• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2002년도 ITC-CSCC -3
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• pp.1932-1935
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• 2002

This paper introduces the downlink Eigen-beamformer with Space-Time Block Code (STBC) 〔1,2〕employed on the MISO (Multiple Input Multiple Output) systems. The proposed scheme is acquired both transmit diversity gain from STBC and beamforming gain from Eigen-beamformer. In general, it is well described that the diversity gain be maximized when channel parameters associated to fingers are mutually independent. Major role f utilizing Eigen-beamformer is to enforce channel parameters being uncorrelated. According to this, the proposed STBC combined with Eigen-beamformer on the downlink significantly improves its performance under the spatially correlated channel. Simulation results are accomplished under three distinct channel conditioned with varying the degree of their correlations. The result indicates hat our proposed scheme is good performance in spatially correlated channel.

• 한국전자파학회논문지
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• 제12권3호
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• pp.470-477
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• 2001

Multucarrier code-division multiple access(MC-CDMA) is one of the promising technique for high capacity wireless communication. Hower the carrier phase error and frequency offest cause the performance degradation of MC-CDMA due to the inter-carrier interference. In this work, downlink performance of the partially coherent MC-CDMA is analytically derived in Rayleigh fading channels. The bit error rate sensitivity by combining method, Maxiaml ratio combining (MRC)and Equal gain combining(EGC), is compared as functions of phase errors. multi-user interference, and received signal-to-noise ratio. The results show that the susceptibility for the performance degradation of EGc and MRC is negligible for loop SNR's of above 15 dB and above 10 dB, respectivtely.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2002년도 ITC-CSCC -3
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• pp.1681-1684
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• 2002

A multilevel modulation with selectable constellations is adopted in the downlink subframe modulation of the IEEE 802.16 standard to increase the total throughput. One of the decision factors of the modulation is the location of SS(Subscriber Station) . Also, for the 802.16, low phase noise of local oscillator is needed due to high operating frequency and severe loss in the propagation channel. We investigate the BER of down-link subframe with the phase jitter under the standard's specified LOS(line of sight) and multipath environment with randomly generated SS locations. Simulation results show BER performance degradation for the modulation corresponding to selected constellations and additionally required SNR to achieve 10$\^$-3/ BER under various phase jitter.

• 한국통신학회논문지
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• 제29권10A호
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• pp.1167-1176
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• 2004

본 논문에서는 위성 하향 링크에서 강우 감쇄와 음영 페이딩에 대한 적응형 전송을 위한 MC-CDMA(multicarrier CDMA) 방식을 제시하고, Ka 대역 이동위성채널에서 페이딩, 강우 감쇄, 재전송 방식에 따른 적응형 MC-CDMA 하향링크의 성능을 비교 분석하였다. 제시된 하향 링크는 광대역 MC-CDMA 전송을 통해 수십 Mbit/s 처리율과 채널 환경에 따라 약 1 bit/s/Hz에서 4.7 bit/s/Hz의 주파수 효율을 제공할 수 있다.

• Journal of Communications and Networks
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• 제8권3호
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• pp.313-322
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• 2006

We consider a power controlled code division multiple access (CDMA) system with multiple flow types. At each of the N nodes, there are F flow types with different signal-to-interference-and-noise-ratio (SINR) requirements. To keep the complexity of the transmitter low, we assume that each node uses the same power level for all its flows. The single flow case has been fully solved and is well-understood. We concentrate on the multiple flow case, and use a novel and different approach. For the uplink problem with N = 2 and F arbitrary, the necessary and sufficient conditions to have a solution are found and proved. For the general N > 1 uplink problem, we provide a necessary condition for the problem to have a solution and an iterative algorithm to find the optimum solution. For the downlink case with F > 1 some properties of the optimal sequences are obtained.

• Journal of Communications and Networks
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• 제9권2호
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• pp.192-197
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• 2007

We analyze the performance of code division multiple access (CDMA) system with multicarrier (MC) that employs precoding in synchronous downlink channels. Even though considerable efforts are undergoing for frequency offset estimation and correction, it is inevitable for the system to bear the remaining frequency offset. Therefore it is important to predict accurately the system performance in the presence of the residual frequency offset. We obtain the bit error rate (BER) performance in terms of the number of users, the spreading factor, the number of sub-carriers, and frequency offset. We assume that the spreading factor is equal to the number of sub-carriers, although we can generalize the case. The simulation results show that the BER of MC-CDMA with precoding shows a performance that varies with frequency offset as well as system loading.

• Journal of Communications and Networks
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• 제4권3호
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• pp.199-208
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• 2002

The downlink rate scheduling problem is considered for CDMA networks with multiple users carrying packets of heterogeneous traffic (voice/audio only, bursty data only or mixed traffic), with each type having its own distinct quality of service requirements. Several rate scheduling algorithms are developed, the common factor of which is that part of the decision on which users to serve is based on a function of the deadline of their head-ofline packets. An approach of Andrews et al., in which the basic Earliest-Deadline-First algorithm is studied for similar systems, is extended to result in better performance by considering a more efficient power usage and by allowing service of more than one user per timeslot if the power resources permit it. Finally, the performance of the proposed schemes is compared through simulations.

• 한국통신학회논문지
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• 제34권6A호
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• pp.494-499
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• 2009

본 논문에서는 하향링크 다중 사용자 Multiple Input Multiple Output (MIMO) 채널 환경에서 시스템 용량을 최대화시키기 위한 효과적인 사용자 선택 기법에 대해서 논의한다. 본 논문에서 제안하는 방법은 사용자 채널 파워와 채널 간의 각도를 이용하여 최적의 사용자 집단을 선택하는 새로운 방법이다. 이 방법은 SUS 방법에 비해 허용 상관도 값을 별도로 생각하지 않아도 되기 때문에 간단한 방법이며, 시스템 성능을 최대화시키는 사용자들을 찾는 방법이기 때문에 향상된 성능을 보인다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제16권1호
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• pp.319-333
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• 2022

In order to enhance system energy efficiency, bidirectional link resource allocation strategy in GFDM-based multiuser SWIPT systems is proposed. In the downlink channel, each SWIPT user applies power splitting (PS) receiver structure in information decoding (ID) and non-linear energy harvesting (EH). In the uplink channel, information transmission power is originated from the harvested energy. An optimization problem is constructed to maximize weighted sum ID achievable rates in the downlink and uplink channels via bidirectional link power allocation as well as subcarriers and subsymbols scheduling. To solve this non-convex optimization problem, Lagrange duality method, sub-gradient-based method and greedy algorithm are adopted respectively. Simulation results show that the proposed strategy is superior to the fixed subcarrier scheme regardless of the weighting coefficients. It is superior to the heuristic algorithm in larger weighting coefficients scenario.

• 한국정보처리학회:학술대회논문집
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• 한국정보처리학회 2007년도 추계학술발표대회
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• pp.1040-1041
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• 2007

본 논문은 차세대 위성 개발을 위한 선행 연구의 일환으로, 다양한 플랫폼에 적용할 수 있는 위성 전자 전산 시스템 개발 검증 장비의 구성 요소인 상/하향 명령 처리 장치를 PC 에서 구동할 수 있도록 개발한 것이다. 이 PC 기반의 상/하향명령처리 시험환경은 위성의 Flight Software 로직의 검증용으로도 활용될 수 있다.