Ho-Shin Cho

A Distributed Data-Gathering Protocol Using AUV in Underwater Sensor Networks

In this paper, we propose a distributed data-gathering scheme using an autonomous underwater vehicle (AUV) working as a mobile sink to gather data from a randomly distributed underwater sensor network where sensor nodes are clustered around several cluster headers. Unlike conventional data-gathering schemes where the AUV visits either every node or every cluster header, the proposed scheme allows the AUV to visit some selected nodes named path-nodes in a way that reduces the overall transmission power of the sensor nodes. Monte Carlo simulations are performed to investigate the performance of the proposed scheme compared with several preexisting techniques employing the AUV in terms of total amount of energy consumption, standard deviation of each node’s energy consumption, latency to gather data at a sink, and controlling overhead. Simulation results show that the proposed scheme not only reduces the total energy consumption but also distributes the energy consumption more uniformly over the network, thereby increasing the lifetime of the network.

A cooperative ARQ scheme in underwater acoustic sensor networks

We propose an efficient cooperative ARQ (Automatic Repeat reQuest) scheme for underwater acoustic communications, in which cooperative nodes are used to provide more reliable alternative paths for a specific source-to-destination connection. Based on the knowledge of inter-node distances, a cooperative region is defined to include all possible candidates for cooperative nodes from a given pair of source-destination nodes. When the destination node receives an erroneous packet, it asks for retransmission from a cooperative node, which is selected in a closest-one-first manner from the nodes in the cooperative region. The selection procedure continues until the retransmission is successful. In this paper, we evaluate the proposed scheme by comparing it with a conventional S&W ARQ in terms of throughput efficiency. Computer simulation results show that the proposed cooperative retransmission scheme can significantly improve the throughput by increasing the probability of successful retransmission.

An Improved ARQ Scheme in Underwater Acoustic Sensor Networks

In underwater acoustic communications, using the property of long propagation delay, a concurrent packet transmission between two nodes could be made feasible without any collision. In this paper, utilizing the channel-sharing property, an efficient ARQ scheme is proposed. By controlling packet size such a way that transmission time becomes smaller than propagation delay, and by scheduling such packets properly, the collision-free transmission between multiple nodes is achieved. In addition, during a packet-relay through multiple hops, the typical acknowledgement (ACK) signal is replaced with overhearing data packet returned back from the next hop. The usage of overhearing as an ACK not only save power consumption but also significantly reduces overhead and transmission latency. Through the mathematical analysis and simulations, we evaluate proposed scheme in terms of the latency by comparing with an existing Stop & Wait ARQ.

Cascading Multi-Hop Reservation and Transmission in Underwater Acoustic Sensor Networks

The long propagation delay in an underwater acoustic channel makes designing an underwater media access control (MAC) protocol more challenging. In particular, handshaking-based MAC protocols widely used in terrestrial radio channels have been known to be inappropriate in underwater acoustic channels, because of the inordinately large latency involved in exchanging control packets. Furthermore, in the case of multi-hop relaying in a hop-by-hop handshaking manner, the end-to-end delay significantly increases. In this paper, we propose a new MAC protocol named cascading multi-hop reservation and transmission (CMRT). In CMRT, intermediate nodes between a source and a destination may start handshaking in advance for the next-hop relaying before handshaking for the previous node is completed. By this concurrent relaying, control packet exchange and data delivery cascade down to the destination. In addition, to improve channel utilization, CMRT adopts a packet-train method where multiple data packets are sent together by handshaking once. Thus, CMRT reduces the time taken for control packet exchange and accordingly increases the throughput. The performance of CMRT is evaluated and compared with that of two conventional MAC protocols (multiple-access collision avoidance for underwater (MACA-U) and MACA-U with packet trains (MACA-UPT)). The results show that CMRT outperforms other MAC protocols in terms of both throughput and end-to-end delay.

Throughput and Energy Efficiency of a Cooperative Hybrid ARQ Protocol for Underwater Acoustic Sensor Networks

Due to its efficiency, reliability and better channel and resource utilization, cooperative transmission technologies have been attractive options in underwater as well as terrestrial sensor networks. Their performance can be further improved if merged with forward error correction (FEC) techniques. In this paper, we propose and analyze a retransmission protocol named Cooperative-Hybrid Automatic Repeat reQuest (C-HARQ) for underwater acoustic sensor networks, which exploits both the reliability of cooperative ARQ (CARQ) and the efficiency of incremental redundancy-hybrid ARQ (IR-HARQ) using rate-compatible punctured convolution (RCPC) codes. Extensive Monte Carlo simulations are performed to investigate the performance of the protocol, in terms of both throughput and energy efficiency. The results clearly reveal the enhancement in performance achieved by the C-HARQ protocol, which outperforms both CARQ and conventional stop and wait ARQ (S&W ARQ). Further, using computer simulations, optimum values of various network parameters are estimated so as to extract the best performance out of the C-HARQ protocol.

A CDMA-Based MAC Protocol in Tree-Topology for Underwater Acoustic Sensor Networks

In this paper, a CDMA-based medium access control (MAC) scheme in underwater acoustic sensor networks is proposed, in which a periodic sleeping mode is jointly employed for the purpose of saving energy. A hierarchical tree-topology is considered where a staggered wakeup schedule is used across the multiple hierarchical levels from bottom-nodes to a top-node to allow long propagation delay of the underwater acoustic channel. The sensor nodes located in the same hierarchical level are multiplexed by means of different orthogonal codes. Both single-code and multi-code allocation schemes are analyzed. Finally, the proposed scheme is compared with Slotted FAMA, which is a representative MAC protocol designed for a multi-hop network, in terms of data throughput.

Impact of MAC on Localization in Large-Scale Seabed Sensor Networks

There are many technical challenges to realize the myriad of applications envisaged for underwater acoustic sensor networks (UASNs), in particular, determining the location of each node or localization. While various schemes have been proposed recently, the impact of MAC protocols for localization has not been studied. A MAC protocol that can enable many sensor nodes in large-scale networks to share the limited channel resource is an indispensable component to maximize localization coverage and speed, while minimizing communication costs. This can be achieved with MAC schemes that require little or no node coordination. In this paper, we evaluate the performance of a multi-stage localization scheme for a large-scale two-dimensional UASN under CSMA (requiring no node coordination) and T-Lohi (requiring light coordination). Our simulation results show that CSMA achieves better localization performance than T-Lohi at the expense of higher communication costs.

SOUNET: Self-Organized Underwater Wireless Sensor Network

In this paper, we propose an underwater wireless sensor network (UWSN) named SOUNET where sensor nodes form and maintain a tree-topological network for data gathering in a self-organized manner. After network topology discovery via packet flooding, the sensor nodes consistently update their parent node to ensure the best connectivity by referring to the time-varying neighbor tables. Such a persistent and self-adaptive method leads to high network connectivity without any centralized control, even when sensor nodes are added or unexpectedly lost. Furthermore, malfunctions that frequently happen in self-organized networks such as node isolation and closed loop are resolved in a simple way. Simulation results show that SOUNET outperforms other conventional schemes in terms of network connectivity, packet delivery ratio (PDR), and energy consumption throughout the network. In addition, we performed an experiment at the Gyeongcheon Lake in Korea using commercial underwater modems to verify that SOUNET works well in a real environment.

Data-Gathering Scheme Using AUVs in Large-Scale Underwater Sensor Networks: A Multihop Approach.

In this paper, we propose a data-gathering scheme for hierarchical underwater sensor networks, where multiple Autonomous Underwater Vehicles (AUVs) are deployed over large-scale coverage areas. The deployed AUVs constitute an intermittently connected multihop network through inter-AUV synchronization (in this paper, synchronization means an interconnection between nodes for communication) for forwarding data to the designated sink. In such a scenario, the performance of the multihop communication depends upon the synchronization among the vehicles. The mobility parameters of the vehicles vary continuously because of the constantly changing underwater currents. The variations in the AUV mobility parameters reduce the inter-AUV synchronization frequency contributing to delays in the multihop communication. The proposed scheme improves the AUV synchronization frequency by permitting neighboring AUVs to share their status information via a pre-selected node called an agent-node at the static layer of the network. We evaluate the proposed scheme in terms of the AUV synchronization frequency, vertical delay (node→AUV), horizontal delay (AUV→AUV), end-to-end delay, and the packet loss ratio. Simulation results show that the proposed scheme significantly reduces the aforementioned delays without the synchronization time-out process employed in conventional works.

An orthogonal coded hybrid MAC protocol with received power based prioritization for M2M networks

Distributed queuing collision avoidance (DQCA) is a hybrid medium access control (MAC) protocol that can inherently accommodate large node densities; however it may not be capable of handling the order of magnitude of devices in Machine-to-Machine (M2M) networks, which is an order higher than the existing WLANs. To address this issue, we propose a hybrid MAC protocol that uses orthogonal codes for channel contention, coupled with a power based priority assignment scheme for scheduling the data transmissions. The simulation results show that the proposed protocol is well suited for M2M networks and outperforms DQCA.