Hoon Oh

A tree-based approach for the Internet connectivity of mobile ad hoc networks

We propose a tree-based integration of infrastructure networks and MANETs (TIIM) to efficiently extend the scope of mobile Internet protocol to mobile ad hoc networks and devise a tree-based routing protocol (TBRP) that is suitable for the TIIM architecture. Infrastructure networks have a number of fixed Internet Gateways that connect two heterogeneous networks. Mobile nodes form a number of small trees named pMANETs, each of them growing from anchor node which can communicate directly with an Internet Gateway. A new node registers with foreign agent and home agent along the tree path without resorting to an inefficient flooding. Furthermore, the TBRP sets up a routing path efficiently by exploiting the tree information without relying on flooding. We show by resorting to simulation that our approach is competitive against the conventional AODV based approach.

A Topology Management Routing Protocol for Mobile IP Support of Mobile Ad Hoc Networks

Management of wireless multi-hop node mobility is required for global Internet connectivity of ad hoc networks. A new tree-based network topology management approach allows for managing node mobility efficiently and finding the shortest path quickly. Every node maintains topology information that includes the members of a tree being a root itself and the neighbors of each member. Then, a node can find the shortest path for a pair of nodes that belong to its topology information. We present simulation results to show that our approach far outperforms the well-known AODV based approach and works well even with an extremely high mobility of nodes.

A demand-based slot assignment algorithm for energy-aware reliable data transmission in wireless sensor networks

This paper proposes a new demand-based slot assignment (DSA) algorithm that allocates time slots based on the bandwidth demand of each node in a tree topology. DSA is basically different from SDA, DAS, or WIRES that assigns one large slot for each sensor node, but is similar to the frame-slot pair assignment (FSA) algorithm used in TreeMAC in that it assigns multiple small size slots for sensor nodes per each data collection round. DSA tackles the shortcomings of FSA in terms of the capability of packet aggregation and filtering, the balance of energy consumption, and bandwidth utilization. In general, nodes at lower tree depths process more packets and consume more energy than ones at higher tree depths, and thus the imbalanced energy consumption shortens network lifetime. The proposed algorithm allocates a sequence of receiving slots and then a sequence of sending slots to each node. This approach not only reduces the power consumption of nodes at lower depths significantly by allowing efficient data aggregation and filtering, but also it improves bandwidth utilization by removing wasted slots. In addition, the RTS and CTS messages are used within a slot for ensuring the reliability of data transmission and updating sync time between a child and its parent. Simulation results show that DSA far outperforms FSA in energy consumption and bandwidth utilization.

Quasi-tree mobility management for internet connectivity of mobile ad hoc networks

The location of mobile nodes must be managed to enable Internet connectivity of mobile ad hoc networks. Node mobility can be managed efficiently using a tree topology in which a mobile node registers with an Internet gateway along a tree path without using flooding. However, a node that loses connectivity to its parent has to find and connect to a new parent through a join-handshaking process. This tends to increase control overhead and impose some delay on on-going communication. Furthermore, the node may join its descendant because of the synchronization delay in updating topology change, creating a loop that significantly increases control overhead. We improve these problems by maintaining a quasi-tree topology in which a node maintains multiple parents. We also present a technique for detection and resolution of loops. The simulation results show that the quasi-tree mobility management approach far outperforms the traditional approaches and is highly robust against the significant increases in tree size and node mobility.

Detecting and resolving a loop in the tree-based mobility management protocol

A loop can take place in the process of managing tree topology for mobility management of mobile nodes in infrastructure-based mobile ad hoc networks The formation of a loop degrades an effective bandwidth of the wireless network by passing the identical message repeatedly within the same loop Therefore, the loop should be resolved quickly to revert the system back to the normal state In this paper, we propose a simple and novel mechanism that detects and resolves a loop quickly by tracking the depth of trees The performance of the proposed approach is compared with existing tree-based approaches as well as the hybrid approach It is shown that the proposed approach shows the superiority of the new approach and far outperforms the other methods, and is robust against the rapid changes in network topology.

A slot demand-based path reservation approach for the timely and reliable delivery of bursty traffic in WMSNs

In case that we build a context‐aware computing‐based Safety Monitoring and Control System (SMOCS) that monitors the safety of the workers, many sensor devices with different data rates are distributed in the target field. Based on these context data, the SMOCS judges the safety of the working environment primarily. If it perceives a dangerous sign, it requests additional bursty data such as still image or video streaming from a particular sensor device in order to confirm the situation. Because these bursty data have to be delivered to the server reliably with time constraints, it is challengeable to process those data with limited energy and bandwidth. In this paper, we propose an efficient approach to deliver bursty data reliably by reserving time slots to transmit the required packets on all the paths from the selected multimedia nodes to the server. The nodes that are not on the selected paths are put into sleep mode to conserve energy during the transmission of bursty data. We evaluate the proposed approach by conducting experiments using the indoor test bed that consists of 30 sensor communication devices. The experimental results show that the proposed approach can satisfy the requirements of multimedia applications well. Copyright

A looping problem in the tree-based mobility management for mobile IP supported ad hoc networks

A loop can take place in the process of managing tree topology for mobility management of mobile nodes in infrastructure-based mobile ad hoc networks. The formation of a loop degrades an effective bandwidth of the wireless network by passing an identical message repeatedly within the same loop. Therefore, the loop should be resolved to revert the system back to the normal state. In this paper, we propose a simple and novel mechanism that detects and resolves a loop quickly by tracking the depth of trees. The mobility management approach that employs the loop resolution method is evaluated comparatively with the original tree-based one and the hybrid one. It is shown that the proposed approach far outperforms the other approaches, and it is robust against the rapid changes in network topology.

An optimized approach for time-constrained and reliable bursty data acquisition in WMSNs

In real-time multimedia application that is used to monitor the safety of workers and working environment in industrial fields, a burst of multimedia data, such as still images and audio or video streams, generated by multimedia nodes equipped with cameras or microphones on demand, is required to be collected at a server within a specified time bound in a reliable manner. However, due to the limited resources in sensor devices, such as process capability, bandwidth, and energy, it is challengeable to satisfy the time constraints of various real-time multimedia applications. Therefore, we introduce an optimized approach in order to shorten the acquisition period of bursty traffic so that it can satisfy more applications with tighter time constraints. For this purpose, we devise a path reservation scheme for an energy-efficient and time-constrained data transmission and a frame-slot scheduling scheme using two channels that enables the concurrent data transmission. Simulation results show that our proposed approach reduces the bursty data acquisition time and enhances network throughput significantly compared to other ones.

Improvement of IEEE 802.11 for multimedia traffic in wireless LAN

In this paper, we propose to add a new queue in IEEE 802.11 MAC protocol for real-time multimedia traffic in wireless LAN. The queue contributes to improving multimedia service quality by reducing end to end delay, a QoS parameter. To control two queues, we use a scheduler based on the PAD algorithm which selects a packet from one of two queues appropriately for forwarding. Moreover, we adapt the value of random backoff in the IEEE 802.11 for multimedia packets, which reduces the channel access delay. We modify the IEEE 802.11 standard with the proposed scheme and evaluate the performance of the modified protocol. The result shows that our approach outperforms the IEEE 802.11 standard in packet loss rate and average packet delay.

A Network-Controlled Approach for the Timely and Reliable Acquisition of Bursty Data in WMSNs

To build a Safety MOnitoring and Control System SMOCS that monitors the safety of the workers and warns them of hazardous situation, many sensor communication devices with different data rates are deployed in the target field. SMOCS collects small scalar data such as temperature, the oxygen content of the air, the occurrence of smoke, gas and/or flame from sensor devices periodically and judges the safety of the working environment primarily. If it perceives a dangerous sign, it acquires still image or video streaming on demand to confirm the situation. Otherwise, the evacuation order by any misjudgment can cause a big loss or annoyance. Since these bursty data have to be delivered to SMOCS reliably and with time constraints, it is challengeable to process those data using a wireless sensor network. A new TDMA-based protocol is designed and is experimented with 30 sensor devices. The results indicate that the new protocol satisfies application requirements well.