中文2800字
毕业设计英文翻译
专业电子信息工程
班级2010级
学生姓名
学号
课题码分多址通信系统的建模、仿真和设计
——初始化模块、基站接收模块
指导教师
2014 年06 月10 日
译文原文
1.1 The basic concept of spread-spectrum communication
Spread spectrum communication’s basic characteristics, is used to transmit information to the signal bandwidth(W) is far greater than practical required minimum(effective) bandwidth (F
?),as the radio of processing gain P G.
=/
G P?
F
W
As we well know,the ordinary AM,FM,or pulse code modulation,GP value in the area more than 10 times,collectively,the “narrow-band communication”,and spread-spectrum communication GP values as hundred or even thousands of times, can be called “broadband communication”.
Due to the spread-spectrum signal,it is very low power transmitters,transmission space mostly drowned in the noise,it is difficult to intercepted by the other receiver ,only spreading codes with the same (or random PN code) receiver, Gain can be dealt with ,and despreading resume the original signal.
1.2 The technology superiority of spread-spectrum communication.
Strong anti-interference, bit error rate is low. As noted above, the spread spectrum communication system due to the expansion of the transmitter signal spectrum, the receiver despreading reduction signal produced spreading gain, thereby greatly enhancing its interference tolerance. Under the spreading gain, or even negative in the signal-to-noise ratio conditions, can also signal from the noise drowned out Extraction, in the current business communications systems, spread spectrum communications systems, spread spectrum communication is only able to work in a negative signal-to-noise ratio under the conditions of communication .
Anti-multi-path interference capability, increase the reliability of system. Spread-spectrum systems as used in the PN has a good correlation, correlation is very weak. Different paths to the transmission signal can easily be separated and may in
time and re-alignment phase, formation of several superimposed signal power, thereby improving the system’s performance to receive increased reliability of the system.
Easy to use the same frequency, improving the wireless spectrum utilization. Wireless spectrum is very valuable,although long-wave microwave have to be exploited, and still can not meet the needs of community. To this end, countries around the world are designed spectrum management, users can only use the frequency applications,rely on the channel to prevent the division between the channel interference.
Due to the use of spread-spectrum communication related receive this high-tech,low signal output power(“a W,as a general-100mW),and will work in the channel noise and thermal noise in the background,easy to duplicate in the same area using the same frequency,can now all share the same narrow-band frequency communication resources.
Spread-spectrum communication is digital communication,particularly for digital voice and data transmission with their own encryption, only in the same PN code communication between users, is good for hiding and confidential in nature, facilitating communication business. Easy to use spread-spectrum CDMA communications, voice compression and many other new technologies, more applicable to computer networks and digitization of voice,image information transmission.
Communication in the most digital circuits, equipment, highly integrated, easy installation, easy maintenance, but also very compact and reliable. The average failure rate no time was very long.
1.3 Spread spectrum communication system
Spread spectrum communication,namely, spread spectrum communications (Spread spectrum communication), with fiber-optic communications,satellite communications,with access to the information age as the three major high-tech communications transmission. Spread spectrum communication is to send the information to be pseudo-random data is coded(Spread spectrum sequence: spread sequence) modulation, spread spectrum and then the realization of transmission; the
receiving end is using the same modem code and related processing, the restoration of the original data. Spread spectrum communication system has three main characteristics.
(1) Carrier is an unpredictable, or so-called pseudo-random broadband signal.
(2) Carrier data bandwidth than the modulation bandwidth is much wilder.
(3) Receiving process is generated by local broadband carrier signal and receiving a copy of the signal to the broadband signal to achieve.
The main way of spread spectrum are as follows: Direct Sequence Spread Spectrum(DSSS) using high-speed pseudo-random code on to the low-speed data transmission spread spectrum modulation; Frequency-hopping system using pseudo-random code to control the carrier frequency in a wider band of the change; TH is the data transmission time slot is a pseudo-random; chirp frequency system is a linear extension of the process of change. Combination of a number of ways of hybrid systems are often applied.
The most important measure pf spread-spectrum system is an indicator of spreading gain, also known as processing gain. It is precisely because of the spread spectrum system itself with its performance characteristics with a series of advantages.
1.4 Code division multiple access
Code division multiple access (CDMA) is a channel access method used by various radio communication technologies. It should not be confused with the mobile phone standards called cdmaOne, CDMA2000(the 3G evolution of cdmaOne) and WCDMA (the 3Gstandard used by GSM carrier), which are often referred to as simply CDMA, and use CDMA as an underlying channel access method.
One of the concepts in data communication is the idea of allowing several transmitters to send information simultaneously over a signal communication channel. This allows several users to share a band of frequencies (see bandwidth). This concept is called multiple access. CDMA employs spread-spectrum technology and a special coding scheme( where each transmitter is assigned a code) to allow multiple user to be multiplexed over the same physical channel. By contrast, time division multiple
access (FDMA) divides it by frequency. CDMA is a form of spread-spectrum signaling, since the modulated coded signal has a much higher data bandwidth than the data being communicated.
1.5 Spread-spectrum characteristic of CDMA
Most modulation schemes try to minimize the bandwidth of this signal since bandwidth is a limited resource. However, spread spectrum use a transmission bandwidth that is several orders of magnitude greater than the minimum required signal bandwidth. One of the initial reasons for doing this was military applications including guidance and communication systems. These system were designed using spread spectrum because if its security and resistance to jamming. Asynchronous CDMA has some level of privacy built in because the signal is spread using a pseudo-random code; this code makes the spread spectrum signals appear random or have noise-like properties. A receiver cannot demodulate this transmission without knowledge of the pseudo-random sequence used to encode the data. CDMA also resistant to jamming. A jamming signal only has a finite amount of power available to jam the signal. The jammer can either spread its energy over the entire bandwidth of the signal or jam only part of the entire signal.
CDMA can also effectively reject narrow band interference. Since narrow band interference affects only a small portion of the spread spectrum signal, it can easily be removed through notch filtering without much loss of information. Convolution encoding and interleaving can be used to assist in recovering this lost data. CDMA signal are also resistant to multipath fading. Since the spread spectrum signal occupies a large bandwidth only a small portion of this will undergo fading due to multipath at any give time. Like the narrow band interference this will result in only a small loss of data and can be overcome.
Another reason CDMA is resistant to multipath interference is because the delayed versions of the transmitted pseudo-random code, and will thus appear as another user, which is ignored at the receiver. In other words, as long as the multipath channel induces at least one chip of delay, 天the multipath channel induces at least one chip of delay,the multipath signals will arrive at the receiver.in other words, as long as the multipath channel induces at least one chip of delay, the multipath signals
will arrive at the receiver such that they are shifted in time by at least one chip from the intended signal. The correlation properties of the pseudo-random codes are such that this slight delay causes the multipath to appear uncorrelated with the intended signal, and it is thus ignored.
Some CDMA devices use a rake receiver, which exploits multipath delay components to improve the performance of the system. A rake receiver combines the information from several correlators, each one tuned to a different path delay, producing a stronger version of the signal than a simple receiver with a signal correlation tuned to the path delay of the strongest signal.
Frequency reuse is the ability to reuse the same radio channel frequency at other cell sites within a cellular system. In the FDMA and TDMA systems frequency planning is and important consideration. The frequencies used in different cells must be planned carefully to ensure signals from different cells do not interfere with each other. In a CDMA system, the same frequency can be used in every cell, because channelization is done using the pseudo-random codes. Reusing the same frequency in every cell eliminates the need for frequency planning in a CDMA system; however, planning of the different pseudo-random sequences must be done to ensure that the received signal from one cell does not correlate with the signal from a nearby cell.
Since adjacent cell use the same frequencies, CDMA systems have the ability to perform soft handoffs. Soft handoffs allow the mobile telephone to communication simultaneously with two or more cells. The best signal quality in selected until the handoff is complete. This is different from hard handoffs utilized in other cellular systems. In a hard handoff situation, as the mobile telephone approaches a handoff, signal strength may vary abruptly. In contrast, CDMA systems use the soft handoff, which is undetectable and provides a more reliable and higher quality signal.
Concluding remarks
spread-spectrum technology in the initial stages of development, it has become a theory and a major technological breakthrough. Later in the development process is the improvement and hardware performance improved. Development to the
present,spread-spectrum technology and the theory has been almost perfect,mainly from the point of view of overall performance, and the other new technology applications. Therefore, the application has been driven by the development of spread-spectrum technology is a power driving force, the future wireless communication systems, such as mobile communication. Wireless LAN, global personal communications, spread-spectrum technology will certainly play an important role.
译文正文
1.扩频通信系统概述
扩频通信，即扩展频谱通信（Spread spectrum communication)，它与光纤通信、卫星通信，一同誉为进入信息时代的三大高技术通信传输方式，扩频通信是将待传送的信息数据被伪随机码调制，实现频谱扩展后再传输；接收端则采用相同的编码进行解调及相关处理，恢复原始信息数据。扩频通信系统具有3个主要特征：
（1）载波是不可预测的，或者称为伪随机的宽带信号
（2）载波的带宽比调制数据的带宽要宽得多
（3）接收过程是通过本地将本地产生的宽带载波信号的复制信号与接收到的宽带信号相关来实现的。
扩展频谱的方式主要有一下几种：直接序列扩频（DSSS）使用高速伪随机码对要传输的低速率数据进行扩频调制；跳频系统则采用伪随机码控制载波频率在一个更宽的频带内变化；跳时则是数据传输时隙是伪随机的；线性调频系统中的频率扩展则是一个线性变化的过程。几种方式组合的混合系统也经常得到应用。
衡量扩频系统最重要的一个指标是扩频增益，又称为处理增益。正是因为扩频系统本身具有的特征使其性能具有一系列的优势。
1.2扩频通信技术的基本概念
扩频通信的基本特点：其传输信息所用信号的带宽（W）远大于信息本身实际所需的最小（有效）带宽（F
?），其比值称为处理增益
=/
G P?
W
F
G值一般都在众所周知，在普通的调幅、调频或者脉冲编码调制通信中，P
十多倍范围内，称为“窄带通信”，而扩频通信的P
G值高达几百甚至几千倍，可以称为“宽带通信”。
由于扩频后的信号，它的发射功率很低，传输时大多数淹没在空间的噪声中，因此很难被其他接收机截获，只有具有相同的扩频码（或称PN码）的接收机，
才能获得处理增益，解扩并恢复出原发的信号。
1.3扩频技术的优越性
抗干扰能力强，误码率低，如上所述，扩频通信系统由于在发送端扩展信号频谱，在接收端解扩还原信号，产生扩频增益，从而大大提高了抗干扰容限。根据扩频增益的不同，甚至在负的信噪比条件下，也可以将信号从噪声的淹没中提取出来，在目前商用的通信系统中，扩频通信是唯一能够工作于负信噪比条件下的通信方式。
抗多径干扰能力强，增加了系统的可靠性。由于扩频系统中采用的PN码具有很好的自相关性，互相关性很弱，不同路径传来的信号很容易被分开，并可在时间相位上重新对齐，形成几路信号功率的叠加，从而改善了接收系统的性能增加了系统的可靠性，易于同频使用，提高了无线频谱利用率。无线频谱十分宝贵，虽然从长波、微波都已得到开发利用，仍然满足不了社会的需求。为此，世界各地都设立了频谱管理机构，用户只能使用申请获得的频率，依靠频率划分来防止信道之间的干扰。
由于扩频通信又采取了相关接收这一技术，信号发送功率极低（＜1W，一般为1~100mW），且可工作在信道噪声和热噪声背景中，易于在同一地区重复使用同一频率，也可以在现今各种窄带通信共享同一频率资源。
扩频通信是数字通信，特别适合数字语音和数据同时传输，扩频通信自身具有加密功能，只能在PN码相同的用户之间进行通信，隐蔽性好，保密性强，便于开展各种通信业务。扩频通信容易采用码分多址、语音压缩等多项新技术，更加适用于计算机网络以及数字化的语音、图像信息传输。
扩频通信绝大多数是数字电路，设备高度集成，安装便捷，易于维护，也十分小巧可靠，平均无故障时间也很长。
1.4码分多址
码分多址（CDMA）是一种用于各种无线通信技术的信道接入方法。它不应该与被用在移动电话标准的要求的cdmaOne，CDMA2000（cdmaOne的的3G演进）和WCDMA相混淆（用于GSM的载波3G标准），它往往被简称为CDMA，并且作为一个潜在的信道接入方法。
在数据通信中有一种想法是允许多个发射机同时发送的信息通过信号通信信道。这允许多个用户共享一个频带（见带宽）。这个概念被称为多址接入。CDMA 采用扩频技术和特殊编码方案（其中每个发射机分配一个码），以允许多个用户被复用在同一物理信道。相比之下，频分多址（FDMA）由频率划分。CDMA 是扩展频谱信号的一种形式，由于调制的编码信号具有比被传送的数据更高的数据带宽。
1.5扩频CDMA的特点
大多数调制方案都尽量减少信号的带宽，因为带宽是有限的资源。然而，扩频技术用比所需的最小信号带宽大几个数量级的传输带宽。这样做的最初原因之一是军事上的应用，包括指导和通信系统。这些系统的设计使用，因为其安全性和抗干扰扩频。异步CDMA有一些内置的隐私级别，因为信号传播使用伪随机码，这个代码使扩频信号出现随机或有噪声性能。不能接收解调不用于编码数据的伪随机序列的信号传输。CDMA还耐干扰。一个干扰信号只有有限的能量去干扰信号。干扰信号可以传播其能量在信号的整个带宽或者信号的整个带宽的一部分。
CDMA还可以有效抑制窄带干扰。由于窄带干扰只影响扩频信号的一小部分，它可以很容易地通过陷波滤波，没有多少信息损失就可以将它除去。卷积编码和交织可以用来协助回收这丢失的数据。CDMA信号也耐多径衰落。由于扩展频谱信号占有相当大的带宽，只一小部分信号将经受衰落由于多路径。像窄带干扰，这将导致只有一小数据丢失，并且可以被克服。
CDMA抗多径干扰的另一个原因是由于所发射的伪随机码的延迟，并且将显示为另一个用户，这样在接收机就会被忽略。换句话说，只要在多径信道产生的至少一个芯片的延迟，多径信号将到达接收机。换句话说，只要在多径信道引起至少一个芯片的延迟，多径信号将到达接收机，这样，它们比预定信号中在时间上移位一个芯片延迟。
伪随机码的相关特性是这样的，这稍微的延迟会导致多路径出现与预期不相关的信号，因此，它会被忽略。
一些CDMA设备使用RAKE接收器，它利用多径时延组件来提高系统的性能。RAKE接收器整合多个相关器的信息，每一个调谐到不同的路径延迟，产生
一个比相关的简单调整，以最强的信号路径延迟接收的信号更强的信号版本。
频率复用是在蜂窝系统内的其他小区站点重复使用相同的无线电频率的能力。在FDMA和TDMA系统中频率规划是重要的考虑因素。在不同小区中使用的频率必须仔细规划，以确保来自不同小区的信号不会相互干扰。在CDMA系统中，在相同的频率可以在每个小区中使用的，因为所使用的伪随机码会进行信道化。在每一个小区内可以重复使用相同的频率，所以在CDMA系统中不需要频率规划;然而，必须得对不同的伪随机序列进行规划，以确保从一个小区接收到的信号不与来自相邻小区的信号相关。
由于相邻小区使用相同的频率，CDMA系统必须有进行软切换的能力。软切换允许移动电话同时与两个或更多个用户通信。选择最佳的信号品质，直到软切换完成。这与其他蜂窝系统的硬切换不同。在硬切换的情况下，当移动电话进行切换，信号强度可能会突然发生变化。相比之下，CDMA系统中使用的软切换，这是不可检测的，并提供了更可靠和更高质量的信号。
结束语
扩频通信在发展的初始阶段，就已经实现了理论与技术上的重大突破，在此之后的发展过程中主要是硬件的改善和性能的提高。发展到现在，扩频技术和理论已经趋于完善，主要应从系统的角度考虑总体性能，且与其他新技术结合使用。因此，应用的驱动一直都是扩频技术发展的强大动力，未来的无线通信系统，如移动通信、无线局域网、全球个人通信等，扩频技术将发挥重要作用。
文献出处: Waitz M. The small and medium-sized enterprise financing under P2P finance [J]. Journal of Business Research, 2016, 8(6): 81-91. 原文 The small and medium-sized enterprise financing under P2P finance Waitz M Abstract Small and medium-sized enterprise financing difficult is worldwide difficult problem. Article introduces the concept of the Internet financial, mainly summarized the P2P financial in the development of financial innovation and integration of science and technology, a combination of academic research on P2P financial now of the five directions of various views and opinions. Points out the current P2P financial problems in the development of risk control, and analyses the trend of the Internet financial. Keywords: P2P financial; Financial innovation; Risk control 1 Introduction Look from the history of enterprise development, a large enterprise originate from small and medium-sized enterprises. Small and medium-sized enterprises (smes) is the most dynamic part of the national economy, often walk in the forefront of technology development, in the high-tech industry, clean energy, green economy, etc, have good performance, play an important role in the economic transformation. Small and medium-sized enterprise financing difficult is worldwide difficult problem. These small and medium-sized enterprise financing environment and narrow channels, more than 60% are unable to get a bank loan. At present, science and technology enterprises and the characteristics of light assets, financing difficulties, become a huge bottleneck of sustainable development. 2 The concept of the Internet financial In the past two years, the Internet financial show explosive growth, since 2014, the Internet financial sector performance strength. Current economic field exists the phenomenon of two special contradiction, one is the small and medium-sized
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Optimum blank design of an automobile sub-frame Jong-Yop Kim a ,Naksoo Kim a,*,Man-Sung Huh b a Department of Mechanical Engineering,Sogang University,Shinsu-dong 1,Mapo-ku,Seoul 121-742,South Korea b Hwa-shin Corporation,Young-chun,Kyung-buk,770-140,South Korea Received 17July 1998 Abstract A roll-back method is proposed to predict the optimum initial blank shape in the sheet metal forming process.The method takes the difference between the ?nal deformed shape and the target contour shape into account.Based on the method,a computer program composed of a blank design module,an FE-analysis program and a mesh generation module is developed.The roll-back method is applied to the drawing of a square cup with the ˉange of uniform size around its periphery,to con?rm its validity.Good agreement is recognized between the numerical results and the published results for initial blank shape and thickness strain distribution.The optimum blank shapes for two parts of an automobile sub-frame are designed.Both the thickness distribution and the level of punch load are improved with the designed blank.Also,the method is applied to design the weld line in a tailor-welded blank.It is concluded that the roll-back method is an effective and convenient method for an optimum blank shape design.#2000Elsevier Science S.A.All rights reserved. Keywords:Blank design;Sheet metal forming;Finite element method;Roll-back method
译文 银行业是必要的而银行不是，互联网时代的金融中介机构的未来 摘要 本文探讨了互联网时代下金融机构和银行作为特殊的金融机构的未来可能是怎样的问题。由于互联网而导致的交易费用的减少会降低进入金融产品市场的壁垒，因为有可能不再需要运行成本密集型的分支的大型系统。但是，对金融机构的职能研究表明，不是每个人都可以销售和经销金融产品。这是真的，因为金融业务中的信息不对称问题需要一个拥有良好信誉的中介，也因为需要限制大型资本基金转换资产的风险。这两个要求变现了进入金融中介市场的重要壁垒。并不是每一个金融产品会因为互联网的崛起而将面临更多的竞争，只有那些标准化和低风险的产品。此外，那些拥有可观资本和良好声誉的大公司可能被视为银行的新竞争者。 关键字：银行业，银行，金融机构，互联网 1、引言 “银行业是19世纪的钢铁行业。”当谈到关于新的信息技术对银行的影响的谈论时，这句话经常被提起。更一般来说，可能有人会问，新信息技术是如何成功的，特别是互联网的，可能会改变商业和金融机构的市场情况。在互联网的帮助下，人们可以执行所有银行的业务，而不需要银行。这意味着传统银行分支机构的中介。此外，互联网已经使客户直接从网上购买股票而不需要访问当地的分支银行。从更广泛的意义上来说，在互联网的帮助下，金融市场的供给和需求可能通过互联网满足，而不需要金融中介机构。互联网的崛起是否真的是金融中介机构的威胁？在急剧减少的交易成本情况下，商业和竞争将如何变化？本文考察了互联网的成功对金融机构和银行的影响。 2、金融机构的发展 几个世纪以来，许多金融交易需要个人的存在。随着现代信息技术的发展，这些都被改变了。如今，客户可以在不进入当地分支银行的情况下进行任何金融交易。转移支付和支付账单可以通过网络进行，个人金融交易以及关于金融问题的信息咨询业可以通过网络进行。此外，互联网创新类似智能卡或者其他电子支付系统消除了为了得到一些现金而访问分支银行的需要。 但是互联网也会改变咨询活动：在许多情况下，它甚至可能减少个人存在的
外文翻译 原文 Foreign T rade o f China Material Source:W anfang Database Author:Hitomi Iizaka 1.Introduction On December11,2001,China officially joined the World T rade Organization(WTO)and be c a me its143rd member.China’s presence in the worl d economy will continue to grow and deepen.The foreign trade sector plays an important andmultifaceted role in China’s economic development.At the same time, China’s expanded role in the world economy is beneficial t o all its trading partners. Regions that trade with China benefit from cheaper and mor e varieties of imported consumer goods,raw materials and intermediate products.China is also a large and growing export market.While the entry of any major trading nation in the global trading system can create a process of adjustment,the o u t c o me is fundamentally a win-win situation.In this p aper we would like t o provide a survey of the various institutions,laws and characteristics of China’s trade.Among some of the findings, we can highlight thefollowing: ?In2001,total trade to gross domestic pr oduct(GDP)ratio in China is44% ?In2001,47%of Chinese trade is processed trade1 ?In2001,51%of Chinese trade is conduct ed by foreign firms in China2 ?In2001,36%of Chinese exports originate from Gu an gdon g province ?In2001,39%of China’s exports go through Hong Kong to be re-exported elsewhere 2.Evolution of China’s Trade Regime Equally remarkable are the changes in the commodity composition of China’s exports and imports.Table2a shows China’s annu al export volumes of primary goods and manufactured goods over time.In1980,primary goods accounted for 50.3%of China’s exports and manufactured goods accounted for49.7%.Although the share of primary good declines slightly during the first half of1980’s,it remains at50.6%in1985.Since then,exports of manufactured goods have grown at a much
本份文档包含：关于该选题的外文文献、文献综述 一、外文文献 标题: Online brokers lead the way for French internet finance 作者: Caffard, Christophe 期刊名称: International Financial Law Review 卷: 20；期: 3；页: 20-24 Online brokers lead the way for French internet finance 1 Regulated brokers Regulated brokers are legal entities which have an investment services licence and are subject to the prudential regulations of the Comite de Reglementation Bancaire et Financiere (CRBF) and the Conseil des Marches Financiers (CMF). * Choice of legal form: regulated brokers are not required to be incorporated in a specific legal form; however, under article 13 of the MAF Law, the CECEI checks whether the legal form of the brokerage company is appropriate for providing investment services. In practice, any type of commercial company is admitted: societes de capitaux (limited companies) or societes de personnes (partnerships). The formalities of share transfer, tax and the scope of liability of a company's management will be relevant factors to the choice of legal form. * Application for an investment services licence from the CECEI: the most important part of the application is the description of the investment services, and a business plan including prospective financial statements for the following three years. The CMF will check whether the business plan is consistent with the investment services licence requested by the broker. The CECEI will ensure that the applicant's own initial funds are consistent with the business plan. The scope of the investment services licence is variable and covers one or more ofthe following investment services: Reception and transmission of orders to another investment services provider on behalf of investors, for execution. This is the core investment service provided by the
扩频通信的特点和优势 The Standardization Office was revised on the afternoon of December 13, 2020
扩频通信的特点和优势 扩频通信是一种信息传输方式，其信号所占有的频带宽度远大于所传信息必需的最小带宽，具有较强的抗干扰能力和较好的保密性能，20 世纪 70年代以来扩频通信的理论和应用方法得到了很大的发展，近年来随着移动通信技术发展，扩频通信已经成为第三代移动的核心技术之一。 扩频通信具有以下几个特点 ? 1、抗干扰能力强 扩频信号的不可预测性，使扩频通信系统具有很强的抗干扰能力。扩频通信系统在传输过程中扩展了信号带宽，所以使信噪比很低，甚至在有用信号功率低于干扰信号功率的情况下，仍然能不受外界干扰。信号的频谱被扩展的越宽，处理增益越高，抗干扰能力就越强。此外，对于单频及多载波信号的干扰，其他伪随机调制信号的干扰，以及脉冲正弦信号的的干扰等，扩频系统都有抑制干扰提高信噪比的作用。简单的说，若将频带展宽 10 倍，在总功率不变的情况下，其干扰强度只是原来的 1/10。而一般频谱带宽至少是信 息带宽的几十倍甚至更高。另外，由于接受端采用了伪随机序列进行相关检测，即使采用同类型信号进行干扰，如果不能检测出有用信号的伪随机序列，干扰也起不了太大作用。 抗干扰性能强是扩频通信最突出的优点。 2、隐蔽性好、低截获性 由于扩频信号的频谱被展宽到很宽的频带上，单位带宽的功率也随之降低，信号功率密度很低，信号被淹没在噪声中、难以被发现，因而不易被敌方截获；加之扩频编码，就更难获取有用信号，而且扩频信号的功率密度极低，对周围的电信设备产生干扰的可能性极小。 3、保密性好 在一定的发射功率下，扩频信号分布在很宽的频带内，无线信道中有用信号功率谱密度很低，有用信号被淹没在噪声下，而且不同的通信在发射时采用不同的扩频序列，只有接受方知道扩频序列的具体内容，其他不知道地接受方几乎不可能破译，因此扩频技术能很好的保证通信的可靠性。 4、抗多路径干扰性能好 多路径干扰是电波传输过程中因遇到各种非期望反射体（如电离层、高山、建筑物等）引起的反射或散射，在接受端的这些反射或散射信号与直接路径信号相互干扰。多路径干扰会严重影响通信。扩频通信系统中增加了扩频调制和解扩过程，从多径信号中分离出最强的有用信号，或者将多径信号中的相同码序列信号叠加，这样就可以有效消除无线通信中因多径干扰造成的信号衰落现象，是扩频通信系统具有良好的抗多径衰落特性。
翻译文献：INVESTIGATION ON DYNAMIC PERFORMANCE OF SLIDE UNIT IN MODULAR MACHINE TOOL （对组合机床滑台动态性能的调查报告） 文献作者：Peter Dransfield, 出处：Peter Dransfield, Hydraulic Control System-Design and Analysis of TheirDynamics, Springer-Verlag, 1981 翻译页数：p139—144 英文译文： 对组合机床滑台动态性能的调查报告 【摘要】这一张纸处理调查利用有束缚力的曲线图和状态空间分析法对组合机床滑台的滑动影响和运动平稳性问题进行分析与研究，从而建立了滑台的液压驱动系统一自调背压调速系统的动态数学模型。通过计算机数字仿真系统，分析了滑台产生滑动影响和运动不平稳的原因及主要影响因素。从那些中可以得出那样的结论，如果能合理地设计液压缸和自调背压调压阀的结构尺寸. 本文中所使用的符号如下： s1-流源，即调速阀出口流量； S el—滑台滑动摩擦力 R一滑台等效粘性摩擦系数： I1—滑台与油缸的质量 12—自调背压阀阀心质量 C1、c2—油缸无杆腔及有杆腔的液容； C2—自调背压阀弹簧柔度； R1, R2自调背压阀阻尼孔液阻， R9—自调背压阀阀口液阻 S e2—自调背压阀弹簧的初始预紧力； I4, I5—管路的等效液感 C5、C6—管路的等效液容： R5, R7-管路的等效液阻； V3, V4—油缸无杆腔及有杆腔内容积； P3, P4—油缸无杆腔及有杆腔的压力 F—滑台承受负载， V—滑台运动速度。本文采用功率键合图和状态空间分折法建立系统的运动数学模型，滑台的动态特性可以能得到显著改善。
提高塔式复合人工湿地处理农村生活污水的 脱氮效率1 摘要： 努力保护水源，尤其是在乡镇地区的饮用水源，是中国污水处理当前面临的主要问题。氮元素在水体富营养化和对水生物的潜在毒害方面的重要作用，目前废水脱氮已成为首要关注的焦点。人工湿地作为一种小型的，处理费用较低的方法被用于处理乡镇生活污水。比起活性炭在脱氮方面显示出的广阔前景，人工湿地系统由于溶解氧的缺乏而在脱氮方面存在一定的制约。为了提高脱氮效率，一种新型三阶段塔式混合湿地结构----人工湿地（thcw）应运而生。它的第一部分和第三部分是水平流矩形湿地结构，第二部分分三层，呈圆形，呈紊流状态。塔式结构中水流由顶层进入第二层及底层，形成瀑布溢流，因此水中溶解氧浓度增加，从而提高了硝化反应效率，反硝化效率也由于有另外的有机物的加入而得到了改善，增加反硝化速率的另一个原因是直接通过旁路进入第二部分的废水中带入的足量有机物。常绿植物池柏（Taxodium ascendens），经济作物蔺草（Schoenoplectus trigueter），野茭白（Zizania aquatica），有装饰性的多花植物睡莲（Nymphaea tetragona），香蒲（Typha angustifolia）被种植在湿地中。该系统对总悬浮物、化学需氧量、氨氮、总氮和总磷的去除率分别为89%、85%、83%、83% 和64%。高水力负荷和低水力负荷（16 cm/d 和32 cm/d）对于塔式复合人工湿地结构的性能没有显著的影响。通过硝化活性和硝化速率的测定，发现硝化和反硝化是湿地脱氮的主要机理。塔式复合人工湿地结构同样具有观赏的价值。 关键词： 人工湿地；硝化作用；反硝化作用；生活污水；脱氮；硝化细菌；反硝化细菌 １. 前言 对于提高水源水质的广泛需求，尤其是提高饮用水水源水质的需求是目前废水深度处理的技术发展指向。在中国的乡镇地区，生活污水是直接排入湖泊、河流、土壤、海洋等水源中。这些缺乏处理的污水排放对于很多水库、湖泊不能达到水质标准是有责任的。许多位于中国的乡镇地区的社区缺乏足够的生活污水处理设备。由于山区地形、人口分散、经济基础差等原因，废水的收集和处理是很成问题的。由于资源短缺，经济欠发达地区所采取的废水处理技术必须低价高效，并且要便于施用，能量输入及维护费用较低，而且要保证出水能达标。建造在城市中基于活性污泥床的废水集中处理厂，对于小乡镇缺乏经济适用性，主要是由于污水收集结构的建造费用高。 1Ecological Engineering，Fen xia ，Ying Li。
互联网金融对传统金融业的影响外文文献翻译(文档含中英文对照即英文原文和中文翻译) 译文： 互联网金融对传统金融业的影响 摘要 网络的发展，深刻地改变甚至颠覆了许多传统行业，金融业也不例外。近年来，金融业成为继商业分销、传媒之后受互联网影响最为深远的领域，许多基于互联网的金融服务模式应运而生，并对传统金融业产生了深刻的影响和巨大的冲击。“互联网金融”成为社会各界关注的焦点。 互联网金融低成本、高效率、关注用户体验，这些特点使其能够充分满足传统金融“长尾市场”的特殊需求，灵活提供更为便捷、高
效的金融服务和多样化的金融产品，大大拓展了金融服务的广度和深度，缩短了人们在时空上的距离，建立了一种全新的金融生态环境；可以有效整合、利用零散的时间、信息、资金等碎片资源，积少成多，形成规模效益，成为各类金融服务机构新的利润增长点。此外，随着互联网金融的不断渗透和融合，将给传统金融行业带来新的挑战和机遇。互联网金融可以促进传统银行业的转型，弥补传统银行在资金处理效率、信息整合等方面的不足；为证券、保险、基金、理财产品的销售与推广提供新渠道。对于很多中小企业来说，互联网金融拓展了它们的融资渠道，大大降低了融资门槛，提高了资金的使用效率。但是，互联网金融的跨行业性决定了它的风险因素更为复杂、敏感、多变，因此要处理好创新发展与市场监管、行业自律的关系。 关键词：互联网金融；商业银行；影响；监管 1 引言 互联网技术的不断发展，云计算、大数据、社交网络等越来越多的互联网应用为传统行业的业务发展提供了有力支持，互联网对传统行业的渗透程度不断加深。20世纪末，微软总裁比尔盖茨就曾断言，“传统商业银行会成为新世纪的恐龙”。如今，随着互联网电子信息技术的发展，我们真切地感受到了这种趋势，移动支付、电子银行早已在我们的日常生活中占据了重要地位。 由于互联网金融的概念几乎完全来自于商业实践，因此目前的研究多集中在探讨互联网金融的具体模式上，而对传统金融行业的影响力分析和应对措施则缺乏系统性研究。互联网与金融行业一向是风险
扩频通信系统的分类 扩频通信系统的关键问题是在发信机部分如何产生宽带的扩频信号，在收信机部分如何解调扩频信号。根据通信系统产生扩频信号的方式，可以分为下列几种。 1 直接序列扩展频谱系统 直接序列扩展频谱系统（Direct Sequece Spread Spectrum Communication Systems，DS-SS），通常简称为直接序列系统或直扩系统，是用待传输的信息信号与高速率的伪随机码波形相乘后，去直接控制射频信号的某个参量，来扩展传输信号的带宽。用于频谱扩展的伪随机序列称为扩频码序列。直接序列扩展频谱通信系统的简化方框图参见图1-5。 在直接序列扩频通信系统中，通常对载波进行相移键控（Phase Shift Keying，PSK）调制。为了节约发射功率和提高发射机的工作效率，扩频通信系统常采用平衡调制器。抑制载波的平衡调制对提高扩频信号的抗侦破能力也有利。 在发信机端，待传输的数据信号与伪随机码(扩频码)波形相乘(或与伪随机码序列模2加)，形成的复合码对载波进行调制，然后由天线发射出去。在收信机端，要产生一个和发信机中的伪随机码同步的本地参考伪随机码，对接收信号进行相关处理，这一相关处理过程通常常称为解扩。解扩后的信号送到解调器解调，恢复出传送的信息。 (a) 图1-5 直接序列扩频通信系统简化图 (a) 发射系统；(b) 接收系统 2 跳频扩频通信系统 跳频扩频通信系统是频率跳变扩展频谱通信系统（Frequecy Hopping Spread Spectrum Communication Systems，FH-SS）的简称，或更简单地称为跳频通信系统，确切地说应叫做“多频、选码和频移键控通信系统”。它是用二进制伪随机码序列去离散地控制射频载波振荡器的输出频率，使发射信号的频率随伪随机码的变化而跳变。跳频系统可供随机选取的频率数通常是几千到20 2个离散频率，在如此多的离散频率中，每次输出哪一个是由伪随机码决定的。频率跳变扩展频谱通信系统的简化方框图参见图1-6。
204/JOURNAL OF BRIDGE ENGINEERING/AUGUST1999
JOURNAL OF BRIDGE ENGINEERING /AUGUST 1999/205 ends.The stress state in each cylindrical strip was determined from the total potential energy of a nonlinear arch model using the Rayleigh-Ritz method. It was emphasized that the membrane stresses in the com-pression region of the curved models were less than those predicted by linear theory and that there was an accompanying increase in ?ange resultant force.The maximum web bending stress was shown to occur at 0.20h from the compression ?ange for the simple support stiffness condition and 0.24h for the ?xed condition,where h is the height of the analytical panel.It was noted that 0.20h would be the optimum position for longitudinal stiffeners in curved girders,which is the same as for straight girders based on stability requirements.From the ?xed condition cases it was determined that there was no signi?cant change in the membrane stresses (from free to ?xed)but that there was a signi?cant effect on the web bend-ing stresses.Numerical results were generated for the reduc-tion in effective moment required to produce initial yield in the ?anges based on curvature and web slenderness for a panel aspect ratio of 1.0and a web-to-?ange area ratio of 2.0.From the results,a maximum reduction of about 13%was noted for a /R =0.167and about 8%for a /R =0.10(h /t w =150),both of which would correspond to extreme curvature,where a is the length of the analytical panel (modeling the distance be-tween transverse stiffeners)and R is the radius of curvature.To apply the parametric results to developing design criteria for practical curved girders,the de?ections and web bending stresses that would occur for girders with a curvature corre-sponding to the initial imperfection out-of-?atness limit of D /120was used.It was noted that,for a panel with an aspect ratio of 1.0,this would correspond to a curvature of a /R =0.067.The values of moment reduction using this approach were compared with those presented by Basler (Basler and Thurlimann 1961;Vincent 1969).Numerical results based on this limit were generated,and the following web-slenderness requirement was derived: 2 D 36,500a a =1?8.6?34 (1) ? ??? t R R F w ?y where D =unsupported distance between ?anges;and F y =yield stress in psi. An extension of this work was published a year later,when Culver et al.(1973)checked the accuracy of the isolated elas-tically supported cylindrical strips by treating the panel as a unit two-way shell rather than as individual strips.The ?ange/web boundaries were modeled as ?xed,and the boundaries at the transverse stiffeners were modeled as ?xed and simple.Longitudinal stiffeners were modeled with moments of inertias as multiples of the AASHO (Standard 1969)values for straight https://www.doczj.com/doc/917953484.html,ing analytical results obtained for the slenderness required to limit the plate bending stresses in the curved panel to those of a ?at panel with the maximum allowed out-of-?atness (a /R =0.067)and with D /t w =330,the following equa-tion was developed for curved plate girder web slenderness with one longitudinal stiffener: D 46,000a a =1?2.9 ?2.2 (2) ? ? ? t R f R w ?b where the calculated bending stress,f b ,is in psi.It was further concluded that if longitudinal stiffeners are located in both the tension and compression regions,the reduction in D /t w will not be required.For the case of two stiffeners,web bending in both regions is reduced and the web slenderness could be de-signed as a straight girder panel.Eq.(1)is currently used in the ‘‘Load Factor Design’’portion of the Guide Speci?cations ,and (2)is used in the ‘‘Allowable Stress Design’’portion for girders stiffened with one longitudinal stiffener.This work was continued by Mariani et al.(1973),where the optimum trans-verse stiffener rigidity was determined analytically. During almost the same time,Abdel-Sayed (1973)studied the prebuckling and elastic buckling behavior of curved web panels and proposed approximate conservative equations for estimating the critical load under pure normal loading (stress),pure shear,and combined normal and shear loading.The linear theory of shells was used.The panel was simply supported along all four edges with no torsional rigidity of the ?anges provided.The transverse stiffeners were therefore assumed to be rigid in their directions (no strains could be developed along the edges of the panels).The Galerkin method was used to solve the governing differential equations,and minimum eigenvalues of the critical load were calculated and presented for a wide range of loading conditions (bedding,shear,and combined),aspect ratios,and curvatures.For all cases,it was demonstrated that the critical load is higher for curved panels over the comparable ?at panel and increases with an increase in curvature. In 1980,Daniels et al.summarized the Lehigh University ?ve-year experimental research program on the fatigue behav-ior of horizontally curved bridges and concluded that the slen-derness limits suggested by Culver were too severe.Equations for ‘‘Load Factor Design’’and for ‘‘Allowable Stress Design’’were developed (respectively)as D 36,500a =1?4?192(3)? ?t R F w ?y D 23,000a =1?4 ?170 (4) ? ? t R f w ?b The latter equation is currently used in the ‘‘Allowable Stress Design’’portion of the Guide Speci?cations for girders not stiffened longitudinally. Numerous analytical and experimental works on the subject have also been published by Japanese researchers since the end of the CURT project.Mikami and colleagues presented work in Japanese journals (Mikami et al.1980;Mikami and Furunishi 1981)and later in the ASCE Journal of Engineering Mechanics (Mikami and Furunishi 1984)on the nonlinear be-havior of cylindrical web panels under bending and combined bending and shear.They analyzed the cylindrical panels based on Washizu’s (1975)nonlinear theory of shells.The governing nonlinear differential equations were solved numerically by the ?nite-difference method.Simple support boundary condi-tions were assumed along the curved boundaries (top and bot-tom at the ?ange locations)and both simple and ?xed support conditions were used at the straight (vertical)boundaries.The large displacement behavior was demonstrated by Mi-kami and Furunishi for a range of geometric properties.Nu-merical values of the load,de?ection,membrane stress,bend-ing stress,and torsional stress were obtained,but no equations for design use were presented.Signi?cant conclusions include that:(1)the compressive membrane stress in the circumfer-ential direction decreases with an increase in curvature;(2)the panel under combined bending and shear exhibits a lower level of the circumferential membrane stress as compared with the panel under pure bending,and as a result,the bending moment carried by the web panel is reduced;and (3)the plate bending stress under combined bending and shear is larger than that under pure bending.No formulations or recommendations for direct design use were made. Kuranishi and Hiwatashi (1981,1983)used the ?nite-ele-ment method to demonstrate the elastic ?nite displacement be-havior of curved I-girder webs under bending using models with and without ?ange rigidities.Rotation was not allowed (?xed condition)about the vertical axis at the ends of the panel (transverse stiffener locations).Again,the nonlinear distribu-