RS码频域纠错编码在激光对潜通信信道中的实现方法

介绍了信道编码在激光对潜通信系统中的重要作用，介绍了频域编译ＲＳ码的基本方法，并给出了脉冲位置调制信道的ＲＳ码频域编译码的计算机模拟方法和结果。     

广义准正则格形码距离谱的计算

本文讨论了格形码距离谱的计算问题，定义了度量空间意义下的广义准正则格形码，对具有Ｉｍａｉ与Ｈｉｒａｋａｗａ［２］和Ｕｎｇｅｒｂｏｅｃｋ［３］定义的典型的时不变网格结构的广义准正则格形码，证明了其距离谱可用全零信息序列对应的码字进行计算。在理论上推广了Ｍ．Ｒｏｕａｎｃｅ与Ｄ．Ｊ．Ｃｏｓｔｅｌｏ的结果，解决了非平方欧几里德度量意义下一类ＴＣＭ信号序列的距离谱计算问题     

国内外中短波调幅广播技术20年来的回顾和展望

文章回顾２０年来国内外调幅广播在调制制式，射频放大系统以及包括单边带，浮动载波和调幅多工等多种功能的发展状况。同时对今后调幅广播技术发展方向发表了几点看法。     

Terrestrial digital video broadcasting for mobile reception using OFDM

Performance of a system design for digital video broadcasting is examined with emphasis on mobile reception. Orthogonal frequency division multiplexing (OFDM) is used to achieve good bandwidth efficiency and to mitigate the intersymbol interference resulting from the channel delay spread. The resulting equivalent channel including OFDM can be modeled as a flat Rayleigh fading channel plus an interchannel interference (ICI) term due to the channel Doppler spread. This ICI term is analyzed and shown to result in an error floor. Performance improvements due to antenna diversity and trellis-coded modulation (TCM) are given. Finally, multiresolution modulation is discussed as a means of achieving graceful degradation and giving degrees of freedom for further performance improvement.This research was supported by the Multimedia Systems R & D Laboratory, Hitachi, Ltd.     

Fabrication and characteristics of tapes and test magnets made from Ag-Clad Bi-2223 superconductors

Pb_0.4Bi_1.8Sr₂Ca_2.2Cu₃O_x (Bi-2223) precursor powder was prepared by a solid-state reaction of carbonates and oxides of lead, bismuth, strontium, calcium, and copper, and the powder was then used to fabricate silver-clad tapes by the powder-in-tube technique. Transport critical current density (J_c) values>4×10⁴ A/cm² at 77K and 2×10⁵ A/cm² at 4.2 and 27K have been achieved in short tape samples. Long lengths of tape were tested by winding them into pancake coils. Recently, we fabricated a test magnet by stacking ten pancake coils, each containing three 16m lengths of rolled tape, and tested it at 4.2, 27 and 77K. A maximum generated field of 2.6 T was measured in zero applied field at 4.2K and the test magnet generated significant self-field in background fields up to 20 T. The results are discussed in this paper.     

Dependence of critical current density on microstructure and processing of high-Tc superconductors

Microstructural origins for reduced weak-link behavior in high-J_c melt-processed YBCO, spray pyrolyzed thick films of Tl-1223, metallic precursor Y-124 polycrystalline powder-in-tube (PIT) wires and PIT Bi-2212/2223 are discussed. Since the materials studied are the highest J_c, polycrystalline, high-T_c superconductors fabricated worldwide, the results provide important guidelines for further improvements in superconducting properties, thereby enabling practical applications of these materials. It is found that strongly linked current flow within domains of melt-processed 123 occurs effectively through a single crystal path. In c-axis oriented, polycrystalline Tl-1223 thick films, local in-plane texture has been found to play a crucial role in the reduced weak-link behavior. Formation of “colonies” of grains with a common c-axis and modest in-plane misorientation was observed. Furthermore, a colony boundary in general has a varying misorientation along the boundary. Large regions comprised primarily of low angle boundaries were observed. Percolative transport through a network of such small angle boundaries appears to provide the nonweak-linked current path. Although powder-in-tube BSCCO 2212 and 2223 also appear to have a “colony” microstructure, there are some important differences. Colonies in BSCCO consist of stacks of grains with similar c-axis orientation in contrast to colonies in Tl-1223 films where few grains are stacked on top of one another. Furthermore, most grains within a colony in BSCCO have the same lateral dimensions as that of the colony, resulting largely largely in “twist” boundaries. Further microstructural characterization of high-J_c PIT 2212 and 2223 is currently underway. In the case of Y-124 wires, weak macroscopic in-plane texture is found. Additional measurements are underway to determine if a sharper, local in-plane texture also exists. It is found that in three of the four types of superconductors studied, reduced weak-link behavior can be ascribed to some degree of biaxial alignment between grains, either on a “local” or a “global” scale.     

受激喇曼散射在掺铒光纤放大器中的影响

本文在分析了均匀掺杂分布式光纤放大器（d－EDFA）的基础上，提出了沿传输方向掺杂浓度单调下降（单变），和降升结合（两变）的两种渐变型分布式光纤放大器，并用传输方程研究了透明传输和最佳掺杂浓度下，受激喇曼散射对均匀、单变和两变型三种d－EDFA的各种特性的影响．     

Analytical general results for handoff dwell time distribution in wireless networks

1 Introduction The calling dwell time characteristic is critical for the user network planning and deployment, e.g., global system for mobile communications (GSM), as well as the next generation wireless multimedia networks, such as, the currently standar…     

非AWGN环境下调制类型自动识别

在非AWGN环境下，针对CW，AM，FM，OOK，PSK，QPSK，16QAM，FSK，MSK，SSB十种混合调制信号，对调制类型特征提取方法和自动识别算法进行了分析、综合、设计和计算机仿真。提出了梯层电平分析方法、频率瞬时信号分析、剔除载波的归一化能量分析、平方后信号的频谱分析、四次方后的信号频谱分析等方法。当SNR=10dB时，计算机仿真结果是正确识别率不低于95％，自动识别的平均处理时间为不超过10s。