• 한국통신학회논문지
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• 제27권3B호
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• pp.179-187
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• 2002

본 논문은 단위 셀 비동기 W-CBMA 시스템 역방향 링크의 다중경로 페이딩 채널에서 동기복조 방식의 다중 사용자 검출을 위한 반복 그룹단위 등지연 간섭제거 (IGEIC : iterative group-wise equal-delay interference cancellation) 알고리즘을 제안하고 성능을 해석하였다. IGEIC 알고리즘은 사용자를 그룹단위로 나누고, 그룹내에서 사용자 수만큼 반복해서 간섭을 제거한 다음, 다시 재확산시켜 다른 사용자 신호성분을 제거한다. IGEIC 알고리즘은 반복 그룹단위 등지연 직렬 간섭제거(IGESIC)와 반복 그룹단위 등지연 병렬 간섭제거(IGEPIC) 알고리즘으로 나누어 제안하였다. 확산부호의 완벽한 상관조건에서 그룹내 사용자 수만큼 간섭제거 후의 IGESIC와 IGEPIC 알고리즘 성능은 동일하며, 그룹내 사용자 수만큼의 간섭제거 직전의 성능은 IGEPIC 알고리즘이 IGESIC 알고리즘보다 우수하다. 또한 두 가지 제안 알고리즘 성능은 직렬 간섭제거 알고리즘 성능보다 3dB 이상 우수한 결과를 얻었다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제12권4호
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• pp.1504-1526
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• 2018

For uplink multi-user massive MIMO systems, conventional minimum mean square error (MMSE) linear detection method achieves near-optimal performance when the number of antennas at base station is much larger than that of the single-antenna users. However, MMSE detection involves complicated matrix inversion, thus making it cumbersome to be implemented cost-effectively and rapidly. In this paper, we first summarize in detail the state-of-the-art simplified MMSE detection algorithms that circumvent the complicated matrix inversion and hence reduce the computation complexity from ${\mathcal{O}}(K^3)$ to ${\mathcal{O}}(K^2)$ or ${\mathcal{O}}(NK)$ with some certain performance sacrifice. Meanwhile, we divide the simplified algorithms into two categories, namely the matrix inversion approximation and the classical iterative linear equation solving methods, and make comparisons between them in terms of detection performance and computation complexity. In order to further optimize the detection performance of the existing detection algorithms, we propose more proper solutions to set the initial values and relaxation parameters, and present a new way of reconstructing the exact effective noise variance to accelerate the convergence speed. Analysis and simulation results verify that with the help of proper initial values and parameters, the simplified matrix inversion based detection algorithms can achieve detection performance quite close to that of the ideal matrix inversion based MMSE algorithm with only a small number of series expansions or iterations.

• 한국통신학회논문지
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• 제34권3C호
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• pp.304-310
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• 2009

본 논문은 M-레벨 QAM 계층 변조 시스템에서 반복 수신기의 복잡도를 줄이기 위한 연속 MAP(maximum a posteriori probability) 검파 방식을 제안한다. 계층 변조 신호 내의 특정 우선 순위를 갖는 신호는 계층 변조 신호를 구성하는 각 신호를 우선 순위에 따라 간섭 신호 성분으로서 제거하거나 가우시안 잡음으로 간주한 후 MAP 방식에 의해 순차적으로 검파된다. 검파 과정을 순차적으로 진행함으로써 반복 수신의 복잡도를 신호 당 전송되는 비트 수에 선형적으로 증가하도록 감소시킬 수 있으며 각 부호화 비트의 연판정 값 계산 시 간섭 제거와 가우시안 가정의 효과를 검파 과정에 반영하여 잡음 분산을 조정함으로써 순차적 검파 방식에 의해 발생할 수 있는 성능 열화를 최소화한다. 전산 모의 실험을 통하여 제안하는 순차적 MAP 검파 방식의 성능이 최적 MAP 검파 방식과 비교하여 0.5dB 미만의 성능열화를 나타내는 것을 보인다.

• ETRI Journal
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• 제30권6호
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• pp.807-817
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• 2008

We present a low-density parity-check (LDPC)-based, threaded layered space-time-frequency system with emphasis on the iterative receiver design. First, the unbiased minimum mean-squared-error iterative-tree-search (U-MMSE-ITS) detector, which is known to be one of the most efficient multi-input multi-output (MIMO) detectors available, is improved by augmentation of the partial-length paths and by the addition of one-bit complement sequences. Compared with the U-MMSE-ITS detector, the improved detector provides better detection performance with lower complexity. Furthermore, the improved detector is robust to arbitrary MIMO channels and to any antenna configurations. Second, based on the structure of the iterative receiver, we present a low-complexity belief-propagation (BP) decoding algorithm for LDPC-codes. This BP decoder not only has low computing complexity but also converges very fast (5 iterations is sufficient). With the efficient receiver employing the improved detector and the low-complexity BP decoder, the proposed system is a promising solution to high-data-rate transmission over selective-fading channels.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2000년도 추계종합학술대회 논문집(1)
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• pp.505-508
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• 2000

The success of target reconstruction in SAR(Synthetic Aperture Radar) imaging system is greatly dependent on the coherent detection. Primary causes of incoherent detection are uncompensated target or sensor motion, random turbulence in propagation media, wrong path in radar platform, and etc. And these appear as multiplicative phase error to the echoed signal, which consequently, causes fatal degradations such as fading or dislocation of target image. In this paper, we present iterative phase error estimation scheme which uses echoed data in all temporal frequencies. We started with analyzing wave equation for one point target and extend to overall echoed data from the target scene - The two wave equations governing the SAR signal at two temporal frequencies of the radar signal are combined to derive a method to reconstruct the complex phase error function. Eventually, this operation attains phase error correction algorithm from the total received SAR signal. We verify the success of the proposed algorithm by applying it to the simulated spotlight-mode SAR data.

• 정보와 통신
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• 제24권12호
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• pp.14-21
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• 2007

This paper aims to improve the design of iterative detection and decoding(IDD) based on the soft interference cancellation with minimum mean squared error(SC-MMSE) detector, which shows low performance compared to the maximum a posteriori(MAP) detector. By means of extrinsic information transfer(EXIT) chart analysis, such low performance may be attributed to that the "pure"(original) turbo principle is not always best for IDD. Thus, we propose a new IDD architecture based on the SC-MMSE detector which uses new a priori information. Simulation results show that the performance of the proposed IDD is very close to that of IDD based on the MAP detector.

• 정보통신설비학회논문지
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• 제2권3호
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• pp.17-23
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• 2003

Turbo decoding in combination with detection strategy for Multi Access Interference (MAI) cancellation has been shown to be very effective for MC-CDMA system in Rayleigh multi-path fading environment. This paper reports new simulation results on the efficacy of joint decoding and detection for MC-CDMA in nonlinear and fading channel.

• ETRI Journal
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• 제26권5호
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• pp.384-390
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• 2004

We propose a new bandwidth-efficient technique that achieves high data rates over a wideband wireless channel. This new scheme is targeted for a multiple-input multiple- output orthogonal frequency-division multiplexing (MIMO-OFDM) system that achieves transmit diversity through a space frequency block code and capacity enhancement through the iterative joint processing of zero-forcing detection and maximum a posteriori (MAP) decoding. Furthermore, the proposed scheme is compared to the coded Bell Labs Layered Space-Time OFDM (BLAST-OFDM) scheme.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제6권2호
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• pp.702-721
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• 2012

In the DVB-T2 system with a multiple-input single-output (MISO) transmission mode, Alamouti coded orthogonal frequency division multiplexing (OFDM) signals are transmitted simultaneously from two spatially separated transmitters in a single frequency network (SFN). In such systems, each transmit-receive link may have a distinct carrier frequency offset (CFO) due to the Doppler shift and/or frequency mismatch between the local oscillators. Thus, the received signal experiences dual CFOs. This not only causes dual phase errors in desired data but also introduces inter-carrier interference (ICI), which cannot be removed completely by simply performing a CFO compensation. To overcome this problem, this paper proposes an iterative detection with dual phase errors compensation technique. In addition, we propose a successive-iterative ICI cancellation technique. This technique successively eliminates ICI in the initial iteration by exploiting pre-detected data pairs. Then, in subsequent iterations, it performs a fine interference cancellation using a priori information, iteratively fed back from the channel decoder. In contrast to previous works, the proposed techniques do not require estimates of dual CFOs. Their performances are evaluated via a full DVB-T2 simulator. Simulation results show that the DVB-T2 receiver equipped with the proposed dual phase errors compensation and the successive-iterative ICI cancellation techniques achieves almost the same performance as ideal dual CFOs-free systems, even for large dual CFOs.

• 방송공학회논문지
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• 제15권6호
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• pp.742-748
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• 2010

최근의 반복 검출 및 복호 (iterative detection and decoding : IDD) 기법에서의 연판정 방식에서는 log-likelihood ratio (LLR) 값의 신뢰도를 높이기 위해 기존의 구복호화 (sphere decoding) 방식보다는 리스트를 형성하는 구복호화방식 (list sphere decoding : LSD)이 대두되고 있다. 기존의 구복호화 방식과는 달리, 리스트 구복호화 방식은 그 성능의 우수함에도 불구하고 여러 격자 포인트들을 검출해야하므로 신호대잡음비 (signal-to-noise ratio : SNR)의 증가에 따른 복잡도의 이득을 거의 취할 수 없다. 또한 리스트 구복호화 기법은 리스트의 크기가 고정되어 있다는 점에서 비효율적이다. 본 논문에서는, 검출 과정에서 LLR에 큰 영향을 미치지 않는 격자 포인트들을 제거하는 기법을 소개한다. 이 과정은 구반경의 최적화를 바탕으로 이루어지며, 제안된 방식은 기존의 리스트 구복호화 기법과 비교하여 성능이 크게 떨어지지 않은 가운데 복잡도를 크게 감소시킨다.