A free monoid containing all prefix codes

In this paper,we exhibit a free monoid containing all prefix codes in connection with the sets of i-th powers of primitive words for all i≥2.This extends two results given by Shyr and Tsai in 1998 at the same time.

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。

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。

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。

A novel OFDM transmission scheme with length-adaptive Cyclic Prefix

Conventional OFDM transmission system uses a fixed-length Cyclic Prefix to counteract Inter-Symbol Inter- ferences (ISI) caused by channel delay spreading under wireless mobile environment. This may cause considerable per- formance 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.

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.

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。

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).

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.

TURBO AIDED CYCLIC PREFIX RECONSTRUCTION FOR CODED SINGLE-CARRIER SYSTEMS WITH FREQUENCY-DOMAIN EQUALIZATION (SC-FDE)

In this paper, a Turbo aided Cyclic Prefix (CP) reconstruction scheme, termed Turbo- CPR, is proposed for Single-Carrier systems with Frequency-Domain Equalization (SC-FDE) that employ insufficient CP in the transmitter. In Turbo-CPR, the decoder output is incorporated in the process of equalization, i.e. Turbo equalizer is employed. It is shown in the simulation results that Turbo-CPR not only recovers the performance loss due to insufficiency of CP, but also provides extra gains over the lower bound of performance for conventional CP reconstruction schemes.

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.

ON THE PERFORMANCE OF DATA-DEPENDENT SUPERIMPOSED TRAINING WITHOUT CYCLIC PREFIX FOR SISO/MIMO SYSTEMS

Compared with channel estimation method based on explicit training sequences,bandwidth is saved for those methods using superimposed training sequences,while it is wasted when Cyclic Prefix(CP) is added.In previous work of McLernon,the Mean Square Error(MSE) performance of Data-Dependent Superimposed Training(DDST) without CP for Single-Input Single-Output(SISO) system was analyzed under the assumption that the data-dependent sequence matrix was a circulant matrix and not interfered by others.In fact,for the system without CP,the data-dependent sequence matrix is not circulant any more and will be interfered.This paper derives the exact expression of MSE for the system without CP and also gives its extension to Multiple-Input Multiple-Output(MIMO) system without CP.

Lexical Generativity of Bengali Prefixes： A Corpus-Based Investigation

Prefixation is a dynamic method of word formation in Bengali. Sometimes prefixes become derivational to create new words, which differ in part-of-speech and meaning from the words with which these are attached. Thus, prefixation acquires an identity of a morphodynamic process in the language through which new words take birth, while old words change their forms, functions, and meanings to increase lexical stock of Bengali. With reference to a large lexical database of prefixed words obtained from the Bengali corpus （Dash, 2009）, this paper tries to explore the nature and type of morphosemantic processes that occur at the time of prefixation to highlight the patterns of change in forms and meaning of prefixed words. Also, it aims at laying a theoretical foundation about the nature of lexical generativity of prefixes used in formation of words. The application relevance of this study may be attested in descriptive linguistics, applied linguistics, and language technology, since analysis of forms and functions of prefixes supplies necessary information for developing text materials for Bengali language teaching, compiling dictionaries, designing systems for machine learning, and developing databases for machine translation. Indirectly, it ventilates into the nature of complexities embedded in linguistic generativity of the Bengali speakers

Accurate channel estimation for MIMO-OFDM system by exploiting cyclic prefix

Multiple-input-multiple-output orthogonal frequency division multiplexing （MIMO-OFDM） systems promise to provide significant increase in system capacity for future wireless communication systems. The channel state information is required to achieve the high capacity of an MIMO-OFDM system. In this pa-per, an improved channel estimation scheme is proposed for MIMO-OFDM system by making full use of the training sequence and CP （cyclic prefix）. The method improves the performance of the channel esti-mator because of using the redundant information in CP. Also, the theoretical mean square error （MSE） bound of the improved estimator is derived. The effectivity of the algorithm is demonstrated by the simula-tion results of MIMO-OFDM systems with two transmit and two receive antennas. The MSE gain is en-hanced by about 1dB.

Enhanced spectrum sensing using a combination of energy detector,matched filter and cyclic prefix

In this paper,we propose a sensing scheme based on energy detection,matched filter and cyclic prefix.Both Equal Gain Combining(EGC)and optimal combination of the aforementioned detectors are investigated in cooperative and non-cooperative spectrum sensing scenarios.In packet transmission systems such as OFDM(Orthogonal Frequency Division Multiple access)systems,the proposed scheme takes advantage of utilizing more samples than individual detectors,i.e.,cyclic prefix,training or pilot samples,and data payload samples.The proposed combine-sensing scheme offers higher detection probability and lower false alarm probability,as compared with the performance of individual detectors over the same frame duration.Simulation results are congruent with the theoretical curves and confirm the validity of our derivations.

A TCAM-based Two-dimensional Prefix Packet Classification Algorithm

Packet classification (PC) has become the main method to support the quality of service and security of network application. And two-dimeusioual prefix packet classification (PPC) is the popular one. This paper analyzes the problem of ruler conflict, and then presents a TCAM-based two-dimensional PPC algorithm. This algorithm makes use of the parallelism of TCAM to lookup the longest prefix in one instruction cycle. Then it uses a memory image and associated data structures to eliminate the conflicts between rulers, and performs a fast two-dimeusional PPC. Compared with other algorithms, this algorithm has the least time complexity and less space complexity.

Brief Exploration of Nasal Assimilation Phenomenonin Negative Prefixes-Comparison Between Chinese Dialect & English

Nasals and assimilation are basic terminologies in phonology,nasal assimilation is a kind of common phonological phenomenon in addition.As is known to all,in English,assimilation mainly happens between consonants and consonants,which is one of the important constitutes of English mutation,for the sake of labor-saving convenience and better fluency.From an applied linguistic view,nasal assimilation in negative prefixes(e.g.un-,ab-,ir-,im-&non-,etc.)is seemingly another interesting phenomenon for an innovative exploration.This paper focuses on some specific enumeration and comparison between Chinese dialect(specifically,Sichuan dialect)as well as English.This brief exploration and analysis might contribute to relative study in years to come.