Parallel concatenated spa ce time trellis code modulation, called Turbo STCM, can efficiently increase the coding gains of the space time codes. However, the complexity of the iterat iv e decoding restricts its ap...Parallel concatenated spa ce time trellis code modulation, called Turbo STCM, can efficiently increase the coding gains of the space time codes. However, the complexity of the iterat iv e decoding restricts its application. This paper introduces a lower complex deco ding algorithm based on soft output Viterbi algorithm (SOVA) for Turbo STCM. S imulational results show that the new SOVA algorithm for the Turbo STCM outperf orms the original space time trellis code (STTC) by 4~6 dB. At the same time, compared with the Max Log MAP (maximum a posteriori) algorithm, the new scheme requires a lower complexity and approaches the performance of Turbo STCM decod ing w ith Max Log MAP.展开更多
Underwater acoustic scattering echoes have time–space structures and are aliasing in time and frequency domains. Different series of echoes properties are not identified when incident angle is unknown. This article i...Underwater acoustic scattering echoes have time–space structures and are aliasing in time and frequency domains. Different series of echoes properties are not identified when incident angle is unknown. This article investigates variations in target echoes of monostatic sonar to address this problem. The mother wavelet with similar structures has been proposed on the basis of preprocessing signal waveform using matched filter, and the theoretical expressions between delay factor and incident angle are derived in the wavelet domain. Analysis of simulation data and experimental results in free-field pool show that this method can effectively separate geometrical scattering components of target echoes. The time delay estimation obtained from geometrical echoes at a single angle is consistent with target geometrical features, which provides a basis for object recognition without angle information. The findings provide valuable insights for analyzing elastic scattering echoes in actual ocean environment.展开更多
下一代宽带无线通信系统的核心技术MIMO—OFDM（Multiple—Input Multiple—Output Orthogonal Frequency Division Multiplexing）能显著提高系统的容量，但要获得该技术所带来的性能优势，快速、准确的信道估计是关键。为降低V—BLAST...下一代宽带无线通信系统的核心技术MIMO—OFDM（Multiple—Input Multiple—Output Orthogonal Frequency Division Multiplexing）能显著提高系统的容量，但要获得该技术所带来的性能优势，快速、准确的信道估计是关键。为降低V—BLASTOFDM（Vertical—Bell Laboratory Layered Space—Time Orthogonal Frequency Division Multiplexing）系统中信道估计的运算复杂度和提高估计精度，提出了一种基于CAZAC（Constant Amplitude Zero Auto CorrelatiOn）序列的信道估计方法。该方法避免了矩阵求逆运算，利用该序列良好的自相关性，通过相关运算明显的抑制了噪声对估计性能的影响，使信道估计的性能得以显著提高。理论分析和计算机仿真结果表明．该方法较传统信道估计算法而言，能显著提高系统性能。展开更多
The time evolution of coal structure during low temperature oxidation was investigated by oxidizing coal samples in air at 120℃ for periods of up to 14 days. The structure of the oxidized coal samples was char- acter...The time evolution of coal structure during low temperature oxidation was investigated by oxidizing coal samples in air at 120℃ for periods of up to 14 days. The structure of the oxidized coal samples was char- acterized by Fourier transform infrared spectroscopy （FFIR） and curve fitting analysis. The results show that carboxyl and ether groups are the main oxygen containing moieties in oxidized coal. Ethers are most abundant during the first 3 days of oxidation, thereafter carboxyl groups predominate. The content of carboxyl and ester functionality increases with oxidation time. The other oxygen containing groups vary in concentration over time. The amount of hydroxyl groups first decreases then increases and finally decrease again during the oxidation. The aliphatic structure and the degree of branching of the aliphatic chains is reduced as the oxidation proceeds. The proportion of aromatic structure increases with oxida- tion time. Obvious decomposition of aromatic rings occurs after about 9 days of oxidation. The aryl ester bands and the CH3/CH2 ratio both have a good linear relationship to oxidation time.展开更多
Ultrafast electron diffraction （UED） is a rapidly advancing technique capable of recording the atomic-detail structural dynamics in real time. We report the establishment of the first UED system in China. Employing ...Ultrafast electron diffraction （UED） is a rapidly advancing technique capable of recording the atomic-detail structural dynamics in real time. We report the establishment of the first UED system in China. Employing this UED apparatus, both the coherent and the concurrent thermal lattice motions in an aluminium thin-film, trigged by ultrafast laser heating, have been observed. These results demonstrate its ability to directly measure a sub-milli-angstrom lattice spacing change on a sub-picosecond time scale.展开更多
文摘Parallel concatenated spa ce time trellis code modulation, called Turbo STCM, can efficiently increase the coding gains of the space time codes. However, the complexity of the iterat iv e decoding restricts its application. This paper introduces a lower complex deco ding algorithm based on soft output Viterbi algorithm (SOVA) for Turbo STCM. S imulational results show that the new SOVA algorithm for the Turbo STCM outperf orms the original space time trellis code (STTC) by 4~6 dB. At the same time, compared with the Max Log MAP (maximum a posteriori) algorithm, the new scheme requires a lower complexity and approaches the performance of Turbo STCM decod ing w ith Max Log MAP.
基金Foundation item： Supported by the National Natural Science Foundation of China（Grant No.51279033） and Natural Science Foundation of Heilongjiang Province, China（Grant No.F201346 ）
文摘Underwater acoustic scattering echoes have time–space structures and are aliasing in time and frequency domains. Different series of echoes properties are not identified when incident angle is unknown. This article investigates variations in target echoes of monostatic sonar to address this problem. The mother wavelet with similar structures has been proposed on the basis of preprocessing signal waveform using matched filter, and the theoretical expressions between delay factor and incident angle are derived in the wavelet domain. Analysis of simulation data and experimental results in free-field pool show that this method can effectively separate geometrical scattering components of target echoes. The time delay estimation obtained from geometrical echoes at a single angle is consistent with target geometrical features, which provides a basis for object recognition without angle information. The findings provide valuable insights for analyzing elastic scattering echoes in actual ocean environment.
文摘下一代宽带无线通信系统的核心技术MIMO—OFDM（Multiple—Input Multiple—Output Orthogonal Frequency Division Multiplexing）能显著提高系统的容量，但要获得该技术所带来的性能优势，快速、准确的信道估计是关键。为降低V—BLASTOFDM（Vertical—Bell Laboratory Layered Space—Time Orthogonal Frequency Division Multiplexing）系统中信道估计的运算复杂度和提高估计精度，提出了一种基于CAZAC（Constant Amplitude Zero Auto CorrelatiOn）序列的信道估计方法。该方法避免了矩阵求逆运算，利用该序列良好的自相关性，通过相关运算明显的抑制了噪声对估计性能的影响，使信道估计的性能得以显著提高。理论分析和计算机仿真结果表明．该方法较传统信道估计算法而言，能显著提高系统性能。
基金supported by the Shaanxi Provincial Project of Special Foundation of Key Disciplinesthe Scientific Research Program Funded by Shaanxi Provincial Education Commission (No. 09JK583)the Seed Fund of Xi’an University of Science and Technology (No. 200745)
文摘The time evolution of coal structure during low temperature oxidation was investigated by oxidizing coal samples in air at 120℃ for periods of up to 14 days. The structure of the oxidized coal samples was char- acterized by Fourier transform infrared spectroscopy （FFIR） and curve fitting analysis. The results show that carboxyl and ether groups are the main oxygen containing moieties in oxidized coal. Ethers are most abundant during the first 3 days of oxidation, thereafter carboxyl groups predominate. The content of carboxyl and ester functionality increases with oxidation time. The other oxygen containing groups vary in concentration over time. The amount of hydroxyl groups first decreases then increases and finally decrease again during the oxidation. The aliphatic structure and the degree of branching of the aliphatic chains is reduced as the oxidation proceeds. The proportion of aromatic structure increases with oxida- tion time. Obvious decomposition of aromatic rings occurs after about 9 days of oxidation. The aryl ester bands and the CH3/CH2 ratio both have a good linear relationship to oxidation time.
基金Supported by the National Natural Science Foundation of China under Grant Nos 10728409, 10734130, 10735050 and 60621063, and the National Basic Research Programme of China under Grant No 2007CB815102.
文摘Ultrafast electron diffraction （UED） is a rapidly advancing technique capable of recording the atomic-detail structural dynamics in real time. We report the establishment of the first UED system in China. Employing this UED apparatus, both the coherent and the concurrent thermal lattice motions in an aluminium thin-film, trigged by ultrafast laser heating, have been observed. These results demonstrate its ability to directly measure a sub-milli-angstrom lattice spacing change on a sub-picosecond time scale.
