• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.3A
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• pp.267-273
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• 2006

This paper improves the effects of clustered OFCDM scheme considering the frequency diversity effect over a frequency selective fading channel. In OFCDM with frequency domain spreading compared to OFDM, we can increase uncorrelated symbols by frequency allocation method of correspondent symbols over the same antenna and different antenna after spreading. The simulation results show that the performance of proposed system is improved by approximately 4 dB in ${\sigma}=0.02{\mu}sec$, the performance is improved by approximately 2.5dB in large delay spread in a 12-path Rayleigh fading channel with overall the root mean squared delay spread and the maximum Doppler frequency of 20 Hz. Also, the required average received Eb/No at the average BER of $10^{-3}$ by optimum method is improved by approximately 2.0 dB, compared to that of STA-OFCDM with frequency rearrange. The new method does not require any bandwidth expansion any feedback from the receiver to the transmitter and its computation complexity is similar to clustered OFCDM.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2003.05a
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• pp.551-555
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• 2003

본 논문에서는 이동 멀티미디어 통신을 위해 송신 다이버시티 STTD(Space Time Transmit Diversity)기법을 적용하였을 경우 발생하는 송신 안테나 상호간의 간섭을 제거 하기 위해 새로운 수신기를 제안하고 이를 적용한 DS-CDMA/QPSK STTD 시스템의 성능을 모의실험으로 확인하였다. 모의실험 결과 제안된 수신기를 적용한 시스템의 성능이 0.5∼2 dB 정도의 성능 개선이 있음을 알수 있었다.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2003.05a
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• pp.138-141
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• 2003

본 논문에서는 STTD(space Time Transmit diversify)를 적용한 적응변조 시스템의 성능을 분석하였다. 무선채널 환경에서는 지연파에 의한 ISI(Intersymbol interference)간섭으로 인해 전송 오율을 증가시키게 된다. 따라서, ISI간섭의 영향을 줄이기 위해 STTD를 적용함으로써 적응변조시스템의 성능개선 정도를 분석하였다. 결과에 의하면, STTD를 적용함에 따라 더 낮은 SNR에서도 변조 다치수가 높은 변조 모드를 선택함으로써 고속ㆍ고품질의 데이터 전송이 가능함을 알 수 있었다.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.13 no.2
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• pp.390-396
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• 2009

MC-DS-CDMA is technique where a single data symbol is transmitted at multiple subcarriers which are orthogonal to each other. With this technique, frequency diversity can be achieved. The performance of PSAM MC-DS-CDMA system with the application of STBC antenna diversity is analyzed. The BER performance of this system over multipath fading environment is evaluated, considering the channel estimation ernr, carrier frequency offset, and the nonlinear high power amplifier.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.10A
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• pp.964-971
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• 2008

This paper compares the performances of cyclic delay diversity and phase rolling techniques for SC-FDE(Single Carrier with Frequency Domain Equalization) systems with multiple transmit antennas assuming time-flat and frequency-flat channels. In OFDM(Orthogonal Frequency Division Multiplexing) systems generation of time varying channels using phase rolling can result in performance gains comparable to those of frequency-selective channels made by cyclic delay diversity However, in SC-FDE systems making time-selective channels may produce better results than creation of frequency-selective channels.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38A no.2
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• pp.127-142
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• 2013

A dual-user multiplexing scheme for a pair of mobiles equipped with single antenna is proposed which incorporates time-delay diversity employing a rotation-based D-BLAST-like layered code. A low-dimension equivalent of the existing partial interference cancellation based group decoder is also proposed for the corresponding receiver. The BER performances of the proposed scheme and those of the ideal scheme are studied comparatively through Monte Carlo simulations.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.11 no.3
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• pp.61-66
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• 2011

Cooperative Communication using relays which include network separated into fixed cooperative relaying and incremental cooperative relaying defending on method receiving signal from a source. If some nodes included network is Primary user ad source and destination, another is Secondary user as relay, The nodes included network excepting source can help PU transmit signal. In the case of all of SU playing a role as relay, destination can get diversity gain, but useless time slot is consumed for transmitting signal. So in this paper, we analysis cooperative relaying which a node succeeding to sense primary signal send signal to destination. We use matlab simulation tool and consider AF, DF, fixed relaying, incremental relaying

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.8B
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• pp.796-801
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• 2002

CL1(closed loop mode 1) is one of the closed loop transmit diversity schemes defined by 3GPP WCDMA and adjusts the relative phases of the transmitted signals at the two transmit antennas, thereby maximizing the power of the received signal at the user equipment. A key component of this scheme is to encode the phase difference between two received signals arrived at the user equipment via two different transmit antennas and to send it back to the base station. This paper proposes a new phase difference representation based on the adaptive delta modulation and compares its performance with the corresponding one of CL1. Computer simulations show that, in a slowly fading environment, the proposed scheme produces more realistic representation of the phase difference than the on of the CL1, resulting in a lower BER.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.3A
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• pp.111-118
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• 2003

The transmit adaptive array requires the forward link channel information for evaluating the optimum transmit weight vector in which a feedback channel provides transmitter with the forward link channel information. The larger transmit adaptive array is, the higher required rate of feedback channel is. Therefore we consider the system that the N-transmit antenna system is expanded to the 2N-transmit antenna system, while the feedback channel is maintained as that of N-transmit antenna system. The increase of the number of antennas can produce the additional diversity gain, however the insufficient feedback bits assigned to each antenna aggravates the quantization error. In this paper, we propose the transmit antenna selection in order to improve the performance of transmit adaptive array having an insufficient feedback channel information. The effective method to transmit the weight vector is also introduced. System performances are investigated for the case of N=4 corresponding to the antenna selection diversity schemes on the flat fading channel and the multipath fading channel. The simulation results show that the proposed scheme can improve the system performance by 1 dB when the N is expanded to the 2N, while the feedback channel is restricted to that of N-transmit antenna system.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.19 no.4
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• pp.442-450
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• 2008

In this paper, the phase diverisity in a direct-conversion receiver for a UHF RFID reader is analyzed and the optimal I/Q signal combining methods is presented with respect to tag modulation. At first, fading characteristics of a single channel receiver is shown to prove the importance of phase diversity due to the phase relationship between the backscattered signal and the local oscillator. And the optimal signal combining methods are presented in order to overcome the signal power reduction due to phase diversity. In case of ASK, the power combining method is presented for the optimal I/Q combining. And the arctangent and principal component combining methods using covariance matrix of I and Q channels are presented for the optimal I/Q combining in case of PSK. In order to analyze the performance of suggested methods, the selection diversity and the optimal combining methods are compared. According to analysis and simulation results, the optimal combining methods have a maximum 3 dB SNR enhancement than selection diversity.