【文章內(nèi)容簡介】 cted)from the ionosphere, which consists of several layers of charged particles ranging in altitude from 50 to 400 km above the surface of the the daytime hours, the heating of the lower atmosphere by the sun causes the formation of the lower layers at altitudes below 120 lower layers, especially the Dlayer, serve to absorb frequencies below 2 MHz, thus severely limiting skywave propagation of AM radio , during the nighttime hours, the electron density in the lower layers of the ionosphere drops sharply and the frequency absorption that occurs during the daytime is significantly a consequence, powerful AM radio broadcast stations can propagate over large distances via sky wave over the Flayer of the ionosphere, which ranges from 140 to 400 km above the surface of the frequently occurring problem with electromagnetic wave propagation via sky wave in the HF frequency range is signal multipath occurs when the transmitted signal arrives at the receiver via multiple propagation paths at different delays, tt generally results in intersymbol interference in a digital munication , the signal ponents arriving via different propagation paths may add destructively, resulting in a phenomenon called signal fading, which most people have experienced when listening to a distant radio station at night when sky wave is the dominant propagation noise at HF is a bination of atmospheric noise and thermal ionospheric propagation ceases to exist at frequencies above approximately 30 MHz, which is the end of the HF , it is possible to have ionospheric scatter propagation at frequencies in the range 3060 MHz, resulting from signal scattering from the lower is also possible to municate over distances of several hundred miles 黃河科技學(xué)院畢業(yè)論文（文獻(xiàn)翻譯）by use of tropospheric scattering at frequencies in the range 40300 results from signal scattering due to particles in the atmosphere at altitudes of 10 miles or , ionospheric scatter and tropospheric scatter involve large signal propagation losses and require a large amount of transmitter power and relatively large above 30 MHz propagate through the ionosphere with relatively little loss and make satellite and extraterrestrial munications , at frequencies in the VHF band and higher, the dominant mode of electromagnetic propagation is lincofsight(LOS) terrestrial munication systems, this means that the transmitter and receiver antennas must be in direct LOS with relatively little or no this reason, television stations transmitting in the VHF and UHF frequency bands mount their antennas on high towers to achieve a broad coverage general, the coverage area for LOS propagation is limited by the curvature of the the transmitting antenna is mounted at a height h m above the surface of the earth, the distance to the radio horizon, assuming no physical obstructions such as mountains, is approximately dr Thus,r represents the “age”(elapsedtime) three mathematical models described above adequately characterize the great majority of the physical channels encountered in three channel models are used in this text for the analysis and design of munication A HISTORICAL PERSPECTIVE IN THE DEVELOPMENT OF DIGITAL COMMUNICATIONS It is remarkable that the earliest form of electrical munication, namely telegraphy, 黃河科技學(xué)院畢業(yè)論文（文獻(xiàn)翻譯）was a digital munication electric telegraph was developed by Samuel Morse and was demonstrated in devised the variablelength binary code in which letters of the English alphabet are represented by a sequence of dots and dashes(code words).In this code, more frequently occurring letters are represented by short code words, while letters occurring less frequently are represented by longer code , the Morse code*was the precursor of the variablelength source coding methods described in Chapter 40 years later, in 1875, Emile Baudot devised a code for telegraphy in which every letter was encoded into fixedlength binary code words of length the Baudot code, binary code elements are of equal length and designated as mark and Morse is responsible for the development of the first electrical digital munication system(telegraphy), the beginnings of what we now regard as modern digital munications stem from the work of Nyquist(1924), who investigated the problem of determining the maximum signaling rate that can be used over a telegraph channel of a given bandwidth without intersymbol formulated a model of a telegraph system in which a transmitted signal has the general form where g（t）represents a basic pulse shape and is the binary data sequence of {177。1} transmitted at a rate of 1/Tbits/ set out to determine the optimum pulse shape that was bandlimited to W Hz and maximized the bit rate under the constraint that the pulse caused no intersymbol interference at the sampling time =0, 177。1, 177。2 ……His studies led him to concludc that the maximum pulse rate is 2W pulses/ rate is now called Nyquist 第二篇：英語文獻(xiàn)翻譯文章1: 題目：集成的人機(jī)交互的發(fā)展到系統(tǒng)開發(fā)生命周期的方法Abstract：將人機(jī)交互（HCI）的角度來看，系統(tǒng)開發(fā)生命周期（SDLC）是必要的信息系統(tǒng)（IS）的成功，反過來，企業(yè)的成功。然而，現(xiàn)代的軟件開發(fā)生命周期模型是基于組織的需求比人類的需要。信息系統(tǒng)的人機(jī)交互方面通常被認(rèn)為是太?。ㄖ挥衅聊唤缑妫?，在太晚的發(fā)展過程（僅在設(shè)計(jì)階段）。因此，往往一個(gè)缺口的表達(dá)。moreists滿足組織的需求和支持和豐富人類用戶之間的。這個(gè)問題可以通過仔細(xì)整合人機(jī)交互的發(fā)展為軟件開發(fā)生命周期過程中實(shí)現(xiàn)真正的以人為本的開發(fā)方法。本文探討了人機(jī)交互系統(tǒng)開發(fā)中的作用，證明考慮人機(jī)交互貫穿整個(gè)軟件開發(fā)生命周期的重要性，提出了一種方法，以人為中心的發(fā)展，并演示了如何應(yīng)用這種方法來發(fā)展以人為中心的信息系統(tǒng)。Keyword：系統(tǒng)開發(fā)生命周期（SDLC）；信息系統(tǒng)；信息系統(tǒng)中人的因素（發(fā)布）；人機(jī)交互（HCI）；信息系統(tǒng)開發(fā)方法；以用戶為中心的設(shè)計(jì)；以人為中心的系統(tǒng)開發(fā)文章2： 題目對(duì)影響敏感的多人–計(jì)算機(jī)相互作用要認(rèn)識(shí)到一個(gè)人的情感狀態(tài)是COM的溝通與情緒智力的核心能力。情感intelligenceisafacetofhumanintelligencethathasbeenarguedtobe不可缺少的也許是最重要的成功的跨個(gè)人的社會(huì)互動(dòng)。本文認(rèn)為，新一代人機(jī)交互（HCI）的設(shè)計(jì)需要包括情商來識(shí)別用戶的情感狀態(tài)，為了更加哼……能力的本質(zhì)morean一樣，更多的有效性，并更有效。情感的激發(fā)調(diào)節(jié)所有非言語municativecues（面部表情，架，和聲樂生理反應(yīng)）。在面對(duì)面的互動(dòng)，人類探測(cè)和解釋這些互動(dòng)的信號(hào)有很少或沒有努力，他們的溝通。然而，一個(gè)自動(dòng)化系統(tǒng)，完成這些任務(wù)的設(shè)計(jì)和開發(fā)是比較困難的。本文調(diào)查了過去的工作由計(jì)算機(jī)在解決這些問題，并提供了一系列建議，為開發(fā)智能多模態(tài)人機(jī)交互的用戶的非語言情感反饋個(gè)性化自動(dòng)分析儀的第一部分。Keyword：情感計(jì)算；人機(jī)交互（HCI）；情感狀態(tài)；非言語交際線索的自動(dòng)分析；多模態(tài)人機(jī)交互的個(gè)性化人機(jī)交互。文章3：題目：人機(jī)交互：跨學(xué)科的根和趨勢(shì)Abstract：方法，理論，在人機(jī)交互（HCI）領(lǐng)域的實(shí)踐都產(chǎn)生互動(dòng)的軟件，可以用來操作，能有效，安全目標(biāo)，并滿意。人機(jī)交互是跨學(xué)科和多學(xué)科的行為在其根。人機(jī)交互的核心概念是可用性，使用加有用緩解。實(shí)現(xiàn)了良好的可用性，需要注意兩個(gè)產(chǎn)品的發(fā)展過程中，特別是對(duì)用戶的交互設(shè)計(jì)，應(yīng)服務(wù)……莫里作為