• Proceedings of the Korean Society of Broadcast Engineers Conference
• /
• 2011.11a
• /
• pp.123-124
• /
• 2011

최근 전송량 및 주어진 SNR(signal to noise ratio)에 따른 수신 성능을 향상시키기 위하여 다중 안테나(multi-input multi-output) 시스템에 대한 연구가 활발하게 이루어지고 있다. 다중 안테나 시스템은 이론적으로 송신 안테나 개수에 비례해서 전송량이 증가하거나 송 수신 안테나 개수에 비례하여 주어진 SNR에 따른 수신 성능을 향상시킨다. 이러한 MIMO 시스템의 서로 다른 송신단에서 서로 다른 성상을 전송할 때 효율적인 전력 할당은 시스템 성능 향상에 큰 영향을 미친다. 이에 본 논문은 4-QAM 및 16-QAM을 송 수신 안테나가 두 개인 V-BLAST 시스템에 적용하고, 전력을 다르게 할당하여 수신 시스템의 성능을 분석하였다. 이러한 서로 다른 전력 할당에 따른 성능 분석 결과를 이용하여 이동 통신 시스템에 적용하기 위한 가능성 및 활용성에 대하여 논의하였다.

• Proceedings of the Korean Society of Broadcast Engineers Conference
• /
• 2012.07a
• /
• pp.134-137
• /
• 2012

최근 ATSC방식의 디지털 방송에서 HD급의 3D 방송 서비스에 대한 관심이 증가 되고 있는 추세이다. HD급의 3D 방송 서비스(이하 3D HDTV)를 제공하기 위해 [2]에서는 ATSC 전송 시스템을 확장하고 BCH 부호와 IRA 타입의 LDPC를 사용하는 수정된 ATSC 전송 시스템을 제안하였다. 본 논문에서는 BCH와 IRA 타입의 LDPC 부호 대신 Reed Solomon 부호와 Block LDPC 부호를 사용하고 16QAM 변조를 사용하여 전송 용량을 증대할 수 있다는 사실을 확인하였다. AWGN 채널에서 모의 실험한 결과 BCH부호와 LDPC부호 및 4PAM을 적용한 수정된 ATSC 전송시스템의 TOV는 약 7dB로 19.33Mbps로 전송되지만[2] 본 논문에서 제안한 RS(207, 187)과 부호율 3/4인 Block LDPC 및 16QAM의 TOV는 약 5.4dB로 29Mbps로 전송되어 기존시스템에 비해 약1.5배의 전송 용량 증대가 가능한 것으로 확인되었다. 이로서 6MHz의 한정된 대역에서 HD급의 3D 방송서비스 실현이 한층 더 가까워지게 될 것으로 예상된다.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.10 no.1
• /
• pp.44-53
• /
• 1999

In this paper, we propose a pilot based time-averaging channel estimation method and analyze error performances for efficient transmission of OFDM(Orthogonal Frequency Division Multiplexing) in multipath fading environment. Frequency domain channel estimations have been used in OFDM systems to compensate signal distortions due to fading on each subcarrier. The frequency domain estimation scheme uses scattered pilot to estimate channel response by simple interpolation. This implies that the estimated channel response includes signal distortions due to the noise. In this paper, we propose time-averaged channel estimation method to remove the distortion by noise. The proposed scheme can effectively remove noise components by taking time-average of the estimated channel response after estimating frequency domain channel. The computer simulations were performed to evaluate the performance of the proposed channel estimator. For the Rician channel, we compared the performance of the proposed method to that of a conventional one using channel estimation by gaussian interpolation when SER(Symbol Error Rate) = $10^{-4}$, and compared to perfect channel estimation case. The proposed method showed differences of 0.07 dB, 0.6 dB compared to perfect channel estimation and improvements of 1.7 dB, 1.9 dB for 16 QAM, 64 QAM respectively compared to conventional method.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.25 no.3A
• /
• pp.353-361
• /
• 2000

The performance of a multi-carrier CDMA system is analyzed considering frequency selective multipath fading and Near/Far effects. The number of multicarrier, multiuser, and arms of RAKE receiver, and the decay ratio of frequency selective multipath fading are used as a parameter for the performance analysis. More over, the distribution and the strength of multiuser interference are also considered. To evaluated the Near/Far effects in a multi-carrier CDMA system, three distribution models are assumed. In the first model. interference to carrier Ratio, I/C, ranges form -4 dB to 4dB, and at each 2 dB interval 20 % of multiuser is assumed to be uniformly distributed. In the second one, I/C ranges from -2 dB to 2 dB, and 33.3% of multiuser is assumed to be equally dispersed at each 2dB interval. The third model is 0 dB of I/C, that is, with perfect power control, multiuser are assumed to be evenly located. In this paper, multi-carrier CDMA system adoption RAKE receiver is proposed to mitigate the frequency selective multipath fading. Form the results, the third model(i.e. perfect power control)shows the best performance, and the narrower range of I/C causes the less effects to the desired signal, which reads to the better performance.

• The Journal of the Institute of Internet, Broadcasting and Communication
• /
• v.14 no.4
• /
• pp.71-76
• /
• 2014

In this paper, we propose a SMMA(Sliced-Multi Modulus Algorithm) adaptive blind equalization algorithm with Flag for high order QAM system. SMMA has improved characteristics by applying the multi contour to MMA. However, SMMA still has a limit that the mismatch problem causes the residual error in the steady state is large. In order to significantly reduce the residual error in the steady state, we propose SMMA, which is controlled by the binary Flag of '1 'or '0' obtained from SMMA and a decision-directed algorithm, and analyze the performance of the proposed algorithm. By computer simulation, it is confirmed that the proposed algorithm has improved performance highly in terms of a residual ISI and a residual error in the steady state compared with MMA and SMMA.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.17 no.3
• /
• pp.268-276
• /
• 1992

In this paper, we present an discrimination method of unknown digital modulated signals in noisy communication environment. We propose the use of an identification procedure based on time domain signal parameters. First, We extract instantaneous envelope. Frequency and difference phase as the basic feature informations from received signals. In order to identify signals using the extracted feature informations, we design the two dimensional feature space. The extracted feature infomations are mapped into2Dfeature space using 2D feature points. The procedure has been tested by simulations on a computer in noisy communication environment, and the considered signals are ASK-W, ASK-4, BPSK, QPSK, 8PSK, FSK, and QAM.

• Journal of the Institute of Electronics and Information Engineers
• /
• v.54 no.5
• /
• pp.123-127
• /
• 2017

This paper fabricated and analyzed the image rejection mixer that uses FET's channel resistance. It can be applied for capacity 64QAM that has 50MHz~90MHz of IF band, 8.17GHz of LO frequency and 8.08~8.12GHz of RF band. When IF input power is -20dBm and LO input power is 10dBm, RF output power is obtained -33.2dBm. In this case, conversion loss is 12.9dB, the suppression of 14.3dB for LO frequency and 10.4dB for image frequency. The result of two tone test shows great IMD characteristics with 51.7dBc.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.12 no.5
• /
• pp.777-786
• /
• 2001

In this paper, as one of countermeasure techniques for a frequency selective fading, a digital slope equalizer(DSE) for 64-QAM digital radio relay system is analyzed in terms of principle, channel modeling, and digital implementation. Also computer simulations have been performed for DSE with a complex 13-tap adaptive time domain equalizer chip. It is shown that about 4.5 dB improvement in system signature can be obtained at the channel edge, and a variety of simulated results are reviewed in view of DSE modeling limit, operating frequency, control coefficient, signal constellation, and system signature. Finally, the functions of DSE chip confirmed up to 61 MHz clock operation are illustrated.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.5 no.3
• /
• pp.494-507
• /
• 2011

In this paper, we propose two schemes to reduce the complexity of fixed-complexity sphere decoder (FSD) algorithm in the ordering and tree-search stages, respectively, while achieving quasi-ML performance. In the ordering stage, we propose a QR-decomposition-based FSD signal ordering based on the zero-forcing criterion (FSD-ZF-SQRD) that requires only a few number of additional complex flops compared to the unsorted QRD. Also, the proposed ordering algorithm is extended using the minimum mean square error (MMSE) criterion to achieve better performance. In the tree-search stage, we introduce a threshold-based complexity reduction approach for the FSD depending on the reliability of the signal with the largest noise amplification. Numerical results show that in 8 ${\times}$ 8 MIMO system, the proposed FSD-ZF-SQRD and FSD-MMSE-SQRD only require 19.5% and 26.3% of the computational efforts required by Hassibi's scheme, respectively. Moreover, a third threshold vector is outlined which can be used for high order modulation schemes. In 4 ${\times}$ 4 MIMO system using 16-QAM and 64-QAM, simulation results show that when the proposed threshold-based approach is employed, FSD requires only 62.86% and 53.67% of its full complexity, respectively.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.33 no.10C
• /
• pp.836-843
• /
• 2008

In this paper we derive the theoretical performance of orthogonal STBC algorithms in spatially correlated Rayleigh fading environments and compare their performances for various correlation conditions. We first derive the theoretical BER of the orthogonal STBC algorithms for both M-ary PSK and M-ary QAM modulation schemes by using the eigenvalues of the channel correlation matrix and then investigate the effect of the spatial correlation on the performance for various transmission rates of $1{\sim}4bps/Hz$. Performance analysis illustrates that the Alamouti scheme provides the better performance than the Tarokh scheme for all the transmission rates in highly correlated fading environments with a correlation being larger than 0.9.