• Journal of KIISE
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• v.43 no.8
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• pp.893-901
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• 2016

In Internet of Things (IoT) environments, users are required to search for IoT devices necessary to access services for accomplishing their tasks. As IoT technologies advance, a user task will utilize various types of IoT-based services that are deployed in an IoT environment. Therefore, to accomplish a user task effectively, the services that utilize IoT devices need to be found in a certain geographical region. In addition, the service discovery needs to be accomplished in a stable manner while considering dynamically changing IoT environments. To deal with these issues, we propose two service discovery methods that consider geographic cohesiveness of services in IoT environments. We compare the effectiveness of the proposed methods against a traditional service discovery algorithm that does not consider geographic cohesiveness.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.21 no.9
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• pp.1649-1654
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• 2017

The route request (RREQ) packet of the GAODV is propagated in a unicast-manner using the location of the destination, but the application of the GAODV is restricted by the assumption for the known destination's location. In this paper, we propose a virtual destination aided GAODV (VDA-GAODV) that alleviates the uncertainty of the destination's location due to the mobility. Instead of the known location of the destination, the VDA-GAODV disseminates a RREQ packet to an imaginary location on the line connecting the source and the destination. We derive an optimal imaginary destination that makes RREQ rebroadcasts cover the possible locations of the destination as much as possible. The VDA-GAODV enables the RREQ propagation to cover 95 % of the one-hop communication area centered at the originally known location of the destination, which is larger than that of the original GAODV by 23 %.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.7B
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• pp.728-733
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• 2009

An ubiquitous environment has features like peer-to-peer and nomadic environments. Such features can be represented by peer-to-peer systems and mobile ad-hoc networks. P2P systems and MANETs share similar features, appealing for implementing P2P systems in MANET environment. However, if a P2P system designed for wired networks was applied to mobile ad-hoc environment, its performance was not good enough. Subsequently, this paper proposes a P2P system to improve performance using cross-layer design and the goodness of a node as a peer by using routing metric and P2P metric to choose favorable peers to connect. It also utilizes proactive approach for distributing peer information. The simulation results showed that the proposed system produced better performance in query success rate, query response time and energy consumption by reducing the routing path length.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38C no.2
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• pp.155-164
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• 2013

Two design techniques for more accurate and more convenient hybrid positioning system with visible light communication (VLC) and ad-hoc wireless network infrastructure are proposed, in order to overcome the problems of high estimation error, high cost, and limited service range of the conventional positioning techniques. First method is based on a non-carrier VLC based hybrid positioning technique for applications involving of low data rate optical sensing and narrow-range visible light reception from transmitter, and long-range positioning. The second method uses a 4 MHz carrier VLC-based hybrid positioning technique for a high data rate optical sensing and wide-range visible light receiving from transmitter, and mid-range positioning applications. In indoor environments with obstacles where there are long-range 7731.4cm and mid-range 2368cm distances between an observer and a target respectively, the hybrid positioning developed with two design techniques are tested, and the proposed system is verified and analyzed in this paper.

• Journal of the Korea Institute of Military Science and Technology
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• v.23 no.4
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• pp.371-380
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• 2020

Video is principal information that facilitates commander's immediate command decision. Due to fading characteristics of radio link, however, it is difficult to stably transmit video in a multi-hop wireless environment. In this paper, we propose a MANET structure composed of a link adaptive routing protocol and a TDMA MAC protocol to stably transmit video traffic in a ultra-narrowband video streaming network. The routing protocol can adapt to link state change and select a stable route. The TDMA protocol enables collision-free video transmission to a destination using multi-hop dynamic resource allocation. As a result of simulation, the proposed MANET structure shows better video transmission performance than proposed MANET structure without link quality adaption, AODV with CSMA/CA, and OLSR with CSMA/CA structures.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.19 no.4
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• pp.105-114
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• 2009

Messages exchanged among vehicles must be authenticated in order to provide collision avoidance and cooperative driving services in VANET. However, digitally signing the messages can violate the privacy of users. Therefore, we require authentication systems that can provide conditional anonymity. Recently, Zhang et al. proposed conditionally anonymous authentication system for VANET using tamper-resistant hardware. In their system, vehicles can generate identity-based public keys by themselves and use them to sign messages. Moreover, they use batch verification to effectively verify signed messages. In this paper, we provide amelioration to Zhang et al.'s system in the following respects. First, we use a more efficient probabilistic signature scheme. Second, unlike Zhang et al., we use a security proven batch verification scheme. We also provide effective solutions for key revocation and anonymity revocation problems.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.4A
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• pp.369-379
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• 2011

During the routing process between nodes on the CR(Cognitive Radio) network conducting for efficient use of limited frequency resources, spectrum handover process due to the appearance of the PU occupies most of the routing latency, and also decreases the reliability of the path. In this paper, a cooperative routing protocol in a multi-channel environment is proposed. The source node broadcasts a message with available channel lists and probability of PU appearance during its route guidance. The intermediate nodes re-transmit the message, received from the source node, and update and maintain the information, status table of the path. The destination node determines the optimal path and sends a reply message to the selected path after it receives the messages from the intermediate nodes. The average probability of the PU appearance and the average time of the PU appearance are updated while transferring data. During data transmission the channel with the lowest probability of appearance of the PU is selected dynamically and if a PU appears on the current channel partial repairment is performed. It is examined that reliability of the selected path considerably is improved and the routing cost is reduced significantly compared to traditional routing methods.

• Journal of the Korea Society of Computer and Information
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• v.16 no.6
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• pp.131-142
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• 2011

In this paper, we propose a new multipath routing protocol and compare it with other multipath routing protocols in mobile ad hoc network (MANET) environments. The new multipath routing establishes the main route using a mechanism based on Ad Hoc On-demand Distance Vector(AODV), after which data transmission starts immediately. The backup route search process takes place while data are transmitted, to reduce the transmission delay. The protocol can also operate in a hybrid node-disjoint/link-disjoint mode, where the protocol finds the node-disjoint backup route first; if the node-disjoint does not exist, the protocol discovers the link-disjoint backup route from the main route. When either of the main route or the backup route is broken, data are transmitted continuously through the other route and the broken route is recovered by the route maintenance process. The results of simulations, based on the Qualnet simulator, show that the proposed multipath routing protocol increases the packet transmission success rate and reduces end-to-end delays, when compared with AODV and AOMDV protocols.

• The KIPS Transactions:PartC
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• v.13C no.5 s.108
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• pp.621-626
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• 2006

A mobile ad hoc network (MANET) is an infrastructureless network that supports multi-hop communication. For the MANET nodes wishing to communicate with nodes in the wired Internet, the global Internet connectivity is required and this functionality can be achieved with the help of the Internet gateway. For the support of reliability and flexibility, multiple Internet gateways can be provisioned for a MANET. In this case, load-balancing becomes one of the important issues since the network performance such as the network throughput can be improved if the loads of the gateways are well-balanced. In this paper, we categorize the load-balancing mechanisms and propose a new metric for load-balancing. Simulation results show that our proposed mechanism using the hop distance and the number of routing table entries as a load-balancing metric enhances the overall network throughput.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.16 no.6
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• pp.1173-1178
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• 2012

In the Cluster-Based Routing Protocol (CBRP) a cluster header in each cluster should be elected. The cluster headers consume energy much more than other nodes because they manage and operate all of mobile nodes in their cluster. The traditional CBRP elects a cluster header without considering the remaining electric energy of each node. So, there exists problems that the cluster header has short average lifetime, and another cluster header should be elected again frequently. In this paper, we propose the improved protocol which prolongs the lifetime of the cluster header and enhances the stability of the path. In order to achieve this, when a cluster header is elected in a cluster, the remaining electric energies of all the nodes are compared with one another, and the node with the highest energy is elected as the cluster header.