Myungwhan Choi

Information delivery scheme of micro UAVs having limited communication range during tracking the moving target

In the proposed scheme, micro Unmanned Aerial Vehicle (micro UAV) is used to find the target and the UAV group is controlled to constantly provide location information to the base while the target is moving. UAVs have a limited communication range and information transmission is only possible through communication among the UAVs. After locating the target within the search area, the UAVs move toward the base station in order to transmit the information to the base station using multihop connectivity. In the proposed scheme, when communication is not possible among the UAVs because the target moves too far away from the base station, UAVs retain the information of the target and move toward the base station, deliver the information to another UAV, return to the target, and repeat the process. The base station calculates the range of target’s location upon receiving the information, and determines whether target tracking is possible with the current number of UAVs. The performance of the proposed scheme was evaluated by a simulation using NS-2.

An Obstacle Avoidance Scheme Maintaining Connectivity for Micro-Unmanned Aerial Vehicles

This paper suggests an obstacle avoidance scheme that enables a group of micro-UAV (Unmanned Aerial Vehicles) to avoid colliding with an obstacle that is found in the course of the flight. This scheme considers a method for UAVs to avoid colliding with such obstacles and a plan of action for when the UAVs in the group lose connectivity during flight. The main goal is for UAVs to reach the target without colliding with any obstacles. To achieve this goal, directly after the UAVs avoid the obstacle at a raised altitude above it, they fly at a higher altitude for a while and then descend to their original height. When this approach is judged to be inefficient because the height of the obstacle is too high, the UAVs divide into two groups and move to either side of it while continuing to fly at the same altitude, thereby avoiding the obstacle. Afterwards, they gather into one group again. We verify the proposed scheme and do the performance evaluation by ns-2.

Practical design recovery techniques for embedded operating system on complying with RTCA/DO-178B and ISO/IEC15408

As robustness, stability, and security have been emphasized as the critical success factors of software and systems in the various fields of industry, achieving certification based on a verification of compliance with standards is regarded as the best solution which proves a reliability of product and provides a great marketing tool. Despite such an importance, most developers have scruple about documenting development processes sufficiently. Furthermore, most of software companies try to get a certification after a development of product. As a result, applicants preparing certification are in a quandary about making sufficient materials for certification process. To solve this problem, we present the practical techniques which could be used to recover the details of software design from product and source code in compliance with RTCA/DO-178B and ISO/IEC15408 standards.

Utility based service differentiation in wireless packet network

A new wireless packet scheduling scheme is proposed to support differential services to different users over the forward wireless links whose transmission speed changes due to the ever-changing channel conditions. The scheme is intended to maximize the overall system satisfaction level using utility function. Internet applications of elastic, delay adaptive real-time, and rate adaptive real-time types are considered. Obtaining the optimal control scheme is a complicated problem, requiring detailed information on the channel statistics. Even if it were known, the computations would be significantly hampered by the curse of dimensionality. So, a heuristic method, which can run online, is proposed and its performance is evaluated.

Anonymization scheme using non-trusted agent for location based services

The possibility for the leakage of a users location information and the content of the service request query in the use of the location based services raised the issue of personal information protection. To solve this problem, in the traditional approaches, an anonymity region was defined and used such that it is hard to identify the user from the knowledge on the content of a specific query and the associated location information. Meanwhile, the system proposed here does not require to form an anonymity region and protects the personal information using non-trusted agent. That is, it does not allow for inferring the user identity from the location information and the query content.

Collision avoidance scheme for micro UAVs delivering information

The focus of this paper is to present our solution in efficiently finding the trajectory of an information delivering UAV in a communication network to minimize delays, avoiding collision with a static or moving obstacle. The UAV can gather only limited information about the obstacle due to the limited sensing capability, so the estimates of the obstacles size, speed and moving direction are used. Velocity obstacle approach is applied in choosing the avoidance maneuvers that the UAV would take to avoid collision. The simulation results are presented and they show that the path chosen by the UAV can guarantee collision avoidance.

Exploring an area by groups of UAVs in the presence of a refueling base

This research investigates the problem of area exploration using groups of unmanned aerial vehicles without service interruption under limited fuel constraints, where each group is assigned backup or search role depending on the situation. This paper presents an exhaustive search approach in finding a way to explore the search area with the least energy consumption. For this, the search length is divided into equal-sized intervals. The end points of these intervals can be designated as switch points where a search group goes back to the base to refuel and the backup group continues the job the returning group was doing before returning. This approach guarantees that the search operation is not interrupted by this switch operation for refueling. Since the exhaustive approach takes exponential time, a measure is proposed to determine the way to search the area that costs the least energy consumption for an allowed maximum execution time.

H.264 Video Broadcast Scheme Using Feedback Information over IEEE 802.11e WLAN

We propose a new H.264 video broadcasting scheme with retransmission feature using feedback information. Our scheme efficiently maps the video data partitioning technique of H.264 onto the QoS control features of the 802.11e based MAC layer. The proposed scheme effectively suppresses the feedback messages which can potentially cause significant increase of network traffic and the processing overhead at the access point. Simulation results show that the significant overall video service quality enhancement can be achieved. Another advantage of the proposed scheme is that it uses the application level retransmission requests and therefore it can be applied without any modification to the existing MAC protocol.

An Integrated Dynamic Online Management Framework for QoS-Sensitive Multimedia Overlay Networks

New multimedia services over cellular/WLAN overlay networks require different Quality of Service (QoS) levels. Therefore, an efficient network management system is necessary in order to realize QoS sensitive multimedia services while enhancing network performance. In this paper, we propose a new online network management framework for overlay networks. Our online approach to network management exhibits dynamic adaptability, flexibility, and responsiveness to the traffic conditions in multimedia networks. Simulation results indicate that our proposed framework can strike the appropriate balance between performance criteria under widely varying diverse traffic loads.

Equivalence of SCFQ and CBFQ Schemes in Packet Scheduling

Self-Clocked Fair Queueing (SCFQ) and Credit-Based Fair Queueing (CBFQ) are well-known fair scheduling schemes for packet-switched network. In this paper, it is shown that SCFQ and CBFQ are equivalent in selecting packets to transmit. For this, we modified the per-packet service tag based SCFQ algorithm to an equivalent per-session service tag based algorithm, SCFQ+, and showed that the service tags for SCFQ+ and CBFQ evolve identically.