast track article: Dynamic address autoconfiguration in hybrid ad hoc networks

The use of ad hoc networking technologies is emerging as a viable and cost-effective solution to extend the range of traditional wireless local area networks (WLANs). In these networks, mobile client traffic reaches the access points through multi-hop wireless paths that are established by using an ad hoc routing protocol. However, several technical challenges have to be faced in order to construct such an extended WLAN. For instance, traditional autoconfiguration protocols commonly used in infrastructure-based WLANs, such as DHCP or Zeroconf, are not directly applicable in multi-hop wireless networks. To address this problem, in this paper we propose extensions to DHCP to enable the dynamic allocation of globally routable IPv4 addresses to mobile stations in hybrid ad hoc networks, which transparently integrate conventional wired technologies with wireless ad hoc networking technologies. Some of the attractive features of our solution are its ability to cope with node mobility, the introduction of negligible protocol overheads, and the use of legacy DHCP servers. We have implemented a prototype of our scheme, and tested its functionalities considering various topology layouts, network loads and mobility conditions. The experimental results show that our solution ensures short address configuration delays and low protocol overheads.

Design and performance evaluation of throughput-aware rate adaptation protocols for IEEE 802.11 wireless networks

Experimental studies have shown that traditional rate adaptation schemes for 802.11 wireless networks suffer from significant throughput degradation in highly congested networks. To address this problem, this paper makes the following two main contributions. First, we design a method to accurately estimate the per-packet transmission times, and we use these measurements to provide a broad classification of the network state and to identify network congestion. Second, we design a new Throughput-Aware Rate Adaptation (TARA) scheme, which uses the congestion estimates to mitigate the negative impact of link-layer collisions on the operations of rate adaptation, without requiring changes in the 802.11 MAC specification. Another key feature of our solution is to minimize probing overheads and limit unnecessary rate decreases by predicting the throughput gain that could be brought about by a change in the transmission rate. Through experiments conducted across a variety of network scenarios and traffic patterns, we show that TARA achieves significantly higher throughput than the other rate adaptation algorithms implemented in the legacy Madwifi driver.

Load-aware routing in mesh networks: Models, algorithms and experimentation

In this paper we consider wireless mesh networks (WMNs) used to share the Internet connectivity of sparsely deployed fixed lines with heterogeneous capacity, ranging from ISP-owned high-speed links to subscriber-owned low-speed connections. If traffic is routed in the mesh without considering the load distribution and the bandwidth of Internet connections, some gateways may rapidly get overloaded because they are selected by too many mesh nodes. This may cause a significant reduction of the overall network capacity. To address this issue, in this paper we first develop a queuing network model that predicts the residual capacity of network paths, and identifies network bottlenecks. By taking advantage of this model, we design a novel Load-Aware Route Selection algorithm, named LARS, which improves the network capacity by allocating network paths to upstream Internet flows so as to ensure a more balanced utilization of wireless network resources and gateways Internet connections. Using simulations and a prototype implementation, we show that the LARS scheme significantly outperforms the shortest-path first routing protocol using a contention-aware routing metric, providing up to 240% throughput improvement in some network scenarios.

Load-balanced routing and gateway selection in wireless mesh networks: Design, implementation and experimentation

Traffic routing and gateway selection for Internet flows play a crucial role in determining the performance of WMNs. Optimal routing strategies have been derived under the assumption that the traffic demands are static and known a priori, or that can be accurately predicted. However, the effectiveness of most of the existing optimization-based routing solutions is still to be demonstrated in real-world deployments. In this paper we present a practical and robust framework for load-balanced routing and gateway selection in WMNs under variable traffic loads, which relies only on real-time measurements of network statistics. Then, we design, implement and evaluate two simple adaptive strategies to automatically select network paths and gateways for flows that dynamically arrive and depart, with the goal of achieving a high network utilization and improved load balancing. We have developed a full-fledged implementation of the proposed mechanisms as an extension of the OLSR protocol, and conducted an experimental study in a trial outdoor mesh network using video streaming traffic. Collected measurements show that our scheme can significantly increase the number of video sessions that can be supported with acceptable quality compared to traditional shortest path routing.

TPA: a transport protocol for ad hoc networks

Several previous works have shown that TCP exhibits poor performance in mobile ad hoc networks (MANETs). The ultimate reason for this is that MANETs behave in a significantly different way from traditional wired networks, like the Internet, for which TCP was originally designed. In this paper we propose a novel transport protocol - named TPA - specifically tailored to the characteristics of the MANET environment. It is based on a completely new congestion control mechanism, and designed in such a way to minimize the number of useless transmissions and, hence, power consumption. Furthermore, it is able to manage efficiently route changes and route failures. We evaluated the TPA protocol in a static scenario where TCP exhibits good performance. Simulation results show that, even in such a scenario, TPA significantly outperforms TCP.

Trickle-L 2 : Lightweight link quality estimation through Trickle in RPL networks

Lightweight link quality estimation is crucial in wireless sensor networks. Indeed, devices with limited capabilities shall trade off between consuming their resources to maintain a precise view of the neighbours link quality and to build routes almost blindly. For instance, the Routing Protocol for Low-Power and Lossy Networks (RPL), which has been recently standardised by the IETF to enable IPv6-based sensor networks, only estimates the quality of the links used to deliver data packets. However, this solution has been demonstrated to cause periods of routing instability and reduced packet delivery rates since it estimates only the quality of utilised links. To address this issue in this work we propose a lightweight link estimation procedure that exploits Trickle-based topology maintenance techniques to simultaneously estimate link qualities and propagate routing information. Our proposed scheme has been integrated in the Contikis RPL prototype implementation. Simulation results demonstrate that our proposal is capable of measuring the quality of the links to neighbours with small overhead, which results into better routing decisions and improved packet delivery rates.