Heungwoo Nam

An ultrasonic sensor based low-power acoustic modem for underwater communication in underwater wireless sensor networks

Applications of underwater sensor networks involve environmental monitoring, disaster prevention, and resource detection. As the importance of these applications has recently grown, underwater sensor networks made up of sensor nodes have to be further investigated. However, little research has been performed to develop an underwater sensor node with communication functionality. In an underwater environment, typical RF-based communication is not appropriate because of two facts. One fact is that radio waves require large antennae and high transmission power. The other fact is that the Berkeley Mica 2 Motes have been reported to have a transmission range of 120cm underwater. Consequently, we have concluded that underwater communication has to use an acoustic or ultrasonic wave rather than a radio wave. The objective of our work is to develop an acoustic modem for underwater communication, where we have to consider an energy-aware acoustic modem. This is because the battery can not easily be recharged underwater as well as in a terrestrial environment. As a consequence, an acoustic modem has to be designed with low-power. In this paper, we describe our implementation of an energy-aware acoustic modem and its performance in underwater experiments.

Energy-Efficient Routing Protocol in Underwater Acoustic Sensor Networks

As the importance of applications, such as ocean sampling, environmental monitoring, disaster prevention, and distribution tactical surveillance, has recently grown, the need for underwater communication has become more pronounced. In order to perform underwater communication effectively for these applications, there are some major impediments which must be overcome in routing protocols, viz. the: 1) underwater channel characteristics including the usage of acoustic waves and long propagation times; 2) severe power limitations imposed by the reliance on attery power. To overcome these obstacles, we propose an energy-efficient, delay-decreasing routing protocol that uses energy-aware data aggregation. This mechanism reconfigures the aggregation tree via a dynamic pruning and grafting function to operate a temporal path from the uw-sources to the uw-sink. The proposed protocol is shown to achieve performance improvements: the energy saving is achieved by minimizing the number of data transmissions, the decrease in the delay is attained through the automatic movement of the aggregation point, and the lifetime extension of underwater sensor networks is also accomplished. In the simulation experiments, we evaluate these performance improvements.

An Energy-Efficient Mechanism using CLMAC Protocol for Wireless Sensor Networks

Energy efficiency is a key issue because most wireless sensor networks use battery-oriented computing and sensing devices. A network of these devices will collaborate for a common application such as environment monitoring. Thus, energy-efficient MAC protocols have focused on minimizing idle listening time at sensor nodes. Recently, energy-efficient protocols such as S-MAC, B-MAC and EA-ALPL proposed to reduce energy consumption. Here, we propose a cross-layer mechanism called cross layer medium access control (CLMAC) protocol that designed for wireless sensor networks. To meet energy-efficient routing, the CLMAC includes routing distance in the preamble field of the B-MAC. Because the CLMAC unified network layer and link layer uses routing distance without big routing table, it enables nodes to reduce control traffic routing overhead. Also, the CLMAC makes it possible to extend the lifetime of the wireless sensor networks that contain a number of nodes. The analytical results show that CLMAC protocol reduces routing overhead of the sensor nodes in wireless sensor networks.

A moving underwater communication system with bio-inspired fish robots

Recently, there has been large interest on short and medium range underwater communication systems for various applications. In this work, we investigate a moving communication system equipped with bio-inspired fish robots. A protocol stack encompassing physical layer, medium access control layer and network layer is designed for a packet-based hierarchical underwater acoustic communication and the related hardware is implemented. The developed components and system prototype are verified and evaluated in the Han River. Since this system provides high mobility and real-time monitoring service, it could be utilized for pollution monitoring and surveillance in rivers and oceans.

Remote monitoring system based on ocean sensor networks for offshore aquaculture

Recently, the need for offshore aquaculture has become increasingly important in raising migratory fish species, such as, tuna and mackerel, in an offshore environment. Moreover, offshore fish cages are located 2-5 km offshore with water depths ranging from 40 to 100 m. Hence, visiting the fish cages directly and daily to obtain the growing environmental data of migratory fish species is time-consuming and increases cost. Therefore, a system to remotely obtain growing environmental data on a regular basis without visiting the fish cages is necessary. The objective of this work is to develop a remote monitoring system based on ocean sensor networks for offshore aquaculture, and to verify the effectiveness of the developed system. The remote monitoring system is composed of two main components: ocean sensor networks installed on fish cages in the ocean and a monitoring center located on land. The fish cages are located approximately 2 km offshore. Thus, the data sensed in the fish cages are transmitted to the monitoring center through RS-485, Zigbee, and CDMA communications in the ocean sensor network, and displayed in the monitoring center. In order to verify the effectiveness of our system, tests to remotely obtain the growing environmental data on tuna were performed. Experimental results show that our developed system can obtain the growing environmental data of the tuna remotely and in real-time. Therefore, scientists as well as fish farmers will be able to remotely obtain the growing environmental data of migratory fish species in offshore fish cages.

Hex-grid based Routing Protocol in Wireless Sensor Networks

This paper presents routing protocol based on hex grid in WSNs, a power saving technique for multi-hop ad hoc wireless networks that reduces energy consumption without significantly diminishing the capacity or connectivity of the network. Proposed protocol builds on the observation that when a region of network system has a sufficient density of nodes, It is a distributed, delegated algorithm where nodes make local decisions on whether to sleep, or to join a forwarding discovery mode as a cluster head. Each node bases its decision on an estimate of how many of its neighbors will benefit from it being awake, and the amount of energy available to it. We give a algorithm where coordinators rotate with residual battery, demonstrating how localized node decisions lead to a connected, capacity-preserving global topology. Improvement in system lifetime due to change cluster head increases as the ratio of idle-to-sleep energy consumption increases. Our simulations show energy model. Additionally, This protocol also improves communication latency and capacity.

PR-RAM: The Page Rank Routing Algorithm Method in Ad-hoc wireless networks

This paper presents the Page Rank Routing Algorithm Method (PR-RAM), which is the Ad-hoc wireless networks routing protocol using Page Rank algorithm. Page Rank is the link analysis algorithm used by the Google internet engine that assigns a numerical weighting to each element of World Wide Web (WWW) with the purpose of measuring its relative importance within the WWW. If any web page has a higher rank than other web page, it means that this web page is more important than other web page. In order to measure the relative importance of mobile node in wireless network environments, this paper uses the Page Rank algorithm in Ad-hoc wireless networks. Mobile nodes Page Rank means how many routing paths are included to this node. This paper also uses available every multiple minimum hop-count routing paths to be more efficient on view of variance of entire mobile nodes energy. PR-RAM is guaranteed the access fairness of source node to Access Point (AP) in Ad-hoc networks environments.

The Architecture of Surface Gateway for Underwater Acoustic Sensor Networks

Recently, the importance of a water resource is highly concerned. Therefore, Underwater Wireless Sensor Networks (UASNs) technologies are vigorously studied for monitoring underwater environment. The UASNs gather various underwater environmental data that should be delivered to a Monitoring Center where nearby or far from UASNs are deployed. To deliver data form underwater to the Monitoring Center or vice versa, a surface gateway should change acoustic signal to RF (Radio Frequency) signal. Depends on the service requirement, the surface gateway can adopt various wireless communication channels such as Cellular network, Zigbee and so on. In this paper, we propose the architecture of surface gateway that has several wireless communication channels and communication protocol.

Low-Power Based Coherent Acoustic Modem for Emerging Underwater Acoustic Sensor Networks

Smart, small, inexpensive sensor nodes are used to construct underwater acoustic sensor networks. In addition, with the recent increase in the importance of underwater applications, the need for underwater communication has become more important. Hence, an acoustic modem capable of effective underwater communications has become more necessary for the sensor nodes to obtain underwater data. To develop an acoustic modem for effective underwater communications, some limitations must be overcome, such as the very short transmission range of radio waves, limited power supply, and high cost of commercial acoustic modems. Recently, low-power, low-cost acoustic modems have been developed. However, the data rates of these modems are so slow that sensor nodes cannot perform energy-efficient protocols. The objective of this work is to develop an acoustic modem capable of supporting high data rates. We introduce a coherent acoustic modem that uses waterproof ultrasonic sensors to process acoustic waves. The proposed modem is based on a low-power, low-cost, short-range concept, and it also supports a high data rate for energy-efficient MAC and routing protocols. Underwater experiments are conducted to evaluate the performance improvements of our modem. Experimental results show that our modem has the best performance among all recently developed low-power modems and that it is preferable to develop a coherent modem able to perform effective underwater communications.

Wireless sensor network using internetworking

We consider the problem of providing internetwork from wireless sensor network. So far, sensor network was use low power RF communication system. But recently, CDMA or WIFI is widely used by advances of technology (like 3G, 4G) and the need to support is arisen for sensor network too. By this situation, the need of operate the sensor which have different communication system at the same time is emerged. In this paper, we will discuss about sensor network routing and clustering which has more than 2 kinds of communication method. By this, organize the sensor network which is optimized the situation and compatible with various kind of sensor even if they have a different communication method are the propose.