• Information and Communications Magazine
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• v.30 no.1
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• pp.58-66
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• 2012

최근 부족한 무선자원을 효율적으로 사용하기 위한 인지 무선 기술이 큰 관심을 받고 있고 필요한 핵심요소 기술에 대한 연구가 집중적으로 이루어 지고 있다. 이에 따라, 실제 인지 무선 단말의 전송을 제어하고 네트워크를 관리하는 정책기반 인지무선 네트워킹 기술에 대한 연구 필요성이 증대되고 있다. 인지 무선 네트워크에서 동작하는 단말은 동적으로 변화하는 무선 환경에서도 단말의 행동을 규제하는 정책을 기반으로 기회적 전송을 수행할 수 있어야 한다. 이를 위해서는 변화하는 무선 환경 조건에 능동적으로 대응할 수 있는 동적 정책 관리 및 제어 기술이 필수적으로 요구된다. 본고에서는 정책 기반 인지 무선 네트워크에서 정책 표현의 확장성을 고려한 정책 기술 언어 동향과 동적 정책 구성 및 적용을 지원하는 정책 기반 인지 무선 네트워크 시스템 구조 기술 동향을 소개한다.

• IEMEK Journal of Embedded Systems and Applications
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• v.14 no.4
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• pp.177-186
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• 2019

In wireless sensor networks, the transmission success ratio would be decreased when the scale of the WSNs increased. To defeat this problem, we propose a multipath routing based on opportunistic routing for improving end-to-end reliability in large-scale wireless sensor networks. The proposed scheme exploits the advantages of existing opportunistic routing and achieves high end-to-end success ratio by branching like a multipath routing through local decision without information of the whole network. As a result of the simulation result, the proposed scheme shows a similar or higher end-to-end transmission success ratio and less energy consumption rather than the existing scheme.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37A no.9
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• pp.762-771
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• 2012

In this paper, we propose an adaptive power control scheme employing a self-optimization concept in femtocell systems, in order to improve system capacity, thereby reducing call-drop probability. In the proposed scheme, each femto base station(FBS) controls individual channel's transmission power base on two parameters; the neighboring cell's transmission power for each individual channel which is delivered from a femto-gateway and the received power strength from neighboring cells which is periodically measured by means of a spectrum sensing. Adaptive adjustment of individual channel's transmission power in accordance with femto mobile station(FMS) mobility features can also reduce undesirable handovers and evenly distribute traffic load over all femtocells. In addition, the manipulative control of channel's transmission power is able to keep the system coverage and the call-drop probability within an acceptable range, regardless of density of femtocells. Computer simulation shows that the proposed scheme outperforms existing schemes in terms of the system coverage and the call-drop probability.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.2 no.3
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• pp.379-388
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• 1998

In this paper we propose a DMR-II shared-medium access control protocol which was developed for the ATM access network users to support isochronous and non-isochronous traffics simultaneously under the bandwidth sharing environment, and describe its architecture and operation principles. The DMR-II protocol uses the slotted-ring topology, and gives the higher transmission priority to the isochronous traffic than the non-isochronous traffic. To support the isochronous traffic it uses the slot reservation mechanism, and maintains the delay variation of the isochronous traffic beyond the threshold value by using the blocking mechanism whenever the total user traffic overflows the network's bandwidth limitation. for the non-isochronous traffic the DMR-II protocol lets all the nodes to have fair transmission chances by using the reset mechanism based on the window counter scheme.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.49 no.5
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• pp.21-26
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• 2012

Intra-session network coding has been proposed to improve throughput by simplifying scheduling of multi-hop wireless network and efficiency of packet transmission. Multi-rate transmission has been used in multihop wireless networks. An opportunistic routing with multirate shows throughput improvement compared with single rate. In this paper, we propose a method of throughput improvement in multi-hop wireless network by using multi-rate and intra-session network coding. We suggest a method to select an local optimal transmission rate at each node. The maximum throughput is evaluated by using linear programming (LP). To solve the LP, we use MATLAB and lp_solve IDE program. The performance evaluation results show that end-to-end throughput is improved by using multirate and intra-session network coding can achieve better throughput than opportunistic routing.

• Proceedings of the Korean Society of Computer Information Conference
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• 2009.01a
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• pp.197-202
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• 2009

과학기술의 발달로 인한 사회 문화적 트렌드의 변화는 새로운 기회와 가능성을 제공해 주며, 정보통신기술은 통신과 방송, 통신과 콘텐츠 등 영역간의 경계를 허물며 융합을 가능하게 하고, 우리의 감성과 상상력을 자극하여 새로운 문화적 가능성을 열어주고 있다. 이러한 상황들은 방송 통신 융합이라는 이름으로 방송과 통신, TV와 PC 온라인과 오프라인 등의 모든 영역에서 다양한 노력이 진행되고 있다. 방송과 통신의 융합은 마치 역사상 신대륙의 개척 과정처럼 새로운 제품과 새로운 시장을 창출해내는 능력을 가지고 있기 때문에, 국내는 물론 세계의 모든 비즈니스 업체들은 이 기회의 땅을 향해 전력 질주하고 있다. 또한, 이에 따르는 콘텐츠의 융합 역시 괄목할만하며, 게임과 영화, 다큐멘터리와 드라마 등의 콘텐츠 간의 융합은 물론이고, 최근에는 모바일에서 영화를 제작하고, 게임과 소설 네트워크가 결합하고, 심지어는 게임 안에서 음악을 유통시키는 유통의 융합까지도 이뤄지고 있다. 이와 같은 다양한 융합의 확산은 미디어와 플랫폼의 등장뿐만 아니라 플랫폼 간 교차와 연결 및 통합이 가능한 미디어 전경(landscape)을 창출해 내고 있으며, 인터넷과 TV의 결합은 다양한 애플리케이션을 구현할 수 있는 전송 메커니즘을 서로 연결시켜 수많은 형태의 다중 플랫폼을 등장시키고 있다. 이로 인하여 방송 서비스와 인터넷 서비스가 네트워크나 전송 플랫폼의 구별 없이, 그리고 디바이스의 선택과 상관없이 활용되는 통합 플랫폼 환경이 폭 넓게 조성되고 있다. 따라서, 방송 통신 융합 환경에 적합한 다중 플랫폼 융합 콘텐츠는 사용자의 요구 및 새로운 비즈니스 모텔에 대한 요구를 만족할 수 있어야 하며, 일관된 기술로 통선 및 서비스간의 호환성을 유지하는 인터페이스의 표준화가 이루어져야한다. 방송 통신 융합 환경에 적합한 다중 플랫폼 융합 콘텐츠는 초고속 데이터 통신망을 활용하는 멀티미디어 및 IP 멀티캐스트 기능을 활용한 서비스들과 연계하여, 관련된 소재 산업들의 파급효과가 매우 크며, 관련 분야에 미치는 효과가 막대하므로, 이에 대한 적절한 육성전략을 고찰해보도록 한다.

• Journal of KIISE:Information Networking
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• v.35 no.2
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• pp.139-148
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• 2008

Many types of sensor data exhibit strong correlation in both space and time. Suppression, both temporal and spatial, provides opportunities for reducing the energy cost of sensor data collection. Unfortunately, existing clustering algorithms are difficult to utilize the spatial or temporal opportunities, because they just organize clusters based on the distribution of sensor nodes or the network topology but not correlation of sensor data. In this paper, we propose a novel clustering algorithm with suppression techniques. To guarantee independent communication among clusters, we allocate multiple channels based on sensor data. Also, we propose a spatio-temporal suppression technique to reduce the network traffic. In order to show the superiority of our clustering algorithm, we compare it with the existing suppression algorithms in terms of the lifetime of the sensor network and the site of data which have been collected in the base-station. As a result, our experimental results show that the size of data was reduced by $4{\sim}40%$, and whole network lifetime was prolonged by $20{\sim}30%$.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.21 no.4
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• pp.37-42
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• 2021

NOMA (Non-orthogonal multiple Access) system has been focused on the next generation cellular system for higher spectral efficiency. However, this requires user scheduling as the NOMA system is a multi-user system which accesses simultaneously. There are two representative scheduling schemes, proportionate scheduling (FP) and cumulative distribution function (CFD) scheduling. The PF scheduling is applied, the cell edge user is hard to obtain a transmit opportunity. Recently, CDF scheduling is obviously noted that it offers the same possibility of transmission for a user regardless of the location in a cell. We consider an uplink NOMA system with CDF scheduling, and obtain the channel access probabilities, the outage probabilities of the system with different number of users and different kinds of weights through simulation. The results indicate that the likelihood of each user accessing the channel is the same and the probability of failure decreases as the number of users increases. We found that the effect of the probability of failure is negligible as the weight of the cell edge user increases.

• Journal of KIISE:Information Networking
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• v.34 no.6
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• pp.514-524
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• 2007

Recent advances in the speed of multi-rate wireless local area networks (WLANs) and the proliferation of WLAN devices have made rate adaptive, opportunistic scheduling critical for throughput optimization. As WLAN traffic evolves to be more symmetric due to the emerging new applications such as VoWLAN, collaborative download, and peer-to-peer file sharing, opportunistic scheduling at the downlink becomes insufficient for optimized utilization of the single shared wireless channel. However, opportunistic scheduling on the uplink of a WLAN is challenging because wireless channel condition is dynamic and asymmetric. Each transmitting client has to probe the access point to maintain the updated channel conditions at the access point. Moreover, the scheduling decisions must be coordinated at all clients for consistency. This paper presents JUDS, a joint uplink/downlink opportunistic scheduling for WLANs. Through synergistic integration of both the uplink and the downlink scheduling, JUDS maximizes channel diversity at significantly reduced scheduling overhead. It also enforces fair channel sharing between the downlink and uplink traffic. Through extensive QualNet simulations, we show that JUDS improves the overall throughput by up to 127% and achieves close-to-perfect fairness between uplink and downlink traffic.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.3B
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• pp.112-122
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• 2008

Basing on Piconet, The Bluetooth System forms network and transmits data. There is one Master and maximum 7 Slave bluetooth devices in one piconet. A job scheduler performed by Master bluetooth device, gives the chance of data transmission to Slave bluetooth devices, which connected to Master, using polling method in piconet. The maximum data rate is 723.2 kb/s when it uses ACL link with DH5 packet type in a piconet which is constructed by two bluetooth devices. However, if there are one master and two slave devices in a piconet, then the maximum data rate is reduced to a half(361.6kb/s), because a master device has to support same data rate for all connected devices. And, there is the defect in scatternet when data transmission rate becomes low(Maximum rate: 302.2kb/s). This paper proposals the new ad-hoc network topology called "DoublePico"for overcome the low data transmission in scatternet which is constructed by piconets. The method of doublepico that represented in this paper makes high data transfer rate(Maximum rate: 457.57kb/s) in bluetooth ad-hoc networks.