基于改进Prefix Span的结构超手册修理方法推荐

针对当前民机结构超手册修理能力提升的迫切需求,提出了一种基于改进Prefix Span的结构超手册修理方法推荐模型。以某型国产民机结构超手册修理案例数据为样本,构建案例特征指标层次并对数据分级和结构化预处理,基于改进Prefix Span算法对案例损伤信息和修理方法频繁序列进行充分挖掘,生成超手册修理关联规则集,通过目标案例和频繁序列间相似度匹配,实现了超手册修理方法的智能推荐。测试结果表明,模型超手册修理方法推荐总准确率可达85.3%,显著高于改进前算法,具备良好的准确性和可用性,可为结构超手册修理决策、方案制定等提供一定的参考依据。

高效前缀约简的三维Hilbert空间填充曲线编解码算法

3维Hilbert空间填充曲线(3D HSFC)的编码和解码效率对空间查询处理、图像处理等领域的应用举足轻重。现有的3维编解码算法独立编解码每一个点,忽略了Hilbert曲线的局部保持特性。为了提高编解码效率,该文设计了高效的3D状态视图,并提出一种新的前缀约简的3D HSFC编码算法(PR-3HE)和前缀约简3D HSFC解码算法(PR-3HD),这两个算法通过公共前缀的定义和识别、公共前缀约简及多种优化技术来最小化需要编码的阶数,从而提高3D HSFC的编解码效率。理论上证明:当编码或解码一个k阶的窗体(窗体内总共含有2k×2k×2k个点)时,PR-3HE平均每个点的编码阶数不超过2,PR-3HD平均解码阶数不超过8/7。相对于传统的基于迭代的方法,编解码时间复杂度从O(k)降低到了O(1)。实验结果表明,该文算法在模拟数据集和真实数据集上的表现显著优于现有算法。

基于CP重构的高时间传输效率CP-UFMC接收方法

针对循环前缀(cyclic prefix,CP)不足的情况对循环前缀通用滤波多载波(cyclic prefix-universal filtered multi-carrier,CP-UFMC)系统的影响进行了数学推导,提出了一种基于CP重构的高时间传输效率CP-UFMC接收方法来改善系统性能,并进一步研究了选择性重构方法的性能。之后仿真研究了不同CP长度,不同载波频率偏移和不同正交振幅调制阶数时的系统误符号率(symbol error rate,SER)表现。仿真结果表明,基于CP重构的CP-UFMC接收方法可以改善CP不足导致的系统SER恶化问题,使其接近CP充足时的SER,并优于对比的其他通用滤波多载波系统接收方法。

改进的PrefixSpan算法及其在序列模式挖掘中的应用

由于序列模式挖掘需要花费大量计算时间,并需要占用大量存储空间.减少计算量、节省存储空间开销成为序列模式挖掘的关键.因PrefixSpan算法不产生候选,而适当应用Bitmap数据结构可避免重复扫描数据库,基于此,本文提出了BM-PrefixSpan算法,用于序列模式挖掘,设计并构造了PFPBM(Prefix of First Position on BitMap)表用于记录序列中的每个项在位图中第1次出现的位置.实验结果表明,BM-PrefixSpan算法综合了PrefixSpan和SPAM算法的优点,能够更快、更好地挖掘出序列模式.

基于检测残差消除的CP-OTFS系统信号检测算法

正交时频空(OTFS)调制技术因其高抗频率色散的性能,有望成为6G中高移动性场景下通信的关键技术。通过在OTFS系统发送端加入循环前缀(CP),可克服信道多径效应导致的码间干扰。针对当前CP-OTFS系统信号检测算法计算复杂度高的问题,提出一种基于检测残差消除的信号检测算法。采用时频域低复杂度初始检测后,结合系统时延-时间域的输入-输出关系计算初始检测残差。以检测残差为迭代变量,通过计算反馈值更新检测信号,并在时延-多普勒域进行逐符号最大似然检测。在迭代计算过程中逐步消除检测残差,并给出了算法停止准则。实验结果表明,该算法在信噪比为15 dB时误码性能比线性最小均方差算法提升了2.79 dB,比消息传递算法提升了1.76 dB,并且具有更好的收敛性和更低的计算复杂度。

Towards Blockchain-Based Secure BGP Routing,Challenges and Future Research Directions

Border Gateway Protocol(BGP)is a standard inter-domain routing protocol for the Internet that conveys network layer reachability information and establishes routes to different destinations.The BGP protocol exhibits security design defects,such as an unconditional trust mechanism and the default acceptance of BGP route announcements from peers by BGP neighboring nodes,easily triggering prefix hijacking,path forgery,route leakage,and other BGP security threats.Meanwhile,the traditional BGP security mechanism,relying on a public key infrastructure,faces issues like a single point of failure and a single point of trust.The decentralization,anti-tampering,and traceability advantages of blockchain offer new solution ideas for constructing secure and trusted inter-domain routing mechanisms.In this paper,we summarize the characteristics of BGP protocol in detail,sort out the BGP security threats and their causes.Additionally,we analyze the shortcomings of the traditional BGP security mechanism and comprehensively evaluate existing blockchain-based solutions to address the above problems and validate the reliability and effectiveness of blockchain-based BGP security methods in mitigating BGP security threats.Finally,we discuss the challenges posed by BGP security problems and outline prospects for future research.

基于数据挖掘的Prefix Span算法网络安全研究

鉴于传统用于网络安全防御的恶意数据检测算法耗时长、识别精度低、适用性差的问题,提出基于数据挖掘的Prefix Span网络安全防御算法研究。该研究在序列模式数据挖掘的理论研究基础上提出了Prefix Span算法,按照序列前缀生成投影数据库并去除非频繁项,引入相关度的概念完成算法的过程优化;基于Prefix Span算法构建了一种网络安全防御模型,对采集到的网络数据实施预处理、序列匹配与判定,实现对入侵数据的识别与检测,确保网络运行安全。仿真实验结果表明,提出的网络安全防御算法能够准确识别出不同类型的入侵数据,在检测精度和检测效率方面都有良好的表现。

巴德Mesh prefix plug在腹股沟疝修补术中的应用

目的：探讨巴德Mesh prefix plug在腹股沟疝修补术中的应用效果。方法：对65例使用巴德Mesh prefixplug无张力修补的腹股沟疝患者进行分析。其中单侧疝61例，双侧疝4例。原发疝56例，复发疝9例。斜疝54例，直疝6例，复合疝5例。结果：手术时间为35～70min。术后阴囊轻度肿胀5例，术后无切口感染及血肿发生。平均住院7d。短期随访效果良好，无复发及腹股沟区明显异物感。结论：巴德Mesh prefix plug适用于成人腹股沟疝修补，特别是老年疝、复发疝的修补尤为适用，是有效、安全、方便的。

云县彝语西山土语“a-”前缀的语法功能

云南省临沧市云县彝语西山土语(以罗罗语为例)词缀一般可分前缀、中缀和后缀。西山土语“a-”前缀可以附加在单音节、双音节和三音节名词之前构成名词前缀;附加在单音节动词之前构成否定前缀;附加在单音节、双音节形容词之前构成否定前缀,附加在单音节叠词之前构成形容词“级”的前缀。“a-”前缀在西山土语中的适用范围比较广泛,可用于名词、否定动词、形容词、时间副词、疑问代词和叹词中,具有构词、构形和韵律的功能,表达了丰富的语法范畴。

利用prefix-hash-tree实现从中文文本到事务数据的转换

电子文档的飞速增长为自动文本分类提供了巨大的机遇和挑战。在现有的众多方法中,关联分类以其较高的准确率和较快的训练时间而成为一种重要的自动文本分类方法。为实现基于关联的文本分类,首先需要将无结构的文本转换为结构化的事务数据,本文提出的prefix-hash-tree是针对汉语的特殊性而设计的一种数据结构,利用它可以方便地将中文文本转化为事务数据,实验证明利用该数据结构相应的查找、插入和重构算法都具有较好的效率。

基于前缀剪枝的大规模向量空间相似检索框架

针对大规模文本集合下基于权重的相似性查询问题,提出一种支持前缀剪枝的高效检索框架。首先给出向量空间模型下相似性及其带权前缀定义,理论证明了带权前缀剪枝的正确性;其次,面向大规模文本查询,提出一种新的倒排索引结构,利用索引叶节点维护记录的前缀权重,并基于该索引构建高效的相似检索算法;最后,在TF/IDF权重策略下证明该方法能够有效支持大规模带权相似检索。结果表明,其查询效率较Lucene的归并验证策略提升了5倍以上。

一种改进的PrefixSpan应用层特征自动提取算法

针对基于DPI的网络流量识别中的指纹特征提取困难问题,文章提出了改进的基于Prefix Span算法的连续序列模式挖掘算法来提取应用层指纹特征。首先,改进的算法在挖掘应用层特征时加入了属性约束。其次,在进行频繁序列投影前,又引入剪枝策略。最后,通过实验表明该改进的算法在挖掘应用层指纹特征方面大大提高了效率,提取出来的特征可有效地应用于网络流量识别技术中。

美国海军舰艇命名体系研究

美国海军舰艇命名体系由任命前缀、舰艇名称、分类代号、舷号4类要素构成,首先分析了每类要素对于命名体系的贡献,然后基于美国海军舰艇命名体系,以美国海军舰艇名册为数据源,通过要素提取、规则建立等步骤分析美国海军现役舰艇组成。经过分析,美国现役715艘舰艇分为战斗舰、辅助舰、战斗艇、支援艇、未在分类代号中定义等5大类67类型177级别,通过对比基于类型与级别规则、基于任命前缀规则的结果挖掘出美国海军现役舰艇组成规律。

基于FPGA的5G物理层LowPHY设计

在对5G O-RAN架构及物理层功能研究的基础上,设计实现了基于现场可编程门阵列(Field Programmable Gate Array,FPGA)的5G物理层LowPHY功能模块。通过对5G物理层LowPHY的功能进行分析,制定了总体设计方案,将功能模块划分为上行LowPHY模块、下行LowPHY模块及物理随机接入信道(Physical Random Access Channel,PRACH)LowPHY模块。针对LowPHY数据处理量大的特点,选用在数据处理方面具备高性能、低时延、低功耗优势的FPGA器件来实现。将设计的LowPHY功能模块与其他模块集成为O-RU单元,在5G NR系统中进行测试验证,测试结果表明本设计满足了项目需求,实现了设计目标。

Adaptive Channel Estimation in OFDM System Using Cyclic Prefix (Kalman Filter Approach)

OFDM is a promising technique for high data rate transmission and the channel estimation is very important for implementation of OFDM. In this paper, cyclic prefix (CP) can be used as a source of channel information which is originally used to reduce inter symbol interference (ISI). Based on this CP observation, we propose two cross coupled dual Kalman filters to track the channel variations without additional training sequences. One Kalman filter AR parameter estimation and another for fading channel estimation.

Reducing Cyclic Prefix Overhead Based on Symbol Repetition in NB-IoT-Based Maritime Communication

With the increasing maritime activities,a great demand of wide-area maritime digital data services is needed.Therefore,Narrowband Internet of Things(NB-IoT)that can provide wide coverage has been expected as an application for maritime communication networks(MCNS).In this paper,we aim to enhance the spectral efficiency in NB-IoT by reducing the cyclic prefix(CP)overhead in random access signal without causing interference.The key point of the proposed scheme is the symbols transmitted for multiple times repeatedly in NB-IoT.Specifically,all CP are removed and multi-path fading effect is eliminated by using a repeated symbol to cover the disturbed symbol to construct a circular convolution structure of the channel with the same effect as adding CP.In addition,a single-tap equalization is still appropriate.To validate the effectiveness of the proposed scheme,simulation results are carried out with respect to the bit error ratio(BER).

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 (1SI) 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 11.5Mb/s higher than conventional non-adaptive system while gaining a 0.65dB power saving at the same BER performance.

The Analysis of Prefixes——Taking mal-and mis-As Examples

The present paper is aimed to testify that the richness and abundance of English vocabulary is closely related to prefixes. Through the analysis of prefixes such as mal-and mis-, a better understanding of word formation from the perspective of semantic factors and functional factors as well as morphology factors will be obtained.

Prefix Subsection Matching Binary Algorithm in Passive RFID System

Identifying speed,tag average response times and reliability are the most important capabilities in passive RFID(radio frequency identification) system.QT(query tree) is a famous algorithm for lowest-cost RFID tags,but its shortcoming is high searching delay and high tag average response times.A prefix subsection matching binary(PSMB) algorithm based on QTalgorithm is proposed.The key idea of PSMB anti-collision algorithm is that,during searching phase,a given reader uses the particular tags ID,which has been searched out formerly,to shorten searching delay and depress tag average response times.The idea of PSMB algorithm can be described as follows.Usually,tag ID is composed of several subsections which have different meanings.Based on the tags ID searched out formerly,a given reader builds a prefix database.In subsequent searching phase,the reader uses its prefix database to deduce searching space of tag ID.Simulation results show that identification delay of PSMB algorithm is about 1/3 of QTalgorithm,tag average response times is about 1/4 of QTalgorithm,and system throughput rate is treble QTalgorithm.

On Ultra Extended Cyclic Prefix in Orthogonal Frequency Division Multiplexing (OFDM) Systems: The Case of LTE Downlink

Orthogonal Frequency Division Multiplexing (OFDM) is a multi-carrier scheme used in modern broadband wireless communication systems to transmit data over a number of orthogonal subcarriers. When transmitted signals arrive at the receiver by more than one path of different length, the received signals are staggered in time;this is multipath propagation. To mitigate the effect of dispersed channel distortion caused by random channel delay spread, Cyclic Prefix (CP) is introduced to eliminate Inter-Symbol Interference (ISI). In the literature, researchers have focused on carrying out investigations (or studies) mainly on the two existing CP insertions, namely: normal and extended CPs. Both CPs have limitations with respect to handling channel delay spreads. In the current work, a new CP, herein referred to as “ultra extended” CP is proposed to address delay spreads beyond the limits of the normal and extended CPs. The efficacy of the proposed ultra extended CP is tested via simulation under different scenarios. It is shown by the results obtained that the proposed CP can efficiently handle delay spreads beyond the limits of the existing normal and extended CP, and can indeed be implemented in the design of future telecommunication systems to accommodate higher channel delay spreads and it ensures wider cell coverage.