• Journal of the Institute of Electronics Engineers of Korea TC
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• v.46 no.8
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• pp.10-15
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• 2009

In this paper, we propose a frequency-domain tone interference cancellation algorithm for direct-sequence spread spectrum systems. In the previously proposed frequency-domain interference cancellation algorithms, the interference signal is estimated and compensated in the frequency-domain and then, with IFFT (inverse Fourier transform), the compensated frequency-domain signal is transformed to the time domain signal for the remaining receiver operations. Unlike the previous works, the proposed algorithm does not requires IFFT and thus, the proposed algorithm not only shows the virtually identical performance but also requires lower hardware complexity compared to the previous works.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.44 no.4 s.316
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• pp.109-116
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• 2007

Most harmonic synthesis methods using phase information employ a quadratic or cubic phase interpolation. The methods are computationally expensive to implement because every component sinewave must be synthesized on a per sample basis. In this paper, we propose a fast harmonic synthesis method for sinusoidal speech/audio coding based on the quadratic and cubic phase function to overcome the complexity problem. To derive the fast harmonic synthesis method, we define the over-sampling function and phase modulation function by constraining the parameter of phase function to be independent for harmonic index and derive the fast synthesis method using IFFT. Experimental results show that the proposed method significantly reduce the complexity of conventional cosine synthesis method while maintaining the performance.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.41 no.12
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• pp.61-68
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• 2004

Wireless mobile communication systems request high speed mobility and high speed data transmission capability. In order to meet the requirements, OFDM(Orthogonal Frequency Division Multiplex) is mainly adopted in the physical layer of the wireless systems. In commercial wireless mobile systems, IEEE802.(11a, 16e, etc) series seem to be used as the modulation method. For supporting multiple air-interfaces in a wireless mobile system, different kinds of OFDM based modulation methods should be supported in one modem chip. It requires a variable point IFFT/FFT or reconfigurable IFFT/FFT processor. In this paper, we propose the design method of a reconfigurable IFFT/FFT processor. In addition, it is shown that a reconfigurable IFFT/FFT processor can he implemented by using the proposed method.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.47 no.10
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• pp.36-42
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• 2010

FFT(Fast Fourier Transform) processor is one of the key components in the implementation of OFDM systems for many wireless standards such as IEEE 802.22. To improve the performances of FFT processors, various studies have been carried out to reduce the complexities of multipliers, memory interface, control schemes and so on. While the number of FFT stages increases logarithmically $log_2N$) as the FFT point-size (N) increases, the number of required registers (or, memories) increases linearly. In large point-size FFT designs, the registers occupy more than 70% of the chip area. In this paper, to reduce the memory size of IFFT for OFDM transmitters, we propose a new IFFT design method based on a combined mapping of modulated data, pilot and null signals. The proposed method focuses on reducing the sizes of the registers in the first two stages of the IFFT architectures since the first two stages require 75% of the total registers. By simulations of 2048-point IFFT design for cognitive radio systems, it is shown that the proposed IFFT design method achieves more than 38.5% area reduction compared with previous IFFT designs.

• Journal of Satellite, Information and Communications
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• v.7 no.3
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• pp.26-29
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• 2012

In this paper, we propose a Single Carrier Frequency Division Multiple Access(SC-FDMA) scheme with greatly enhanced tolerance of timing offset among the users. The type of the proposed scheme is similar to code spread Multiple Carrier Direct Spread Code Division Multiple Access(MC DS CDMA). The proposed scheme performs partial Discrete Fourier Transform(DFT) in order to solve high Peak to Average Power Ratio(PAPR) of the MC DS CDMA before Inverse Fast Fourier Transform(IFFT). Exploiting the property Properly Scrambled Walsh-Hadamard(PSW) code has zero correlation despite ${\pm}1$ chip timing offset, the proposed scheme achieves Multiple Access Interference free performance with the timing offset up to ${\pm}1$ OFDM symbol duration with low PAPR. In contrast, the other existing schemes in comparison undergo severe performance degradation even with small timing offset in multipath fading channel.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.10A
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• pp.1548-1553
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• 2000

In this paper, an effective peak power reduction scheme for a downlink OFDM-CDMA system is proposed. Using the partial parallel transform(PPT) structure, peak-to-average power ratio(PAPR) can be reduced. The patterns of inputs of Inverse Fast Fourier Transform(IFFT) are more randomized in this structure by allotting the subcarriers to each users. At the cost of complexity we can obtain reduced PAPR and multiple access interference(MA) Computer simulations are carried out from the viewpoint of PAPR and demonstrated the improved PAPR performance.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.8C
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• pp.806-813
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• 2009

This paper presents a modem chip design for high-speed wireless communications. Among the high-speed communication technologies, we design the UWB (Ultra-Wideband) modem SoC (System-on-Chip) Chip based on a MB-OFDM scheme which uses wide frequency band and gives low frequency interference to other communication services. The baseband system of the modem SoC chip is designed according to the standard document published by WiMedia. The SoC chip consists of FFT/IFFT (Fast Fourier Transform/Inverse Fast Fourier Transform), transmitter, receiver, symbol synchronizer, frequency offset estimator, Viterbi decoder, and other receiving parts. The chip is designed using 90nm CMOS (Complementary Metal-Oxide-Semiconductor) procedure. The chip size is about 5mm x 5mm and was fab-out in July 20th, 2009.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.6C
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• pp.565-571
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• 2007

In order to improve PAPR (Peak-to-Average Power Ratio) reduction performance of the conventional SLM (Selective Mapping) for OFDM (Orthogonal Frequency Division Multiplexing) signals, we propose an effective SLM-PRSC (PAPR Reduction Sub-Carrier) hybrid scheme. In the proposed scheme, after performing the SLM for the frequency domain OFDM symbol excluding pre-determined PRSC positions, the SLM-PRSC hybrid sequence with the lowest PAPR generated by adding the time domain PRSC sequence to the results of the SLM, is selected as the transmitted OFDM signal. Since the identical PRSC sequences generated a priori are repeatedly used for every OFDM symbol, excessive IFFT (inverse Fast Fourier Transform) calculation is avoided. Simulation results show that the proposed scheme significantly improves the PAPR reduction performance of the conventional SLM, while avoiding excessive increase of IFFT calculation and the overhead for the SLM.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.12C
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• pp.1142-1148
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• 2007

In this paper, we propose ASLM (Adaptive Selective Mapping; ASLM) scheme based on peak observation for PAPR (Peak-to-Average Power Ratio) reduction of OFDM (Orthogonal Frequency Division Multiplexing) signals. The proposed scheme is composed of three steps: peak scaling, sequence selection, and SLM procedures. In the first step, the peak signal samples in the IFFT (Inverse Fast Fourier Transform) outputs of the original input sequence are scaled down. In the second step, the sub-carrier positions where the power difference between the original input sequence and the FFT output of the scaled signal is large, are identified. Then, the phase sequences having the maximum number of phase-reversed sequence words only for these positions are selected. Finally, the generic SLM procedure is performed by using only the selected phase sequences for the original input sequence. Simulation results show that the proposed scheme significantly reduces the complexity in terms of IFFT and PAPR calculation than the conventional SLM, while maintaining the PAPR reduction performance.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2019.05a
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• pp.597-599
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• 2019

When frequency domain high amplitude impulse is inserted before IFFT in OFDM transmitter, the PAPR of OFDM signal in tme domain can be effectively reduced. In this paper, the degree of PAPR improvement of OFDM communication system with CQAM subcarrier modulation is analysed by adopting impulse insertion technique before IFFT of transmitter. Furthermore, it is verified that additional PAPR performance improvement can be obtained by finding optimum position of impulse insertion for maximizing PAPR reduction.