Edoardo Biagioni

The Application of Remote Sensor Technology To Assist the Recovery of Rare and Endangered Species

We describe a wireless sensor network designed for the long-term study of rare and endangered species of plants. We wish to monitor plants and their environment via high-resolution cameras and temperature, humidity, rainfall, wind, and solar radiation sensors. Our units must be “invisible” (camouflaged), very low energy, and must allow distributed local computation. Data rates are 1 to 100 bytes/second per node, but networks can be large — an early prototype had 60 nodes. Failures are expensive and we must exploit redundancy whenever possible. Nodes are stationary but for energy reasons may decline to participate in transmissions. We have designed two wireless routing protocols that satisfy these constraints. Multipath On-demand Routing (MOR) computes multiple optimal routes to avoid depleting the energy at any given node. Geometric Routing scales to large networks, relying on Geographic Routing when possible and on selected global information otherwise. We have simulated and are implementing both protocols.

Wireless sensor placement for reliable and efficient data collection

Sensors can be paired with radio units and deployed to form a wireless ad-hoc sensor network. Actual deployments must consider the coverage that can be achieved with a given number of sensors: this coverage varies with the range of the radios and the maximum allowable distance between any point in the area and the nearest sensor. Deployments must also preserve connectivity in spite of possible failure or energy depletion in a subset of the units. This paper presents and analyzes a variety of regular deployment topologies, including circular and star deployments as well as deployments in square, triangular, and hexagonal grids.

Ad hoc and sensor networks

The articles in this special section focus on ad hoc and sensor networks. Today we are witnessing an interesting paradigm shift from the traditional client-server computing model, and the Internet of Things (IoT) is driving it. The reality is that the cost of Internet connectivity for wearable and mobile technology is decreasing, and our daily routines depend more on the use of devices that come equipped with more sensors and much more interesting capabilities at much lower costs. As a result, sensors, connected machinery, and many other things are all becoming connected devices. New enterprises take opportunity from this by exploiting data being collected from such connected devices, for new services and products designed to react to data in the most personalized ways. There is a growing trend in companies dominating their respective industries without owning estates or tangible assets, all thanks to data.

Topics in ad hoc and sensor networks

The mobile ad hoc networking field has produced several important theoretical results, but in terms of real world implementation and industrial deployment, such net works are suffering scarce exploitation and low interest from the industry and users. This, as discussed in the arti cles of the April 2007 issue of this Series, was mainly due to a lack of realism in the research approach/objectives that produced tons of scientific papers but only a very lim ited number of real deployments, with limited involvement of real users and no killer application. However, by learning the lessons of mobile ad hoc net working and exploiting the theoretical results in realistic networking scenarios, the scientific community has been able to design a set of novel mobile ad hoc networking paradigms that are currently penetrating the mass market. Mesh networks, where the multihop ad hoc networking paradigm is extended to include some infrastructure ele ments to provide a cost-effective wireless broadband exten sion of the Internet, is currently a reality, and we can find mesh network installations in many cities and campuses. While a more comprehensive analysis of those paradigms derived by Mobile Ad Hoc Networking, this issue presents two papers that survey the research in two of those paradigms: the vehicular networks and the opportunistic networks.

A structured TCP in standard ML.

This paper describes the design of an implementation of the Transmission Control Protocol using an extension of the Standard ML (SML) language. SML supports higher-order functions, modularity, and type-safe module composition. We find that by using SML we can achieve good structure and good performance simultaneously. Good structure includes a modular decomposition of the protocol stack and of the TCP implementation, a control structure that imposes a total ordering on all events and processes them synchronously, and a test structure that allows component testing to catch problems before system integration. Strategies that help achieve good performance include using fast algorithms, using language constructs that make it easy to stage function evaluation, and language implementation features such as compacting garbage collection.

Signatures for a network protocol stack: a systems application of Standard ML

Advanced programming languages such as Standard ML have rarely been used for systems programming tasks such as operating systems and network communications. In order to understand more fully the requirements of systems programming, we have implemented a suite of industry-standard network communication protocols in a completely type-safe extension of Standard ML. While the implementation has only recently become operational, we already observe acceptable communications throughput. We make careful use of the Standard ML modules system, with the core component of the implementation being a signature which is generic to all communications protocols. This generic protocol is then specialized for specific protocols, and these are implemented by functors parameterized by generic protocols. This leads naturally to a layered system structure and also provides an important and useful “mix-and-match” capability in composing protocols into complex networking systems. We have found the advanced features of Standard ML, in particular the modules system, static typing, and higher-order functions, to be extremely useful in building complex communications systems. The type compatibility of the various components of a system is guaranteed by the compiler. Furthermore, we find it significant that most of the information needed to understand the structure and interactions in our code can be obtained from a study of the signatures alone. Perhaps most important is that we have been able to use the expressive power of Standard ML modules to give concrete expression to previously ad hoc system-structuring concepts developed by other researchers in the field of network communications. For language designers and implementors, our experience has also pointed out specific areas for further work that may lead to advanced languages that are useful for systems programming.

A reliability layer for ad-hoc wireless sensor network routing

We have been studying communication in wireless ad-hoc sensor networks. One of the authors has designed the multipath on-demand routing (MOR) protocol (Shu Hui Chen, 2003), which makes use of all possible paths to a given destination. Each node in MOR has, wherever possible, a choice of next hops for a given destination. We have designed and implemented a MOR reliability layer to take advantage of this. The basic strategy is to use a different node on each retransmission, and to keep track of which transmissions are successful. The main benefit is that a packet is likely to be delivered even if a given neighbor is temporarily unavailable, thus improving the delivery ratio or decreasing the number of end-to-end retransmissions. A further benefit is that nonresponsive nodes are removed from the routing table after a number of consecutive failures. In a sensor network transmission may be unreliable for a number of reasons, but particularly when congestion results in collisions. Without our reliability layer, collisions would cause packet loss and route loss. If the transport protocol is reliable, this results in end-to-end retransmission, which requires additional energy. We simulated transmission in congested conditions in different realistic sensor networks and compared MOR to available protocols. In our tests, the reliability layer helped MOR deliver data faster and less energy usage than the other protocols.

A Network Protocol Stack in Standard ML

The FoxNet is an implementation of the standard TCP/IP networking protocol stack using the Standard ML (SML) language. SML is a type-safe programming language with garbage collection, a unique and advanced module system, and machine-independent semantics. The FoxNet is a user-space implementation of TCP/IP that is built in SML by composing modular protocol elements; each element independently implements one of the standard protocols. One specific combination of these elements implements the standard TCP/IP stack. Other combinations are also possible and can be used to easily and conveniently build custom, non-standard networking stacks. This paper describes in detail the final design and implementation of the FoxNet, including many of the details that are crucially affected by the choice of SML as the programming language.

Topics in ad hoc and sensor networks [Series Editorial]

The Series on Ad Hoc and Sensor Networks of IEEE Communications Magazine started an interesting debate on research methodologies and approaches in the April 2007 issue. Theoretical research and simulation studies are fundamental for understanding the behavior of phenomena, and their relevance is even higher in such areas as wireless and mobile networking, where experimentation is not easy to realize. However, there is a need to conduct these studies in a very solid convincing way. In the past issue we discussed the importance of considering realistic scenarios, since otherwise the results may lead to conclusions that will not be confirmed in real experiments. In this issue we continue this discussion by presenting other related aspects, such as the role of information theory and simulation, as well as the introduction of novel approaches such as knowledge exploitation to coordinate mobile and wireless networks.

Algorithms for Communication in Wireless multi-hop ad hoc Networks using Broadcasts in Opportunistic Large Arrays (OLA)

A new physical layer technique in Hong, Y-W abd Scaglione, A., (2003) for broadcasting in multi-hop wireless ad hoc networks makes broadcast a much more efficient building block than traditional flooding broadcast. This broadcasting technique requires that all nodes that receive a message retransmit it at the same time. Because the messages are identical, interference can be constructive rather than destructive, and the multiple transmitters act as an antenna array - an Opportunistic Large Array, or OLA -to transmit the message farther and ultimately with fewer hops than it could have been transmitted by conventional means. This paper presents several networking algorithms for utilizing such physical layer broadcast to solve problems that are common within distributed systems, including wireless ad hoc sensor networks, mesh networks, and mobile ad hoc networks. In such an environment, broadcasting may be more efficient than conventional algorithms and protocols that employ unicast or multicast communications, including routed communications. This paper uses broadcasting in wireless ad-hoc networks to addresses issues and requirements common to different applications of wireless ad hoc networks. Some of these requirements, such as broadcasting, multicasting, polling, geocasting, and synchronization, are straightforward given an efficient broadcasting mechanism. This paper considers some of the specific benefits available for these cases when employing broadcasting using OLAs. Other common requirements can also be satisfied by implementations using this building block. As well as considering the challenge of assigning unique identifiers, these include associative access to the data in the network as well as selecting a unique leader among all the nodes.