Albert F. Harris

Encounter: based routing in DTNs

Current work in routing protocols for delay and disruption tolerant networks leverage epidemic-style algorithms that trade off injecting many copies of messages into the network for increased probability of message delivery. However, such techniques can cause a large amount of contention in the network, increase overall delays, and drain each mobile node’s limited battery supply. We present a new DTN routing algorithm, called Encounter-Based Routing (EBR), which maximizes delivery ratios while minimizing overhead and delay. Furthermore, we present a means of securing EBR against black hole denialof-service attacks. EBR achieves up to a 40% improvement in message delivery over the current state-of-the-art, as well as achieving up to a 145% increase in goodput. Also, we further show how EBR outperforms other protocols by introduce three new composite metrics that better characterize DTN routing performance.

Energy-Efficient Routing Schemes for Underwater Acoustic Networks

Interest in underwater acoustic networks has grown rapidly with the desire to monitor the large portion of the world covered by oceans. Fundamental differences between underwater acoustic propagation and terrestrial radio propagation may call for new criteria for the design of networking protocols. In this paper, we focus on some of these fundamental differences, including attenuation and noise, propagation delays, and the dependence of usable bandwidth and transmit power on distance (which has not been extensively considered before in protocol design studies). Furthermore, the relationship between the energy consumptions of acoustic modems in various modes (i.e., transmit, receive, and idle) is different than that of their terrestrial radio counterparts, which also impacts the design of energy-efficient protocols. The main contribution of this work is an in-depth analysis of the impacts of these unique relationships. We present insights that are useful in guiding both protocol design and network deployment. We design a class of energy-efficient routing protocols for underwater sensor networks based on the insights gained in our analysis. These protocols are tested in a number of relevant network scenarios, and shown to significantly outperform other commonly used routing strategies and to provide near optimal total path energy consumption. Finally, we implement in ns2 a detailed model of the underwater acoustic channel, and study the performance of routing choices when used with a simple MAC protocol and a realistic PHY model, with special regard to such issues as interference and medium access.

SYNAPSE: A Network Reprogramming Protocol for Wireless Sensor Networks Using Fountain Codes

Wireless reprogramming is a key functionality in wireless sensor networks (WSNs). In fact, the requirements for the network may change in time, or new parameters might have to be loaded to change the behavior of a given protocol. In large scale WSNs it makes economical as well as practical sense to upload the code with the needed functionalities without human intervention, i.e., by means of efficient over the air reprogramming. This poses several challenges as wireless links are affected by errors, data dissemination has to be 100% reliable, and data transmission and recovery schemes are often called to work with a large number of receivers. State-of-the-art protocols, such as Deluge, implement error recovery through the adaptation of standard automatic repeat request (ARQ) techniques. These, however, do not scale well in the presence of channel errors and multiple receivers. In this paper, we present an original reprogramming system for WSNs called SYNAPSE, which we designed to improve the efficiency of the error recovery phase. SYNAPSE features a hybrid ARQ (HARQ) solution where data are encoded prior to transmission and incremental redundancy is used to recover from losses, thus considerably reducing the transmission overhead. For the coding, digital fountain codes were selected as they are rateless and allow for lightweight implementations. In this paper, we design special fountain codes and use them at the heart of SYNAPSE to provide high performance while meeting the requirements of WSNs. Moreover, we present our implementation of SYNAPSE for the Tmote Sky sensor platform and show experimental results, where we compare the performance of SYNAPSE with that of state of the art protocols.

Mitigating Performance Degradation in Congested Sensor Networks

Data generated in wireless sensor networks may not all be alike: some data may be more important than others and hence may have different delivery requirements. In this paper, we address differentiated data delivery in the presence of congestion in wireless sensor networks. We propose a class of algorithms that enforce differentiated routing based on the congested areas of a network and data priority. The basic protocol, called congestion-aware routing (CAR), discovers the congested zone of the network that exists between high-priority data sources and the data sink and, using simple forwarding rules, dedicates this portion of the network to forwarding primarily high-priority traffic. Since CAR requires some overhead for establishing the high-priority routing zone, it is unsuitable for highly mobile data sources. To accommodate these, we define MAC-enhanced CAR (MCAR), which includes MAC-layer enhancements and a protocol for forming high-priority paths on the fly for each burst of data. MCAR effectively handles the mobility of high-priority data sources, at the expense of degrading the performance of low-priority traffic. We present extensive simulation results for CAR and MCAR, and an implementation of MCAR on a 48-node testbed.

When underwater acoustic nodes should sleep with one eye open: idle-time power management in underwater sensor networks

The current interest in underwater sensor networks stems from the potential to use long term sensing devices to monitor the large mass of oceans on the planet (e.g., underwater seismic event monitoring or underwater oil rig monitoring). To accomplish this, the sensor nodes must have the ability to self-configure the communication network and provide energy-efficient data transmission. To this end, researchers have begun devising MAC-layer protocols that minimize energy consumption for data transmission. Acoustic modems typically present a number of modes of operation, similar to radio interfaces (e.g., transmit, receive, sleep, etc.), each of which consumes different levels of energy. In radio communications, the cost of keeping the interfaces idle is high; therefore, a number of idle-time power management solutions have been devised (e.g., GAF [1], STEM [2], TITAN [3]) to conserve energy during times of no communication. It is natural to attempt to use these same methods for energy conservation in underwater sensor networks. However, there are significant differences between acoustic modems and radios transceivers, making it doubtful whether previous conclusions will be valid for the underwater environment. The relative costs of various interface modes are significantly different for acoustic devices than for radios. Typical radio interfaces [4] have similar costs for transmitting, receiving and idling. On the other hand, acoustic modems have very high transmission costs with respect to receive costs, and have very low idle costs.

Energy-efficient reliable broadcast in underwater acoustic networks

Underwater acoustic networks have the potential to support a large variety of applications, such as environmental and equipment monitoring. However, underwater protocol design is in its infancy. Although there has been some work in routing and MAC layer protocols, they only address some of the challenges. A fundamental primitive that has not yet been researched for underwater networks is reliable broadcast. Reliable broadcast is required by many different applications, such as in-network node reprogramming. In this paper, we present three reliable broadcasting protocols (SBRB, FSBRB, and DBRB) that address the specific challenges of the underwater channel. We also compare our approach to two standard reliable broadcast protocols through extensive simulation, and show that our protocols provide significant gains in terms of both energy consumption and time to complete the broadcast. Moreover, our results demonstrate the importance of addressing the peculiar relationship between bandwidth and distance exhibited by an underwater acoustic channel.

On the Design of Energy-efficient Routing Protocols in Underwater Networks

Research in underwater acoustic networks has grown rapidly with the desire to monitor the large portion of the world covered by oceans. Fundamental differences between underwater acoustic propagation and terrestrial radio propagation call for new criteria for the design of networking protocols. In this paper, we focus on one of these fundamental differences, namely the dependence of usable bandwidth on transmission distance. The main contribution of this work is an in-depth analysis of the impacts of this unique relationship. Furthermore, the relationship between the energy consumptions of acoustic modems in various modes (i.e., transmit, receive, and idle) is different than that of their terrestrial radio counterparts, which also impacts the design of energy-efficient protocols. We present novel insights that are useful in guiding both protocol design and network deployment. We design an energy-efficient routing protocol for underwater sensor networks based on the insights gained in our analysis. This protocol is tested in a number of relevant network scenarios, and shown to significantly outperform greedy minimum link energy protocols, and to provide near optimal total path energy consumption. Finally, we implemented the underwater acoustic channel model in ns2 and used it to analyze the impact of multiple flows on our routing protocols performance.

GRACE-2: integrating fine-grained application adaptation with global adaptation for saving energy

Energy efficiency has become a primary design criterion for mobile multimedia devices. Prior work has proposed saving energy through coordinated adaptation in multiple system layers, in response to changing application demands and system resources. The scope and frequency of adaptation pose a fundamental conflict in such systems. The Illinois GRACE project addresses this conflict through a hierarchical solution which combines: 1) infrequent (expensive) global adaptation that optimises energy for all applications in the system, 2) frequent (cheap) per-application (or per-app) adaptation that optimises for a single application at a time. This paper demonstrates the benefits of the hierarchical adaptation through a second-generation prototype, GRACE-2. Specifically, it shows that in a network bandwidth constrained environment, per-app application adaptation yields significant energy benefits over and above global adaptation.

The Design, Deployment, and Analysis of SignetLab: A Sensor Network Testbed and Interactive Management Tool

The emergence of small, inexpensive, network-capable sensing devices led to a great deal of research on the design and implementation of sensor networks. A critical step in taking protocols from theory to actual deployment is comprehensive testing on physical sensor networks. Sensor network testbeds provide one way to facilitate such testing without requiring the deployment of a specialized sensor network for each protocol. However, for such testbeds to be useful, they must not overwhelm researchers with maintenance tasks and high learning curves. Previous work in testbed design has primarily focused on creating interfaces to maximize their usage by convenient scheduling of jobs and output access. In this work, we present two contributions to sensor network testbed design. The first is a unique management tool that allows users to program, interact with, and receive data from nodes in the network, filling a gap in current testbed management solutions. The second is the design, deployment, and analysis of the SignetLab testbed. The analysis of the testbed and its results provide quantitative measurements of the impact of physical deployment on signal propagation characteristics. Additionally, we present two case studies where researchers have used the testbed and discuss the user experiences and lessons learned.

Improving Energy Conservation Using Bulk Transmission over High-Power Radios in Sensor Networks

Low power radios, such as the CC2420, have been widely popular with recent sensor platforms. This paper explores the potential for energy savings from adding a high-power, high-bandwidth radio to current sensor platforms. High-bandwidth radios consume more power but significantly reduce the time for transmissions. Consequently, they offer net savings in total communication energy when there is enough data to offset wake-up energy overhead. The analysis on energy characteristics of several IEEE 802.11 radios show that a feasible crossover point exists (in terms of data size) after which energy savings are possible. Based on this analysis, we present a bulk data transmission protocol for dual radio systems. The results of simulations and prototype implementation show significant energy savings at the expense of introducing acceptable delay.