• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2003.11a
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• pp.384-388
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• 2003

In this paper, we have proposed a OFDM/QPSK-DMR(Orthogonal frequency Division Multiplexing/Quadrature Phase Shift Keying Modulation-Digital Microwave Radio)system using BL-PSF(Band-limited pulse shaping filter) over the Microwave channel. In the proposed DMR system, STS-1(51.84 Mbps) of SONET(Synchronous Optical NETwork) is first modulated by OFDM/QPSK symbol and used Band-limited pulse shaping filter. The advantage of the proposed DMR system is to simplify system complexity and increase IFFT/FFT block use-efficiency. The system performance of single carrier and OFDM systems is already proved that those of DMR systems have the same performance over AWGN(Additive White Gaussian Noise) channel environment. Therefore, the system is analyzed between proposed OFDM/QPSK-DMR and single carrier DMR systems and simulated by BER performance and Signature curve over Microwave channel environment. Simulation result is that the proposed system performances are approaching to the performance of single carrier DMR system as the number of Sub-carriers increasing.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.4C
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• pp.200-206
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• 2005

Adaptive transmission techniques can improve the performance of wireless communication system by adaptively changing the transmission parameter such as modulation, code-rate, and power according to the channel state. For orthogonal frequency division multiplexing (OFDM) system, the adaptive transmission techniques can be applied to each subcarrier unit. In this paper, we consider the adaptive code-rate OFDM system in which optimal code-rate is applied to each subcarrier according to the subchannel state. Performance analysis show that $3\sim6$dB gain of SNR or up to $30\sim50\%$ increase of data rate are achieved in the condition of bit error rate $10^{-6}$.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.12C
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• pp.1257-1264
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• 2006

The carrier frequency offset causes loss of orthogonality between sub-carriers, thus leads to inter-carrier interference (ICI) in the OFDM symbol. This ICI causes severe degradation of the BER performance of the OFDM receiver. In this paper, we propose a new ICI cancellation algorithm which estimates frequency offset at the time-domain by using CP-ICA method to the received sub-carriers phase rotation. This algorithm is based on a statistical blind estimation method, which mainly utilizes the EVD, rotating phase and the $4^{th}-cumulants$. Since our scheme does not need any training and pilot symbol in estimation, we can expect enhanced bandwidth efficiency in OFDM systems. Simulation results show that the proposed frequency offset estimator is more accurate than the other estimators in $0.0<\varepsilon<1.0$.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.9C
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• pp.1279-1288
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• 2004

In this paper, the DMR(Digital Microwave Radio) system-based OFDM(Orthogonal Frequency Division Multiplexing) scheme in microwave channel environments has been proposed and system performances have been evaluated. The existing single carrier DMR system has a complex system structure due to using high-level QAM(Quadrature Amplitude Modulation) modulation scheme and so charmel capacity is limited by sensitive effects from fading. Therefore, in the proposed DMR system, it uses that the OFDM scheme for enhancement of fading distortion and also uses that the band-limited pulse shaping filter instead of windowing for no additional data such as GI/GB and for using efficient of IFFT/FFT block. The performance of OFDM/QPSK-DMR system and single carrier DMR system are analysed by computer simulation using two-ray model under the microwave channel environments The computer simulation results confirm that the fade margin of the proposed OFDM/QPSK-DMR system is highly increased as the number of sub-carriers is larger.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.11C
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• pp.1076-1084
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• 2009

We propose an ATI (Adaptive Tone Injection) scheme based on clipping noise for PAPR (Peak-to-Average Power Ratio) reduction of OFDM (Orthogonal Frequency Division Multiplexing) signals. The proposed scheme is composed of three steps: clipping, tone selection, and TI procedures. In the first step, the peak samples in the IFFT (Inverse Fast Fourier Transform) outputs are scaled down by clipping. In the second step, the sub-carrier position where the power of the clipping noise is the maximum, is selected. Finally, the generic TI procedure is performed. Simulation results show that the proposed scheme does not require all the possible combinations of the original TI procedures, while maintaining the PAPR reduction performance.

• The Journal of the Korea institute of electronic communication sciences
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• v.14 no.5
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• pp.817-824
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• 2019

We propose an ATR (Adaptive Tone Reservation) scheme based on clipping noise for PAPR (Peak-to-Average Power Ratio) reduction of OFDM (Orthogonal Frequency Division Multiplexing) signals. The proposed scheme is composed of three steps: clipping, tone selection, and TR procedures. In the first step, the peak samples in the IFFT (Inverse Fast Fourier Transform) outputs are scaled down by clipping. In the second step, the sub-carrier position where the power of the clipping noise is the maximum, is selected. Finally, the generic TR procedure is performed. Simulation results show that the proposed scheme does not require all the possible combinations for the original TR procedures, while maintaining the PAPR reduction performance.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.10
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• pp.1030-1035
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• 2003

In this paper, we compare the performance of IS-OFDM(interference suppressing orthogonal frequency division multiplexing) system with that of the conventional OFDM system. Each parallel branch symbol of IS-OFDM is multiplied by the orthogonal sequence and distributed into all sub-carriers. Then, each sub-carrier transmits information composed of the symbol components of all parallel branches in the given frame. The structure of IS-OFDM shows the frequency diversity characteristic. Therefore, IS-OFDM can be robust to the narrowband interference. BER performances are found in the narrow-band interference and a harmonic noise channels. When JSR(Jamming to signal ratio) increases from -10 dB to +10 dB in the constant interference bandwidth, IS-OFDM outperforms the conventional OFDM and the BER difference between IS-OFDM and OFDM is reduced as JSR increases. Also, the similar properly can be shown when interference bandwidth increases at the constant JSR. In the harmonic noise channel, we can find the good performance of IS-OFDM when the h-rate(harmonic noise bandwidth to signal bandwidth ratio) increases from 0.01 to 0.8. So, simulation results show that the IS-OFDM is more robust to the interference than the conventional OFDM.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.7
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• pp.34-42
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• 2013

In this paper, we compare the performance of wavelet OFDM (Orthogonal Frequency Division Multiplexing) and FD-OFDM(Frequency diversity OFDM) system with conventional OFDM system. Wavelet OFDM system uses wavelet transform rather than Fourier transform and contains intermediate characteristics of CDM (Code Division Multiplexing) and OFDM. In wavelet OFDM system, inter-symbol interference (ISI) can be suppressed effectively and adjacent channel interference can be also minimized well. In FD-OFDM system, each parallel branch symbol is multiplied by the orthogonal sequence and distributed into all sub-carriers. Then, each sub-carrier transmits information composed of the symbol components of all parallel branches in the given frame. FD-OFDM contains the frequency diversity characteristic and, therefore, FD-OFDM can be robust to the narrowband interference. For the comparison among different systems, BER (Bit-Error Rate) performances are evaluated in the presence of narrow-band interference and a harmonic noise channel. From the evaluation results, compared to the conventional OFDM, wavelet OFDM and FD-OFDM shows better robustness against the interference and, especially, wavelet OFDM is the most robust in harmonic noise channel.

• Proceedings of the Korea Information Processing Society Conference
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• 2003.11b
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• pp.1041-1044
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• 2003

현재의 이동통신에서는 다양한 영상 서비스를 제공해야 하는데, 이는 여러 종류의 고품질 데이터를 전송해야 함을 의미하며, 이를 위해 4 세대 광대역 이동통신을 위한 변조방식중의 하나로 OFDM(Orthogonal Frequency Division Multiplexing) 변조방식이 연구되고 있다. 본 논문에서는 OFDM의 각 직교 부반송파(Sub-carrier)들이 잠재적으로 다른 변조방식을 가질 수 있다는 특징에 single modulation(OFDM과 QPSK, OFDM과 16QAM), multi-modulation(OFDM과 (QPSK+16QAM))을 결합하여 시뮬레이션을 통해 성능을 비교하였고 실제 이미지를 전송하여 전송효과를 확인하였으며, 전송하고자 하는 데이터 종류와 채널환경에 따른 다중변복조 방식을 제안 분석하였다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.5A
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• pp.521-526
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• 2004

OFDM is a very attractive technique for achieving high-bit-rate data transmission and high spectrum efficiency. However, one of disadvantages of OFDM signal is the high PAPR characteristic when multi-carriers are added up coherently. In this Paper, we propose-scrambling scheme using correlator for PAPR reduction and reducing the amount of PAPR calculations. The simulation results show that this scheme has less computational complexity and reasonable PAPR reduction capability compared to PTS technique.