• Journal of Electrical Engineering and Technology
• /
• v.5 no.2
• /
• pp.228-238
• /
• 2010

There is an increasing interest in research to help overcome the energy crisis that has been focused on energy storage applications in various parts of power systems. Energy storage systems are good at enhancing the reliability or improving the efficiency of a power system by creating a time gap between the generation and the consumption of power. As a contribution to the various applications of storage devices, this paper describes a novel algorithm that determines the power and storage capacity of selected energy storage devices in order to improve upon railroad system efficiency. The algorithm is also demonstrated by means of simulation studies for the Korean railroad lines now in service. A part of this novel algorithm includes the DC railroad powerflow algorithm that considers the mobility of railroad vehicles, which is necessary because the electric railroad system has a distinct distribution system where the location and power of vehicles are not fixed values. In order to derive a more accurate powerflow result, this algorithm has been designed to consider the rail voltage as well as the feeder voltage for calculating the vehicle voltage. By applying the resultant control scheme, the charging or discharging within a specific voltage boundary, energy savings and a substation voltage stabilization using storage devices are achieved at the same time.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.17 no.8
• /
• pp.1811-1819
• /
• 2013

In this paper, we carried out a study on how to find an appropriate helper node for cooperative communications, the role of which is very import to enhance system throughput of wireless communication system. The busy tone cooperative MAC (BT-COMAC) protocol proposed in this paper is a new cooperative MAC protocol with a reactive helper node scheme and maximizes the benefits of existing schemes while making up for their shortcomings. We conducted performance evaluation of this new protocol using computer simulation experiment. System throughput in bps and channel access delay are utilized as performance measures. We used a random way point mobility model where every communication node moves independently one another, and slow fading channel where every communication node decided its transmission rate with received power basis. Numerical results show that the new MAC protocol enhances system throughput as much as 15% of the existing scheme.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.35 no.6A
• /
• pp.600-610
• /
• 2010

In this paper, a multicast mechanism is proposed for intermittently disconnected networks where the nodes move forward in formation or within a limited area. The proposed scheme extends the well-known tree-based multicast routing mechanism called MAODV by modifying the tree construction and data delivery scheme. Especially, an algorithm is introduced which determines the flooding hop count k estimating the degree of the movement of children in the tree. The performance evaluation was done by the simulation and the proposed scheme was compared with MAODV and two multicast routing schemes for DTN (Disruption Tolerant Network) including the Epidemic routing and ST-multicast. The evaluation results show that our scheme improves the original MAODV from the aspect of tree reconstruction events and message delivery ratio. Compared with the Epidemic routing scheme, our scheme achieves 85% message delivery ratio with less than 50% message delivery overhead.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.19 no.1
• /
• pp.50-60
• /
• 2015

A Block-Time-Bounded Time Division Multiple Access (BTB-TDMA) medium access control protocol, which estimates the propagation delay of nodes according to their location and moving velocity information, has been proposed for underwater acoustic networks. BTB-TDMA provides nodes with their transmission schedules by a time block that is a time unit, newly designed for BTB-TDMA. In this paper, we investigate how the receiver collision, that is induced by the asymmetry between node's uplink and downlink propagation delay due to its mobility, affects the performance of BTB-TDMA. To do this, we analytically obtain the collision rate, the channel access delay, and the channel utilization by considering the asymmetry of propagation delay. Then, simulations are extensively performed with respect to the length of a time block by varying the number of nodes, the network range, and the node's velocity. Thus, the simulation results can suggest performance criteria to determine the optimal length of a time block which minimizes the collision rate and concurrently maximizes the channel access delay and the channel utilization.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.12 no.4
• /
• pp.1523-1531
• /
• 2011

Multi-axle driving vehicle are favored for military use in off road operations because of their high mobility on extreme terrains and obstacles. Especially, Military Vehicle needs an ability to driving on hills of 60% angle slope. This paper presents the improvement of the ability of hill climbing for 6WD/6WS vehicle through the optimal tire force distribution method. From the driver's commands, the desired longitudinal force, the desired lateral force, and the desired yaw moment were obtained for the hill climbing of vehicle using optimal tire force distribution method. These three values were distributed to each wheel as the torque based on optimal tire force distribution method using friction circle and cost function. To verify the performance of the proposed algorithm, the simulation is executed using TruckSim software. Two vehicles, the one the proposed algorithm is implemented and the another the tire's forces are equivalently distributed, are compared. At the hill slop, the ability to driving on hills is improved by using the optimum tire force distribution method.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.7 no.2
• /
• pp.213-218
• /
• 2006

In this paper, we evaluate and compare performance between position-based and non-position-based routing protocols in a vehicular ad-hoc network. The protocols evaluated in this paper for many performance evaluation aspects are a position-based routing protocol, GPSR (Greedy Perimeter Stateless Routing), and the non-position-based such as AODV (Ad-hoc On-Demand Distance Vector) and DSR (Dynamic Source Routing) protocols. The three protocol characteristics such as Packet Delivery Ratio, Latency of first packet per connection, and Average number of hops depending on distance are compared and evaluated. As the result of simulation, the AODV performed better than the DSR. However, due to the high mobility characteristic of a vehicular ad-hoc network, GPSR, the position-based routing performs better than the non-position-based routing protocols such as AODV and DSR in a vehicular ad-hoc network environment.

• Nuclear Engineering and Technology
• /
• v.43 no.6
• /
• pp.567-572
• /
• 2011

A sensitivity analysis of the methods used to evaluate the transport properties of a CdZnTe detector was performed using two different radiations (${\alpha}$ particle and gamma-ray) emitted from an $^{241}Am$ source. The mobility-lifetime products of the electron-hole pair in a planar CZT detector ($5{\times}5{\times}2\;mm^3$) were determined by fitting the peak position as a function of biased voltage data to the Hecht equation. To verify the accuracy of these products derived from ${\alpha}$ particles and low-energy gamma-rays, an energy spectrum considering the transport property of the CZT detector was simulated through a combination of the deposited energy and the charge collection efficiency at a specific position. It was found that the shaping time of the amplifier module significantly affects the determination of the (${\mu}{\tau}$) products; the ${\alpha}$ particle method was stabilized with an increase in the shaping time and was less sensitive to this change compared to when the gamma-ray method was used. In the case of the simulated energy spectrum with transport properties evaluated by the ${\alpha}$ particle method, the peak position and tail were slightly different from the measured result, whereas the energy spectrum derived from the low-energy gamma-ray was in good agreement with the experimental results. From these results, it was confirmed that low-energy gamma-rays are more useful when seeking to obtain the transport properties of carriers than ${\alpha}$ particles because the methods that use gamma-rays are less influenced by the surface condition of the CZT detector. Furthermore, the analysis system employed in this study, which was configured by a combination of Monte Carlo simulation and the Hecht model, is expected to be highly applicable to the study of the characteristics of CZT detectors.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.5 no.9
• /
• pp.1492-1512
• /
• 2011

Due to multiple hops, mobility and time-varying channel, supporting delay sensitive real-time traffic in wireless local area network-based (WLAN) mesh networks is a challenging task. In particular for real-time traffic subject to medium access control (MAC) layer control overhead, such as preamble, carrier sense waiting time and the random backoff period, the performance of real-time flows will be degraded greatly. In order to support real-time traffic, an efficient adaptive packet scheduling (APS) scheme is proposed, which aims to improve the system performance by guaranteeing inter-class, intra-class service differentiation and adaptively adjusting the packet length. APS classifies incoming packets by the IEEE 802.11e access class and then queued into a suitable buffer queue. APS employs strict priority service discipline for resource allocation among different service classes to achieve inter-class fairness. By estimating the received signal to interference plus noise ratio (SINR) per bit and current link condition, APS is able to calculate the optimized packet length with bi-dimensional markov MAC model to improve system performance. To achieve the fairness of intra-class, APS also takes maximum tolerable packet delay, transmission requests, and average allocation transmission into consideration to allocate transmission opportunity to the corresponding traffic. Detailed simulation results and comparison with IEEE 802.11e enhanced distributed channel access (EDCA) scheme show that the proposed APS scheme is able to effectively provide inter-class and intra-class differentiate services and improve QoS for real-time traffic in terms of throughput, end-to-end delay, packet loss rate and fairness.

• Journal of Internet Computing and Services
• /
• v.15 no.2
• /
• pp.9-18
• /
• 2014

The sensors attached on/in a person are moved since human body frequency changes their activity, therefore in wireless body area networks, nodal mobility and non-line-of-sight condition will impact on performance of networks such as energy efficiency and reliable communication. We then proposed schemes which study on forwarding decisions against frequent change of topology and channel conditions to increase reliable connections and improve energy efficiency. In this work, we control the size of packets, forwarding rate based on ratio of input links and output links at each node. We also robust the network topology by extending the peer to peer IEEE 802.15.4-based. The adaptive topology from chain-based to grid-based can optimal our schemes. The simulation shows that these approaches are not only extending network lifetime to 48.2 percent but also increase around 6.08 percent the packet delivery ratio. The "hot spots" problem is also resolved with this approach.

• The Journal of The Korea Institute of Intelligent Transport Systems
• /
• v.14 no.1
• /
• pp.57-67
• /
• 2015

A large amount of work has been done in the areas of routing, MAC, QoS, capacity, location service, cooperative communication, fault tolerance, mobility models and various applications of mesh networks thanks to their merits of cost-effective way of deployment and flexibility in extending wireline services. Although multi-path routing protocols have been proposed to be used to provide QoS and fault-tolerance, there has not been any significant results discussed that support both in the literature to our best knowledge as they are often required in military and public safety applications. In this paper, we present a novel routing protocol for a mesh network based on the OFDM-TDMA collision-free MAC that discovers and maintains multiple paths that allows retransmitting and forwarding packets that have been blocked due to a link failure using an alternative next-hop node such that the delay-capacity tradeoff is reduced and the reliability is enhanced. Simulation results show that the proposed protocol performs well in terms of both the QoS and delivery ratio.