• 한국산학기술학회:학술대회논문집
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• 한국산학기술학회 2010년도 추계학술발표논문집 1부
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• pp.16-19
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• 2010

본 논문에서는 송신국과 릴레이에서의 오류확률을 고려한 복호 후 전달 릴레이(DF: Decoded and Forward) 시스템에 대하여 정확한 비트 오류율 분석을 수행하고자 한다. 성능 분석에서는 복호 후 전달 릴레이 시스템의 노드들 간의 채널을 상호 독립적인 레일리 페이딩 채널로 가정하고 변조 방식으로는 BPSK(Binary Phase Shift Keying)를 사용한다. 우선, 정확한 평균 오류율 분석을 위하여 송신국-수신국 링크와 릴레이-수신국 링크 결합시 릴레이노드의 복호결과 오류 유무에 따라 수신 SNR(Signal to Noise Ratio)을 각각 유도하고 복호결과가 오류일 때 수신 SNR이 양수인 경우와 음수인 경우를 고려하여 그에 대한 PDF(Probability Density Function)를 계산한다. 그리고 각각의 경우에 대한 평균 오류율을 유도하였다. 또한 모의실험 결과와의 비교를 통하여 제안된 성능 분석 기법의 정확성을 검증하였다.

• Journal of Astronomy and Space Sciences
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• 제27권2호
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• pp.129-134
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• 2010

Rain attenuation can cause a serious problem that an availability of space communication link on Ka band becomes low. To reduce the effect of rain attenuation on the error performance of space communications in Ka band, an adaptive coding and modulation (ACM) scheme is required. In this paper, to achieve a reliable telemetry data transmission, we propose an adaptive coding and modulation level using turbo code recommended by the consultative committee for space data systems (CCSDS) and various modulation methods (QPSK, 8PSK, 4+12 APSK, and 4+12+16 APSK) adopted in the digital video broadcasting-satellite2 (DVB-S2).

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2000년도 추계종합학술대회
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• pp.166-171
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• 2000

현대 무선 통신에서는 제한된 주파수 자원을 효율적으로 사용하기 위해 스펙트럼 효율성이 매우 중요한 문제로 여겨지고 있다. 또한 시스템구조 측면에서는 저 가격, 저 전력 및 초경량에 목표를 두고 제작되고 있다. 본 논문에서는 직접 디지털 주파수합성기(DDS ; Direct Digital Synthesize.)를 이용하여 스펙트럼 효율이 우수한 BCPFSK(Binary Continuous Phase Frequency Shift Keying)를 직접 변조하였으며, 시스템 구조로는 직접 변환(Direct Conversion) 구조를 적용하여, 433 MHz대의 BCPFSK 출력을 갖는 송 ·수신기를 설계하고 성능을 평가하였다.

• 한국통신학회논문지
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• 제29권11A
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• pp.1237-1243
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• 2004

This paper presents and analyses the closed-form expression of the average bit error rate (BER) for an asynchronous direct-sequence code division multiple access (DS-CDMA) system with coherent binary phase shift keying (BPSK) modulation scheme using a maximal ratio combining (MRC) diversity over a Rician fading channel. In addition to the average BER, outage probability, and user capacity of system are estimated as performance measures. The results are general enough so that it includes Rayleigh fading and nonfading channel with zero and infinite Rician factor, respectively, as special cases. The effects of various channel models, processing gains, and diversity orders on the system performances are also considered for the typical multipath delay profiles characterized by Rician fading channel.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2004년도 Proceedings of ISRS 2004
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• pp.498-500
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• 2004

QPSK (Quaternary Phase Shift Keying) will be adopted as the modulation of HRIT (High Rate Information Transmission) which is transmitted to COMS (Communication, Ocean and Meteorological Satellite) through HPA (High Power Amplifier) in ground segment. Due to the nonlinearity of HPA, IMD (Inter-Modulation Distortion) of multi-carrier signals and PAPR (Peak-to-Average Power Ratio) of modulated HRIT must be considered to estimate the output power of HPA. In this paper, we measured the PAPR to various the roll-off factor of RRC (Root Raised Cosine filter) which is filtering the modulated HRIT signal for reducing ISI (Inter-Symbol Interference) and bandwidth. It was found that the minimum PAPR is 2.78dB at 0.5 of roll-off factor for scrambled data. It's 2.78dB of P APR will be in output power selecting in COMS earth station.

• ETRI Journal
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• 제27권2호
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• pp.223-226
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• 2005

This paper presents the application of a turbo coding technique combined with a bandwidth efficient method known as trellis-coded modulation. A transformation applied to the incoming I-channel and Q-channel symbols allows the use of an off-the-shelf binary/quadrature phase shift keying (B/QPSK) turbo decoder without any modifications. A conventional turbo decoder then operates on transformed symbols to estimate the coded bits. The uncoded bits are decoded based on the estimated coded bits and locations of the received symbols.

• 대한전자공학회논문지
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• 제27권5호
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• pp.645-655
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• 1990

A hybrid DS/SFH spread spectrum system is used to achieve a larger gain in some applications. The probability of error for a hybrid DS/SFH(direct sequence/slow frequency hopped) spread-spectrum system is calculated over a channel which suffers from multiple-tone jamming and additive white Gaussian noise. BPSK(binary phase shift keying) is considered as modulation scheme. The probability of error is computed for various system parameters such as a DS/SFH hybrid ratio, the number of jamming tones, a jamming-to-signal ratio, and a siganl-to-noise ratio. It is shown that a DS system or a SFH system achieves smaller probability of error than a hybrid DS/SFH system for most values of system parameters. However, it is also shown that there are hybrid ratios with which a hybrid DS/SFH system achieves smaller probability of error than a DS system and a SFH system achieve for some values of system parameters.

• Journal of information and communication convergence engineering
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• 제1권4호
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• pp.194-198
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• 2003

Recently, the use of TCP/IP protocols over wireless LANs poses significant problems. In this paper, we have analyzed transmission control protocol (TCP) packet transmission time for mobile IP over wireless local area networks (LANs) using a proposed a new random backoff scheme. We call it as a proxy backoff scheme. It is considered the transmission time of TCP packet on the orthogonal frequency division multiplexing (OFDM) in additive white gaussian noise (AWGN) channel. From the results, a proposed proxy backoff scheme produces a better performance than an original random backoff in mobile IP over wireless LANs environment. Also, in OFDM/quadrature phase shift keying (QPSK) medium access control (MAC), we have obtained that the transmission time in wireless channel decreases as the TCP packet size increases.

• Journal of Communications and Networks
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• 제12권6호
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• pp.616-623
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• 2010

In this paper, exact closed-form expressions for outage probability and bit error probability (BEP) are presented for multi-hop decode-and-forward (DF) relaying schemes in conjunction with cooperative diversity, in which selection combining technique is employed at each node. We have shown that the proposed protocol offers remarkable diversity advantage over direct transmission as well as the conventional DF relaying schemes with the same combining technique. We then investigate the system performance when different diversity schemes are employed. It has been observed that the system performance loss due to selection combining relative to maximal ratio combining is not significant. Simulations are performed to confirm our theoretical analysis.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2004년도 하계학술대회 논문집 D
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• pp.2559-2561
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• 2004

This paper proposes the new signal-to-noise ratio(SNR) that is different from the conventional signal-to-noise ratio (SNR) in direct-sequence code-division multiple-access communication system employing offset quadrature phase-shift keying(OQPSK) and using a chip waveform. The conventional SNR value is so different from a real SNR value. Therefore, we propose a new SNR equation approximated to real SNR. The multiple-access interference(MAI) in DS-CDMA communication system has an effect on SNR performance and MAI is concerned with the correlation functions of the chip waveform. For this reason, we considered all possible correlations of chip waveforms. In conclusion, the SNR value of proposed method is enclosed to the real SNR value.