Rodolfo W. L. Coutinho

Geographic and Opportunistic Routing for Underwater Sensor Networks

Underwater wireless sensor networks (UWSNs) have been showed as a promising technology to monitor and explore the oceans in lieu of traditional undersea wireline instruments. Nevertheless, the data gathering of UWSNs is still severely limited because of the acoustic channel communication characteristics. One way to improve the data collection in UWSNs is through the design of routing protocols considering the unique characteristics of the underwater acoustic communication and the highly dynamic network topology. In this paper, we propose the GEDAR routing protocol for UWSNs. GEDAR is an anycast, geographic and opportunistic routing protocol that routes data packets from sensor nodes to multiple sonobuoys (sinks) at the seas surface. When the node is in a communication void region, GEDAR switches to the recovery mode procedure which is based on topology control through the depth adjustment of the void nodes, instead of the traditional approaches using control messages to discover and maintain routing paths along void regions. Simulation results show that GEDAR significantly improves the network performance when compared with the baseline solutions, even in hard and difficult mobile scenarios of very sparse and very dense networks and for high network traffic loads.

GEDAR: Geographic and opportunistic routing protocol with Depth Adjustment for mobile underwater sensor networks

Efficient protocols for data packet delivery in mobile underwater sensor networks (UWSNs) are crucial to the effective use of this new powerful technology for monitoring lakes, rivers, seas, and oceans. However, communication in UWSNs is a challenging task because of the characteristics of the acoustic channel. In this work, we present a feasible solution for improving the data packet delivery ratio in mobile UWSN. The GEographic and opportunistic routing with Depth Adjustment-based topology control for communication Recovery (GEDAR) over void regions uses the greedy opportunistic forwarding to route packets and to move void nodes to new depths to adjust the topology. Simulation results shown that GEDAR outperforms the baseline solutions in terms of packet delivery ratio, latency and energy per message.

Design guidelines for opportunistic routing in underwater networks

The unique characteristics of the underwater acoustic channel impose many challenges that limit the utilization of underwater sensor networks. In this context, opportunistic routing, which has been extensively investigated in terrestrial wireless ad hoc network scenarios, has greater potential for mitigating drawbacks from underwater acoustic communication and improving network performance. In this work, we discuss the two main building blocks for the design of opportunistic routing protocols for underwater sensor networks: candidate set selection and candidate coordination procedures. We propose classifying candidate set selection procedures into sender-side, receiver-side, and hybrid approaches, and candidate coordination procedures into timer-based and control-packet-based approaches. Based on this classification, we discuss particular characteristics of each approach and how they relate to underwater acoustic communication. Furthermore, we argue that those characteristics should be considered during the design of opportunistic routing protocols for different scenarios in underwater sensor networks.

A novel void node recovery paradigm for long-term underwater sensor networks

Aquatic environment corresponds to more than 70% of the Earths surface mostly still unknown and unexplored. Underwater wireless sensor networks have recently been proposed as a way to observe and explore these environments. However, the efficient data delivery is still a challenging issue in these networks because of the impairments of the acoustic transmission. To cope with this problem, we present a novel geographic forwarding protocol and two topology control mechanisms for long-term non-time-critical underwater sensor networks. The proposed routing protocol considers the anycast network architecture in the data forwarding process. The proposed centralized topology control (CTC) and the distributed topology control (DTC) mechanisms organize the network via depth adjustment of some nodes. Simulation results show that with these mechanisms, the data packet delivery ratio achieves more than 90% even in hard and difficult scenarios of very sparse or very dense networks, and the end-to-end delay and energy consumption per delivered packet are reduced.

Movement assisted-topology control and geographic routing protocol for underwater sensor networks

Underwater sensor networks have recently been proposed as a way to observe and to explore the lakes, rivers, seas, and oceans. A challenging issue in these networks is the communication, mainly due to the impairments of the acoustic transmission. Thus, efficient mechanisms to improve the data delivery must be proposed. In this work we present a novel anycast greedy geographic forwarding protocol and two topology control mechanisms. The proposed geo-routing protocol considers the anycast network architecture in the data forwarding process. The proposed centralized topology control (CTC) and distributed topology control (DTC) mechanisms organize the network via depth adjustment of some nodes. The simulation results show that with these mechanisms, the data packet delivery ratio achieves more than 90% even in hard and difficult scenarios of very sparse or very dense networks, the end-to-end delay and energy consumption per delivered packet is reduced.

On the design of green protocols for underwater sensor networks

Underwater sensor networks have enabled a new era in scientific and industrial underwater monitoring and exploration applications. However, these networks are energy-constrained and, more problematically, energy-hungry, as a consequence of the use of underwater acoustic links. In this work, we thoroughly review potential techniques for greening underwater sensor networks. In a top-down approach, we discuss the principal design and challenges of the appealing highlighted techniques. We also exemplify their use by surveying recent proposals in underwater sensor networks. Finally, we describe potential future research directions for energy conservation in underwater networks.

Modeling and Analysis of Opportunistic Routing in Low Duty-Cycle Underwater Sensor Networks

The problem of reliable data delivery at low energy cost arises as one of the most challenging research topics in underwater wireless sensor networks (UWSNs). Reliable data delivery is demanding because of the acoustic channel impairments and channel fading. Moreover, it is energy hungry given the high cost of acoustic communication. In wireless ad hoc & sensor networks, separately, opportunistic routing has been employed to improve data delivery whereas duty cycled operation mode has been adopted to achieve energy efficiency and prolonging network lifetime. In this paper, we investigate the benefits and drawbacks of collision between opportunistic routing paradigm and duty cycle techniques in UWSNs. We propose an analytical model to study and evaluate the performance of opportunistic routing protocols under duty cycled settings designed from three mainly paradigms: simple asynchronous, strobed preamble and receiver initiated; and different network densities and traffic loads. The results show that while duty cycle reduces the energy consumption, it affects negatively in the opportunistic routing performance, increasing the delay and the expected number of transmissions to deliver a packet. The simple duty cycled approach is shown to be suitable for applications that require long-lived network and can tolerate some degree of packet losses. Our results indicate that strobed preamble-based duty cycle is the most effective approach to be integrated with opportunistic routing, when high fidelity monitoring is required, even having not the best performance in terms of energy savings.

A Novel Centrality Metric for Topology Control in Underwater Sensor Networks

In underwater sensor networks, the design of energy efficient and reliable data collection protocols is a daunting challenge. In this context, topology control and opportunistic routing are promising techniques for improving reliability and conserve energy. However, due to the challenges of the underwater acoustic channel, the vast knowledge acquired and the solution proposed so far in the context of terrestrial wireless ad hoc sensor networks cannot be applied directly to underwater acoustic sensor networks. In this work, we shed light on network topology modeling from a routing viewpoint. We model the probabilistic multipath routing behavior driven by opportunistic routing protocols in underwater sensor networks. Afterward, we propose the PCen centrality metric to measure the importance of underwater sensor nodes to the data delivery task through opportunistic routing protocols. PCen is aimed to identify critical nodes that can be used to guide topology control solutions. Our simulation results consider different network densities and reveal the presence of a few number of nodes with high PCen centrality value that will have a high rate of carried traffic, being critical for the network performance.

Local Maximum Routing Recovery in Underwater Sensor Networks: Performance and Trade-offs

Local maximum problem, where the node fails in determine the next-hop neighbor to continue forwarding the packet towards the destination, severely degrades the performance of geographic routing protocols. This degradation is more substantial in underwater sensor networks, that intrinsically have harsh environments and high energy consumption due to the underwater acoustic communication characteristics. In this work, we focus on the performance of the most commonly three methodologies used in design of local maximum recovery procedures of geographic routing protocols for underwater sensor networks: power control, bypassing void regions, and mobility controlled. Taking into consideration the underwater acoustic communication characteristics, we further develop a network energy consumption model for representative solutions of local maximum recovery procedure designed from these methodologies and then we evaluate their performance in terms of the improvements on routing task and the energy consumption. Simulation results show that all three methodologies improve the routing even in hard scenarios of lower network density whereas particularities of each methodology impacts on the network energy consumption.

Transmission power control-based opportunistic routing for wireless sensor networks

Energy efficient and reliable communication are two very important and conflicting requirements in the design of large-scale, self-organizing wireless sensor networks (WSNs). By reducing the transmission power level of the nodes, energy conservation is achieved whereas the communication reliability is degraded. We propose a novel opportunistic routing protocol to reduce the energy consumption while keep the communication reliability in acceptable levels. Transmission power Control-based Opportunistic Routing (TCOR) saves energy by reducing the transmission power of the nodes while maintains the communication reliability by employing the opportunistic forwarding paradigm, leveraging the broadcast nature of wireless transmission medium. We propose an expected energy cost function for next-hop forwarder set selection, which considers the multiple available transmission power levels and the impact of each one on the next-hop packet reception probability. Simulation results show the proposed TCOR routing protocol can lower the energy consumption per packet by an average of 80% as compared with two opportunistic routing related protocols using the maximal power transmission. While significantly reduces the energy cost to deliver a data packet, TCOR keeps the packet delivery ratio in acceptable levels, being only 4% less than when maximum power level is used.