MIMO-OFDM迭代时变频偏估计算法

MIMO-OFDM是一种高速的通信技术,满足了未来舰载雷达协同通信时隙小、数据量大的要求。但是舰船间的相对速度会导致通信频率的不断变化,而且MIMO-OFDM技术对频偏又十分敏感,因此必须对时变频偏进行估计。本文假设每一帧信号的频偏都是随机变量,提出了利用期望最大化（EM）和最大后验概率（MAP）译码算法相结合的时变频偏估计和信号检测算法。计算机仿真结果表明,该算法可以准确地估计时变频偏,而且系统的误码率性能和频偏估计精度可以随着迭代次数的增多而提高。     

多中继AF协作系统功率分配研究

功率分配是协作通信中一个重要的研究方向,文章分析了放大转发（AF）协作方式下,基于正交信道的多协作中继系统模型,在此基础上推导了系统中断概率。并以最小化系统中断概率为目标,给出系统功率分配约束表达式,进一步分析了功率分配与中继节点位置的关系,计算求得单中继和两中继情况系统最优功率分配系数。系统仿真表明最优功率分配相对常规的等功率分配,系统性能明显提升。     

一种基于有限信息反馈的最佳中继选择协议研究

针对多用户的TDMA无线自组织协同通信网络,深入研究了基于有限信息反馈的最佳编码协作中继选择策略,在瑞利和莱斯信道条件下对该协议的中断概率和误码率性能进行了计算机仿真,并对协议做了进一步细化和优化。仿真和分析结果表明,该中继选择策略的中断概率和误比特率性能较传统策略有较大提升,且改进后的方案能明显减少协同交互信息开销。     

A novel IEEE 802.11‐based MAC protocol supporting cooperative communications

Cooperative diversity is a transmission technique, where multiple terminals form a virtual antenna array that realizes spatial diversity gain in a distributed fashion. The concept of cooperation has already been introduced to MAC layer to design MAC protocol. But it does not take advantage of physical layer's cooperation. In this paper, we present a novel MAC protocol based on IEEE 802.11, called C‐MAC, which is able to support the basic building block of cooperative system. In other words, in C‐MAC, a source would invite a relay node into data transmission if there exits an available one. During data transmission, the source sends the signal to destination in the first time slot. The relay node will retransmit the overheard information to the destination in the second time slot. The destination combines two signals from the source and the helper to create the spatial diversity and robustness against channel fading. The C‐MAC is backward compatible to the legacy IEEE 802.11 system. The performance of C‐MAC mainly depends on physical layer's performance as it just provides the support for cooperation at the MAC layer. If the physical layer works well, C‐MAC would outperform IEEE 802.11 when considering packet error rate (PER). We also perform extensive simulation using ns‐2 with assumptive physical parameters. The results show that C‐MAC would outperform 802.11 if PER is over some threshold, e.g. when PER is 0.4, C‐MAC can achieve up to 11.5% higher throughput than IEEE 802.11. Copyright © 2011 John Wiley & Sons, Ltd.     

基于EMRP算法的多UAV协同航迹规划

为解决作战环境中的多无人机协同航迹规划问题,提出一种基于层次分解策略的航迹规划方法.通过骨架化算法生成规划空间,利用基于进化计算的多航迹规划(EMRP)算法为各UAV找到K条备用航迹,实现了利用EMRP算法与数学形态学相结合解决多UAV协同航迹规划问题,并对生成的初始航迹进行平滑处理,得到满足UAV机动要求的可行航迹....     

New design of no-zero-entry single symbol ML decodable STBCs based on group precoding

In multiple-input multiple-output(MIMO)systems,space-time block codes(STBCs)from orthogonal designs(ODs)and coordinate interleaved orthogonal designs(CIOD)have been attracting wider attention due to their amenability for fast(single symbol)maximum-likelihood(ML)decoding,and full-rate with full-rank over quasi-static fading channels.However,most of these codes,for transmitting antennas more than 4,have large number of zero entries in their codeword matrix.Due to the zero entries in the design,the transmitting antennas need to be switched on and off imposing severe hardware constraints.To solve this problem,we propose a method to generate a new class of no-zero-entry single symbol maximum likelihood decodable STBCs(NZESSDCs),which is based on coordinate interleaving and group precoding technique.The ability of the proposed group precoding based NZESSDCs(called G-NZESSDCs)on single symbol ML Decoding and full diversity are analyzed and derived.The performance evaluation is accomplished by numerical simulation and is compared with recently reported NZESSDCs(called C-NZESSDCs).Compared with C-NZESSDCs,the proposed G-NZESSDCs have same bit-error-rate(BER)performance and better peak-to-average ratio(PAPR)performance.     

Versatile and Large-Scale Synthesis of Functional Dithiocarbamates in Water

Structural diversity is possible in direct access to functional dithiocarbamates based on a highly efficient and simple one-pot reaction of CS₂, amines, and alkyl halides in nearly quantitative yields in water.     

The N?H Functional Group in Organometallic Catalysis

The organometallic approach is one of the most active topics in catalysis. The application of NH functionality in organometallic catalysis has become an important and attractive concept in catalyst design. NH moieties in the modifiers of organometallic catalysts have been shown to have various beneficial functions in catalysis by molecular recognition through hydrogen bonding to give catalyst–substrate, ligand–ligand, ligand–catalyst, and catalyst–catalyst interactions. This Review summarizes recent progress in the development of the organometallic catalysts based on the concept of cooperative catalysis by focusing on the NH moiety.     

频率分集雷达抗干扰效能分析

基于频率分集雷达原理,并与单频雷达进行比较,分析了频率分集雷达的抗干扰效能,同时对其进行建模。该模型包括抗干扰改善因子的计算模型、雷达作用距离和发现概率的计算模型。通过建模分析得出:在总功率与单频雷达保持相同的情况下,频率分集雷达并不能改善雷达接收到的信干比,频率分集雷达实现抗干扰的途径是提高雷达工作的可靠性,而不是提高雷达对目标的检测性能。