• Proceedings of the IEEK Conference
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• 2001.09a
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• pp.631-634
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• 2001

OFDM(orthogonal frequency division multiplexing) 시스템은 유효심볼의 뒷부분 일부를 복사하여 유효심볼 이전에 미리 전송하는 보호구간을 이용하여 다중경로에 의한 왜곡을 줄일 수 있다. 그러나, 유효심볼의 시작점을 정확히 판단하더라도 열악한 다중경로 또는 프리-고스트(pre-ghost) 채널의 영향으로 인해 심볼간 간섭(inter-symbol interference)이 발생한다. 본 논문에서는 다중경로 환경하의 기존 시스템에서 발생하던 심볼간 간섭을 제거할 수 있는 프레임 선택 알고리듬을 제안한다. 프레임 선택 알고리듬은 FFT 입력으로 유효심볼의 뒤 알부 대신 보호구간의 일부를 사용한다. FFT 입력으로 사용된 보호구간내 교체구간은 다중경로 환경에 따라 달라져야 하는데, 교체구간 판단을 위한 네 가지 알고리듬도 소개한다. 제안한 알고리듬을 DVB-T(digital video broadcasting-terrestrial) 시스템에 적용한 모의실험을 통하여 3 dB 이상의 성능향상을 얻을 수 있다.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.1
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• pp.9-14
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• 2013

In this paper, we propose a low complexity bilateral search SIC for OFDM in fast time-varying channels. Due to the possibility of error propagation in SIC, symbol detection ordering within the block of symbols has a significant effect on the overall performance. In this paper, the first symbol to be detected is determined based on CSEP values, and then the next symbol to be detected is selected according to the updated CSEP while bilaterally searching from the boundary of the detected symbol group. Through computer simulations, we show that the proposed method has performance improvements with almost the same computation complexity over the conventional methods in the high SNR region. It has a performance approaching the MFB, known as the performance upper bound, within 2dB at the BER of $10^{-5}$.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.10
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• pp.1030-1035
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• 2003

In this paper, we compare the performance of IS-OFDM(interference suppressing orthogonal frequency division multiplexing) system with that of the conventional OFDM system. Each parallel branch symbol of IS-OFDM is multiplied by the orthogonal sequence and distributed into all sub-carriers. Then, each sub-carrier transmits information composed of the symbol components of all parallel branches in the given frame. The structure of IS-OFDM shows the frequency diversity characteristic. Therefore, IS-OFDM can be robust to the narrowband interference. BER performances are found in the narrow-band interference and a harmonic noise channels. When JSR(Jamming to signal ratio) increases from -10 dB to +10 dB in the constant interference bandwidth, IS-OFDM outperforms the conventional OFDM and the BER difference between IS-OFDM and OFDM is reduced as JSR increases. Also, the similar properly can be shown when interference bandwidth increases at the constant JSR. In the harmonic noise channel, we can find the good performance of IS-OFDM when the h-rate(harmonic noise bandwidth to signal bandwidth ratio) increases from 0.01 to 0.8. So, simulation results show that the IS-OFDM is more robust to the interference than the conventional OFDM.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.7
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• pp.34-42
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• 2013

In this paper, we compare the performance of wavelet OFDM (Orthogonal Frequency Division Multiplexing) and FD-OFDM(Frequency diversity OFDM) system with conventional OFDM system. Wavelet OFDM system uses wavelet transform rather than Fourier transform and contains intermediate characteristics of CDM (Code Division Multiplexing) and OFDM. In wavelet OFDM system, inter-symbol interference (ISI) can be suppressed effectively and adjacent channel interference can be also minimized well. In FD-OFDM system, each parallel branch symbol is multiplied by the orthogonal sequence and distributed into all sub-carriers. Then, each sub-carrier transmits information composed of the symbol components of all parallel branches in the given frame. FD-OFDM contains the frequency diversity characteristic and, therefore, FD-OFDM can be robust to the narrowband interference. For the comparison among different systems, BER (Bit-Error Rate) performances are evaluated in the presence of narrow-band interference and a harmonic noise channel. From the evaluation results, compared to the conventional OFDM, wavelet OFDM and FD-OFDM shows better robustness against the interference and, especially, wavelet OFDM is the most robust in harmonic noise channel.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.20 no.9
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• pp.1688-1695
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• 2016

Underwater communication has multipath error because of reflection by sea-level and sea-bottom. The multipath of underwater channel causes signal distortion and error floor. The excessive multipath encountered in underwater communication channel creates inter symbol interference, which is a limiting factor to achieve a high data rate and bit error rate performance. Therefore, to increase throughput efficiency and improve performance, this paper consider FTN (Faster-than-Nyquist) signalling based on turbo equalization. FTN signalling is a technique of transmitting information at a rate higher than the allowed Nyquist limit. This paper presented efficient decoder structure of FTN transmission in the environment of multipath underwater channel and we compare the performance between FTN method and conventional punctured method in lake experimentation. As a results of lake experiment, we confirmed FTN method based on turbo equalization is applicable and efficiency in underwater communication.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.22 no.9
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• pp.2005-2013
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• 1997

The MCMA adaptive blind equalization algorithm has a excellent phase correction capabilities in addition to channel amplitude equalization, but has an inevitable error by mismatching between the original constellation points in arriving at the perfect equalization since unique new type constellation points are used as desired response instead of original constellation points and follows the slow convergence speed of CMA. In this paper, We propose an adaptive blind equalization algorithm with dual-mode, which has decision regions. Inside the decision regions, it operates as considering the moudlus of original data symbol point and outside the decision region, it operates as considerin gthe modulus of new constellation points. The proposed algorithm has a lower error in the steady state and rapid convergence speed toward steady state using the original data symbol points instead of new constellation points in the decision regions. From computer simulation, we confirm that the propposed algorithm has the performance superiority in residual ISI, convergence speed compared with the cnventional adaptive blind equalization algorithms, CMA, MCMA, Stop-and-Go algorithm.

• Proceedings of the IEEK Conference
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• 2000.09a
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• pp.577-580
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• 2000

본 논문에서는 비동기식 Zipper 방식의 VDSL(Very High Blt-rate Digital Subscriber Line) 시스템에서 cyclic extension 을 최소화 하는 기법을 제안하고, 전형적인 전화채널 환경 하에서 제안된 방식의 성능을 분석한다. Zipper 방식에서는 각 DMT(discrete-multitone) 블록에cyclic prefix(CP) 와 cyclic suffix(CS)가 추가로 사용되는데, 여기서 CP 는 심볼간 간섭과 부채널간 간섭을 방지하기 위하여 삽입되며, CS는 upstream 과 downstream 부반송파간의 직교성을 유지하기 위하여 추가되어 near-end crosstalk (NEXT)을 방지한다. 이 방식이 동기식 Zipper 방식으로 CS에 의해 NEXT를 제거하기 위해서는 한 binder 내의 모든 송신단의 동기를 맞추어야 한다. 그러나 비동기식 Zipper 방식은 다른 송신단과의 동기가 맞지 않아 CS가 NEXT에 아무런 영향을 주지 못한다 본 논문에서는 CS를 사용하지 않는 비동기식 Zipper 방식의 VDSL 시스템을 제안한다. 컴퓨터 모의실험을 통하여 제안된 방식이 전형적인 채널환경 하에서 기존 Zipper 방식의 VDSL 시스템과 비교하여 비슷한 전송능력을 갖게 됨을 보인다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.6A
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• pp.575-585
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• 2006

In Orthogonal Frequency Division Multiple Access (OFDMA) systems, timing synchronization in uplink is accomplished by an initial uplink synchronization called an initial ranging process. The Base Station's receiver synchronizes the symbol timing to specific user's symbol and the other user's symbols have some Symbol Timing Offset (STO). Linear phase shift is occurred by each user's STO in an OFDMA symbol. The Multiple Access Interference (MAI) caused by the summation of each user's linear phase shift degrades the performance of ranging code detection. In this paper, we propose an initial ranging symbol structure with common ranging code for phase shift estimation and compensation. We car estimate the average of phase shift that is generated by each user's STO and compensate this phase shift by using common ranging code. This scheme will suppress the MAI and provide better detection performance than conventional process.

• The Journal of the Acoustical Society of Korea
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• v.34 no.4
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• pp.295-302
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• 2015

Acoustic channels are characterized by long multipath spreads that cause inter-symbol interference. The way in which this fact influences the design of the receiver structure is considered. To satisfy performance and throughput, we presented consecutive iterative BCJR (Bahl, Cocke, Jelinek, Raviv) equalization to improve the performance and throughput. To achieve low error performance, we resort to powerful BCJR equalization algorithms that iteratively update probabilistic information between inner decoder and outer decoder. Also, to achieve high throughput, we divide long packet into consecutive small packets, and the estimate channel information of previous packets are compensated to next packets. Based on experimental channel response, we confirmed that the performance is improved for long length packet size.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.11C
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• pp.1037-1043
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• 2006

In this paper, we introduce a two-dimensional modulation code for holographic data storage systems(HDSS), which is a candidate for the next generation data storage system. The two-dimensional(2D) intersymbol interference(ISI) induces higher bit error rate(BER). The balanced number of zeros(dark) and ones(light) in each page reduces inter-page interference(IPI). The code rate is 519. Although the proposed code has higher code rate than other 2D code with rate 4/9, the BER performances of two codes are similar.