• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2015.11a
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• pp.13-15
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• 2015

본 논문에서는 하나의 중계기가 하나의 송신기로부터 신호를 받아 증폭한 후에 수신기로 재전송하는 방식으로 송신기와 수신기 사이의 통신을 돕는 네트워크를 고려하였다. 중계기가 독자적인 에너지원이 없는 경우 일정한 양을 에너지를 확보하여 중계에 사용하기 위해서 송신기로부터의 신호를 에너지로 하베스팅하는 모델을 생각하였다. 또한, 나아가 현재의 다양한 무선통신 네트워크에서 사용중인 적응변조를 적용하여 항상 일정이상의 비트오율을 만족할 수 있는 더욱 현실적인 모델이 되도록 하였다. 이러한 모델에서 정해진 만큼의 시간을 하베스팅에 사용했을 경우 처리율을 구하였으며, 나아가 그 시간을 최적화하여 유도한 처리율을 최대화하는 문제를 만들었다.

• Proceedings of the KIEE Conference
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• 2001.07d
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• pp.2511-2512
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• 2001

디스크의 탄젠셜 성분의 틸트가 생긴 경우 발생하는 체널의 변화에 대해 적응형 부분 응답 신호처리 과정인 비터비 디코더를 적용하게 되면 비트오율에 상당한 효과를 가져온다. 이러한 적응 과정을 효과적으로 진행하기 위한 간략화된 오류 발생 알고리즘을 제안한다.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 1998.05a
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• pp.150-154
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• 1998

CDMAPCS 시스템은 Rake 수신기를 이용만 경로 다이버시티를 채택하여 우수한 시스템 향상을 얻을 수 있어 주로 TDMA 시스템에서 적용하고 있는 등화기를 사용할 필요가 없다. 그러나 CDMA PCS 시스템의 역방향 링크에서는 순방향과는 달리 채널의 크기 및 위상 추정에 필요한 파이롯 채널이 없어 성능의 저하를 가져오게 된다. 따라서 역방향 링크에서 채널환경에 따라 Rake 수신기의 성능에 미치는 영향을 분석하는 것은 중요하다. 본 논문에서는 시스템 성능 및 광대역 채널 파라미터 분석을 위해 광범위한 라이브러리와 시스템 구성의 유연성을 가지고 있는 Ptolemy [1] 플랫폼에서 CDMA PCS 시스템의 역방향 링크 규격에 따라 각 블록을 사용자 정의로 구현하였다. Ptolemy 시뮬레이터를 이용하여 CDMA PCS 시스템의 역방향 링크 비트오율 성능을 채널의 특성과 연관지어 분석하였다. 그리고 가상할 수 있는 각 채널 모델을 이용하여 CDMA PCS 시스템의 성능과 광대역 채널 파라미터 (예: 지연확산)와의 상관 관계를 파악하였다. 본 연구에서 CDMA PCS 시스템에서는 일반적으로 알려져 있는 지연확산보다 평균지연 파라미터가 더 높은 상관 관계가 있음을 발견하였다.

• Journal of Advanced Navigation Technology
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• v.11 no.3
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• pp.274-280
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• 2007

An ultra-wideband signal is characterized by a radiated spectrum with wide bandwidth around a relatively low center frequency. In this paper, the bit error rate (BER), packet error rate (PER), and data throughput performance for an ultra-wideband system with M-ary correlation receiver are analyze in additive white Gaussian noise (AWGN) and co-channel interference channel. To evaluate the performance of UWB system, a set of UWB communication waveform as pulse position modulated (PPM) signals consisting of more than one UWB pulse is used. The M-ary PPM signals are defined to be equally correlated in order to simplify the system performance analysis. The analysis for system performance shows that the wireless channel error significantly degrades throughput performance and can be effectively increased by hybrid ARQ scheme. Also, an attempt for comparing the data throughput of ultra-wideband system on different performance improvement schemes and parameters has been made. From the performance evaluation process, it is shown that the effects of wireless channel and hybrid ARQ scheme for ultra wideband M-ary PPM system can be evaluated by means of a suitable combination of the PER, throughput vs. signal-to-noise power ratio per bit.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.9 no.2
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• pp.191-198
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• 1998

The error are equation of DC-CDMA/MDPSK signal has been derived in m-distribution and Rician fading channels. Predeteception multipath MRC(Maximal Ratio Combining) diversity technique is employed for improving the bit error rate performance. The suitability of modeling a Rician fading environment by properly chosen m-distribution model is examined. Using the derived equation the error performance has been evaluated and shown in figures as a function of PN code sequence length(N), user number(U), multipath number(P), fading index(m), Rician factor(K), number of diversity branches(L) and ($E_b/N_o$). The results show that the error performance in Rician fading agrees well with that in m-distribution fading as fading becomes weak and as user number(U) increases and as multipath number(P) increases and diversity number(L) increases.

• Journal of the Institute of Convergence Signal Processing
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• v.9 no.4
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• pp.304-312
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• 2008

Orthogonal codes like Walsh and Golay codes may have large correlation value when they are not synchronized, hence they are seldom used in asynchronous CDMA systems. Wysocki[1] showed that by multiplying the original Walsh-Hadamard matrix with an orthogonal transformation matrix the resultant matrix sustains orthogonality between row vectors and their cross-correlation can be reduced. Soberly and Wysocki[2] proposed similar scheme on Golay codes. This implies that using the proper orthogonal transformation cross-correlation of Walsh and Golay codes can be reduced, and the transformed codes can be used for user separation in the CDAM reverse link. In this paper we discuss cross-correlation related parameters which affect the performance of an asynchronous CDMA link, and we investigate the correlation properties of the transformed codes. When we designed orthogonal transformation matrices for Walsh and Golay codes, we minimized the maximum value of aperiodic cross-correlation of the codes ($ACC_{max}$) or the mean square value of the aperiodic cross-correlation($R_{cc}$) with preserving the orthogonality of the modified codes. We also evaluate the asynchronous CDMA system that uses the transformed Walsh and Golay codes.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.4C
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• pp.331-340
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• 2006

In this Paper, we propose to extend the TSS-LS(Two-Step Search scheme with Linear search based Second step) scheme which was already proposed by the authors for coherent UWB(Ultra Wide Band) systems, to rapid and reliable acquisition of noncoherent UWB systems in multipath channels. The proposed noncoherent TSS-LS employing simple energy window banks utilizes two different thresholds and search windows to achieve fast acquisition. Furthermore, the linear search is adopted for the second step in the proposed scheme to correctly find the starting point in the range of effective delay spread of the multipath channels, and to obtain reliable BER(Bit Error Rate) performance of the noncoherent UWB systems. Simulation results with multipath channel models by IEEE 802.15.3a show that the proposed two-step search scheme can achieve significant reduction of the required mean acquisition time as compared to general search schemes. ]n addition, the proposed scheme achieves quite good BER performance for large signal-to-noise ratios, which is favorably comparable to the case of ideal perfect timing.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.46 no.4
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• pp.148-156
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• 2009

This paper presents a new image rejection algorithm based on the analysis of the distortion of a single-frequency continuous-wave (CW) signal due to the I/Q mismatch. Existing methods estimated the gain mismatch and phase mismatch on RF receivers and compensated them However, this paper shows that the circular trajectory of a single-frequency CW signal is distorted elliptic-type trajectory due to the I/Q mismatch. Utilizing the analysis, we propose a I/Q mismatch compensation method. It has two processing steps. In the first processing step, the generated signal is rotated to align the major axis of the elliptic-type trajectory diagram with the x-axis. In the second processing step, the Q-channel signal in the regenerated signal is scaled to align the regenerated signal with the transmitted single-frequency CW signal. Simulation results show that a receiver using the proposed image rejection algorithm can achieve an image rejection ratio of more than 70dB. And, simulation results show that the bit error rate performances of receivers using the proposed image rejection algorithm are almost the same as those of conventional coherent demodulators, even in fading channels.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.7C
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• pp.680-690
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• 2006

In this paper, we present a bit allocation scheme based on grouped sub-channels for MIMO-OFDM (Multiple Input Multiple Output-Orthogonal Frequency Division Multiplexing) systems using V-BLAST (Vertical-Bell laboratories LAyered Space-Time) detector. A fully adaptive modulation and coding scheme may provide optimal performance in the MIMO-OFDM systems, however it requires excessive feedback information. Instead, SBA (Simplified Bit Allocation) scheme for reduction of feedback overhead, which applies the same modulation and coding to all the good sub-channels, may be considered. The proposed scheme in this paper named SBA-GS (Simplified Bit Allocation based on Grouped Sub-channels) groups sub-channels and assigns the same modulation and coding to the set of selected sub-channel groups. Simulation results show that the proposed scheme achieves comparable bit error rate performance of the conventional SBA scheme, while significantly reducing the feedback overhead in multipath channels with small delay spreads.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.13 no.5
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• pp.338-343
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• 2020

In this paper, it was shown that the decoding method of Hamming codes using soft values can be applied to molecular communication channels. A soft value criterion that can be used for decoding of Hamming codes for a molecular communication channel was proposed, and it has been shown through simulation that the decoding method using these values can improve reliability even in the molecular communication channel. A diffusion-based molecular communication channel was assumed, and information symbols were transmitted using BCSK modulation. After demodulating the number of molecules absorbed by the receiver at each symbol interval with an appropriate threshold, the number of molecules is no longer used. In this paper, the BER performance of the decoder was improved by utilizing information on the number of molecules that are no longer used as soft values in the decoding process. Simulation was performed to confirm the improvement in BER performance. When the number of molecules per bit is 600, the error rate of the Hamming code (15,11) was improved about 5.0×10^-3 to the error rate of the BCSK system without the Hamming code. It can be seen that the error rate of (15,11) Hamming code with the soft values was improved to the same extent. In the case of (7,4) Hamming code, the result is similar to that of (15,11) Hamming code. Therefore, it can be seen that the BER performance of the Hamming code can be greatly improved even in the molecular communication channel by using the difference between the number of molecules absorbed by the receiver and the threshold value as a soft value.