• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.3B
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• pp.398-407
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• 2010

Due to increase of user requirement for various traffics and the advance of network technology, each distinct network has converge into FMC(Fixed Mobile Convergence) networks. However, we need to research the performance analysis of VoIP(Voice over Internet Protocol) in the FMC network to provide QoE for the voice user of FMC network. Therefore, this paper introduces the scenario which is the situation of voice quality degradation when a user uses VoIP to communicate with other users in the FMC network. Especially, this paper presents scenario in terms of the component of the network and finds the improvement point of voice quality. In the simulation results, three improvement points of voice quality are found as following: voice quality degradation by packet loss in the physical layer of the HSDPA network, by utilizing GGSN without QoS parameter mapping mechanism which is gateway between 3GPP and IP backbone, and by using non-QoS AP in the WLAN network.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.2A
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• pp.195-202
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• 2007

A differential space-frequency block code - orthogonal frequency division multiplexing (SFBC-OFDM) scheme as a multiple-input multiple-output (MIMO) transmission technique for next-generation digital multimedia broadcasting (DMB) is proposed in this paper. A linear decoding method for differential SFBC, which performs comparably to the ML decoding method, is derived for the cases of two or four transmit antennas. A simple table lookup method is proposed to improve the efficiency of the encoding/decoding process of DSFBC for the case of non-constant modulus constellations. A DMB MIMO channel model, developed by extending the 3GPP MIMO model to fit DMB environments, is used to compare BER performances of differential space block code schemes for various channel environments. Simulation results show that the differential SFBC-16QAM scheme using either four transmit antennas with one receive antenna or two transmit antennas with two receive antennas achieves a performance gain of 12dB than that of the conventional DQPSK scheme, even with a data rate twice faster.

• Electronics and Telecommunications Trends
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• v.38 no.2
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• pp.1-11
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• 2023

The recent explosion in the number of low earth orbit (LEO) satellites launched to space allows to easily anticipate that the number of satellites in orbit will sustain a dramatic increase. As satellite components are integrated and unified with terrestrial cellular networks, they will play a key role in providing coverage and resilience for future cellular networks. We provide a brief overview of typical scenarios and network architectures for cellular-based LEO satellite communication systems. In addition, we outline 3GPP standardization trends in non-terrestrial networks and satellite access based on 5G/5G Advanced systems and analyze future evolution prospects of cellular-based satellite communication systems.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.12A
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• pp.1291-1297
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• 2004

In this paper, the new scheduling algorithm that supports the maximization of system throughput and the proportional fairness among non-real time traffic users is proposed in OFDMA wireless mobile communication systems. The concept of the proposed algorithm is based on the proportional fairness algorithm, which is deployed in 3GPP2, and sorting method. The proportional fairness algorithm is adapted to allocate the number of subcarrier per user. A sorting method is contributed to the maximization of system throughput in the practical allocation of subcarrier per user. Simulation results show that new algorithm had better performance than the max rate rule in case of fairness, higher throughput than the scheduling algorithm without sorting method. Even though the system throughput of the proposed algorithm is almost same with the iteration scheme using subcarrier swapping method between users, the computational time of the former is reduced up to 3 times than the latter.

• Journal of the Korea Society of Computer and Information
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• v.25 no.2
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• pp.83-92
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• 2020

In this paper, we propose an efficient session management scheme for low-latency communications in 5G systems. The main idea of the proposed scheme is to prevent unnecessary reattempt signalling overhead when the session establishment for low-latency communications fails. Also, this method avoids network resource waste and battery drain of mobile devices. If a UE(User Equipment) fails to establish an Always-on PDU session for low-latency communications with the 5G systems because of network failure or resource unavailability, the proposed method prevents the UE's re-establishment of the Always-on PDU session by the specific information in the NAS(Non-Stratum) message from the 5G systems. Through simulation, we show that the proposed efficient session management scheme (ESMS) minimizes unnecessary signalling overhead and improves battery efficiency of mobile devices compared to existing legacy mechanism in 5G systems.

• Journal of Internet Computing and Services
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• v.22 no.5
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• pp.9-16
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• 2021

Recently, the traffic volume of mobile communications increases rapidly and the small-cell is one of the solutions using two offload schemes, i.e., local IP access (LIPA) and selected IP traffic offload (SIPTO), to reduce the end-to-end delay and amount of mobile data traffic in the core network (CN). However, 3GPP describes the concept of LIPA and SIPTO and there is no decision algorithm to decide the path from source nodes (SNs) to destination nodes (DNs). Therefore, this paper proposes a dynamic mobile data traffic offload scheme using small-cells to decide the path based on the SN and DN, i.e., macro user equipment, small-cell user equipment (SUE), and multimedia server, and type of the mobile data traffic for the real-time and non-real-time. Through analytical models, it is shown that the proposed offload scheme outperforms the conventional small-cell network in terms of the delay of end-to-end mobile data communications and probability of the mobile data traffic in the CN for the heterogeneous networks.

• ETRI Journal
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• v.36 no.1
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• pp.31-41
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• 2014

The heterogeneous network (HetNet) has been discussed in detail in the Long-Term Evolution (LTE) and LTE Advanced standards. However, the standardization of High-Speed Packet Access HetNet (HSPA HetNet) launched by 3GPP is pushing at full steam. Interference coordination (IC), which is responsible for dealing with the interference in the system, remains a subject worthy of investigation in regard to HSPA HetNet. In this paper, considering the network framework of HSPA HetNet, we propose a quasi-distributed IC (QDIC) scheme to lower the interference level in the co-channel HSPA HetNet. Our QDIC scheme is constructed as slightly different energy-efficient non-cooperative games in the downlink (DL) and uplink (UL) scenarios, respectively. The existence and uniqueness of the equilibrium for these games are first revealed. Then, we derive the closed-form best responses of these games. A feasible implementation is finally developed to achieve our QDIC scheme in the practical DL and UL. Simulation results show the notable benefits of our scheme, which can indeed control the interference level and enhance the system performance.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.47 no.7
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• pp.29-35
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• 2010

The cooperative transmission between sectors in next generation communications standards, e.g., 3GPP LTE-Advanced and IEEE 802.16m, has become an important research issue. Hence methods to decide the optimal antenna tilting angle in cooperative transmission between sectors are needed. This paper proposes methods to decide the optimal antenna tilting angle in cases of non-cooperative and cooperative transmissions between sectors. The proposed methods use an objective function that maximizes the cell average log rate or the cell average rate for users distributed uniformly within the radius of the sector. Also, the objective function which maximizes the cell average rate determined by adaptive modulation and coding (AMC) used in actual cellular systems is considered. When the cell average rate becomes the objective function, the system rate efficiency increases significantly for both cooperative and non-cooperative transmission. When the cell average log rate and the AMC rate become the objective functions, an optimal antenna tilting decision method which effectively increases the efficiency of cell boundary users is discussed.

• BMB Reports
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• v.29 no.6
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• pp.525-529
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• 1996

Ligand binding properties of muscarinic acetylcholine receptors (mAChRs) in the nematode Caenorhabditis elegans (C. elegans) were characterized by using filtration binding assays. Scatchard analysis using $[^{3}H]N-methylscopolamine$ ($[^{3}H]NMS$) showed that the dissociation constant ($K_d$) and the maximum binding value ($B_{max}$) were $3.3{\pm}0.8{\times}10^{10}$ M and $9.0{\pm}1.1$ fmol/mg protein, respectively. Binding competition experiments indicated that the affinities of C. elegans mAChRs to atropine, scopolamine, and oxotremorine were similar to those of mammalian mAChRs. Pirenzepine binding experiments revealed that the binding pattern of mAChRs in C. elegans closely resembled that of mAChRs in rat brain, suggesting that the receptors consist primarily of Ml subtype. The affinity of mAChRs for oxotrernorine was significantly affected by guanylylimidodiphosphate (Gpp(NH)p), a non hydrolyzable GTP analog, suggesting that mAChRs in C. elegans might be coupled to G proteins. The data presented here indicate the possibility that C. elegans provides a living animal model to study the action mode of the muscarinic cholinergic system.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.12 no.6
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• pp.2841-2860
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• 2018

Vehicular networks play an important role in current intelligent transportation networks and have gained much attention from academia and industry. Vehicular networks can be enhanced by Long Term Evolution-Vehicle (LTE-V) technology, which has been defined in a series of standards by the 3rd Generation Partnership Project (3GPP). LTE-V technology is a systematic and integrated V2X solution. To guarantee secure LTE-V communication, security and privacy issues must be addressed before the network is deployed. The present study aims to improve the security functionality of vehicular LTE networks by proposing an efficient and secure ID-based message authentication scheme for vehicular networks, named the ESMAV. We demonstrate its ability to simultaneously support both mutual authentication and privacy protection. In addition, the ESMAV exhibit better performance in terms of overhead computation, communication cost, and security functions, which includes privacy preservation and non-frameability.