Intermittently Connected Network Research Articles

On Erasure Coding in Intermittently Connected Networks

An intermittently connected network (ICN) is defined as a mobile network that uses cooperation between nodes to facilitate communication when a connected path between the source and destination does not exist. This cooperation consists of nodes carrying messages from other nodes to help deliver them to their destinations. An ICN does not require an infrastructure and routing information is not retained by the nodes. While this may be a useful environment for message dissemination, there are challenges in routing messages. In particular, providing satisfactory delivery performance while maintaining a low overhead ratio is difficult without routing information or a network infrastructure. In this paper, erasure coding is employed to improve the delivery rate in an ICN. The message delivery probability is derived and used to evaluate the performance. It is shown that the use of erasure coding can significantly improve the message delivery rate.

Timescale Decoupled Routing and Rate Control in Intermittently Connected Networks

We study an intermittently connected network (ICN) composed of multiple clusters of wireless nodes. Within each cluster, nodes can communicate directly using the wireless links. However, these clusters are far away from each other such that direct communication between the clusters is impossible except through contact nodes. These mobile contact nodes are data carriers that shuffle between clusters and transport data from the source to the destination clusters. There are several applications of our network model, such as clusters of mobile soldiers connected via unmanned aerial vehicles. Our work here focuses on a queue-based cross-layer technique known as the back-pressure algorithm. The algorithm is known to be throughput-optimal, as well as resilient to disruptions in the network, making it an ideal candidate communication protocol for our intermittently connected network. In this paper, we design a back-pressure routing/rate control algorithm for ICNs. Though it is throughput-optimal, the back-pressure algorithm has several drawbacks when used in ICNs, including long end-to-end delays, large number of potential queues needed, and loss in throughput due to intermittency. We present a modified back-pressure algorithm that addresses these issues. We implement our algorithm on a 16-node experimental testbed and present our experimental results in this paper.

Cooperative Search and Survey Using Autonomous Underwater Vehicles (AUVs)

In this work, we study algorithms for cooperative search and survey using a fleet of Autonomous Underwater Vehicles (AUVs). Due to the limited energy, communication range/bandwidth, and sensing range of the AUVs, underwater search and survey with multiple AUVs brings about several new challenges since a large amount of data needs to be collected by each AUV, and any AUV may fail unexpectedly. To address the challenges and meet our objectives of minimizing the total survey time and traveled distance of AUVs, we propose a cooperative rendezvous scheme called Synchronization-Based Survey (SBS) to facilitate cooperation among a large number of AUVs when surveying a large area. In SBS, AUVs form an intermittently connected network (ICN) in that they periodically meet each other for data aggregation, control signal dissemination, and AUV failure detection/recovery. Numerical analysis and simulations have been performed to compare the performance of three variants of SBS schemes, namely, Alternating Column Synchronization (ACS), Strict Line Synchronization (SLS), and X Synchronization (XS). The results show that XS can outperform other SBS schemes in terms of the survey time and the traveled distance of AUVs. We also compare XS with nonsynchronization-based survey and the lower bound on the survey time and traveled distance. The results show that XS achieves a close to optimal performance.