• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.10 no.5
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• pp.147-151
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• 2010

In this paper, we propose network-coding based two-way relay communication using adaptive modulation scheme for satisfying relay QoS(Quality of Service) according to channel environment between user and relay. Two-way relay communication is bidirectional cooperative communication that users exchange own signal with help of relay. Network-coding based two-way relay communication can achieve high throughput compared to conventional scheme through reducing time slots. we propose adaptive M-QAM modulation scheme in network-coding based two-way relay communication for satisfying QoS of relay. Simulation result shows that the proposed scheme satisfies goal QoS of system.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.7
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• pp.761-768
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• 2010

This paper presents an effective method to achieve the wideband waveform for high resolution SAR(Synthetic Aperture Radar) using the frequency multiplication technique. And also this paper analyzes the root causes for the spectral regrowth due to 3rd-order intermodulation in chirp bandwidth expansion scheme using quadrature modulator and frequency multipliers. The amplitude and phase imbalance requirement are defined based on the simulation results in terms of quadrature channel imbalance. This minimizes the degradation of range resolution, peak sidelobe ratio and integrated sidelobe ratio. The wideband chirp generator using the frequency multiplier and memory map scheme was manufactured and the compensation technique was presented to reduce the spectral regrowth of SAR waveform by minimizing the amplitude and phase imbalance. After I and Q channel imbalance adjustment, the carrier level reduces －28.7 dBm to －53.4 dBm. Chirp signal with 150 MHz bandwidth at S-band expands to 600 MHz bandwidth at X-band. The sidelobe levels are reduced by about 8 to 9 dB by compensating the amplitude balance between I and Q channels.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.12
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• pp.3702-3707
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• 2009

In this paper, a new approximated MAP algorithm for soft bit decision from QAM symbols is proposed for Gray Coded QAM signals, based on the Max-Log-MAP and a Gray coded QAM signal can be separated into independent two Gray coded PAM signal, M-PAM on I axis with M symbols and N-PAM on Q axis with N symbols. The Max-Log-MAP used distance comparisons between symbols to get the soft bit decision instead of mathematical exponential or logarithm functions. But in accordance with the increase of the number of symbols, the number of comparisons also increase with high complexity. The proposed algorithm is used with the Euclidean distance and constituted with plain arithmetic functions, thus we can know intuitively that the algorithm has low implementing complexity comparing to conventional ones.

• Journal of The Institute of Information and Telecommunication Facilities Engineering
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• v.4 no.1
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• pp.37-44
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• 2005

본 논문에서는 멀티 코드 CDMA(Code Division Multiple Access)시스템에서 고속의 멀티미디어 서비스를 지원하기 위해 정보 데이터열을 QAM(Quadrature Amplitude Modulation) 부호화하는 방법을 제안한다. 송신 구조는 입력 비트를 정진폭 다중부호 이진직교 변조(Constant amplitude code biorthogonal modulation: 이하 CACB라 칭함)로 부호화하여 전송 심볼의 크기를 일정하게 하고 이렇게 이진화된 신호를 QAM 부호화하여 전송속도를 높인다. 복조기의 구조는 수신된 신호로부터 QAM 연판정기 블록을 거쳐 생성된 신호를 CACB 복호화기를 거쳐 데이터를 복조해 낸다. 제안된 시스템은 기존의 멀티 코드 방식에 비해 대역폭 효율을 크게 개선시킬 수 있어 전송 속도를 많이 향상시킬 수 있고, 멀티 코드 방식을 기반으로 하기 때문에 디지털 가전기기나 3세대 이동통신과, WPAN과 관련된 무선 네트워크 응용과 같은 미래의 고속의 무선 멀티미디어 서비스를 지원하기에 적합하다.

• Proceedings of the IEEK Conference
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• 1999.11a
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• pp.775-779
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• 1999

This paper presents design of AGC(Automatic Gain Control) and DC offset remover suitable for cable modem which makes use of QAM(Quadrature Amplitude Modulation) scheme. Since QAM has multi-level signal characteristic, for high-order QAM, the constellation is dense and the distance of decision boundary between adjacent symbols is short. So AGC and DC offset remover must be designed optionally for preventing performance degradation. AGC is designed into feedback type and is related to the STR(Symbol Timing Recovery)and Paff interpolation algorithm. Whereas AGC need to perform average power detection during many symbols by comparison with the reference power, DC offset remover uses only the instant polarity decision such that simple implementation can be achieved with good performance. Though the AGC and DC offset remover are simulated here only for 256 QAM scheme for convenience'sake, it can be applied to other multi-level QAM or PSK modulation scheme.

• Journal of the Institute of Convergence Signal Processing
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• v.10 no.2
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• pp.136-140
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• 2009

The performances of M-ary signals using L-branch maximum ratio combining (MRC) diversity reception in correlated Nakagami fading channels are derived theoretically. The coherent reception of M-ary differential phase shift keying (MDPSK), phase shift keying (MPSK), and quadrature amplitude modulation (MQAM) is considered. It is assumed that the fading parameters in each diversity branch are identical. The general formula for evaluating symbol error rate (SER) of M-ary signals in the independent branch diversity system is presented using the integral-form expressions. Until now, results did not extend to the various M-ary case for a coherent reception. The numerical results presented in this paper are expected to provide information for the design of radio system using M-ary modulation method for above mentioned channel environment.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.11
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• pp.2121-2130
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• 2015

In this paper, we analyze LM-MIMO (load-modulation multiple-input multiple-output) system with single RF chain. And then, we confirm that load modulation technique can support generation of high-order m-PSK modulation and m-QAM modulation in LM-MIMO system. Finally we evaluate performance of LM-MIMO system with load modulation. Conventional MIMO system requires a number of RF chains for expansion of MIMO dimension. A number of RF chains can cause various problems. On the other hand, although LM-MIMO system is expanded, LM-MIMO system requires single RF chain only. Therefore, LM-MIMO system has low-complexity and low power consumption. As results, we can confirm that load modulation of T-model can modulate high-order m-PSK and m-QAM singal. Also, we can confirm that $4{\times}4$ LM-MIMO system using load modulation has a similar performance to conventional $4{\times}4$ MIMO system.

• ETRI Journal
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• v.34 no.6
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• pp.800-806
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• 2012

Transmission performances of direct detection-based 100-Gb/s modulation formats are investigated and compared for metro area optical networks. The effects of optical signal-to-noise ratio sensitivity, chromatic dispersion, cross-channel nonlinearity, and transmission distance on the performance of differential 8-ary phase-shift keying (D8PSK), differential phase-shift keying plus three-level amplitude-shift keying (DPSK+3ASK), and dual-carrier differential quaternary phase-shift keying (DC-DQPSK) are evaluated. The performance of coherent dual-polarization quadrature phase-shift keying (DP-QPSK) with block phase estimation and coherent DP-QPSK with digital differential detection are also presented for reference. According to our analysis, all three direct detection modulation formats could transmit a 100-Gb/s signal over several hundred kilometers of a single-mode fiber link. The results also show that DC-DQPSK outperforms D8PSK and DPSK+3ASK, and the performance of DC-DQPSK is comparable to that of coherent DP-QPSK with digital differential detection. The maximum transmission distance of DC-DQPSK is over 1,000 km, which is enough distance for metro applications.

• Journal of the Korea Society of Computer and Information
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• v.13 no.1
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• pp.135-141
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• 2008

The utilization techniques for multiple transmit and receive antennas or high capacity modulation schemes are essential to cope with the rapidly increasing demand for realizing more diverse wireless communication services with high rates. However, employing multiple receive antennas at the mobile units seems less practical due at the size and power limitations. Therefore, transmit diversify techniques have been extensively investigated for the downlink transmission to improve the performance In order to overcome the above mentioned problems, we construct a simulation model which combines STC and polarization diversity which scheme is requiring less cost to realize. Multi-level quadrature amplitude modulation (MQAM) is an attractive modulation scheme for wireless communication due to the high spectral efficiency it provides. Thus, the performance for our scheme is presented when 16QAM modulation techniques are applied. and compared with the former schemes.

• ETRI Journal
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• v.39 no.4
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• pp.535-545
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• 2017

This paper presents a novel K-band (18 GHz) 16-quadrature amplitude modulation (16-QAM) orthogonal frequency-division multiplexing (OFDM)-based $2{\times}2$ line-of-sight multi-input multi-output communication system. The system can deliver 356 Mbps on a 56 MHz channel. Alignment mismatches, such as amplitude and/or phase mismatches, between the transmitter and receiver antennas were examined through hardware experiments. Hardware experimental results revealed that amplitude mismatch is related to antenna size, antenna beam width, and link distance. The proposed system employs an alignment mismatch compensation method. The open-loop architecture of the proposed compensation method is simple and enables facile construction of communication systems. In a digital modem, 16-QAM OFDM with a 512-point fast Fourier transform and (255, 239) Reed-Solomon forward error correction codecs is used. Experimental results show that a bit error rate of $10^{-5}$ is achieved at a signal-to-noise ratio of approximately 18.0 dB.