Biblio

In this work, a magneto inductive (MI) link design is studied to achieve high speed transmission applied to a high density underwater network. For a small loop antenna, a design procedure is described to define the optimal operating frequency constrained on the system bandwidth and range. A coherent link is established between two nodes in a controlled underwater environment. For a small coil with radius of 5 cm, simulation results indicate that a range above 10 meters can be achieved in the low frequency spectrum spanning 10 kHz to 1 MHz. The design procedure is validated through measurements in seawater: a very high output SNR equal to 31.4 dB is realized at the output of the equalizer, and in these conditions a perfectly reliable 8-kbps link is demonstrated at a center frequency of 22.5 kHz.

Underwater sensing is envisioned using inexpensive underwater sensor nodes distributed over a wide area, deployed close to the bottom, and networked through underwater acoustic communications. In this paper, an underwater acoustic sensor node to perform the underwater sensing is designed and implemented. Specifically, we describe the design criteria, architecture and functional modules of underwater acoustic sensor node. Moreover, we give the experiment results of ocean current field estimation using the designed underwater acoustic sensor nodes at the sea area of Liuheng, Zhoushan, China.

In this study, we evaluate a multipath diversity reception in underwater CDMA system by performing a lake experiment. First, we design CDMA transmitter and receiver equipped with a multipath diversity with equal gain combining (EGC) and maximal ratio combining (MRC). Then, an experiment is performed at Lake Kyungcheon, South Korea to show that the diversity combining successfully corrects bit errors caused by multipath fading.

The harsh environment in the water has imposed challenges for underwater sensor networks (USNs), which collect the sensed data from the underwater sensors to the sink on land. The time-varying underwater acoustic channel has low band-width and high bit error rate, which leads to low data collection efficiency. Furthermore, the heterogeneous model of USNs that uses acoustic communications under the water and wireless communication above the water makes it difficult in efficient routing and forwarding for data collection. To this end, we propose a novel on-surface wireless-assisted opportunistic routing (SurOpp) for USNs. SurOpp deploys multiple buoy nodes on surface and includes all of them in the forwarding candidates to form a receive diversity. The opportunities of reception and forwarding in buoy nodes are exploited to improve the end-to-end transmissions. SurOpp also adopts rateless codes in the source to achieve opportunistic reception in the sink. The cooperation of both opportunistic reception in the buoys and the sink further decreases the messages of control overhead. The wireless interface in the buoy undertakes all the message exchanges in forwarding coordination to compensate the bandwidth limit of the acoustic channel. Simulations in NS3 show that SurOpp outperforms the traditional routing and existing opportunistic routing in terms of packet delivery ratio, end-to-end delay and energy consumption.

The development process of short-range underwater communication systems consists of different phases. Each phase comprises a multitude of specific requirements to the development platform. Typically, the utilized hardware and software is custom-built for each phase and wireless technology. Thus, the available platforms are usually not flexible and only usable for a single development phase or a single wireless technology. Furthermore, the modification and adaption between the phases and technologies are costly and time-consuming. Platforms providing the flexibility to switch between phases or even wireless technologies are either expensive or are not suitable to be integrated into underwater equipment. We developed a flexible and modular platform consisting of a controller and different front ends. The platform is capable of performing complex tasks during all development phases. To achieve high performance with more complex modulation schemes, we combine an embedded Linux processor with a field programmable gate array (FPGA) for computational demanding tasks. We show that our platform is capable of supporting the development of short-range underwater communication systems using a variety of wireless underwater communication technologies.

The design of medium access control (MAC) protocols for Underwater Acoustic Sensor Networks (UASNs) pose many challenges due to low bandwidth and high propagation delay. In this paper, a new medium access control (MAC) protocol called Handshake Triggered Chained-Concurrent MAC (HTCC) is proposed for large-scale applications in UWSNs. The main idea of HTCC is to establish a chained concurrent transmission accomplishing spatial reuse. The novelties of HTCC lie in: firstly, the protocol allows multi-direction handshake with different nodes simultaneously; secondly, a random access mechanism is integrated with the handshake mechanism for improve channel utilization. Simulation results show that HTCC outperforms extended version of Slotted floor acquisition multiple accesses (Ext-sFAMA) in terms of network throughput, the RTS efficiency, as well as fairness in representative scenarios.

Underwater Acoustic Sensor Networks (UWASNs) have the wide of applications with the proliferation of the increasing underwater activities recently. Most of current studies are focused on designing protocols to improve the network performance of WASNs. However, the security of UWASNs is also an important concern since malicious nodes can easily wiretap the information transmitted in UWASNs due to the vulnerability of UWASNs. In this paper, we investigate one of security problems in UWASNs - eavesdropping behaviours. In particular, we propose a general model to quantitatively evaluate the probability of eavesdropping behaviour in UWASNs. Simulation results also validate the accuracy of our proposed model.

Using the sparse feature of the signal, compressed sensing theory can take a sample to compress data at a rate lower than the Nyquist sampling rate. The signal must be represented by the sparse matrix, however. Based on the above theory, this article puts forward a sparse degree of adaptive algorithms which can be used for the detection and reconstruction of the underwater target radiation signal. The received underwater target radiation signal, at first, transits the noise energy into signal energy under test by the stochastic resonance system, and then based on Gerschgorin disk criterion, it can make out the number of underwater target radiation signals in order to determine the optimal sparse degree of compressed sensing, and finally, the detection and reconstruction of the original signal can be realized by utilizing the compressed sensing technique. The simulation results show that this method can effectively detect underwater target radiation signals, and they can also be detected quite well under low signal-to-noise ratio(SNR).

Virtualization technology has become ubiquitous in the computing world. With it, a number of security concerns have been amplified as users run adjacently on a single host. In order to prevent attacks from both internal and external sources, the networking of such systems must be secured. Network intrusion detection systems (NIDSs) are an important tool for aiding this effort. These systems work by analyzing flow or packet information to determine malicious intent. However, it is difficult to implement a NIDS on a virtualized system due to their complexity. This is especially true for the Xen hypervisor: Xen has incredible heterogeneity when it comes to implementation, making a generic solution difficult. In this paper, we analyze the network data flow of a typical Xen implementation along with identifying features common to any implementation. We then explore the benefits of placing security checks along the data flow and promote a solution within the hypervisor itself.