差分跳频码性能检验研究

差分跳频是一种新的扩展频谱通信技术.在介绍差分跳频基本原理的基础上,将差分跳频的频率跳变过程建模成齐次马尔可夫链.分析了G函数的功能,重点讨论了差分跳频码性能的检验方法,包括不可约性、频隙滞留、均匀性和随机性检验,其中频隙滞留是首次提出应用于差分跳频码性能的检验.这些检验方法对于差分跳频G函数的设计具有一定的指导意义.     

The structure of the defense industry and the security needs of the country: a differentiated products model

This paper models the interactions between the defense needs of the USA and Western Europe, which produce several heterogeneous defense goods, and the defense industry market structure. The results show that net defense costs of the USA and Europe are lower when the number of defense firms in each arms‐producing country is small and when the world prices of the defense goods are high. The model predicts that the increase in world prices will crowd‐out countries in the developing world from the market for modern weapon systems and may force them to develop and use ‘cheap and dirty’ weapon systems.     

Estimating defence budget saving from disarmament: the United States’ case

Probing the technology in the production of US national defence by using a dynamic cost‐function model with adjustment costs, this paper evaluates the effect of reducing the level of national defence on the defence budget saving. Our inquiry involves estimating the defence production structure without output data for non‐market goods that are normally unavailable. Our findings include: (i) the United States behaves rationally to minimize cost in the production of national defence; (ii) the adjustment costs are larger in disarmament than in military build‐up; (iii) due to the adjustment costs peculiar to disarmament, the defence budget saving from disarmament appears small, but cutbacks allow great savings on the defence budget.     

数字伺服系统中角的表示方法

介绍了数字伺服系统中用十六位二进制数表示角的方法和误差角的计算。使数字伺服系统设计者从根本上树立角与数关系的正确看法,从而有助于正确、简练地设计控制算法程序。     

准静态受遮蔽的Rician衰落信道中空时格码的性能上界

针对准静态受遮蔽的 Rician 衰落信道,在收端已知信道状态信息的条件下,文中分析了空时格码的性能.推导了码字差相关阵为对角阵的空时格码系统的成对差错概率的确切表达式,得到了相应空时格码在准静态受遮蔽的 Rician 衰落信道中的性能上界。仿真结果表明,在遮蔽不太严重的信道中,文中得到的 union 界与相应编码系统的实际性能有很好的近似度。     

基于准循环双对角阵的LDPC码编码算法

针对校验矩阵形如准循环双对角阵的结构化LDPC码,对比研究了两类高效的编码算法:矩阵分解编码算法和分项累加递归编码算法,证明了两类算法从实现角度是等价的,但分项累加递归编码算法推导更为直观,且便于硬件并行实现。基于分项累加编码算法,提出了一种适合准循环双对角LDPC码的部分并行编码结构,设计实现了IEEE 802.11n标准中的LDPC码编码器。FPGA实现结果表明,所设计的LDPC编码器具有硬件开销较小、吞吐率高的优点,在码长为1944bit、码率为5/6时信息比特吞吐率最高可达13Gbps。     

The effect of deployment on first‐ and second‐term re‐enlistment in the US active duty force

Why should deployment affect re‐enlistment? In our model, members enter the military with naïve beliefs about deployment and use actual deployment experience to update their beliefs and revise their expected utility of re‐enlisting. Empirically, re‐enlistment is related to the type and number of deployments, consistent with the learning model. Non‐hostile deployment increases first‐term re‐enlistment but hostile deployment has little effect except for the Army, where the effect is positive. Both types increase second‐term re‐enlistment. Interestingly, first‐term members with dependants tend to respond to deployment like second‐term members. In addition, deployment acts directly to affect re‐enlistment, not indirectly through time to promotion.     

GPS L1C信号LDPC译码器设计

GPS现代化中的L1C信号使用了LDPC码,以提高接收机的弱信号接收能力。L1C信号中使用的LDPC码没有循环或准循环结构,这为译码器设计带来了难度。为了降低译码器实现复杂度,在分析L1C信号LDPC码校验矩阵结构的基础上,通过对校验节点分类和改变变量节点更新方法,提出了一种低存储量和简化译码器控制逻辑的低复杂度译码器结构,并通过仿真验证了译码器译码结果的正确性。     

AWGN信道中Turbo码的性能和仿真

主要对Turbo码的解码算法进行了研究,分析了常用的MAP解码算法,对Turbo码在AWGN信道中应用不同的解码算法进行了仿真,针对不同解码算法和解码迭代次数等因素对Turbo码性能影响进行分析,结果表明Turbo码在AWGN信道中和低信噪比条件下具有优良的性能。     

栅格数据处理中邻域型算法的并行优化方法

随着并行计算的成熟,众多数据密集型的栅格处理算法亟需利用并行计算来缩减执行时间.针对其中一类邻域型算法,构建了用于估计是时间代价的串行/并行时域模型,分析了各个组成的代价影响因素,提出了降低数据I/O代价的并行I/O方法和降低数据通信代价的光圈预测方法.实验证明,所提的两个优化方法可以使邻域型栅格处理算法的并行程序更加充分地利用并行计算资源,进而在一般并行化的基础上进一步提升其并行性能.