• The Journal of Korean Institute of Communications and Information Sciences
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• v.26 no.8A
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• pp.1367-1377
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• 2001

고전력 증폭기의 비선형성, 수신 주파수 편차 및 심볼 타이밍 편차가 모두 존재하는 실제 IEEE 802.11a 무선 LNA 시스템의 성능을 분석하였다. 이러한 시스템에서 데이터가 OFDM 변조된 후 주파수 선택적 Rayleigh 페이딩 채널을 통하여 전송될 때의 비트 오류율을 구하였다. 증폭기의 최대 출력 전력 대 평균 출력 전력비가 6dB이며 주파수 편차가 0.01이고 심볼 타이밍 편차가 2 샘플링 주기 시간인 경우에, 이 무선 LAN 시스템에서 10-5의 비트 오류율을 얻기 위하여 필요한 $E_{b}$ /$N_{o}$ 의 크기는 대략 20~24dB로 분석되었다. 이와 같은 실제 시스템과 정확한 채널 추정, 선형 증폭기, 정확한 주파수 동기 및 심볼 동기 가정의 이상적인 시스템간의 성능을 비교한 결과, 같은 크기의 비트 오류율을 얻기 위하여 이 실제 시스템에서 대략 1~3dB 정도의 $E_{b}$ /$N_{o}$ 가 더 소요된다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.8C
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• pp.645-654
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• 2012

In this paper, we consider a two-way relay (TWR) system, where two user nodes exchange their information within two transmission phases, by the help of a relay node adopting physical layer network coding. In the system, two users transmit their binary phase shift keying symbols simultaneously in the first phase, and the relay node decodes the XORed version of two user data and broadcasts it back to two users in the second phase. The performance of the system is analyzed in terms of the average end-to-end symbol error probability in Nakagami-m fading channels, for which a tight upper bound is derived in a closed form to provide an accurate and handy estimate on the performance. The results show that our upper bounds are almost indistinguishable from simulation results for various channel and system configurations. In addition, the optimal relay location and power allocation for various conditions can be obtained quickly with our analysis.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.7C
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• pp.618-627
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• 2010

In this paper, we propose an adaptive K-best algorithm in which the number K of candidates is changed according to the differences of level radii. We also compare the bit error performance and complexity of the proposed algorithm with those of several conventional K-best algorithms, where the complexity is defined as the total number of candidates of which partial Euclidean distances have to be calculated. The proposed algorithm adaptively decides K at each level by eliminating the symbols, whose differences of radii are larger than a threshold, from the set of candidates, and the maximum or average value of differences can be adopted as the threshold. The proposed decoding algorithm shows the better bit error performance and the lower complexity than a conventional K-best decoding algorithm with a constant K, and also has a similar bit error performance and the lower complexity than other adaptive K-best algorithms.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.23 no.9A
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• pp.2173-2183
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• 1998

We consider a frequency-hopped multiple-access communication system that employs reed-solomon code over GF(Q) and M-ary FSK signaling ($M{\leq}Q$) in rayleigh fading channel. We investigate the tradeoff among the modulation symbol size (M), the number of frequency slots, and the code rate in maximizing the average number of successfully transmitted information bits per unit time and unit bandwidth (called normalized throughput). We find that it is desirabel to use a large M in noise-limited environment. In interference-limited environment, it is more improtant to prevent errors (hits) by increasing the number of frequency slots than to correct them with formward error correction techniques or to reduce the error rate by increasing M.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38A no.7
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• pp.552-559
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• 2013

In this paper, the multiple-input multiple-output (MIMO) system with a precoder is considered in the transmit-correlated Rayleigh channels. We specifically target the MIMO system employing the minimum mean square error receivers. Based on random matrix theory, we first present a direct and generalized formulation for deriving a probability density function (PDF) of the signal-to-interference-plus-noise ratio (SINR). Then, we derive the accurate closed-form SINR PDFs for a small number of transmit and receive antennas. Based on the SINR PDFs, tight closed-form approximations of the symbol error rate (SER) are derived. Our analysis suggests that the SER approximations can be used to accurately estimate the error probabilities or as a useful tool for the system design.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.2C
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• pp.166-173
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• 2007

In Orthogonal Frequency Division Multiplexing (OFDM) systems, Narrow-Band Jamming (NBJ) over pilot tones used for channel estimation degrades the system performance. In this paper, we propose a new jammed pilot detection and elimination algorithm to overcome this problem. Moreover, the average Mean-Squared Error (MSE) on one OFDM symbol both under jammed and removed pilot subcarrier is analyzed. And then, the Symbol Error Rate (SER) performance of the channel estimation scheme using the proposed algorithm is evaluated by simulation. We can confirm that the channel estimator with the proposed algorithm improves the channel estimation performance at a high jamming power.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.26 no.8A
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• pp.1298-1310
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• 2001

이 논문에서는 채널 상태가 천천히 변할 때, 직교 주파수 분할 다중화-부호분할 다중접속 시스템에 적합한 채널 추정 방법을 제안하고 성능을 분석한다. 제안한 채널 추정 방법은 시간과 주파수 영역 모두에 파일럿 심볼을 삽입하고, 이산 퓨리에 변환 후 영을 채워 넣는 방법을 이용한 내삽법으로 모든 부채널의 전달 함수를 얻는다. 또한 변환 영역에서 저대역 여파를 통해 받은 파일럿 신호에 존재하는 가산성 백색 정규 잡음의 영향을 상당히 줄일 수 있다. 이 때 저대역 여파기의 차단 주파수는 채널의 다중경로 수에 따라 정해진다. 같은 방법을 이용한 내삽법을 시간축으로 적용하여 시간에 따라 변하는 부채널의 채널 응답을 얻을 수 있다. 이 논문에서는 여러 가지 내삽법에 대한 평균 제곱 오차 성능을 수식적으로 제시한다. 제안한 저대역 여파를 결합한 내삽법을 쓰면 채널의 통계적 특성에 관한 정보 없이, 그리고 훨씬 적은 계산량으로 선형 최소 평균 제곱 오차 추정기와 비슷한 성능을 얻는다. 레일리 감쇄 채널에 대한 모의 실험을 통해 같은 비트 오류율에 대한 신호 대 잡음 비의 이득이 있음을 보인다.

• Journal of Satellite, Information and Communications
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• v.10 no.2
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• pp.109-114
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• 2015

Frame synchronization is achieved by correlation between received symbols and a preamble pattern which is periodically appended at a frame header. In this paper, we deal with a frame detection method complaint with satellite-based DVB-S2 system. In DVB-S2, frame synchronization is performed under the low signal-to-noise ratio(SNR), a large frequency offset which can be up to 20% of a symbol transmission rate and unknown modulation schemes ranging from QPSK to 32-APSK. In this environment, we propose a method combining differential correlation based on SOF and PLSC with an accumulated correlation method for the detection of frame structures. In addition, detection performances about mean acquisition time(MAT) and detection error probability are evaluated via computer simulations.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.23 no.4
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• pp.976-987
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• 1998

In this paper, the effect of nonllinear distortion, caused by a high-power amplifier(HPA) in an orthogonal frequency division multiplexing (OFDM) system, on the receiver part is analyzed. Since the HPA, which can be modeled by a memeoryless Volterra system, distorts OFDM signals in a nonlinear fashion, the received signal at each subchannel includes the multiplicative distortion of 1-st order as well as additive nonlinear distortion of high-order. the nonlinear distortion can be viewed as a nonlinear interchannel interference (NICI) since it consists of harmonic distortions and intermodulation distortions, produced by oother subchannels affecting the subchannel of interest. In this paper, we analytically derive the variance of NICI in terms of average input power using the volterra model for HPA, and then calculate the bit-effor rate(BER) performance of an OFDM system. Also, we propose a simple method to compensate for the phase distortion in OFDM system amplified by HPA, OFDM system employing 16-QAM constellation input.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.11
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• pp.1406-1409
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• 2016

In this paper, we propose the heuristic signal grouping algorithm to estimate channel state value over full blind communication situation which means that there is no information about the modulation scheme and the channel state information between the transmitter and the receiver. Hereafter, using the constellation rotation method and the probability density function(pdf) the modulation scheme is determined to perform automatic modulation classification(AMC). Furthermore, the modulation type and a channel state value estimation capability is evaluated by comparing the proposed scheme with other conventional techniques from the simulation results in terms of the symbol error rate(SER) and the root mean square error (RMSE).