Haining Mo

Comparing underwater MAC protocols in real sea experiments

Underwater acoustic networks (UANs) have drawn significant attention from both academia and industry in recent years. Even though many underwater MAC protocols have been proposed and studied based on simulations and theoretical analysis, few work has been conducted to test and evaluate these protocols in a multi-hop real sea experiment. Due to the harsh acoustic channel condition caused by complex multi-path environment, fast varying acoustic channel and heterogenous channel quality, current simulators can hardly tell us how the protocols work in the real world. Along this direction, we conduced real sea experiments at Atlantic Ocean with 9 nodes deployed forming a multi-hop string network. In this experiment, the performance of three representative MAC protocols, random access based UW-Aloha, handshaking based SASHA, and scheduling based pipelined transmission MAC (PTMAC) are compared and analyzed at both packet behavior and node behavior levels. The end-to-end performance of these three protocols are also tested and studied in terms of throughput, delay, and packet delivery ratio. From field experiment results, the high packet loss rate and significant channel asymmetry, temporal and spatial transmission range uncertainty and delayed data transmissions are discovered to have evidential effects on the MAC performance. We provide some inspirations to address these observed issues in MAC design for real multi-hop networks.

Fountain code based Adaptive multi-hop Reliable data transfer for underwater acoustic networks

In this paper, we investigate multi-hop reliable data transfer for underwater acoustic networks. We propose a new protocol, called FOuntain Code based Adaptive multi-hop Reliable data transfer (FOCAR). FOCAR is essentially a hybrid ARQ scheme which integrates Fountain codes with hop-by-hop retransmission-upon-failure. It considers the half duplex nature of the underwater acoustic modems and adapts the block size of each hop to optimize the end-to-end delay for the multi-hop network scenario. Extensive simulation results show that FOCAR can achieve high reliability with low end-to-end delay and high energy efficiency.

Practical Coding-based Multi-Hop Reliable Data Transfer for underwater acoustic networks

In this paper, we investigate reliable data transfer for multi-hop underwater acoustic networks. Motivated by experiences from real-world field tests, we propose a Practical Coding-based Multi-hop Reliable Data Transfer (PCMRDT) protocol. For the per-hop reliable data transfer, PCMRDT combines random linear coding and selective repeat to achieve high reliability and efficiency. We analyze the data recovery capability for random linear coding so that we can set an appropriate coding rate. In addition, PCMRDT utilizes a multi-hop coordination mechanism to eliminate collisions and decreases average end-to-end delay over multiple hops. Simulation results show that PCMRDT can significantly reduce the network delay with high energy efficiency.

UW-HARQ: An underwater hybrid ARQ scheme: Design, implementation and initial test

In this paper, we investigate reliable end-to-end data transfer in Underwater Acoustic Networks. A hybrid ARQ scheme, named UW-HARQ is proposed, which combines FEC coding and ARQ. For the FEC coding, Random Binary Linear Coding is employed due to its low coding and decoding complexity. An adaptive coding ratio estimation scheme, which incorporates the PER information, is proposed to minimize the number of retransmissions between the source and the destination. For the ARQ, NACK packets are utilized to inform the source node how many and which packets to send out in a retransmission and ACK packets are used as indications of data packet recovery success. We implemented UW-HARQ on real UAN nodes by leveraging our hardware and software platform. Initial lab test results show that UW-HARQ achieves a larger throughput than TCP-like approaches with a comparable overhead.

Cyber-physical systems

A retrospective analysis of cyber-physical systems theory is given, and its current state is characterized. A number of problems arising in the theory of hybrid automata is investigated. A semigroup transition system is considered, which underlies the extension of the algebraic theory of interaction of labeled transition systems to cyber-physical systems.

Coding based multi-hop coordinated reliable data transfer for underwater acoustic networks: Design, implementation and tests

Motivated by some critical observations from field tests, in this paper, we design and implement a Coding based multi-hop Coordinated Reliable Data Transfer (CCRDT) protocol for underwater acoustic networks. CCRDT is based on hop-by-hop reliable data transfer with multi-hop coordination. For the per-hop data transfer, a GF(256) Random Linear Coding scheme and a coding ratio estimation approach are proposed to guarantee the reliability and efficiency of data transfer. In addition, a multi-hop coordination scheme is designed to enable transmission pipelining that allows multiple nodes to transmit simultaneously. By carefully scheduling the transmission of every node, our multi-hop coordination scheme effectively eliminates packet collisions, which further improves the end-to-end throughput. We implement CCRDT on a lab testbed and conducted extensive tests to evaluate its performance. Our results show that CCRDT achieves a higher end-to-end throughput than other existing reliable data transfer protocols which have been implemented in real systems.

Evaluating selective ARQ and slotted handshake based access in real world underwater networks

Medium Access Control (MAC) is an essential component of protocol stacks in Underwater Acoustic Networks (UANs). Numerous dedicated UAN MAC protocols have been proposed and studied via analysis and simulations. However, limited work has been done on evaluating these protocols in real ocean environments. To achieve a better understanding on how MAC protocols perform in real world UANs, we implemented Selective ARQ and Slotted Handshake based Access (SASHA) on UAN nodes. SASHA embraces some most essential and representative techniques in UAN MAC design, including selective ARQ, time slotting, handshake and collision avoidance. Moreover, a sea test was conducted at Atlantic Ocean to evaluate the performance of SASHA. With the experimental data, we are able to study how the aforementioned techniques affect the performance of SASHA. we also analyze the hop-by-hop and end-to-end behavior of SASHA. Specifically, we investigate the transmission delay and queuing delay of a data packet on one hop. From the findings, some issues are discovered and the corresponding design guidelines are emerged.

NAMS: A networked acoustic modem system for underwater applications

In this paper, we present a networked acoustic modem system (NAMS) by integrating a high-speed OFDM modem and a comprehensive underwater network protocol stack for underwater applications. This integrated system allows different underwater network protocols to run on top of the OFDM modem platform and can provide high-speed, reliable and efficient communications in underwater environments.

Traffic estimation based receiver initiated MAC for underwater acoustic networks

Due to the long preamble problem in underwater acoustic networks (UANs), traditional sender initiated handshaking MAC protocols are facing high overhead of control messages. To mitigate this problem, we propose a traffic estimation based receiver initiated MAC (FERI MAC) for UANs. In FERI MAC, a traffic prediction based adaptive data polling approach is used to help receiver request the data from neighbors at the right time. Via simulations, we evaluate the performance of FERI MAC, in terms of energy efficiency, channel utilization and one-hop delivery delay. FERI MAC shows a stable energy efficiency and channel utilization with arbitrary network traffic patterns. Our results also illustrate that, compared with existing receiver initiated MAC protocols, FERI MAC can achieve a higher energy efficiency while with some delay penalty. This confirms the strength of FERI MAC for delay tolerant underwater applications.

Receiver-Initiated Spectrum Management for Underwater Cognitive Acoustic Network

Cognitive acoustic (CA) is emerging as a promising technique for environment-friendly and spectrum-efficient underwater communications. Due to the unique features of underwater acoustic networks (UANs), traditional spectrum management systems designed for cognitive radio (CR) need an overhaul to work efficiently in underwater environments. In this paper, we propose a receiver-initiated spectrum management (RISM) system for underwater cognitive acoustic networks (UCANs). RISM seeks to improve the performance of UCANs through a collaboration of physical layer and medium access control (MAC) layer. It aims to provide efficient spectrum utilization and data transmissions with a small collision probability for CA nodes, while avoiding harmful interference with both “natural acoustic systems”, such as marine mammals, and “artificial acoustic systems”, like sonars and other UCANs. In addition, to solve the unique challenge of deciding when receivers start to retrieve data from their neighbors, we propose to use a traffic predictor on each receiver to forecast the traffic loads on surrounding nodes. This allows each receiver to dynamically adjust its polling frequency according to the variation of a network traffic. Simulation results show that the performance of RISM with smart polling scheme outperforms the conventional sender-initiated approach in terms of throughput, hop-by-hop delay, and energy efficiency.