• Journal of electromagnetic engineering and science
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• 제11권2호
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• pp.113-121
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• 2011

Multiple-input multiple-output with orthogonal frequency division multiplexing technology (MIMO-OFDM) is considered to be the ultimate solution for increasing system throughput and for enhancing communication reliability. In this paper, we propose to increase the uplink (UL) throughput by assigning the same UL resources to multiple single-antenna mobile stations. This leads to the loss of orthogonality among sub-carriers. Thus, at the base station (BS), MIMO-OFDM detection techniques are used to separate the streams of different users assigned the same UL resources. To obtain a realistic performance evaluation, different channel scenarios are applied with different correlation values among the antennas of the users. Simulation results show that the proposed MIMO-OFDM system linearly increases the uplink capacity of the OFDM system while maintaining a mobile station transmitter as simple as that used in a conventional OFDM system. For instance, when 4 users are assigned the same UL resources, the throughput of the proposed system is 3.07 times that achieved by a conventional single input single output OFDM system.

• 한국정보시스템학회지:정보시스템연구
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• 제30권4호
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• pp.153-171
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• 2021

Purpose This study is to phenomenologically discover key antecedents and outcomes of behavioral process of SNS users who have multiple SNS sub-accounts. Unlike previous studies that focused on user behavior in the context of a specific SNS platform, this study attempts to describe how and why individual manages their multiple sub-accounts across a variety of SNS platforms. Design/methodology/approach By applying the grounded theory methodology (GTM) to elucidate the unique behavior in SNS platforms, this study has conducted in-depth interview with 14 respondents who handle multiple accounts across the SNS platforms. As a results of analyzing the interview manuscripts, this study has extracted 47 concepts, 10 sub-categories and 6 main categories by conducting open coding, axis coding, and selective coding. Findings By analyzing interview data, this study has derived main categories such as account management, impression management, self-categorization, authority to determine the relationship, digital shadow work, and portfolio SNS accounts from qualitative interview data. This study has also conducted a process analysis that represents how main categories could be inter-related. Based on findings, this study provides a new phenomenological perspective to understand the behavioral process of SNS users' sub-account usage experience.

• 한국통신학회논문지
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• 제39C권10호
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• pp.930-936
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• 2014

본 논문에서 소개하는 스마트 멀티탭은 스마트 폰으로 서버 PC를 통해 제어되는 전자기기이다. 네트워크 망에서 동작하는 스마트 멀티탭은 기존 멀티탭에 무선통신 프로토콜인 Zigbee 통신 모듈을 내장시켜서 사용자가 홈서버를 통해 원격에서 가전기기의 전원을 제어할 수 있게 한다. 게이트웨이의 역할을 하는 홈 서버는 인터넷을 통해 스마트 기기와 연결되어 있다. 본 논문의 최종 결과물을 통해 사용자는 스마트 기기로 멀티탭의 ON/OFF 상태정보를 확인하고 즉시 제어를 하거나 사용자가 원하는 시간에 맞춰 제어를 할 수 있다. OFF시에는 SSR모듈로 전기가 지나가는 통로를 막기 때문에 스마트 멀티탭을 구동하는데 드는 미량의 전력 소모(2watt) 이외에 모든 대기전력이 차단된다. 이를 통해 전기에너지 절감 효과를 기대할 수 있다.

• 한국위성정보통신학회논문지
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• 제6권1호
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• pp.32-36
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• 2011

이 논문에서는 상향링크에서 분산형 직교 주파수 분할 다중 접속방식(interleaved orthogonal frequency division multiple access: IFDMA)을 이용하는 전송 시스템에서 주파수 옵셋에 의해 발생하는 다중접속간섭을 제거하는 방법을 제안하고자 한다. IFDMA 시스템에서 주파수 옵셋이 발생하면 인접한 다른 사용자의 부반송파 성분이 간섭신호로 유입되어 시스템의 성능이 크게 저하된다. 이 논문에서는 시간 영역에서 주파수 옵셋을 보상한 후 주파수 영역에서 병렬 간섭 제거기법을 적용하여 다중접속간섭을 제거하는 방법을 제안한다. 모의실험을 통하여 제안방법이 특히 사용자의 수가 많을 때 효과적으로 다중접속간섭을 제거할 수 있음을 보인다.

• 전자공학회논문지A
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• 제32A권9호
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• pp.1184-1201
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• 1995

Two multiple access protocols are proposed for a multichannel WDM optical fibre local area network or metropolitan area network in which users are interconnected using a passive star topology. Each user has a single tunable transmitter and a single tunable receiver. A transmitter sends a control packet before its data packet transmission so that its intended receivers can tune to the proper data channel wavelength. The maximum throughput of the proposed protocols are independent of the effective normalized propagation delay which may include the transmitter and receiver tuning times and the processing delays. The maximum throughputs of the protocols are analyzed and compared with those of the existing ones by numerical examples. The message delay of the R- Aloha/synchronous N-server switch protocol which is suitable for the queued users is also analyzed.

• Journal of Communications and Networks
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• 제16권5호
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• pp.559-567
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• 2014

In this paper, a framework for power allocation of downlink transmissions in orthogonal frequency division multiple access-based decode-and-forward cellular relay networks is investigated. We consider a system with a single base station communicating with multiple users assisted by multiple relays. The relays have limited power which must be divided among the users they support in order to maximize the data rate of the whole network. Advanced power allocation schemes are crucial for such networks. The optimal relay power allocation which maximizes the data rate is proposed as an upper bound, by finding the optimal power requirement for each user based on knapsack problem formulation. Then by considering the fairness, a new relay power allocation scheme, called weighted-based scheme, is proposed. Finally, an efficient power reallocation scheme is proposed to efficiently utilize the power and improve the data rate of the network. Simulation results demonstrate that the proposed power allocation schemes can significantly improve the data rate of the network compared to the traditional scheme.

• 디지털산업정보학회논문지
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• 제8권4호
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• pp.129-133
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• 2012

Coordinated multi-point transmission (CoMP) is a candidate technique for next generation cellular communications systems. One of the primary elements discussed in LTE-Advanced technology is CoMP, which can improve cell edge user data rate as well as spectral efficiency due to multiple input multiple output - orthogonal frequency division multiplex (MIMO-OFDM). We consider a system with multiple cells in which base stations coordinate with each other by sharing user channel state information (CSI), which mitigates inter cell interference (ICI), especially for users located at the cell edge. We introduce a new user scheduling method of ICI cancellation and the loss reduction of effective channel gain during the beamforming process, the proposed method improves the system sum rate, when compared to the conventional method by an average of 0.55bps/Hz in different number of total users per cell. It also outperforms the conventional method by approximately 0.38bps/Hz using different SNRs.

• Journal of Communications and Networks
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• 제14권1호
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• pp.63-74
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• 2012

Multicast data communication is an efficient communication scheme, especially inmulti-hop ad hoc networks where the media access control (MAC) layer is based on one-hop broadcast from one source to multiple receivers. Compared to unicast, multicast over a wireless channel should be able to deal with varying channel conditions of multiple users and user mobility to provide good quality to all users. IEEE 802.11 does not support reliable multicast owing to its inability to exchange request-to-send/clear-to-send and acknowledgement packets with multiple recipients. Thus, several MAC layer protocols have been proposed to provide reliable multicast. However, additional overhead is introduced, as a result, which degrades the system performance. In this paper, we propose an efficient wireless multicast MAC protocol with small control overhead required for reliable multicast in multi-hop wireless ad hoc networks. We present analytical formulations of the system throughput and delay associated with the overhead.

• 한국정보통신학회논문지
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• 제24권1호
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• pp.145-148
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• 2020

Wearable computing is growing rapidly as research on body area communication network using wireless sensor network technology is actively conducted. In particular, there is an increasing interest in smart clothing measuring unrestrained and insensitive bio signals, and research is being actively conducted. However, research on smart clothing is mainly based on 1: 1 wireless communication. In this paper, we propose a multi-access monitoring system that can measure bio-signals by multiple users wearing smart clothing. The proposed system consists of wireless access device, multiple access control server and monitoring system. It also provides a service that allows multiple users to monitor and measure bio signals at the same time.

• 한국통신학회논문지
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• 제40권3호
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• pp.529-540
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• 2015

NGN에서는 사용자가 여러 개의 단말을 사용할 수 있는 환경을 지원해야 한다. 특히 사용자가 이동하면서 동적으로 발견하는 단말을 통해 끊김 없는 서비스를 제공받을 수 있어야 하며, 이를 위해서 서비스 연속성 지원이 필수적이다. 현재의 IMS는 서비스 연속성 제어를 위한 세션 제어 방법에 대해서는 다루고 있으나, 세션을 이동할 단말을 어떻게 찾을 수 있는가에 대해서는 제한적인 방법만을 제시하고 있다. 사용자가 이동하면서 발견하는 단말은 물리적으로 사용자와 가까이 위치해 있을 가능성이 상당히 높고, 여러 사람에 의해 공유되어 사용되는 단말일 가능성이 있다. 그러므로 사용자에게 보다 나은 서비스 경험을 제공하기 위해서는 물리적으로 가까이 있는 단말을 사용자가 마치 자신의 단말인 것처럼 사용할 수 있도록 하는 방법이 필요하다고 할 수 있다. 본 논문에서는 전술한 문제를 해결하기 위해 NFC 기반의 가상 ISIM을 통해 사용자가 소유한 기존 단말에 저장된 IMS 가입 정보를 동적으로 발견한 단말로 전달하여 그 단말을 IMS에 등록시키는 방법을 제안하고, 더불어 이를 통해 서비스 연속성 제공이 어떻게 이루어질 수 있는지를 논한다.