• Applied Chemistry for Engineering
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• v.16 no.3
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• pp.422-426
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• 2005

Visible-light activated polymer nanocomposites (PNC) were designed to be used for dental restoration. Hybrid-filler composed of barium silicate and nano-sized silica was adopted as a filler system. To improve the interfacial be havior of the resin matrix of bisphenol A glycerolate methacrylate/triethyleneglycol dimethacrylate, the surface of filler was hydrophobically treated with a silane coupling agent. Mechanical properties of PNC were investigated by measuring the abrasion resistance, and it was discovered that PNC showed excellent properties with an increase of nanofiller content. However, the polymerization shrinkage was consistently maintained under 3 vol% and the shrinkage continued even after photo-polymerization. In addition, a slight color difference between PNC specimens was observed with increase of nanofiller content.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.8
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• pp.3841-3861
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• 2017

Virtualized small cell network is a promising architecture which can realize efficient utilization of the network resource. However, conventional full duplex self-backhauls lead to residual self-interference, which limits the network performance. To handle this issue, this paper proposes a virtual resource allocation, in which the residual self-interference is fully exploited by employing a physical-layer network coding (PNC) aided self-backhaul scheme. We formulate the features of PNC as time slot and information rate constraints, and based on that, the virtual resource allocation is formulated as a mixed combinatorial optimization problem. To solve the problem efficiently, it is decomposed into two sub problems, and a two-phase iteration algorithm is developed accordingly. In the algorithm, the first sub problem is approximated and transferred into a convex problem by utilizing the upper bound of the PNC rate constraint. On the basis of that, the convexity of the second sub problem is also proved. Simulation results show the advantages of the proposed scheme over conventional solution in both the profits of self-backhauls and utility of the network resource.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.7 no.12
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• pp.3018-3036
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• 2013

In this paper, we investigate power allocation scheme and outage performance for a physical-layer network coding (PNC) relay based secondary user (SU) communication in cognitive multi-antenna relay networks (CMRNs), in which two secondary transceivers exchange their information via a multi-antenna relay using PNC protocol. We propose an optimal energy-efficient power allocation (OE-PA) scheme to minimize total energy consumption per bit under the sum rate constraint and interference power threshold (IPT) constraints. A closed-form solution for optimal allocation of transmit power among the SU nodes, as well as the outage probability of the cognitive relay system, are then derived analytically and confirmed by numerical results. Numerical simulations demonstrate the PNC protocol has superiority in energy efficiency performance over conventional direct transmission protocol and Four-Time-Slot (4TS) Decode-and-Forward (DF) relay protocol, and the proposed system has the optimal outage performance when the relay is located at the center of two secondary transceivers.

• Journal of Communications and Networks
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• v.17 no.5
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• pp.463-472
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• 2015

This paper considers a limited feedback system for two-way wireless relaying channels with physical network coding (PNC). For full feedback systems, the optimal structure with the PNC has already been studied where a modulo operation is employed. In this case, phase and power of two end node channels are adjusted to maximize the minimum distance. Based on this result, we design new quantization methods for the phase and the power in the limited feedback system. By investigating the minimum distance of the received constellation, we present a code-book design to maximize the worst minimum distance. Especially, for quantization of the power for 16-QAM, a new power quantization scheme is proposed to maximize the performance. Also, utilizing the characteristics of the minimum distance observed in our codebook design, we present a power allocation method which does not require any feedback information. Simulation results confirm that our proposed scheme outperforms conventional systems with reduced complexity.

• Journal of Korea Multimedia Society
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• v.14 no.12
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• pp.1559-1571
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• 2011

In wireless ad hoc networks, nodes communicate with each other using multihop routed transmission in which hop-by-hop cooperative diversity can be effectively employed. This paper proposes (i) two cooperation models for per-link cooperation (PLC) and per-node cooperation (PNC) for exploiting cooperative diversity in wireless ad hoc networks and (ii) a cooperative routing algorithm for the above models in which best relays are selected for cooperative transmission. First, two cooperation models for PLC and PNC are introduced and represented as an edge-weighted graph with effective link quality. Then, the proposed models are transformed into a simplified graph and a cooperative routing algorithm with O(n2) time is developed, where n is the number of nodes in the network. The effectiveness of the algorithm is confirmed for the two cooperation models using simulation.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.42 no.5
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• pp.999-1008
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• 2017

In this paper, we propose a pipeline network coding (PNC) scheme for efficient data transmission in wireless networks, a data authentication scheme for verifying the integrity of data, and a node authentication scheme for a virtual source. PNC is a technique that improves the overall network performance by relaying data such that the relay node performing network coding transmits to the sender instead. However, network coding is vulnerable to a pollution attack, which is an attack by a malicious attacker to inject modified data into the network. To prevent this, hash-based message authentication code (HMAC) is used. For this purpose, in order to generate a tag used for data authentication, a key must be distributed to the nodes performing authentication. We applied a hash chain to minimize the overhead of key distribution. A null vector is used as the authentication scheme for the virtual source. Finally, we analyze the safety and complexity of the proposed scheme and show he performance through simulation.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.6B
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• pp.350-357
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• 2007

The IEEE 802.15.3 high-rate WPAN has been developed to communicate with devices within l0m. A piconet consists of one Piconet Coordinator (PNC) and several devices. The devices associated with a parent piconet can become child PNCs in order to form child piconets. A mesh network made up of a parent piconet and several child piconets can support multi-hop communications. In this paper, we analyze the maximum level and the avaliable superframe size to make the best use of bandwidth for multi-hop communications, and compare the analysis with the simulation results in terms of time to discover devices for multi-hop communications. The average number of levels in mesh networks is shown to be about 1.9 when the number of devices increases within a fixed area. We have also shown that the maximum available superframe size is 52ms and the discovery time is approximately 155ms.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.42 no.11
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• pp.1-12
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• 2005

In wireless personal area networks(PANs), the successful design of channel time allocation algorithm is a key factor in guaranteeing the various quality of service(QoS) requirements for the stringent real-time constraints of multimedia services. In this paper we propose a dynamic channel time allocation algerian for providing delay guarantees to multimedia traffics such as MPEG streams in the IEEE 802.15.3 high-rate WPANs. The dynamic algorithm exploits the characteristics of MPEG stream, wherein the devices (DEVs) send their channel time requests only at the end of superframe boundaries. The algerian uses mini packets for feedback control in order to deliver dynamic parameters for channel time requests from the DEVs to the piconet coordinator (PNC). In this scheme, the duration of channel time allocated to a DEV during a superframe is changed dynamically depending on the MPEG frame type, traffic load and delay bound of the frame, etc. Performance of the proposed scheme is investigated by simulation. Our results show that compared to traditional scheme, the proposed scheme is very effective and has high performance while guaranteeing the delay bound.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.9
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• pp.2131-2139
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• 2014

In this paper, a binary-coded physical-layer network coding (PNC) is considered when high-order modulation techniques are used at source nodes in wireless communication environments. In the conventional PNC schemes, tight power control and phase compensation are required at a relay node. However, they may not be feasible in practical wireless communication environments. Thus, we do not assume the pre-equalization in this paper, and we only utilize the channel state information at receiver (CSIR). We propose a signal detection method for the binary-coded PNC with high-order modulation, such as QPSK and 16QAM, at the source nodes, while the conventional scheme only consider the BPSK at source nodes. We also analyze the bit-error performance of the proposed technique in both uncoded and coded cases.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.306-307
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• 2006

The sinter-bonding behavior of iron based powder mixtures was investigated. To produce the green compacts to be joined the following powders based on $H{\ddot{o}}gan{\ddot{a}}s$ AB grade NC 100.24 plain iron powder were used: NC 100.24 as delivered, PNC 30, PNC 60 and NC 100.24 + 4%Cu powder mixtures. Dimensional behaviour of all those materials during the sintering cycle was monitored by dilatometry. Simple ring shaped specimens as the outer parts and cylindrical as the inner parts were pressed. The influence of parts' composition on joining strength was established. Diffusion of alloying elements: copper and phosphorous, across the bonding surface was controlled by metallography, SEM and microanalysis.