• Proceedings of the KIEE Conference
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• 2003.07d
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• pp.2693-2695
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• 2003

M진 직교 진폭 복조기(M-ary QAM Demodulator)를 위한 개선된 이중모드 MCMA 블라인드 등화기법을 제안하였다. 최소 교란 원리(the principle of minimum disturbance)를 MCMA에 적용함으로써 개선된 블라인드 등화기법과 반송파 위상 복구 능력을 얻으며 dicision-directed algorithm과 함께 이중모드로 동작함으로써 향상된 안전성(stability)과 견고성(robustness)얻을 수 있다. 잡음 특성과 시변채널에 대해 컴퓨터 모의 실험을 통하여 제안된 이중모드 알고리즘의 개선된 성능을 검증하였다.

• Proceedings of the Korea Information Processing Society Conference
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• 2007.11a
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• pp.1042-1045
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• 2007

본 논문에서는 MAI 제거 기법으로서 다단병렬간섭제거기 (MPIC : Multistage Parallel Interference Canceller) 와 부분 다단병렬간섭제거기 (partial MPIC) 및 다치진폭계수를 이용한 MPIC를 채용한 비동기 (asynchronous) DS-CDMA/M-ary QAM 시스템의 성능 개선을 이론적으로 분석하고 이를 검증하기 위한 컴퓨터 시뮬레이션을 수행하였다.연구결과에서 MPIC, partial MPIC 및 다치진폭계수를 이용한 MPIC를 실제 시스템에 적용하여 구현할 경우 BER 성능, 채널용량 개선, 신호처리 계산량 및 하드웨어 복잡도 사이에 타협 (trade-off) 이 필요하다.

• Journal of Advanced Navigation Technology
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• v.11 no.4
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• pp.423-429
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• 2007

Since the wireless smart card has played a main role in the identification security application for the building access; this research has its purpose to improve the performance of the smart card system and aims to offer more convenient to user. The contactless cards do not require insertion into a card reader and can work up to centimeters away from the reading device. To be able to cope with this performance the controlling of power consumption through the adaptive modulation and error control is needed. This paper addresses a forward error control (FEC) scheme with the adaptive Reed-Solomon code rate and an M-ary frequency shift keying (M-FSK) modulation scheme with the varying symbol size M over the link. The result of comparing energy efficiencies of adaptive error correction and adaptive modulation to other various static schemes shows to save over 50% of the energy consumption.

• Journal of IKEEE
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• v.24 no.3
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• pp.814-820
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• 2020

In the M-ary DCSK system up to now, as M increases, the distance between constellation signal points becomes closer and performance deteriorates. we propose a hybrid modulation scheme based on PPM and DCSK to improve the BER performance. one part of the bit is modulated by the PPM and the other part by DCSK. Thus, the information bearing signal is modulated simultaneously according to the selected pulse position of the PPM determined by the information bit and the additional information bit. The analytical BER performance of the proposed plan is derived and verified by simulation. The results show that the proposed scheme outperforms conventional M-DCSK, code index modulation DCSK and rectified code index DCSK in additional white Gaussian noise and multipath Rayleigh fading channels.

• ETRI Journal
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• v.34 no.6
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• pp.892-899
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• 2012

We analyze a wideband spectrum in a cognitive radio (CR) network by employing the optimal adaptive multiband sensing-time joint detection framework. This framework detects a wideband M-ary quadrature amplitude modulation (M-QAM) primary signal over multiple nonoverlapping narrowband Gaussian channels, using the energy detection technique so as to maximize the throughput in CR networks while limiting interference with the primary network. The signal detection problem is formulated as an optimization problem to maximize the aggregate achievable secondary throughput capacity by jointly optimizing the sensing duration and individual detection thresholds under the overall interference imposed on the primary network. It is shown that the detection problems can be solved as convex optimization problems if certain practical constraints are applied. Simulation results show that the framework under consideration achieves much better performance for M-QAM than for binary phase-shift keying or any real modulation scheme.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.43 no.2 s.344
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• pp.7-15
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• 2006

Recently, Ultra-wideband (UWB) Communication systems have become a popular research topic. UWB system is characterized by the fact that the digital information represented by a subnanosecond pulses is transmitted through the air. In this paper, we consider the PPSM scheme that combine PPM and PSM. We provide the performance in AWGN and SV multipath channel which consists of $CM1\~CM4$. The optimal symbol set for M-ary system in multipath channel which shows good performance is also presented. The simulation results show that the performance in CM4 is worse than that in CMI due to long delay spread, many multipath components, 4-ary system outperforms binary system in Low$E_b/N_0$ but not in high $E_b/N_0$. We find system have the optimal symbol set in multipath channel.

• Electrical & Electronic Materials
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• v.9 no.6
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• pp.578-583
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• 1996

The magnetic properties have been investigated for the system of $Y_{1-x}$Yb$_{x}$Ba$_{2}$Cu$_{3}$F$_{y}$O$_{y}$ with x=0.0, 0.1, 0.2, 0.3, 0.4 and 0.5. In the magnetic hysteresis measurements, the values of the magnetic critical current densities are in the range of 10$^{4}$-10$^{5}$ A/cm$^{2}$ at the maximum external field 1.4 T. The upper critical field is over 100 T. The critical current density is estimated by the magnetization width .DELTA.M through the Bean critical state model. As the field strength is increased, the .DELTA.M diminishes slowly. The .DELTA.M for the fluorinated sample also decreases slowly with increasing field. It is considered that the large J, value results from this type is due to enhanced pinning center in grain boundary.y.ary.y.

• Journal of Communications and Networks
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• v.18 no.5
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• pp.677-687
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• 2016

Multi-way relay networks (MWRNs) allow multiple users to exchange information with each other through a single relay terminal. MWRNs are often incorporated with capacity achieving lattice codes to enable the benefits of high-rate signal constellations to be extracted. In this paper, we analytically characterize the symbol error rate (SER) performance of a functional decode and forward (FDF) MWRN in the presence of channel estimation errors. Considering M-ary quadrature amplitude modulation (QAM) with square constellations as an important special case of lattice codes, we obtain asymptotic expressions for the average SER for a user in FDF MWRN. The accuracy of the analysis at high signal-to-noise ratio is validated by comparison with the simulation results. The analysis shows that when a user decodes other users with better channel conditions than itself, the decoding user experiences better error performance. The analytical results allow system designers to accurately assess the non-trivial impact of channel estimation errors and the users' channel conditions on the SER performance of a FDF MWRN with M-QAM modulation.

• Journal of Communications and Networks
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• v.12 no.6
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• pp.544-557
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• 2010

This paper addresses the problem of controlling the envelope's power peak of single carrier modulated signals, band limited by root-raised cosine (RRC) pulse shaping filters, in order to reduce power amplifier back-off for very small aperture terminals ground stations. Magnitude modulation (MM) is presented as a very efficient solution to the peak-to-average power ratio problem. This paper gives a detailed description of the MM concept and its recent evolutions. It starts by extending the look-up-table (LUT) based approach of the MM concept to M-ary constellations with M ${\leq}$ 16. The constellation and RRC symmetries are explored, allowing considerable reduction on LUT computation complexity and storage requirements. An effective multistage polyphase (MPMM) approach for the MM concept is then proposed. As opposed to traditional LUT-MM solutions, MM coefficients are computed in real-time by a low complexity multirate filter system. The back-off from high-power amplifier saturation is almost eliminated (reduction is greater than 95%) with just a 2-stage MPMM system even for very demanding roll-off cases (e.g., ${\alpha}$ = 0,1). Also, the MPMM is independent of modulation in use, allowing its easy application to constellations with M > 16.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.12C
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• pp.1208-1213
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• 2005

Recently, ultra wideband(UWB) is emerging as a solution for the IEEE 802.15.3a(TG3a) standard because of its potential to enable high-speed data transmission with low power consumption. One of the submitted systems as s PHY proposal is M-ary biorthogonal keying direct sequence ultra wideband(M-BOK DS-UWB). In this paper, adaptive multiple antenna transmission scheme for achieving high capacity and reliability in M-BOK DS-UWB is proposed. This proposed system can overcome the limitations of STBC and V-BLAST, such as bit error rate performance and throughput.