http://chineseinput.net/에서 pinyin(병음)방식으로 중국어를 변환할 수 있습니다.
변환된 중국어를 복사하여 사용하시면 됩니다.
Real-domain decoder for full-rate full-diversity STBC with multidimensional constellations
Heunchul Lee,Jungho Cho,Jong-kyu Kim,Inkyu Lee IEEE 2009 IEEE TRANSACTIONS ON COMMUNICATIONS Vol.57 No.1
<P>In this letter, we present a new maximum likelihood (ML) decoding algorithm for space time block codes (STBCs) that employ multidimensional constellations. We start with a lattice representation for STBCs which transforms complex channel models into real matrix equations. Based on the lattice representation, we propose a new decoding algorithm for quasi-orthogonal STBCs (QO-STBC) which allows simple ML decoding with performance identical to the conventional ML decoder. Multidimensional rotated constellations are constructed for the QO-STBCs to achieve full diversity. As a consequence, for quasi-orthogonal designs with an arbitrary number of transmit antennas N(Nges4), the proposed decoding scheme achieves full rate and full diversity while reducing the decoding complexity from O(M<SUB>c</SUB> <SUP>N/2</SUP>) to O(M<SUB>c</SUB> <SUP>N/4</SUP>) in a M<SUB>c</SUB>-QAM constellation.</P>
New Approach for Error Compensation in Coded V-BLAST OFDM Systems
Lee, Heunchul,Lee, Inkyu Institute of Electrical and Electronics Engineers 2007 IEEE transactions on communications Vol.55 No.2
<P>In this paper, we investigate coded layered space-time architectures for frequency-selective fading multiple-input multiple-output orthogonal frequency-division multiplexing (OFDM) channels. By computing outage capacity formulas, we will show that the capacity of the vertical Bell Labs layered space-time (V-BLAST) architecture can closely approach the Shannon capacity in the frequency-selective OFDM environment. Motivated by the capacity analysis, we propose pragmatic approaches which preserve the optimality of the layered space-time concept. We present methods to prevent the error propagation from catastrophically affecting the signal detection in subsequent layers. First, we start with a comprehensive signal modeling which includes error propagation. We derive an improved signal detector and describe the optimal soft-bit log-likelihood ratio value-computation method by taking decision errors into account for soft-input channel decoding. Then, to further enhance the V-BLAST performance, we show that cancellation using decoded decisions from previous layers makes the decision errors almost completely disappear, so that the layered space-time architecture can approach the attainable channel capacity. Finally, simulations confirm that the proposed schemes show a significant performance improvement over the conventional methods</P>
MIMO Systems Based on Modulation Diversity
Heunchul Lee,Paulraj, A IEEE 2010 IEEE TRANSACTIONS ON COMMUNICATIONS Vol.58 No.12
<P>This letter proposes a new approach to achieve the maximum diversity gain in the vertical Bell Laboratories Layered Space-Time (V-BLAST) system over multiple-input multiple-output (MIMO) Rayleigh channels. First, we will briefly review the modulation diversity scheme based on real-valued multidimensional rotated constellations that has been proposed to obtain high diversity orders for single-input single-output (SISO) systems. Then, this letter extends the modulation diversity scheme to V-BLAST MIMO systems in order to achieve the maximum diversity gain without additional power or bandwidth consumption. The proposed method is particularly suitable for MIMO applications which employ channel codes with high rate in order to support high spectral efficiency.</P>
Orthogonalized Spatial Multiplexing for Closed-Loop MIMO Systems
Lee, Heunchul,Park, Seokhwan,Lee, Inkyu Institute of Electrical and Electronics Engineers 2007 IEEE transactions on communications Vol.55 No.5
<P>In this paper, we propose a novel spatial multiplexing (SM) scheme for transmission over flat-fading multiple-input multiple-output (MIMO) channels, which allows simple maximum-likelihood decoding at the receiver with small feedback information. We begin with a real-valued representation of the complex-valued system model, and show that we can achieve orthogonality between transmitted signals by applying a proper rotation to transmitted symbols. Compared with other closed-loop methods, the proposed scheme significantly reduces the processing complexity at both transmitter and receiver as well as the feedback overhead. We also combine the proposed orthogonalization method with antenna-selection techniques, and then discuss a criterion based on the minimum Euclidean distance between received vectors for selecting the optimal subset of multiple transmit antennas. Using geometrical properties of the receive constellations, we also present a simple antenna-selection metric for the proposed SM systems. Simulation results demonstrate that our SM system performs close to the optimum closed-loop system with much-reduced complexity</P>
Channel Capacity of BLAST based on the Zero-Forcing criterion
이흔철(Heunchul Lee),김희진(Heejin Kim),이인규(Inkyu Lee) 대한전자공학회 2008 電子工學會論文誌-TC (Telecommunications) Vol.45 No.12
본 논문에서는 신호 대 잡음 비의 관점에서 Zero-Forcing 기반의 BLAST(Bell Labs Layered Space-Time) 구조의 채널 capacity를 점근적으로 분석하고자 한다. MIMO 채널 capacity에 관한 새로운 관계를 소개하고, ZF에 기반한 간섭 무효화를 수행할 때 DBLAST(Diagonal BLAST)에 의해 MIMO 채널의 하한값에 이름을 증명한다. 채널 capacity의 확률 밀도 함수의 정확한 최종식을 분석하고, 각 계층의 채널 capacity의 점근적 현상에 기반한 점근적 ergodic capacity의 최종식을 BLAST에서 유도한다. 본 논문에서 다뤄진 분석에 의해 MIMO 채널의 capacity 현상에 대한 통찰할 수 있다. 모의 실험의 결과를 통해서, 본 논문에서 다뤄진 광범위한 안테나 배열 사이즈에 대한 분석의 타당성과 정확성을 보여주고자 한다. In this paper, we present an asymptotical analysis of channel capacity of Bell labs layered space-time (BLAST) architectures based on a zero-forcing (ZF) criterion in the sense of signal-to-noise ratio (SNR). We begin by introducing a new relationship related to multi-input multi-output (MIMO) channel capacity. We prove that Diagonal Bell Labs Space-Time (DBLAST) attains the lower bound for MIMO channels when interference nulling is carried out based on the ZF-criterion. An exact closed-form expression for the probability density function of the channel capacity is analyzed. Based on the asymptotic behavior of the channel capacity of each layer, closed-form expressions for the asymptotic ergodic capacity are derived for BLAST. Based on the analysis presented in this paper, we gain an insight on the channel capacity behavior for a MIMO channel. Computer simulation results have verified the validity and accuracy of the proposed analysis for a wide range of antenna array sizes.
A new beamforming structure based on transmit-MRC for closed-loop MIMO systems
Seok-Hwan Park,Heunchul Lee,Sang-Rim Lee,Inkyu Lee IEEE 2009 IEEE TRANSACTIONS ON COMMUNICATIONS Vol.57 No.6
<P>This paper proposes an efficient beamforming scheme which attains optimality as singular value decomposition (SVD) based systems with low complexity utilizing transmit maximum-ratio combining (TMRC) techniques. The TMRC scheme is the optimum structure for single beamforming systems in terms of received signal-to-noise ratio (SNR) in multiple-input single-output (MISO) channels. In this paper, we generalize the TMRC scheme to multiple beamforming multiple-input multiple-output (MIMO) systems which support more than one data stream in coded systems. We express each beamforming vector as a linear combination of TMRC vectors whose coefficients are optimized in a successive manner. Optimization of the beamforming vector is followed by the decorrelation process. All TMRC vectors used as a basis of the remaining beamforming vectors are made orthogonal to previously computed beamforming vectors. Exploiting the concept of the gradient ascent algorithm, we propose a simple non-iterative method of computing the precoder which obtains the near optimal performance. Also we derive a closed form expression of the output SNR distribution for the proposed scheme. Simulation results demonstrate that the proposed scheme achieves the almost identical link performance as the SVD-based system for arbitrary configurations with reduced complexity.</P>