Sung-Hyup Lee

Directional AODV Routing Protocol for Wireless Mesh Networks

In most application scenarios, Wireless Mesh Networks (WMNs) are stationary or quasi-stationary with support of minimal mobility, in which most of their traffic is destined to the Internet through a gateway. Ad hoc On-demand Distance Vector (AODV) is not appropriate for such WMNs, because flooding-based route discovery is both redundant and very expensive in terms of control message overhead. In this paper, we propose a directional AODV (D-AODV) routing protocol based on hop count to a gateway. In the route discovery to a gateway, D-AODV can reduce the number of broadcasting route request (RREQ) packets by using a restricted directional flooding technique. Simulation results showed that D-AODV could significantly reduce routing overhead by RREQ packets and enhance overall throughput performance.

Enhanced fast handover mechanism using MIH services in MIPv6

In this paper, we propose an enhanced handover mechanism with new additional primitives and parameters to the media independent handover (MIH) services as defined in IEEE 802.21. The proposed scheme can reduce handover latency for MIPv6 (mobile IPv6) by removing the router discovery time. Moreover, when the proposed mechanism is applied to a FMIPv6 (fast handovers for MIPv6), we can increase the probability that FMIPv6 can be per-formed in a predictive mode by reducing the handover initiation time. As a result, we can get the reduced handover latency in FMIPv6. In addition, with the proposed scheme, we can design the cost-effective network by reducing cover-age overlap between adjacent cells. This is due to the decreased handover initiation time in FMIPv6. From simulation results, it is proven that the proposed scheme can provide a higher goodput for UDP and TCP because it has less service disruption during handovers.

Enantioselectivity of 6-O-alkyldimethylsilyl-2,3-di-O-methyl-β-cyclodextrins as chiral stationary phases in capillary GC

SummaryThree new 2,3-di-O-methyl-β-cyclodextrins having different 6-O-alkyldimethylsilyl groups, 6-O-isopropyldimethylsilyl-2,3-di-O-methyl-β-cyclodextrin (IPDM-β-CD), 6-O-thexyldimethylsilyl-2,3-di-O-methyl-β-cyclodextrin (TXDM-β-CD) and 6-O-cyclohexyldimethylsilyl-2,3-di-O-methyl-β-cyclodextrin (CHDM-β-CD), have been prepared and their enantioselectivities for the separation of a range of test racemic compounds in capillary gas chromatography investigated. IPDM-β-CD gave good separations of all of the test componds studied while TXDM-β-CD showed the highest enantioselectivity for the test compounds except for three nonpolar compounds. CHDM-β-CD showed very low enantioselectivity. Differences in enantioselectivities among the CD derivatives were rationalized in terms of the steric hindrance and hydrophobicity effects influencing the inclusion of the guest in the host CD derivatives.

Network mobility management using predictive binding update

This paper proposes an efficient network mobility management scheme for mobile networks such as trains and buses moving on the predetermined path. In this scheme, each mobile router maintains a database about the list of access routers, their network prefixes, and cell radii on the moving path. The mobile router therefore knows in advance network prefixes and its care-of addresses of all subnets without beacon signals. Using this database and current location information, the mobile router can prepare network layer hand-over with predictive binding update before link layer handover occurs, thereby the service disruption time due to handover will be reduced to the link layer handover latency.

An efficient preemption-based channel scheduling algorithm for service differentiation in OBS networks

Optical burst switching (OBS) is a promising switching technology for realization of an economical optical Internet. Quality-of-service (QoS) support is an important challenging issue of OBS networks, and a number of schemes have been proposed. However, the existing schemes have some limitations, such as QoS performance degradation, low wavelength utilization, and high implemental complexity. This paper proposes a bufferless preemption-based channel scheduling algorithm for service differentiation in OBS networks, which combines a preemption channel selection algorithm and a channel partitioning algorithm. The proposed preemption channel selection algorithm minimizes the length of preempted bursts to improve channel efficiency, and the channel partitioning algorithm controls the degree of service differentiation between service classes with low implemental complexity. An analytical model is derived and simulations are conducted to evaluate the performance. The results showed that the proposed scheme can improve channel efficiency and effectively provide controllable service differentiation for multi-class traffic in terms of the burst blocking probability and end-to-end throughput.

Fast IP handover for multimedia services in wireless train networks

This paper proposes a fast IP handover scheme for multimedia services in wireless train networks This scheme uses the peculiar mobility characteristics of public vehicles such as trains and buses Their moving pattern has a tendency to be predictable, because the moving path and direction are very routine This enables a mobile router on the train to predict and to prepare the next IP layer handover before the link layer handover occurs, thereby the service disruption time due to handover will be reduced to the link layer handover latency In order to perform the predictive IP handover, this scheme uses three mechanisms, such as predictive handover decision, predictive handover initiation, and predictive binding update Analytical results showed that the proposed scheme can provide excellent performance in terms of service disruption time and packet loss ratio, compared with the existing IP handover scheme for mobile networks.

A data-centric self-organization scheme for energy-efficient wireless sensor networks

In this paper, we propose a new self-organization scheme, DICSION (Data-centrIC Self-organizatION), which can improve the energy efficiency and prolong network lifetime of wireless sensor networks. Since a large number of sensor nodes are densely deployed, neighboring nodes may be very close to each other. Therefore, we assume that sensor nodes have a high possibility to collect the duplicate data about the same event. DICSION can considerably reduce the energy consumption because a zone head only can transmit and receive a representative data to base station or neighboring zone heads after zone formation. Our performance evaluation results demonstrate that DICSION outperforms to STEM.

Directional Flooding Scheme with Data Aggregation for Energy-Efficient Wireless Sensor Networks

We propose a directional flooding with data aggregation (DFDA) using hop-count values of sensor nodes for energy-efficient wireless sensor networks. In DFDA, the hop-counts of sensor nodes are used to discover the route to the sink. The packets of sensor nodes are aggregated in intermediate nodes and delivered to the sink or neighbors with direction to the sink. In addition, we develop a constrained data aggregation mechanism that discards the redundant data in intermediate nodes. Data aggregation is widely accepted as an essential paradigm for energy-efficient routing in wireless sensor networks. The proposed scheme, DFDA, achieves energy savings by reducing the redundant transmissions using directional flooding based on hop-count and data aggregation. Our simulation results show that DFDA achieves significant improvement in energy consumption.

Energy-Efficient Data-Aware Routing Protocol for Wireless Sensor Networks

An energy-efficient and data-aware routing protocol is proposed for wireless sensor networks. In the proposed scheme, data is sensed as either normal or urgent according to its time exigency, then different data delivery mechanisms are used depending on what kind of data is sensed, thereby improving both the energy-efficiency and reliability of a wireless sensor network. First, normal data is delivered to the sink using a single-path-based data forwarding mechanism to improve the energy-efficiency, as this data is not as important or contingent on time. Meanwhile, urgent data is transmitted to the sink using a hop-count-based directional flooding mechanism to guarantee high reliability, as this data must reach the sink. Simulation results show that the proposed scheme can achieve a significant improvement in energy consumption, along with high reliability for urgent data delivery.

Seamless network mobility management for realtime service

A mobile network is a set of IP subnets connected to the Internet through one or more mobile routers. When a mobile router moves into or out of a subnet, it suffers from the same handover problems as a mobile node does in the Mobile IP. A seamless handover scheme with dual mobile routers is proposed for a large and fast moving network such as trains. Each of the dual mobile routers is located at each end of the moving network for space diversity, but they perform a handover as one logical mobile router. Since one of the two mobile routers can continuously receive packets from its home agent, the proposed scheme can provide no service disruption time resulting in no packet losses during handovers. Performance evaluation showed that the proposed scheme can provide excellent performance for realtime service, compared with existing schemes.