利用一种新LDPC码的编码OFDM系统性能分析

提出了一种新的构造LDPC码的方法, 并把用该方法产生的LDPC码应用到编码正交频分复用(OFDM)系统中进行了研究. 该方法拓展了单位阵移位构造的LDPC码, 它利用简单的不等式可确保在置换单位阵构造中不会产生Tanner图中的短圈, 使得产生的LDPC码的Tanner图最小圈长为8. 由于该类码是准循环码以及其校验矩阵所固有的分层结构, 编码器和解码器都易于实现, 它们分别是线性可编和线性可译的. 所提出的LDPC码码率范围较大, 可以灵活选取. 利用迭代解码进行计算机仿真, 发现新的LDPC码比其他的规则LDPC码在编码OFDM系统中具有更好的性能.     

一种具有可分级转码能力的空时OFDM视频传输方法

结合空时OFDM和转换编码技术,提出了一种无线衰落信道下具有可分级转码能力的鲁棒视频传输方法.采用可分级转码器将高质量的MPEG-2压缩视频转换为低码率、低分辨率MPEG-4可分级码流来满足网络带宽和终端设备显示的要求.在接收端采用一种层干扰抑制算法,使得分层空时OFDM系统不同层的传输性能存在差异,从而使系统具有不对等保护能力.根据分级码流的重要程度不同,将转码输出的可分级码流分别由分层空时编码OFDM系统的不同层来实现视频的鲁棒传输.实验结果表明:在典型的随机突发错误的无线环境下,提出的具有可分级转码能力的系统的视频传输性能优于传统的非分级转码的视频传输系统.     

Faculty and Academic Integrity: The Influence of Current Honor Codes and Past Honor Code Experiences

This survey of faculty at honor code and non-honor code institutions investigated the influence of honor codes on faculty attitudes and behaviors. As hypothesized, we found that honor code faculty have more positive attitudes toward their schools' academic integrity policies and are more willing to allow the system to take care of monitoring and disciplinary activities. Faculty in noncode institutions have less positive attitudes and are more likely to take personal actions designed to both catch and deal with cheaters. We also investigated the potential influence of a student honor code experience on faculty attitudes. We found that, in noncode environments, faculty who had an honor code experience as a student were more likely to believe that students should be held responsible for peer monitoring and to say that they deal personally with cheating. Implications for higher education institutions are discussed.     

Nonlinear analytical solution for one-dimensional consolidation of soft soil under cyclic loading

INTRODUCTION Conventional consolidation analysis based on Terzaghi’s one-dimensional theory neglects the non-linearity of soil for the sake of mathematical expediency, which is considered to be one of the theory’s shortcomings. Many researchers have pro-posed one-dimensional (1D) consolidation models where the coefficient of volume compressibility mv, coefficient of permeability kv, and coefficient of consolidation cv, vary with either depth or time. Schiffman (1958), Davis and Raymon…     

利用集合论构造一类Cartesion认证码

利用集合论构造了一个Cartesion认证码 ,并计算了码参数 ,敌方假冒、替换成功的概率和r阶欺骗成功的概率 ,并推广了王永传、杨义先等人的结果     

Pt/C和PtRu/C在低温燃料电池中的电氧化比较

利用循环伏安法分别研究了Pt/C和PtRu/C两种商业催化剂在甲醇和乙醇中的电化学特性,并且对其不同之处进行了分析和讨论,从中可以发现PtRu/C在避免催化剂中毒和提高反应的起始电位和催化活性方面具有明显的优点。     

循环矩阵的逆矩阵的一种求法

本文给出一种求循环矩阵的递矩阵的方法,进而推出几个特殊循环矩阵的求递公式。     

先秦两汉现实女性题材赋研究

先秦两汉现实女性题材赋经历了漫长曲折的发展历程,根据赋家之创作主旨和表达内容,将其概括为“言志”、“抒情”和“其他”三类进行分析论述。联系当时的社会文化环境,试图对其发展状况与嬗变轨迹给予较为合理的解释。     

《兄弟》:从寓言到"写真"

《兄弟》暗示了余华小说艺术发生的新变。其《兄弟》之前的作品多是寓言性的,《兄弟》逐步走向了"写真",作品因而消解了隐喻性和荒诞性色彩;人物也不再是小说叙事结构中的符号和工具,而是具备了性格特征且具有个性魅力的形象;小说的主题内容也从"闹剧"走了出来,而成为描绘人物命运、揭示历史真相的正剧,其中也透露出作家的情感和价值立场。     

A novel OFDM transmission scheme with length-adaptive Cyclic Prefix

Conventional OFDM transmission system uses a fixed-length Cyclic Prefix to counteract Inter-Symbol Interferences(ISI)caused by channel delay spreading under wireless mobile environment. This may cause considerable performance deterioration when the CP length is less than the channel RMS delay spread,or may decrease the system power and spectrum efficiency when it is much larger. A novel Orthogonal Frequency Division Multiplexing(OFDM)transmission scheme is proposed in this paper to adapt the CP length to the variation of channel delay spread. AOFDM-VCPL utilizes the preamble or pilot sub-carriers of each OFDM packet to estimate the channel RMS delay spread; and then uses a criterion to calculate the CP length,which finally affects the OFDM transmitter. As illustrated in the simulation section,by deploying this scheme in a typical wireless environment,the system can transmit at data rate 11.5 Mb/s higher than conventional non-adaptive system while gaining a 0.65 dB power saving at the same BER performance.