Mobile Underwater Acoustic Networks Research Articles

Algorithm Design and Performance Analysis of Target Localization Using Mobile Underwater Acoustic Array Networks

Space-air-ground-sea integrated network, as a promising networking paradigm for the sixth generation (6 G) communications, connects satellite networks, aerial networks, terrestrial networks, and marine networks. As a fundamental application of marine networks, efficient target localization in the ocean is significant for many marine and underwater applications, including oceanic environmental monitoring, subsea resource exploration, and navigation safety. In this paper, to bring more scalability and feasibility of underwater localization, a mobile underwater acoustic array network is utilized to locate underwater moving targets by leveraging linear frequency modulated (LFM) signals. In the mobile underwater acoustic network, one node is constantly broadcasting LFM signals. Based on the reflected signals received by other nodes, a method that jointly utilizes the propagation delay and the Doppler effect is proposed to simultaneously estimate the position and the velocity of the moving target. Specifically, a two-phase iterative algorithm with low computational complexity is designed to improve the estimation accuracy. Closed-form expressions of positioning and velocity estimation error are also presented. Performance evaluation shows that the proposed method clearly outperforms the least squares based approach. Moreover, the estimation accuracy of the proposed method can approach the Cramér-Rao low bound (CRLB) within two iterations. Decently good localization and velocity estimation error performance can be achieved even with an array network formed by a small number of nodes.

An Efficient Medium Access Control Scheme Based on MC-CDMA for Mobile Underwater Acoustic Networks

Performing effective medium access control (MAC) encounters great challenges for mobile underwater acoustic networks (UANs), because it suffers from low signal-to-noise ratio, Doppler shift, large communication latency, and so on. Multi-carrier code-division multiple access (MC-COMA) is a promising modulation technique appropriate for solving the above restrictions. In this article, we design a novel MC-COMA-based cross-layer MAC scheme for mobile UANs, called MCI-MAC, to achieve efficient high-concurrency communication. Specifically, this method allocates spread spectrum sequences dynamically on the basis of velocity, propagation distance, data size, and data grade to improve robustness and flexibility of communication. Moreover, we propose an ant-colony-based optimal channel selection algorithm to decrease inter-carrier interference and inter-symbol interference, which concurrently maximizes energy efficiency and network throughput. In addition, we further propose a solution to solve multihop networks' collisions. Simulation results show that MCI-MAC is more effective than the state-of-the-art methods in mobile UANs.

Mu-Net: Community-shared infrastructure for mobile underwater acoustic networks

It is well recognized that there is a strong need for shared testbeds to promote research growth in underwater communities. We are developing an open-source, open-architecture, community-shared infrastructure for mobile underwater acoustic networks, namely mu-Net. The overall goal is to support research and education in the joint communities of underwater signal processing, communications, networking, and robotics. The mu-Net infrastructure consists of three main components: an indoor testbed, a lake testbed, and underlying open-architecture software. The mu-Net software uses a service-oriented architecture to interface with open-access autonomy suites, such as MOOS-IvP and ROS. Functions associated with sensing, communication, networking, vehicle behaviors, and navigation are compartmentalized as modular service units. The indoor testbed is developed for lab tests with a moderate number of nodes, for example, eight nodes, for deployments in a swimming pool. The lake testbed uses two commercial autonomous underwater vehicles (AUVs) that can be deployed in a lake. We will provide shared access to both testbeds for data collection and algorithm validation. We will present the software architecture, hardware instruments, and the obtained acoustic measurements from the testbeds.

Distortion performance of underwater acoustic mobile networks

The paper considers the distortion performance of mobile underwater acoustic networks. The network is composed of autonomous underwater vehicles (AUV’s) that utilize multihop transmissions to route the information through the network. The mobility model is direction persistent. The distortion is evaluated in the context of an independent identically distributed (i.i.d.) Gaussian source and single description coding. Each AUV-to-AUV channel experiences frequency dependent path loss and Ricean fading, as well as interference from other network transmissions. Numerical examples illustrate the distortion performance.

A hybrid localization algorithm for multi-hop mobile underwater acoustic networks

Self-localization is an essential issue for mobile underwater acoustic networks. Recently most localization schemes focus on the static networks, while only a few methods are for MUANs which also have some drawbacks such as low accuracy, small scale, large communication overhead, etc. In this paper, we propose a hybrid localization algorithm which separates the network into some stages. Nodes in different stages will use different methods to localize themselves and both range-based and range-free methods are adopted during the procedure. The proposed algorithm can be used in a multi-hop network and can improve the localization accuracy as well as reducing the communication cost. Besides the advantages above, the algorithm does not need most of the prior knowledge about movement speed which can be more easier to use in underwater environment. Simulation results show that the proposed algorithm can balance the trade-off between the localization accuracy and the communication cost; meanwhile, the performance of the proposed algorithm is better than the previews and can perform well in the underwater environment.

A Hierarchical Time Division Multiple Access Medium Access Control Protocol for Clustered Underwater Acoustic Networks

A hierarchical time division multiple access (HTDMA) medium access control (MAC) protocol is proposed for clustered mobile underwater acoustic networks. HTDMA consists of two TDMA scheduling protocols (i.e., TDMA1 and TDMA2) in order to accommodate mobile underwater nodes (UNs). TDMA1 is executed among surface stations (e.g., buoys) using terrestrial wireless communication in order to share mobility information obtained from UNs which move cluster to cluster. TDMA2 is executed among UNs, which send data to their surface station as a cluster head in one cluster. By sharing mobility information, a surface station can instantaneously determine the number of time slots in a TDMA2 frame up to as many as the number of UNs which is currently residing in its cluster. This can enhance delay and channel utilization performance by avoiding the occurrence of idle time slots. We analytically investigate the delay of HTDMA, and compare it with that of wellknown contention-free and contention-based MAC protocols, which are TDMA and Slotted-ALOHA, respectively. It is shown that HTDMA remarkably decreases delay, compared with TDMA and Slotted-ALOHA.

Multichannel Detection for Wideband Underwater Acoustic CDMA Communications

Direct-sequence (DS) code-division multiple access (CDMA) is considered for future wideband mobile underwater acoustic networks, where a typical configuration may include several autonomous underwater vehicles (AUVs) operating within a few kilometers of a central receiver. Two receivers that utilize multichannel (array) processing of asynchronous multiuser signals are proposed: the symbol decision feedback (SDF) receiver and the chip hypothesis feedback (CHF) receiver. Both receivers use a chip-resolution adaptive front end consisting of a many-to-few combiner and a bank of fractionally-spaced feedforward equalizers. In the SDF receiver, feedback equalization is implemented at symbol resolution, and receiver filters, including a decision-directed phase-locked loop, are adapted at the symbol rate. This limits its applicability to the channels whose time variation is slow compared to the symbol rate. In a wideband acoustic system, which transmits at maximal chip rate, the symbol rate is down-scaled by the spreading factor, and an inverse effect may occur by which increasing the spreading factor results in performance degradation. To eliminate this effect, feedback equalization, which is necessary for the majority of acoustic channels, is performed in the CHF receiver at chip resolution and receiver parameters are adjusted at the chip rate. At the price of increased computational complexity (there are as many adaptive filters as there are symbol values), this receiver provides improved performance for systems where time variation cannot be neglected with respect to the symbol rate [e.g., low probability of detection (LPD) acoustic systems]. Performance of the two receivers was demonstrated in a four-user scenario, using experimental data obtained over a 2-km shallow-water channel. At the chip rate of 19.2 kilochips per second (kc/s) with quaternary phase-shift keying (QPSK) modulation, excellent results were achieved at an aggregate data rate of up to 10 kb/s