• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.14 no.10
• /
• pp.2215-2222
• /
• 2010

A Wireless Access for Vehicular Environment (WAVE) system based on Orthogonal Frequency Division Multiplexing (OFDM) is made for vehicle to vehicle wireless communications. The physical layer standard of the WAVE system is very similar to that of the IEEE802.11a wireless local area network (WLAN). Therefore, the performance of the WAVE system is degraded by continual channel variation in the WAVE multipath fading channels after starting initial channel estimation. In this paper, we research the performance improvement of equalization in 64 Quadrature Amplitude Modulation (QAM) transmission in WAVE environment. The proposed algorithms use the training sequence and the midamble sequence which is used for fast channel variation such as WAVE environments. Additionally, various interpolation methods are also used for the channel tracking.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.35 no.2C
• /
• pp.203-209
• /
• 2010

In this paper, we propose a new selected mapping (SLM) scheme for reducing peak to average power ratio (PAPR) of orthogonal frequency division multiplexing (OFDM) signals modulated with quadrature amplitude modulation (QAM), called amplitude and phase variant SLM (APSLM). Contrary to the conventional SLM which rotates the phases of QAM symbols in the frequency domain, the proposed scheme changes the magnitudes as well as the phases of QAM symbols by applying binary sequences to the binary data sequence before mapped to QAM symbols. Simulation results show that the proposed scheme has better PAPR reduction performance than the conventional SLM scheme for the QAM modulated OFDM signals, especially for the small number of subcarriers.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.12 no.2
• /
• pp.343-351
• /
• 2008

In this paper, we investigate the design of the QAM(Quadrature Amplitude Modulation) method for the CACB(Constant Amplitude Coded Multicode Biorthogonal) scheme. The modulation method fan improve the transmission data rate by increasing the BE(Bandwidth Efficiency). Additionally, we can improve the system performance by using the QAM SD(Soft Decision) method with the MDSA(Minimum Distance Selection Algorithm). Finally, the DFE(Decision Feedback Equalizer) for the CACB-QAM is simulated under the MPF(MultiPath Fading) channel for real implementation. The proposed scheme can be used for the PHY(PHYsical layer) standard of the WPAN(Wireless Personal Area Network) requiring high rate data transmission.

• Proceedings of the Korean Society of Broadcast Engineers Conference
• /
• 2010.11a
• /
• pp.47-50
• /
• 2010

최근 3D HDTV (3-Dimensional High Definition Television)에 대한 연구가 활발히 진행되고 있다. 국내에서도 3D HDTV 방송 서비스를 위하여 기존의 ATSC (Advanced Television Systems Committee) 8-VSB (8-Vestigial Side Band) 시스템을 수정하려는 연구가 진행되고 있다. 그 중에서도 프레임 생성 과정에서 프레임 헤드 부분에 PN (Pseudo-Noise)심볼을 사용하는 새로운 시스템의 개념을 제안하고, 이 시스템을 수정된 ATSC 시스템이라 부를 것이다. 수정된 ATSC 시스템은 기존 ATSC 8-VSB 시스템에서 사용되던 VSB 변조방식을 사용한다. 본 논문에서는 수정된 ATSC 시스템에 적용 가능한 반송파 주파수 복구 방식을 제안한다. 제안된 반송파 주파수 복구 방식은 Fitz 알고리즘을 사용하는 거친 주파수 복구부와 간단한 PN심볼 상관 알고리즘을 사용하는 미세 주파수 복구부로 구성된다. 그리고 진폭만을 변조하여 사용하는 VSB 변조 방식의 경우 심볼 정보가 동위상 채널에만 존재하고, 직교위상 채널은 단순히 동위상 채널의 힐버트 변환된 값에 지나지 않는다. 그러므로 VSB 변조된 심볼은 QAM 변조된 심볼 처럼 일정한 배열을 가지지 않고, 반송파 주파수 옵셋에 더욱 민감하게 된다. 이를 극복하기 위하여 수신된 PN심볼에 대한 위상 보정 과정을 수행하고, 이 과정은 수정된 ATSC 시스템의 반송파 주파수 복구 시 성능을 향상 시킨다.

• Journal of the Korea Institute of Military Science and Technology
• /
• v.17 no.3
• /
• pp.336-341
• /
• 2014

When using a higher-order modulation scheme, there are variations in bit-reliability depending on the bit position in a modulation symbol. Variations of bit-reliability in the codeword block lower the decoding performance. Also, the decoding performance increases as the sum of the bit-reliabilities in the codeword block increases. This paper presents a novel hybrid automatic repeat request scheme that increases the sum of the reliabilities of the transmitted bits by lowering the modulation order, and decreases the variations of bit-reliability in the codeword block by preferentially retransmitting bits with low reliability. The proposed scheme outperforms the constellation rearrangement scheme. Furthermore, the proposed scheme also provides a good solution in cases where the size of the retransmission block is smaller than the size of the initial transmission block.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.39A no.5
• /
• pp.229-236
• /
• 2014

Quadrature Amplitude Modulation (QAM) is widely used in contemporary wired and wireless communications systems. In this paper, I propose a generalized triangular quadrature amplitude modulation (gTQAM) that includes the square quadrature amplitude modulation (SQAM), TQAM, and ${\Theta}$-QAM as special cases. Therefore, the proposed gTQAM forming a lattice of arbitrary triangles provides a versatile structure in signal constellations compared to other QAM schemes. For M-ary gTQAM, I derive an exact closed-form expression for the bit error rate (BER), and present the optimal signal constellations for given SNR values from the derived BER expression. Finally, I validate the derived BER results through computer simulations.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.46 no.7
• /
• pp.39-44
• /
• 2009

It is well-known that the performance of turbo codes can be improved by allocating different energies per code symbol. In this paper, based on this observation, we propose a joint encoding and modulation scheme for quadrature amplitude modulated turbo code systems. In the proposed scheme, the amount of energy difference between the turbo coded symbols is optimized by optimizing the constellation of quadrature amplitude modulation (QAM). The proposed scheme offers better coding gain compared to the conventional combination of binary turbo code and QAM at the bit error rate of 10$^{-5}$. Also, the performance of binary turbo codes with the proposed QAM constellation for various code symbol mapping strategies are verified.

• Proceedings of the Korean Society of Broadcast Engineers Conference
• /
• 2010.07a
• /
• pp.96-97
• /
• 2010

다중 홉 중계기술은 차세대 무선통신을 위한 핵심 기술로 최근 전 세계적으로 활발히 연구되고 있으며, 셀 용량 증대, 셀영역 확장, 음영지역 축소 등의 장점으로 인하여, IEEE 802.11s, 802.15.4, 802.16j 등의 표준화에의 반영을 위한 논의가 활발히 진행되고 있다. 본 논문에서는 간섭신호가 존재하지 않는 이상적 네트워크 환경을 고려한 기존 연구의 한계를 극복하기 위해, 다중 간섭신호가 존재하는 레일레이(Rayleigh) 페이딩 채널에서 이중 홉(dual-hop) 복호후재전송(DF : decode-and-forward) 중계시스템의 시스템 모델을 제안하고, 모의실험을 통하여 불능확률 및 4진 직교 진폭 변조(4-QAM)를 위한 평균비트오율 (average bit error rate) 성능을 살펴본다.

• Composites Research
• /
• v.17 no.2
• /
• pp.28-33
• /
• 2004

Failure detection in a cross-ply laminated composite beam under tensile loading were performed using a fiber Bragg grating (FBG) sensor. A Passive Mach-Zehnder interferometric demodulator was proposed to enhance sensitivity and bandwidth. The proposed FBG sensor system without active device such as a phase modulator is very simple in configuration, easy to implement and enables the measurement of high-frequency vibration with low strain amplitude such as impact or failure signal. Failure signals detected by a FBG sensor had offset value corresponding to the strain shift with vibration at a maximum frequency of several hundreds of kilohertz. at the instant of transverse crack propagation in the 90 degree layer of composite beam.

• Journal of Korea Multimedia Society
• /
• v.10 no.1
• /
• pp.66-73
• /
• 2007

SDR technology is a fundamental wireless access technology that combines and accommodates multiple wireless communication standards in one transceiver system through just modifying software using modular communication platforms without any hardware modifications for RF and IF signal processing on the basis of high performance DSP devices. Various communication systems that are designed under diverse and complex network environments require the communication platforms on the basis of SDR supporting reorganization to guarantee simple and fast communication interfaces among the respective wireless networks. This paper introduces a main idea on the implementation of platform on the basis of SDR and a communication platform is designed for experiments that is composed of a DSP board with TMS320C6713 CPU, a FPGA board processing IF signals, and a module with RF transceiver processing wireless LAN frequency bandwidth. Various modulation schemes(BPSK, QPSK, and 16QAM) used in communication systems are applied and tested on the designed platform and the test results shows that it is possible to design a reconfigurable communication terminal platform.