• Journal of the Institute of Electronics Engineers of Korea TC
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• v.45 no.1
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• pp.8-13
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• 2008

The high peak-to-average power ratio(PAPR) of the transmitted signals is one of the major drawbacks of the orthogonal frequency division multiplexing(OFDM). The partial transmit sequences(PTS) technique can improve the PAPR statistics of the OFDM signals. However, in the PTS technique, the computational complexity to select phase weighting factors increases exponentially with the number of sub-blocks. In this paper, a search algorithm that has no limit on the values of phase weighting factors and requires no additional operations for the search is presented. To evaluate the performance, the proposed search algorithm is compared with the full search algorithm in terms of the complementary cumulative distribution function(CCDF) of the PAPR and the computational complexity. It is shown through simulations that the proposed technique can achieve significant reductions in the computational complexity with little performance degradation compared with the full search algorithm.

• Proceedings of the KIEE Conference
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• 2001.07d
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• pp.2606-2609
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• 2001

We propose a robust channel equalization algorithm. which is called a 1-tap additional coefficient decision feedback equalizer(ACDFE), to improve the Doppler shift performance for the OFDM receiver. The algorithm is based on the frequency domain DFE with additional coefficients which are independent of the OFDM subcarriers. Test results on OFDM-16QAM signals confirm that the proposed ACDFE is robust against fading channel due to Doppler shifts and outperforms the conventional DFE in terms of SER, MSE, and convergence speed.

• 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.

• IEIE Transactions on Smart Processing and Computing
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• v.6 no.2
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• pp.117-123
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• 2017

N-continuous orthogonal frequency division multiplexing (OFDM) is a precoding method for sidelobe suppression of OFDM signals and seamlessly connects OFDM symbols up to the high-order derivative for sidelobe suppression, which is suitable for suppressing out-of-band radiation. However, it severely degrades the error rate as it increases the continuous derivative order. Two schemes for orthogonal precoding of N-continuous OFDM have been proposed to achieve an ideal error rate while maintaining sidelobe suppression performance; however, the large size of the precoder matrices in both schemes causes very high computational complexity for precoding and decoding. This paper proposes matrix decomposition of precoder matrices with a large size in the orthogonal precoding schemes in order to reduce computational complexity. Numerical experiments show that the proposed method can drastically reduce computational complexity without any performance degradation.

• ETRI Journal
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• v.43 no.4
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• pp.660-673
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• 2021

To efficiently use frequency resources, the next 6th generation mobile communication technology must solve the problem of out-of-band emission (OoBE) of cyclic prefix (CP) orthogonal frequency division multiplexing (OFDM), which is not solved in 5th generation technology. This study describes a new zero insertion technique to replace an existing filtering scheme to solve this internal problem in OFDM signals. In the development of the proposed scheme, a precoder with a two-dimensional structure is first designed by generating a two-dimensional mapper and using the specialty of each matrix. A spectral shaping technique based on zero insertion instead of a long filter is proposed, so it can be applied not only to long OFDM symbols, but also very short ones. The proposed method shows that the transmitted signal is completely blocked at the bandwidth boundaries of signals according to the current standards, and it is confirmed that the proposed scheme is ideal with respect to bit error rate (BER) performance because its BER is the same as that of CP-OFDM. In addition, the proposed scheme can transformed into a real time structure through vectorizing process with minimal complexity.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.10 s.89
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• pp.931-937
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• 2004

This study examines the channel capacity of a multiple antenna system based on OFDM(Othogonal Frequency Division Multiplexing) when there are correlations among received signals in the frequency selective Rayleigh fading. As for a case that two transmitting and two receiving antennas are used, the channel capacity is derived as a function of correlation in a closed-form and the effect on channel capacity is analyzed when the mean value of the of received signal power is identical/ non-identical between the two receiving antennas. Analytical results show that the channel capacity decreases with the correlation coefficient of the received signals, and the decreasing rate is accelerated when the correlation coefficient of the received signals is greater than 0.7. In addition, the channel capacity reaches its peak when the received mean signal power of each branch is identical.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.8 no.8
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• pp.2783-2795
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• 2014

Orthogonal frequency division multiplexing with offset quadrature amplitude modulation (OFDM-OQAM) technique has drawn significant interests in recent years. However, most of the existing OFDM peak-to-average ratio (PAPR) reduction schemes cannot be used in the OFDM-OQAM system directly. In this paper, a modified scheme called overlapped segmental clipping (OS-clipping) is proposed to deal with the high PAPR problem specifically in the OFDM-OQAM system. For the proposed OS-clipping scheme, the input signals are divided into a number of overlapped segments and then the clipping operation is processed on each segment. Simulation results show that the modified scheme used in the OFDM-OQAM system can provide better performance than conventional clipping scheme directly used in the OFDM-OQAM system, and even outperforms conventional clipping scheme applied in the OFDM system.

• 전자공학회논문지 IE
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• v.46 no.4
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• pp.78-82
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• 2009

We analyze an analysis of the performance of OFDM(Orthogonal Frequency Division Multiplexing) under multipath channel conditions, and to allow for different OFDM configurations. In this paper, the effects on multipath delay spread, peak power dipping, channel noise and time synchronization errors for the OFDM Signals are analyzed.

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

• ETRI Journal
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• v.28 no.2
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• pp.235-238
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• 2006

In this letter, a block code that minimizes the peak-to-average power ratio (PAPR) of orthogonal frequency division multiplexing (OFDM) signals is proposed. It is shown that peak envelope power is invariant to cyclic shift and codeword inversion. The systematic encoding rule for the proposed code is composed of searching for a seed codeword, shifting the register elements, and determining codeword inversion. This eliminates the look-up table for one-to-one correspondence between the source and the coded data. Computer simulation confirms that OFDM systems with the proposed code always have the minimum PAPR.