Acoustic Communication Networks for Distributed Autonomous Underwater Platforms: Progress Report

The ultimate goal of this project is to design and develop an experimental platform for testing and evaluation of mobile underwater acoustic networking. This report represents a cumulative summary of research and engineering efforts pursued from the beginning of the project up to this date. The project has focused on three topics: 1. Design and performance analysis of communication protocols for mobile acoustic networks; 2. Development of the software-defined reconfigurable acoustic modem; and 3. Design and development of a small autonomous underwater vehicle (the micro AUV)

GMOs for Development

Given the increasing world population, prices and greenhouse gas emissions, there is a need to innovate agriculture in order to accelerate crop productivity sustainably. These issues are compounded in developing countries, which often face severe droughts, famine, and have limited access to drinking water. Genetically modified organisms (GMOs) are the proposed solution to these concerns, with an increasing number of countries reaping the benefits of the new technology. GMOs are a hotly debated topic in the European Union (EU), but for very different reasons. Namely, a negative public perception on GMO safety and ethics has led to a restrictive and precautionary approach to GMO regulation. EU’s GMO policy has shown an international impact, mainly in the poorest countries, many of which are in sub-Saharan Africa. To bring a fresh perspective to EU’s GMO debate, this thesis will analyse the coherence of EU’s GMO policy with its international development objectives, outlined in EU’s framework Policy Coherence for Development. Linking GMO’s to the Millennium Development Goals, data suggests that they can have a positive effect, e.g. on reducing hunger and poverty. Conversely, EU’s GMO policy can act as a deterrent to developing country GMO acceptance, which would suggest that it is not coherent with its international development objectives. Key words: European Union, Genetically Modified Organisms, Policy Coherence for Development, Millennium Development Goals, sub-Saharan Africa

Random Linear Network Coding For Time Division Duplexing: Energy Analysis

We study the energy performance of random linear network coding for time division duplexing channels. We assume a packet erasure channel with nodes that cannot transmit and receive information simultaneously. The sender transmits coded data packets back-to-back before stopping to wait for the receiver to acknowledge the number of degrees of freedom, if any, that are required to decode correctly the information. Our analysis shows that, in terms of mean energy consumed, there is an optimal number of coded data packets to send before stopping to listen. This number depends on the energy needed to transmit each coded packet and the acknowledgment (ACK), probabilities of packet and ACK erasure, and the number of degrees of freedom that the receiver requires to decode the data. We show that its energy performance is superior to that of a full-duplex system. We also study the performance of our scheme when the number of coded packets is chosen to minimize the mean time to complete transmission as in [1]. Energy performance under this optimization criterion is found to be close to optimal, thus providing a good trade-off between energy and time required to complete transmissions.Comment: 5 pages, 6 figures, Accepted to ICC 200

On the Relationship between Transmission Power and Capacity of an Underwater Acoustic Communication Channel

The underwater acoustic channel is characterized by a path loss that depends not only on the transmission distance, but also on the signal frequency. As a consequence, transmission bandwidth depends on the transmission distance, a feature that distinguishes an underwater acoustic system from a terrestrial radio system. The exact relationship between power, transmission band, distance and capacity for the Gaussian noise scenario is a complicated one. This work provides a closed-form approximate model for 1) power consumption, 2) band-edge frequency and 3) bandwidth as functions of distance and capacity required for a data link. This approximate model is obtained by numerical evaluation of analytical results which takes into account physical models of acoustic propagation loss and ambient noise. The closed-form approximations may become useful tools in the design and analysis of underwater acoustic networks.Comment: 6 pages, 9 Figures, Awaiting acceptance to IEEE Oceans 08 (Conference), Kobe, Japa

Broadcasting in Time-Division Duplexing: A Random Linear Network Coding Approach

We study random linear network coding for broadcasting in time division duplexing channels. We assume a packet erasure channel with nodes that cannot transmit and receive information simultaneously. The sender transmits coded data packets back-to-back before stopping to wait for the receivers to acknowledge the number of degrees of freedom, if any, that are required to decode correctly the information. We study the mean time to complete the transmission of a block of packets to all receivers. We also present a bound on the number of stops to wait for acknowledgement in order to complete transmission with probability at least $1-\epsilon$, for any $\epsilon>0$. We present analysis and numerical results showing that our scheme outperforms optimal scheduling policies for broadcast, in terms of the mean completion time. We provide a simple heuristic to compute the number of coded packets to be sent before stopping that achieves close to optimal performance with the advantage of a considerable reduction in the search time.Comment: 6 pages, 5 figures, Submitted to Workshop on Network Coding, Theory, and Applications (NetCod 2009

Random Linear Network Coding For Time Division Duplexing: When To Stop Talking And Start Listening

A new random linear network coding scheme for reliable communications for time division duplexing channels is proposed. The setup assumes a packet erasure channel and that nodes cannot transmit and receive information simultaneously. The sender transmits coded data packets back-to-back before stopping to wait for the receiver to acknowledge (ACK) the number of degrees of freedom, if any, that are required to decode correctly the information. We provide an analysis of this problem to show that there is an optimal number of coded data packets, in terms of mean completion time, to be sent before stopping to listen. This number depends on the latency, probabilities of packet erasure and ACK erasure, and the number of degrees of freedom that the receiver requires to decode the data. This scheme is optimal in terms of the mean time to complete the transmission of a fixed number of data packets. We show that its performance is very close to that of a full duplex system, while transmitting a different number of coded packets can cause large degradation in performance, especially if latency is high. Also, we study the throughput performance of our scheme and compare it to existing half-duplex Go-back-N and Selective Repeat ARQ schemes. Numerical results, obtained for different latencies, show that our scheme has similar performance to the Selective Repeat in most cases and considerable performance gain when latency and packet error probability is high.Comment: 9 pages, 9 figures, Submitted to INFOCOM'0