ChungJae Lee

Fuzzy Search Controller in Unstructured Mobile Peer-to-Peer Networks

Typical mobile P2P protocols largely relied on inflexible techniques such as, flooding, replicating, random walks and selective forwarding to route queries and discover objects of interest, which incur a relatively high search time due to remarkable network traffic, multiple copies and duplication of query messages. Recently proposed P2P protocols are able to reduce search time but due to peer mobility, these protocols cause low hit rate and high overhead. Thus, this article proposes novel fuzzy controller based probabilistic walk for unstructured mobile P2P networks to reduce search time. The search time is reduced by jumping a query walker to 2-hop away selected ultrapeer through fuzzy controller. Furthermore, each ultrapeer share its pong cache with its directly connected ultrapeer to increase hit rate and reduce network overhead. Simulations show that the fuzzy search controller gives better performance than the competing protocols in terms of reducing response time by 10% and increasing hit rate by 15% in different mobility scenarios.

An architecture for (m, k)-firm real-time streams in wireless sensor networks

Despite increasing demand of application specific requirements in wireless sensor networks, lots of research is still going on under assumption of general requirement without considering specific traffic model as well as several constraints. To address this issue, we have already introduced a new real-time application with (m, k)-firm model and developed communication protocols for multimedia sensor networks. But, scalability problem and lack of architecture for (m, k)-firm stream are major research challenges that remain unsolved. Based on corresponding demands, in this paper, we propose a new integrated architecture for (m, k)-firm stream in wireless sensor networks with following functions, that is, flow aggregation based on compositional hierarchical model, velocity based routing protocol, hybrid medium access control protocol, and congestion control scheme. Simulation results are given to prove the suitability of the architecture and performance improvement under several scenarios.

Delay bounded spray and wait in delay tolerant networks

Recently, application-specific requirement becomes one of main research challenges in the area of routing for delay tolerant networks. Among various requirements, in this paper, we focus on achieving the desired delivery ratio within bounded given deadline. For this goal, we use analytical model and develop a new forwarding scheme in respective phase. The proposed protocol dynamically adjusts the number of message copies by analytical model and the next hop node is determined depending on the delivery probability and the inter-meeting time of the encountering nodes as well as remaining time. Simulation results demonstrate that our proposed algorithm meets bounded delay with lower overhead than existing protocols in an adaptive way to varying network conditions.

A Deadline Aware DTN Approach Based on Epidemic Routing

Delay Tolerant Networks (DTN) has been proposed to provide communication between nodes where they are intermittently connected. In this situation, a new routing approach, store-carry-forward, is used to deliver data between source and destination. Even though long delay is acceptable in DTN, however some applications occasionally require predetermined bounded delay. To meet this requirement, some approaches have been proposed. However, due to dependency on assumption such as infinite buffer size and mobility pattern, they suffer from deployment problem. To defeat this problem, in this paper, we propose a new probabilistic epidemic routing with time constraint and delay. We adjust forwarding probability on each node depending on bounded delay, elapsed time, and current networks environment. Simulation results reveal that the proposed scheme can meet required delivery ratio and consume little resource rather than original one and competitive protocol.

Design of hierarchical routing protocol for heterogeneous airborne ad hoc networks

Due to recent research interests in airborne ad hoc networks, many research works have been conducted in each layer by developing communication protocols which take into unique properties of node (aircraft) as well as operating environments account. Among them, as the research efforts in network layer, several routing protocols have been proposed to improve packet delivery ratio even though a node moves faster than one in existing ad hoc networks. Related to routing protocol, as proved in many previous research works, hierarchical routing protocol can be considered as appropriate approach in airborne ad hoc networks due to its stability against dynamic change on topology. To meet above demand, in this paper, we present how to form two level hierarchies for heterogeneous networks by extending current geographical routing protocol. Furthermore, the proposed scheme introduces how to improve the packet delivery ratio by applying DTN (Delay Tolerant Networks) routing protocol adaptively for network partition. Simulation results are given to prove suitability of proposed protocol in heterogeneous airborne ad hoc networks.

Beaconless Geographic Routing Protocol with Adaptive Delay Timer in Wireless Sensor Networks

Even though geographical routing protocol is regarded to energy-efficient and scalable approach in wireless sensor networks, position information through beacon messages should be exchanged prior to forwarding procedure. This is another control overhead when it comes to consider nodes constraints. Thus, recently beacons graphical routing have been proposed to perform data forwarding without information exchange by distance-based delay timer and overhearing technique. However, existing schemes causes additional recurrent and redundant delay in cases of network dynamics or partial network holes in each hop. Specially, if the networks are not uniformly deployed, current schemes cannot be applied. To solve this problem, in this paper, we propose a new fast beaconless protocol, which enables neighbor nodes of a sending node to adjust their delay time depending on whether any node is identified by localized backlearning scheme or not. Also, simulation results are presented and analyzed to prove the decreased end-to-delay delay and increased packet delivery ratio.

Dynamic Culling Scheme Based on Altitude for Real-Time Rendering System

Dynamic culling scheme is usually implemented to handle overhead caused by rendering the massive large-scale terrain data in flight simulator. However, existing culling scheme without considering altitude is not suitable for flight simulator due to additional computational overhead. To solve this problem, in this paper, we propose hybrid approach by applying two dynamic culling schemes depending on altitude. In addition, we remove unnessary computational overhead by creating different z-map resolution when aircraft changes its altitude. The proposed scheme is implemented with open graphic library and tested with real terrain data. Through the experimental results, we can recognize the improved rendering speed about 8 to 73 percents as compared to existing scheme.

A new hybrid culling scheme for flight simulator

In flight simulator, real-time rendering system processes most of scenarios at high altitude. Therefore, overload process of real-time rendering system tends to ignore altitude distinction through applying only view-frustum culling. However, even though the flight of the aircraft operates at high altitude, but dynamic culling according to altitude is demanded because of several situations such as takeoff, landing and flight at low altitude. According to this problem statement, in this paper, we propose how to adjust dynamic culling in case of low altitude. To achieve this goal, first, we classify high altitude and low altitude depending on the height of the aircraft motion simulation. Moreover, we apply fuzzy logic into classifies for ambiguous altitude state. If altitude state is low, we use both view-frustum and back-face culling at once in order to reduce complexity of the operations caused by the visibilitytest to dynamically generate the resolution of the ZMap for back-face culling at low altitude state. We use OSG(Open Scene Graph) graphic library and test real world terrain data. Through test results, our proposed algorithm decreases triangles of 15~80% in real-time rending, and improves frame per second of 8~73% as compared to existing one.

Novel Clustering Scheme to Guarantee Lifetime of Wireless Sensor Networks

Besides main quality of service features the guaranteed lifetime is one of the key characteristic of many applications for efficient operations, therefore guaranteeing the lifetime of the entire wireless sensor networks is mainly considered in the scheme. In this paper, a novel scheme to guarantee the lifetime of wireless sensor networks in terms of distributed and randomized clustering with scary energy is proposed. We then extend this algorithm to checks the status of every cluster head and conclude that how much energy is spent during performing different operations. The cluster head will also aware of the time for which it will perform duty as a local base for its member nodes. Simulation results validate the effect of the proposed clustering algorithm to guarantee scary lifetime of wireless sensor networks.

Implementation of Display Based on Pilot Preference

As the many functions on the aircraft are implemented through software, they provide the pilots with more flexible and extensible controls. Among them, display is one of the important instruments in that information on the aircraft is recognized through it. While previous display was static with fixed layout, a new display is dynamic by employing floating layout on the screen through the help of software. In this paper, we propose a new display method, which automatically returns to the layout of instruments on the aircraft according to the pilot preference. To achieve this, the software records current layout and suggests the best matching layout to the pilot whenever the same event occurs. We explain the design and implementation issues to add this function into the current system.