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Linear Codes with Two Weights or Three Weights from Two Types of Quadratic forms

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Transactions of Nanjing University of Aeronautics and Astronautics 2017年第1期34卷 62-71页

作者： Zhu Xiaoxing xu dazhuan Department of Mathematics Nanjing University of Aeronautics and AstronauticsNanjing 210016P.R.China College of Electronic and Information Engineering Nanjing University of Aeronautics and AstronauticsNanjing 210016P.R.China

Let F_qbe afinite field with q=pmelements,where pis an odd prime and mis apositive integer.Here,let D_0={(x_1,x_2)∈F_q^2\{(0,0)}:Tr(x_1^(pk1+1)+x_2^(pk2+1))=c},where c∈F_q,Tr is the trace function fromFF_qtoFpand m/(m,k_1)is odd,m/(m,k_2)is even.Define ap-ary linear code C_D =c(a_1,a_2):(a_1,a_2)∈F_q^2},where c(a_1,a_2)=(Tr(a_1x_1+a_2x_2))_((x1,x2)∈D).At most three-weight distributions of two classes of linear codes are settled.

关键词： linear codes weight distribution Gauss sum Weil sum

A simplified bit metric calculation method for high-order PSK

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Science China(Information Sciences) 2013年第7期56卷 109-117页

作者： WANG Lei xu dazhuan ZHANG XiaoFei College of Information Science and Technology Nanjing University of Aeronautics and Astronautics

This paper proposes a simplified bit metric calculation method for high-order PSK signal with Gray-mapping. This method calculates the bit metric recursively by the symmetry of Gray code. Analysis and simulation results show that the proposed method can significantly reduce the computational complexity and maintain similar performance compared to ML and Max-Log bit metric. Additionally, this method generates bit metrics of PSK signals with different modulation order in the same way, so it can be applied to adaptive modulation system.

关键词： phase shift keying high order modulation bit metric soft demodulation

The design and analysis of unequal error protection fountain coding for multiple source networks over binary erasure channels

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Science China(Information Sciences) 2014年第8期57卷 9-17页

作者： SHAO HanQin xu dazhuan ZHANG XiaoFei College of Electronic and Information Engineering Nanjing University of Aeronautics and Astronautics

A novel network model of multiple source fountain coding is developed and a novel class of generic multiple source fountain codes with unequal error protection(UEP)property is proposed.The And–Or tree analysis technique is generalized to analyze the asymptotic performance of the proposed codes and a joint optimization method employing both linear and nonlinear programs is developed to optimize the degree distributions.Furthermore,we propose three basic methods to achieve UEP property and the performance of each method is discussed.We employ these analytical results and optimization method to design and discuss several UEP codes with two and four sources for different application scenarios.Simulation results verify that the proposed codes can be applied to the networks with any number of sources and can provide strong UEP property in various ways based on the proposed three basic methods.

关键词： asymptotic analysis fountain codes binary erasure channels network coding linear program nonlinear program unequal error protection multiple source networks

耕地利用隐性形态三维测度及其地域类型研究——以黄淮海地区为例

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地理研究 2024年第1期43卷 180-199页

作者：周贵鹏龙花楼戈大专徐林增李思捷中国科学院地理科学与资源研究所区域可持续发展分析与模拟重点实验室北京100101 中国科学院大学资源与环境学院北京100049 广西大学公共管理学院南宁530004 南京师范大学地理科学学院江苏省地理信息资源开发与利用协同创新中心南京210023

基于耕地利用隐性形态视角,聚焦探索快速工业化与城镇化进程中区域农业发展态势。从投入形态、产出形态和规模潜力形态入手,创新耕地利用隐性形态的理论解析视角和解析框架,提出理论假设,并尝试量化隐性形态。以黄淮海地区为研究区,开... 详细信息

基于耕地利用隐性形态视角,聚焦探索快速工业化与城镇化进程中区域农业发展态势。从投入形态、产出形态和规模潜力形态入手,创新耕地利用隐性形态的理论解析视角和解析框架,提出理论假设,并尝试量化隐性形态。以黄淮海地区为研究区,开展耕地利用隐性形态的定量测度、时空解析和地域类型划分,并证实了理论假设。结论如下:①2000—2020年研究区耕地利用隐性形态的综合水平不断优化,呈现“南高北低”格局,且南北分化不断拉大。投入形态值的“南高北低”是分异的主因。北部地区投入形态恶化以及南部地区产出形态和规模潜力形态的加速优化,导致了南北分化拉大。②研究区各单元的投入形态和规模潜力形态缓慢分化,产出形态快速分化,最终三维隐性形态均显著分化。③理论假设基本被证实:研究区整体的投入形态先优化后遭遇不利因素,后期不利因素在于大量农业劳动力的非农转移、农业机械化缓慢和化肥的控制施用;产出形态大幅稳步优化,规模潜力形态加速优化。④研究区的耕地利用隐性形态存在8种地域类型,至2020年已形成较明显的空间分异:投入显著型、产出显著型和投产显著型多聚集于南部的苏皖豫境内,归因于南部耕地“投入-产出”的结构和数量更丰富;规模显著型多聚集于北部的渤海沿岸平原地市,归因于当地地势平坦、耕地丰富,较高的城镇化率缓解了农民对耕地的矛盾和依赖;综合弱势型局限于边缘地带,一般发展型则填充剩余的大量地区。⑤未来研究区应加快农业机械化、现代化建设,及时应对劳动力投入空缺;警惕对化肥的依赖与生态风险;关注耕地“非粮化”对社会保障功能的削弱;深入推进新型城镇化,进一步解除小农式耕地依赖,缓解人地矛盾,促进耕地适度规模经营;引导三维隐性形态的空间耦合协调与耕地利用效益及潜能的高水平释放。

关键词：农业投入产出经营规模土地利用形态土地利用转型黄淮海地区

Blind CFO estimation algorithm for OFDM systems by using generalized precoding and trilinear model

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Journal of Systems Engineering and Electronics 2012年第1期23卷 10-15页

作者： Xiaofei Zhang dazhuan xu Electronic Engineering Department Nanjing University of Aeronautics and Astronautics Nanjing 210016 R R. China

This paper discusses the blind carrier frequency offset （CFO） estimation for orthogonal frequency division multiplexing （OFDM） systems by utilizing trilinear decomposition and genera- lized preceding. Firstly, the generalized precoding is employed to obtain multiple covariance matrices which are requisite for the trilinear model, and then a novel CFO estimation algorithm is proposed for the OFDM system. Compared with both the joint diagonalizer and estimation of signal parameters via rotational invariant technique （ESPRIT）, the proposed algorithm enjoys a better CFO estimation performance. Furthermore, the proposed algorithm can work well without virtual carriers. Simulation results illustrate the performance of this algorithm,

关键词： carrier frequency offset （CFO） orthogonal frequency division multiplexing （OFDM） generalized precoding trilinear model.

Angle estimation in bistatic MIMO radar using improved reduced dimension Capon algorithm

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Journal of Systems Engineering and Electronics 2013年第1期24卷 84-89页

作者： Xiaofei Zhang dazhuan xu Electronic Engineering Department Nanjing University of Aeronautics and Astronautics

This paper discusses the problem of direction of departure （DOD） and direction of arrival （DOA） estimation for a bistatic multiple input multiple output （MIMO） radar, and proposes an improved reduced-dimension Capon algorithm therein. Compared with the reduced-dimension Capon algorithm which requires pair matching between the two-dimensional angle estimation, the pro- posed algorithm can obtain automatically paired DOD and DOA estimation without debasing the performance of angle estimation in bistatic MIMO radar. Furthermore, the proposed algorithm has a lower complexity than the reduced-dimension Capon algorithm, and it is suitable for non-uniform linear arrays. The complexity of the proposed algorithm is analyzed and the Cramer-Rao bound （CRB） is also derived. Simulation results verify the usefulness of the proposed algorithm.

关键词： multiple input multiple output （MIMO） radar angle estimation Capon algorithm non-uniform array.

Improved scheme with cooperative diversity based on distributed space-time block coding

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Journal of Systems Engineering and Electronics 2009年第3期20卷 463-469页

作者： Du Na xu dazhuan Coll. of Information Science & Technology Nanjing Univ. of Aeronautics and Astronautics Nanjing 210016 P. R. China

An improved scheme with cooperative diversity based on distributed space-time block coding （WCD- DSTBC） is proposed, which effectively achieves diversity gains and improves the performance of the system by sharing some single-antenna users＇ antennas to form a virtual antenna array and combining with distributed spacetime block coding （DSTBC） mode. Then the relation between the system BER and the interuser BER for WCDDSTBC scheme is theoretically derived and the closed-form expression of BER for WCD-DSTBC system is obtained. The simulation results show that the proposed WCD-DSTBC scheme achieves distinct gains over the non-cooperative multi-carrier CDMA （MC-CDMA） system. When system BER is le-3 and interuser BER is le-3, about 2.5 dB gain can be gotten. When interuser channel state information （CSI） outgoes the users＇ individual CSI, about 3 dB gain is also achieved.

关键词： multiple input multiple output cooperative diversity distributed space-time block coding multicarrier CDMA.

Blind channel estimation for multiple antenna OFDM system subject to unknown carrier frequency offset

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Journal of Systems Engineering and Electronics 2014年第5期25卷 721-727页

作者： Xiaofei Zhang dazhuan xu Department of Electronic Engineering Nanjing University of Aeronautics and Astronautics

The problem of channel estimation for multiple an- tenna orthogonal frequency division multiplexing （OFDM） systems subject to unknown carrier frequency offset （CFO） is addressed. Multiple signal classification （MUSIC）-Iike algorithm, which generally has been used for direction estimation or frequency estimation, is used for channel estimation in multiple antenna OFDM systems. A reduced dimensional （RD）-MUSIC based algorithm for channel estimation is proposed in multiple antenna OFDM systems with unknown CFO. The Cramer-Rao bound （CRB） of channel estimation in multiple antenna OFDM systems with unknown CFO is derived. The proposed algorithm has a superior performance of channel estimation compared with the Capon method and the least squares method.

关键词： channel estimation orthogonal frequency division multiplexing （OFDM） multiple antennas multiple signal classification （MUSIC）.

UPLINK PERFORMANCE OF CWP-MC-CDMA WITH SPACE DIVERSITY COMBINING TECHNIQUE OVER RAYLEIGH FADING CHANNEL

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Journal of Electronics(China) 2006年第6期23卷 837-841页

作者： Yu Xiangbin Zhang Xiaodong xu dazhuan Bi Guangguo Information and Communication Engineering Postdoctoral Research Station Nanfing University o/Aeronautics and Astronautics Nanjing 210016 China National Mobile Communications Research Laboratory Southeast University Nanjing 210096 China

In this paper, a Complex Wavelet Packet based Multi-Carrier Code Division Multiple Access (CWP-MC-CDMA) system uplink model is proposed, based on the analysis of the principle of MC-CDMA and the use of the optimized complex wavelet packet. Considering that the base station can adopt multiple re-ceiver antennas in the uplink, we employ the Space Diversity Combining (SDC) technique to improve the sys-tem performance via multiple antennas. The uplink performance of proposed CWP-MC-CDMA system with SDC technique is investigated over Rayleigh fading channel, and corresponding bit error rate analysis is given in detail. The system can avoid the decrease of spectrum efficiency of conventional MC-CDMA due to insert-ing cyclic prefix. Theoretical analysis and simulation result show that the application of SDC technique can improve the CWP-MC-CDMA system ability to combat spatial fading and various interferences effectively. Moreover, the proposed system based on SDC technique has superior Bit Error Rate (BER) performance over the Discrete Fourier Transform (DFT) and SDC based MC-CDMA system and the real wavelet packet and SDC based MC-CDMA system.

关键词：多载波技术代码分割多重通路 CDMA 复合波包 MRC