The Experts below are selected from a list of 309 Experts worldwide ranked by ideXlab platform
I-tai Lu - One of the best experts on this subject based on the ideXlab platform.
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Out-of-Band Emission suppression techniques based on a generalized OFDM framework
EURASIP Journal on Advances in Signal Processing, 2014Co-Authors: Juan Fang, I-tai LuAbstract:Orthogonal frequency division multiplexing (OFDM)-based cognitive radio (CR) systems suffer from the large out-of-Band Emission (OOBE) that may interfere with other users. Since most existing OFDM OOBE suppression schemes are derived on the base of an original OFDM system without any other scheme, we first propose a generalized OFDM framework that is capable of describing these schemes no matter whether any one or more of the schemes is applied. Then, according to the place where these schemes are implemented in our framework, they are classified into three groups, namely symbol mapping techniques, precoding techniques, and time-domain techniques. Finally, based on the proposed framework, we propose three new schemes by combining a precoding scheme named singular value decomposition (SVD) precoding with three other schemes from the three groups, namely spectral precoding, N-continuous symbol mapping, and filtering. Numerical results show the power spectral density (PSD), peak-to-average power ratio (PAPR), and bit error rate (BER) performances of the three proposed schemes. Since the individual schemes have complementary characteristics, the three proposed combined schemes are constructed to maintain the merits and avoid the drawbacks of the individual schemes involved. Thus, it is demonstrated that the proposed framework can be employed to develop other new combined OOBE suppression schemes tailoring to some specific practical needs.
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Precoder designs for jointly suppressing out-of-Band Emission and peak-to-average power ratio in an orthogonal frequency division multiplexing system
IET Communications, 2014Co-Authors: Juan Fang, I-tai LuAbstract:High peak-to-average-ratio (PAPR) and large out-of-Band Emission (OOBE) are the two main shortcomings of orthogonal frequency division multiplexing (OFDM) signals for cognitive radios. Among all the existing techniques, it has been shown that precoding is an effective way for either reducing the PAPR or suppressing the OOBE. However, no work has focused on designing an effective precoding approach to reduce the PAPR and suppress the OOBE simultaneously. In this study, three new precoding approaches that can jointly suppress OOBE and reduce PAPR simultaneously are presented. The simulation results show that, firstly, all the three proposed precoding approaches can achieve the same power spectral density performance as the typical OOBE-suppression precoding approach with the same spectral efficiency. Secondly, their PAPR performances are only slightly worse than the typical PAPR-reduction precoding approach with a similar computational complexity. Finally, two of the three proposed precoding approaches do not cause any bit error rate (BER) performance degradation with respect to the conventional OFDM system. The abilities to suppress OOBE and PAPR jointly and to maintain the good BER performance make two of the three proposed approaches very favourable for practical applications.
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MILCOM - Resource Block Based Precoding Schemes for Suppressing Out-of-Band Emission
MILCOM 2013 - 2013 IEEE Military Communications Conference, 2013Co-Authors: Juan Fang, I-tai Lu, Jialing Li, Rui YangAbstract:Orthogonal Frequency Division Multiplexing (OFDM) systems suffer from large out-of-Band Emission (OOBE). As one of the approaches to suppress the OOBE, the precoding technique is able to achieve significant OOBE suppression with a small spectral efficiency loss and does not depend on the input data. In this paper, a low-complexity individual precoded OFDM (I-P-OFDM) by precoding each contiguous frequency Band independently is presented. Furthermore, two resource block (RB) based precoding schemes, namely, the U-RB-P-OFDM and NU-RB-P-OFDM are presented. The RB structures utilized in these two schemes enables mitigation of the precoding matrix dependency on the spectrum allocation. Numerical results show that all three schemes can achieve satisfying spectrum containment without any degradation in BER performance, and provide various tradeoffs between spectral efficiency, computational complexity, and PAPR performance.
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MILCOM - Hybrid Combination of N-Continuous and Null-Space Precoding for Out-of-Band Emission Suppression
MILCOM 2013 - 2013 IEEE Military Communications Conference, 2013Co-Authors: Juan Fang, I-tai LuAbstract:Orthogonal frequency division multiplexing (OFDM) based cognitive radio (CR) systems suffer from the large out-of-Band Emission (OOBE) that interferes with other users. Among the schemes that have been proposed to reduce the OOBE, precoding techniques encode the input data vectors before the inverse fast Fourier transform (IFFT) process, and decode them at the receiver after the fast Fourier transform (FFT) process. They provide significant OOBE suppression and do not cause any degradation of bit error rate (BER) performance. Therefore, two existing precoding techniques, which in this paper are called SVD precoding and N-continuous precoding, are investigated in this paper. Then a combined approach which maintains the merits of these two techniques is proposed. Numerical results show that, no matter whether there is a cyclic prefix (CP) or not, the proposed method gives significant further improvement on OOBE suppression and almost no extra degradation in the system performances such as the increase of BER or peak-to-average power ratio (PAPR) than either of the two original techniques.
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Efficient multiuser spectral precoding for reducing out-of-Band Emission for OFDM-based cognitive radios
2013 IEEE Long Island Systems Applications and Technology Conference (LISAT), 2013Co-Authors: Juan Fang, I-tai LuAbstract:When multiple users in an OFDM system can be synchronized, a novel efficient multiuser precoding approach for reducing out-of-Band Emission (OOBE) is developed. The main idea is to view all users as a virtual single user and design a common virtual precoder for all users. The precoder of a particular user is then constructed using the corresponding columns of the virtual precoder according to the allocated spectrum of that user. Without suffering from any degradation in BER performance, the proposed approach achieves higher spectral efficiency, larger OOBE reduction and better peak to average power ratio (PAPR) performance than the existing precoding approaches at the cost of higher complexity. Moreover, unlike the existing approaches, the spectral efficiency loss of the proposed approach does not increase as the number of users increases. It is also remarkable that the proposed approach allows each user to use noncontiguous spectra without losing additional spectral efficiency; this property is essential for enabling granular resource allocations.
Juan Fang - One of the best experts on this subject based on the ideXlab platform.
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Out-of-Band Emission suppression techniques based on a generalized OFDM framework
EURASIP Journal on Advances in Signal Processing, 2014Co-Authors: Juan Fang, I-tai LuAbstract:Orthogonal frequency division multiplexing (OFDM)-based cognitive radio (CR) systems suffer from the large out-of-Band Emission (OOBE) that may interfere with other users. Since most existing OFDM OOBE suppression schemes are derived on the base of an original OFDM system without any other scheme, we first propose a generalized OFDM framework that is capable of describing these schemes no matter whether any one or more of the schemes is applied. Then, according to the place where these schemes are implemented in our framework, they are classified into three groups, namely symbol mapping techniques, precoding techniques, and time-domain techniques. Finally, based on the proposed framework, we propose three new schemes by combining a precoding scheme named singular value decomposition (SVD) precoding with three other schemes from the three groups, namely spectral precoding, N-continuous symbol mapping, and filtering. Numerical results show the power spectral density (PSD), peak-to-average power ratio (PAPR), and bit error rate (BER) performances of the three proposed schemes. Since the individual schemes have complementary characteristics, the three proposed combined schemes are constructed to maintain the merits and avoid the drawbacks of the individual schemes involved. Thus, it is demonstrated that the proposed framework can be employed to develop other new combined OOBE suppression schemes tailoring to some specific practical needs.
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Precoder designs for jointly suppressing out-of-Band Emission and peak-to-average power ratio in an orthogonal frequency division multiplexing system
IET Communications, 2014Co-Authors: Juan Fang, I-tai LuAbstract:High peak-to-average-ratio (PAPR) and large out-of-Band Emission (OOBE) are the two main shortcomings of orthogonal frequency division multiplexing (OFDM) signals for cognitive radios. Among all the existing techniques, it has been shown that precoding is an effective way for either reducing the PAPR or suppressing the OOBE. However, no work has focused on designing an effective precoding approach to reduce the PAPR and suppress the OOBE simultaneously. In this study, three new precoding approaches that can jointly suppress OOBE and reduce PAPR simultaneously are presented. The simulation results show that, firstly, all the three proposed precoding approaches can achieve the same power spectral density performance as the typical OOBE-suppression precoding approach with the same spectral efficiency. Secondly, their PAPR performances are only slightly worse than the typical PAPR-reduction precoding approach with a similar computational complexity. Finally, two of the three proposed precoding approaches do not cause any bit error rate (BER) performance degradation with respect to the conventional OFDM system. The abilities to suppress OOBE and PAPR jointly and to maintain the good BER performance make two of the three proposed approaches very favourable for practical applications.
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MILCOM - Resource Block Based Precoding Schemes for Suppressing Out-of-Band Emission
MILCOM 2013 - 2013 IEEE Military Communications Conference, 2013Co-Authors: Juan Fang, I-tai Lu, Jialing Li, Rui YangAbstract:Orthogonal Frequency Division Multiplexing (OFDM) systems suffer from large out-of-Band Emission (OOBE). As one of the approaches to suppress the OOBE, the precoding technique is able to achieve significant OOBE suppression with a small spectral efficiency loss and does not depend on the input data. In this paper, a low-complexity individual precoded OFDM (I-P-OFDM) by precoding each contiguous frequency Band independently is presented. Furthermore, two resource block (RB) based precoding schemes, namely, the U-RB-P-OFDM and NU-RB-P-OFDM are presented. The RB structures utilized in these two schemes enables mitigation of the precoding matrix dependency on the spectrum allocation. Numerical results show that all three schemes can achieve satisfying spectrum containment without any degradation in BER performance, and provide various tradeoffs between spectral efficiency, computational complexity, and PAPR performance.
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MILCOM - Hybrid Combination of N-Continuous and Null-Space Precoding for Out-of-Band Emission Suppression
MILCOM 2013 - 2013 IEEE Military Communications Conference, 2013Co-Authors: Juan Fang, I-tai LuAbstract:Orthogonal frequency division multiplexing (OFDM) based cognitive radio (CR) systems suffer from the large out-of-Band Emission (OOBE) that interferes with other users. Among the schemes that have been proposed to reduce the OOBE, precoding techniques encode the input data vectors before the inverse fast Fourier transform (IFFT) process, and decode them at the receiver after the fast Fourier transform (FFT) process. They provide significant OOBE suppression and do not cause any degradation of bit error rate (BER) performance. Therefore, two existing precoding techniques, which in this paper are called SVD precoding and N-continuous precoding, are investigated in this paper. Then a combined approach which maintains the merits of these two techniques is proposed. Numerical results show that, no matter whether there is a cyclic prefix (CP) or not, the proposed method gives significant further improvement on OOBE suppression and almost no extra degradation in the system performances such as the increase of BER or peak-to-average power ratio (PAPR) than either of the two original techniques.
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Efficient multiuser spectral precoding for reducing out-of-Band Emission for OFDM-based cognitive radios
2013 IEEE Long Island Systems Applications and Technology Conference (LISAT), 2013Co-Authors: Juan Fang, I-tai LuAbstract:When multiple users in an OFDM system can be synchronized, a novel efficient multiuser precoding approach for reducing out-of-Band Emission (OOBE) is developed. The main idea is to view all users as a virtual single user and design a common virtual precoder for all users. The precoder of a particular user is then constructed using the corresponding columns of the virtual precoder according to the allocated spectrum of that user. Without suffering from any degradation in BER performance, the proposed approach achieves higher spectral efficiency, larger OOBE reduction and better peak to average power ratio (PAPR) performance than the existing precoding approaches at the cost of higher complexity. Moreover, unlike the existing approaches, the spectral efficiency loss of the proposed approach does not increase as the number of users increases. It is also remarkable that the proposed approach allows each user to use noncontiguous spectra without losing additional spectral efficiency; this property is essential for enabling granular resource allocations.
Young Rag Do - One of the best experts on this subject based on the ideXlab platform.
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surface plasmon enhanced Band Emission of zno nanoflowers decorated with au nanoparticles
Chemistry: A European Journal, 2012Co-Authors: Saji Thomas Kochuveedu, Ji Hye Oh, Young Rag DoAbstract:A simple strategy was used to enhance Band Emission through the transfer of defect Emission from ZnO to Au by using the energy match between the defect Emission of ZnO and the surface plasmon absorbance of Au NPs through decorating the surface of ZnO nanoflowers with Au nanoparticles (Au NPs). The ZnO nanostructure, which was comprised of six nanorods that were attached on one side in a flower-like fashion, was synthesized by using a hydrothermal method. The temperature-dependent morphology and detailed growth mechanism were studied. The influence of the density of the Au NPs that were deposited onto the surface of ZnO on photoluminescence was investigated to optimize the configuration of the ZnO/Au system in terms of the maximum Band Emission. The sequential transfer of defect energy from ZnO to Au and electron transfer from excited Au to ZnO was proposed as a possible mechanism for the enhanced Band Emission.
Saji Thomas Kochuveedu - One of the best experts on this subject based on the ideXlab platform.
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surface plasmon enhanced Band Emission of zno nanoflowers decorated with au nanoparticles
Chemistry: A European Journal, 2012Co-Authors: Saji Thomas Kochuveedu, Ji Hye Oh, Young Rag DoAbstract:A simple strategy was used to enhance Band Emission through the transfer of defect Emission from ZnO to Au by using the energy match between the defect Emission of ZnO and the surface plasmon absorbance of Au NPs through decorating the surface of ZnO nanoflowers with Au nanoparticles (Au NPs). The ZnO nanostructure, which was comprised of six nanorods that were attached on one side in a flower-like fashion, was synthesized by using a hydrothermal method. The temperature-dependent morphology and detailed growth mechanism were studied. The influence of the density of the Au NPs that were deposited onto the surface of ZnO on photoluminescence was investigated to optimize the configuration of the ZnO/Au system in terms of the maximum Band Emission. The sequential transfer of defect energy from ZnO to Au and electron transfer from excited Au to ZnO was proposed as a possible mechanism for the enhanced Band Emission.
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Surface‐Plasmon‐Enhanced Band Emission of ZnO Nanoflowers Decorated with Au Nanoparticles
Chemistry: A European Journal, 2012Co-Authors: Saji Thomas Kochuveedu, Ji Hye OhAbstract:A simple strategy was used to enhance Band Emission through the transfer of defect Emission from ZnO to Au by using the energy match between the defect Emission of ZnO and the surface plasmon absorbance of Au NPs through decorating the surface of ZnO nanoflowers with Au nanoparticles (Au NPs). The ZnO nanostructure, which was comprised of six nanorods that were attached on one side in a flower-like fashion, was synthesized by using a hydrothermal method. The temperature-dependent morphology and detailed growth mechanism were studied. The influence of the density of the Au NPs that were deposited onto the surface of ZnO on photoluminescence was investigated to optimize the configuration of the ZnO/Au system in terms of the maximum Band Emission. The sequential transfer of defect energy from ZnO to Au and electron transfer from excited Au to ZnO was proposed as a possible mechanism for the enhanced Band Emission.
Ying-chang Liang - One of the best experts on this subject based on the ideXlab platform.
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Closed-form approximations to the out-of-Band Emission due to nonlinear power amplifier
2013 IEEE Wireless Communications and Networking Conference (WCNC), 2013Co-Authors: Meng Wah Chia, Yonghong Zeng, Ying-chang LiangAbstract:The total out-of-Band Emission (OOBE) from the secondary users (SU) is determined not only by the baseBand signaling waveforms, but also by the design of the transmitter chain, which includes the nonlinear power amplifier (PA). The increase in OOBE due to a nonlinear PA has been well-observed, but its characterization involves complicated analysis. In this paper, we present a closed-form approximation to the power spectral density (PSD) of a signal at the output of a nonlinear PA, or more specifically, the solid-state power amplifier (SSPA). The SSPA's response can be approximated using a third order nonlinear model (TONM) which has been proposed in literature. Using the TONM, we proposed a statistical approximation, together with a piecewise linear model, to determine a closed-form estimate to the OOBE of the PA output signal. Simulation results show a close fit between the theoretical expression for the derived PSD and the simulated model. Since the nonlinear PA increases the OOBE due to spectral regrowth, the ability to characterize this behavior is of particular importance to the application of TV Band devices (in television broadcast frequency Bands) that need to fulfill certain OOBE limits.
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WCNC - Closed-form approximations to the out-of-Band Emission due to nonlinear power amplifier
2013 IEEE Wireless Communications and Networking Conference (WCNC), 2013Co-Authors: Meng Wah Chia, Yonghong Zeng, Ying-chang LiangAbstract:The total out-of-Band Emission (OOBE) from the secondary users (SU) is determined not only by the baseBand signaling waveforms, but also by the design of the transmitter chain, which includes the nonlinear power amplifier (PA). The increase in OOBE due to a nonlinear PA has been well-observed, but its characterization involves complicated analysis. In this paper, we present a closed-form approximation to the power spectral density (PSD) of a signal at the output of a nonlinear PA, or more specifically, the solid-state power amplifier (SSPA). The SSPA's response can be approximated using a third order nonlinear model (TONM) which has been proposed in literature. Using the TONM, we proposed a statistical approximation, together with a piecewise linear model, to determine a closed-form estimate to the OOBE of the PA output signal. Simulation results show a close fit between the theoretical expression for the derived PSD and the simulated model. Since the nonlinear PA increases the OOBE due to spectral regrowth, the ability to characterize this behavior is of particular importance to the application of TV Band devices (in television broadcast frequency Bands) that need to fulfill certain OOBE limits.