• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.10 no.1
• /
• pp.36-41
• /
• 2006

In this paper, we present the performance of iterative decoding with a Turbo decoder and a M-ary QAM(Quadrature Amplitude Modulation) demapper. The demappers are designed with Max-Log-MAP algorithm and it's approximated one. In addition, we provide implementing block for the approximated algorithm. From the results of computer simulations, the approximated algorithm of the Max-Log-MAP has little bit worse than the Max-Log-MAP but suggests low complexity for practical implementation.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.8 no.8
• /
• pp.2783-2795
• /
• 2014

Orthogonal frequency division multiplexing with offset quadrature amplitude modulation (OFDM-OQAM) technique has drawn significant interests in recent years. However, most of the existing OFDM peak-to-average ratio (PAPR) reduction schemes cannot be used in the OFDM-OQAM system directly. In this paper, a modified scheme called overlapped segmental clipping (OS-clipping) is proposed to deal with the high PAPR problem specifically in the OFDM-OQAM system. For the proposed OS-clipping scheme, the input signals are divided into a number of overlapped segments and then the clipping operation is processed on each segment. Simulation results show that the modified scheme used in the OFDM-OQAM system can provide better performance than conventional clipping scheme directly used in the OFDM-OQAM system, and even outperforms conventional clipping scheme applied in the OFDM system.

• ETRI Journal
• /
• v.27 no.3
• /
• pp.257-266
• /
• 2005

Many multi-modulus blind equalization algorithms (MMA) have been presented in the past to overcome the undesirable high misadjustment exhibited by the well-known constant modulus algorithm. Some of these MMA schemes, specifically tailored for quadrature amplitude modulation (QAM) constellations, have also been proved to fix the phase offset error without needing any rotator at the end of the equalizer stage. In this paper, a new multi-modulus algorithm is presented for QAM signals. The contribution lies in the technique to incorporate the sliced symbols (outcomes of decision device) in the multi-modulus-based weight adaptation process. The convergence characteristics of the proposed sliced multi-modulus algorithm (S-MMA) is demonstrated by way of simulations, and it is shown that it gives better steady-state performance in terms of residual inter-symbol interference and symbol-error rate. It has also been shown that the proposed algorithm exhibits lesser steady-state misadjustment compared to the best reported MMA.

• 제어로봇시스템학회:학술대회논문집
• /
• 2004.08a
• /
• pp.1355-1359
• /
• 2004

The two way subscriber transmission systems have tendency to spread its carrier frequency bandwidth or information bit rate and average bit error rate according to popularization of high speed information through the digital communication system, transmission medium and the Internet. This fact is an important incentive to realize new systems. These two way subscriber transmission systems usually use same cable or same carrier frequency bandwidth for up stream channel and down stream channel. In the systems, the disturbances of noise, crosstalk or fading affect the characteristics. Specifically, these disturbances cause the decrease of information bit rate and degradation of transmission quality. This paper proposes the improved method of their degradations using the particular feature of two way subscriber transmission systems and it makes clear proposed method is effective by theoretically and some numerical examples.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.10 no.8
• /
• pp.3772-3790
• /
• 2016

It is well known that the constant modulus algorithm (CMA) presents a large steady-state mean-square error (MSE) for high-order quadrature amplitude modulation (QAM) signals. In this paper, we propose a low-complexity hybrid adaptive blind equalization algorithm, which augments the CMA error function with a novel constellation matched error (CME) term. The most attractive advantage of the proposed algorithm is that it is computationally simpler than concurrent CMA and soft decision-directed (SDD) scheme (CMA+SDD), and modified CMA (MCMA), while the approximation of steady-state MSE of the proposed algorithm is same with CMA+SDD, and lower than MCMA. Extensive simulations demonstrate the performance of the proposed algorithm.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.8 no.5
• /
• pp.983-987
• /
• 2004

Pilot symbol assisted modulation (PSAM) can be used for the channel estimation. However, imperfect channel estimates degrade the bit error rate (BER) performance. I derive the exact BER of 16-level quadrature amplitude modulated (16-QAM) orthogonal frequency division multiplexing (OFDM) systems with PSAM in time dispersive Rayleigh fading channels. In real system, there is 2.5 dB penalty in $\overline{\gamma_b}$for the same BER relative to ideal system with perfect channel estimation.

• Proceedings of the Korea Information Processing Society Conference
• /
• 2003.05b
• /
• pp.1373-1376
• /
• 2003

본 논문에서는 DS-CDM-QPSK방식 위성 DAB 시스템(ITU-R BO. 1130-4 시스템 E)의 위성 중계기 고출력 증폭기(HPA) 비선형 특성으로 인한 전력효율 저하를 개선하기 위해 QPSK 변조기법 대신 부드러운 위상천이와 진폭변이가 적은 SQAM 변조기법을 적용한 DS-CDM-SQAM (Superposed Quadrature Amplitude Modulation) 방식을 제안하고 성능을 분석하였다. 비선형 다중경로 이동수신 환경에서 전산모의 실험 결과, 제안하는 DS-CDM-SQAM 방식은 기존의 DS-CDM-QPSK 방식보다 $BER=1{\times}10^{-3}$에서 Eb/No=1.7dB 성능 향상됨을 확인할 수 있었다. 따라서 DS-CDM-SQAM 시스템은 비선형 육상 이동 위성 DAB환경에서 전력효율을 크게 향상할 수 있다.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.7 no.4
• /
• pp.167-172
• /
• 1982

We have studied and discussed the error rate performance of Quadrature Amplitude Modulation(QAM) in an environment of cochannel QAM interference and impulsive noise. A general equation of error probability for L-level QAM signal has been derived and the error rate of the 16-QAM signal, as an example, has been calculated as functions of carrier-to-noise power ratio(CNR), carrier-to-interferer power ratio(CIR), impulsive indes, and the phase difference between signal and interferer.

• Journal of the Korean Institute of Telematics and Electronics A
• /
• v.32A no.5
• /
• pp.14-23
• /
• 1995

A new dual-mode algorithm for blind equalization of quadrature amplitude modulation (QAM) signals is proposed. To solve the problem that the constant modulus algorithm (CMA) converges to the constellation with the arbitrary phase rotation, with the modification of the CMA, the proposed algorithm accomplishes blind equalization and carrier phase recovery simultaneously. In addition, the dual-mode algorithm combining the modified constant modulus algorithm (MCMA) with decision-directed (DD) algorithm achieves the performance enhancement of blind convergence speed and steady-state residual ISI. So we can refer the proposed algorithm to as a scheme for joint blind equalization and carrier phase recovery. Simulation results for i.i.d. input signals confirm that the dual-mode algorithm results in faster convergence speed, samller residual ISI, and better carrier phase recovery than those of the CMA and DD algorithm without any significant increase in computational complexity.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2008.10a
• /
• pp.890-893
• /
• 2008

In this paper, we present a low complexity modified multi-level sphere decoder (SD) for multiple-input multiple-output (MIMO) systems employing quadrature amplitude modulation (QAM) signals. The proposed decoder, exploiting the multi-level structure of the QAM signal scheme, first decomposes the high-level constellation into low-level 4-QAM constellations, so-called sub-constellations. Then, it deploys SD in the sub-constellations in parallel. In addition, in the searching stage, it uses the optimal low-complexity sort method. Computer simulation results show that the proposed decoder can provide near optimal maximum-likelihood (ML) performance while it significantly reduces the computational load.