• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2009.11a
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• pp.379-382
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• 2009

본 논문에서는 폐회로 다중 안테나 송수신 (closed-loop multiple-input multiple-output) 기법을 사용하는 적응형 협동 다중 홉 중계 시스템을 제안한다. 중계기와 기지국 사이의 이동성이 낮기 때문에, 폐회로 다중 안테나 송수신 기법은 개회로 다중 안테나 송수신 기법보다 높은 다이버시티 이득을 얻을 수 있다. 이 때, 한 개 이상의 중계 터미널들은 기지국으로 전송을 공유하고 프리코딩 가중치벡터를 피드백하기 위해 하나의 협동 그룹에 포함되어야 한다. 피드백 비트의 증가로 인한 전송량 감소를 최소화 하기 위해 코드북 기반의 최대비 전송 기법을 사용하여 비트백 비트수를 제한한다. 기지국은 협동 중계 그룹 중에서 채널 상태가 가장 좋은 중계기를 선택하고, 프리코딩을 위한 인덱스 값을 중계기에 피드백한다. 이러한 중계 시스템을 위해 피드백 형태와 선택 프로토콜 시나리오를 제안하고, 모의실험을 통해 중계기 선택에 따른 성능을 확인한다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.6C
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• pp.423-428
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• 2008

We consider the use of cooperative diversity in a multiuser wireless data network. This paper provides an analysis of the interaction between cooperative diversity and multiuser diversity on downlink channels. By using approximation of the signal-to-noise ratio (SNR) distribution of each cooperative diversity link by Gamma distribution, an analytic expression is derived for the average throughput of a single-cell wireless system with multiple cooperative diversity links combined with a fair-access scheduler. The proposed analytic approach is verified through comparisons with simulated results and shows that cooperative diversity makes the detrimental impacts on multiuser diversity.

• Information Systems Review
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• v.7 no.1
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• pp.153-171
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• 2005

As the mobile telecommunications industry in Korea boasts record-high revenue from its businesses, consumers and other industries are looking for new business applications and opportunities using mobile technologies. Many firms are seeking guidelines or business models for an effective use of this new mobile technology in their operations. This paper reviews the characteristics that distinguish mobile marketing, and analyzes marketing approaches which utilize the potential of the new mobile technologies. This paper shows that the new mobile advertising channel is not only complementary to traditional marketing channels, but also delivers benefits for multiple parties involved in mobile marketing. The key success factors in the new OB (Oriental Brewery) marketing campaign include a shortening of the stages in the AIDMA model and a broadening of customer contact points by exposing the brand through well-coordinated marketing efforts. The OB case shows that a mutually beneficial relationship between co-marketing participants can lead to a win-win marketing strategy. It also highlights that collaborative channel management in mobile marketing methodology is critical for successful mobile marketing.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.3A
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• pp.290-296
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• 2007

We propose new routing scheme, Cooperative Diversity-based Routing (CDR) which utilizes the cooperative space diversity for power saving and performance enhancement of wireless ad-hoc networks. The improved performance is compared with Multi-hop Relay Routing (NRR) by analytical methods. When the required outage probability is $1\times10^{-3}$ at the destination node in ad-hoc networks with 7 nodes, we noticed that each node can save power consumption by 15.5 dB in average, by using our proposed CDR compared to MRR.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.16 no.7 s.98
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• pp.709-719
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• 2005

The forward link of the 3 G CDMA system may become limited under the increasing of the number of users. The conventional channelization code, Walsh code, has not enough sizes for much possible non, therefore, the quasi orthogonal function(QOF), which process optimal cross-correlation with Walsh code, is considered. In this paper, we investigate quasi orthogonal function on Jacket matrices, which can lead lower correlations values and better performance in 3 G CDMA system. Moreover, to simple the detector and improve the BER performance, a novel detection for QOF CDMA system is proposed. Finally, the simple recursive generation of the bent sequences for QOF mask function is discussed.

• 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 the Institute of Internet, Broadcasting and Communication
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• v.12 no.5
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• pp.17-23
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• 2012

Recently, for spectral efficiency and power saving, an incremental best relay selection of a cooperative diversity scheme is proposed. However during the best relay selection process, there may exist a delay between channel estimation and actual data transmission. Consequently, this delay causes outdated channel state information (CSI). We analytically derive the effect of the outdated CSI to an incremental best relay selection diversity scheme. It is noted that the system performance deteriorates with decreasing the value of the correlation coefficient sensitively. When the correlation coefficient reduces from 1 to 0.9, the most performance degradation is denoted. However, the performance degradation is diminished with decreasing the correlation coefficient.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.16 no.3
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• pp.65-71
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• 2016

Cooperative relaying systems have been studied actively to improve the system performance effectively in wireless fading channels. Most of the cooperative relay studies are assumed fixed relay, recently the performance analysis of the cooperative relaying systems with spatially random relays considering the practical mobile environment are introduced. However the comparative studies for relay selection methods of incremental cooperative relay systems, the performance of which is influenced by the selection methods, have not been studied. Therefore we derive the performance of the system which has MRC(Maximal-ratio combining) with Max SNR(signal-to-noise ratio) selection or Max-min SNR selection, respectively. And the outage performances of the system with Max or Max-min selection method are compared for different transmit power allocation to the source and to the relays. The analytical results serve as useful tools for relay selection and power allocation to transmit nodes for opportunistic incremental relaying systems.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37C no.11
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• pp.1084-1093
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• 2012

For large multihop networks, large time synchronization (TS) errors can accumulate with conventional methods, such as TPSN, RBS, and FTSP, since they need a large number of hops to cover the network. In this paper, a method combining Concurrent Cooperative Transmission (CCT) and Semi- Cooperative Spectrum Fusion (SCSF) is proposed to reduce the number of hops to cover the large network. In CCT, cooperating nodes transmit the same digitally encoded message in orthogonal channels simultaneously, so receivers can benefit from array and diversity gains. SCSF is an analog cooperative transmission method where different cooperators transmit correlated information simultaneously. The two methods are combined to create a new distributed method of network TS, called the Cooperative Analog and Digital (CANDI) TS protocol, which promises significantly lower network TS errors in multi-hop networks. CANDI and TPSN are compared in simulation for a line network.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.11
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• pp.1311-1317
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• 2010

In this paper, for a uplink space division multiple access system named cooperative spatial multiplexing(CSM), radio resource management(RRM) algorithms are proposed based on sharing uplink channel information among a serving base station(BS) and interfering BSs in a uplink coordinated wireless communication system. A constrained maximum transmit power algorithm is proposed for mobile station(MS) to limit uplink inter-cell interference(ICI). And joint scheduling algorithm among coordinated BSs is proposed to enhance uplink capacity through ICI mitigation by using channel information from interfering BSs. It is shown that the proposed RRM algorithm provides a considerable uplink capacity enhancement by effective ICI mitigation only with moderate complexity.