【正文】 下“原理圖”按鈕，就可以看到BASK通信系統(tǒng)的simulink模型。(1)時域波形當(dāng)數(shù)據(jù)率R是1bit/s、噪聲峰值功率 100Hz、仿真時間t為60s時，時域波形如圖51。 BASK系統(tǒng)數(shù)據(jù)率為1bit/s時的各信號波形圖51中，從上到下，依次為發(fā)送信號波形、BASK調(diào)制信號波形、抽樣判決前的信號波形和接收信號的波形。由于相關(guān)參數(shù)設(shè)計的不夠好，誤碼率較高，從原理圖的顯示模塊可以看到。表51這與理論上是一致的。 噪聲對系統(tǒng)誤碼率的影響(1)仿真結(jié)果改變峰值噪聲功率，再進(jìn)行仿真，所得的結(jié)果如表52。噪聲 對BASK系統(tǒng)誤碼率r的影響 數(shù)字通信系統(tǒng)R/ /w/Hzt/srBASK1010060BASK1010060(2)結(jié)論由表52可知，噪聲越大，誤碼率也越高，這與理論相符[13]。 BFSK通信系統(tǒng)由圖可見，接收信號與發(fā)送信號相比，存在延時，這是由于抽樣判決器在符號的中間時刻才抽樣判決造成的[14]。圖52 數(shù)據(jù)率R對BFSK系統(tǒng)誤碼率r的影響 數(shù)字通信系統(tǒng)R/ /w/Hz/Hzt/srBFSK12460BFSK1012460BFSK10012460(3)結(jié)論比較設(shè)計的參數(shù)和誤碼率，可知數(shù)據(jù)率越大，誤碼率就越高。噪聲 對BFSK系統(tǒng)誤碼率r的影響 數(shù)字通信系統(tǒng)R/ /w/Hz/Hzt/srBFSK1012460BFSK1012460(2)結(jié)論可知，噪聲越大，誤碼率也越高。 數(shù)據(jù)率對系統(tǒng)誤碼率的影響(1) 時域波形圖53由圖可見，接收信號與發(fā)送信號相比，存在延時，這是由于抽樣判決器在符號的中間時刻才抽樣判決造成的[15]。(2)仿真結(jié)果改變數(shù)據(jù)率，再進(jìn)行仿真，所得的結(jié)果如表55。 數(shù)據(jù)率R對BPSK系統(tǒng)誤碼率r的影響 數(shù)字通信系統(tǒng)R/ /w/Hzt/srBPSK10060BPSK11010BPSK1010060(3)結(jié)論比較設(shè)計的參數(shù)和誤碼率，可知數(shù)據(jù)率越大，誤碼率就越高。表56 這與理論相符。 BASK、BFSK和BPSK系統(tǒng)性能比較歸納以上的仿真，可得表57的結(jié)果。 BASK、BFSK和BPSK系統(tǒng)誤碼率r比較 數(shù)字通信系統(tǒng)R/ /w/Hz/Hzt/srBASK10060BASK1010060BFSK和BPSK系統(tǒng)的誤碼率相等，而理論上，BFSK系統(tǒng)的誤碼率應(yīng)大于BPSK系統(tǒng)的誤碼率。 結(jié)論與展望利用MATLAB軟件的圖形用戶界面GUI和SIMULINK模塊，制作出可視化的數(shù)字通信系統(tǒng)2ASK、2PSK和2PSK。數(shù)字通信由來已久，各種資料很多，然而對我有用的卻不多。我學(xué)過通信原理，他是學(xué)位課，我學(xué)得還行。通過這次設(shè)計我學(xué)會了如何查找資料以及取舍綜合運用資料。找了很多資料，很多我一看就放棄了，還有一開始做的通信系統(tǒng)模型，由于效果不太好，也不易更改，我毅然放棄了。 展望由于時間的原因，數(shù)字通信有點復(fù)雜且對我有用資料不多，畢業(yè)設(shè)計還存在不足的地方。原理圖中對應(yīng)地方接上頻譜儀時，仿真后，頻譜儀中什么都不顯示，這個問題如何解決，目前還不知道。再次，演示系統(tǒng)只做了最簡單最基本的二進(jìn)制ASK、FSK和PSK數(shù)字通信系統(tǒng)，DPSK數(shù)字通信系統(tǒng)以及多進(jìn)制數(shù)字通信系統(tǒng)等很多系統(tǒng)沒時間做。[15] 蘇金明，張蓮花．MATLAB工具箱應(yīng)用 [M]．電子工業(yè)出版社，2004． 謝 錄附錄A makes debugging and correction can be made on spot.The benefits of MATLAB e with a heavy price tag. MATLAB is very slow pared with other piled programmes. Loops are the main culprit. When dealing with arrays and matrices, one should avoid traditional loops such as ‘for’ and ‘while’, and utilizes MATLAB’s matrix properties instead. In addition, MATLAB uses double precision floating point as a default numerical value which contributes to high utilization of memory.MathWorks , which develops MATLAB, offers a solution to the problem of slow running MATLAB. It provides a library for calling and executing prepiled dynamic link libraries. The library is called MEX file and can be written using the C or Fortran language .The piled libraries then can be called and executed like normal file functions. 2 Digital munications what is data municationData munication is the transfer of data or information between a source and a receiver. The source transmits the data and the receiver receives it. Data munication is mainly interested in the transfer of data, the method of transfer and the preservation of the data during the transfer process.The purpose of data munication is to the rules or regulations that allow puters with different disk operating systems, languages, cabling and location to share resources. The rules and regulations are called protocols and standards in data munication. General FormDigital data is universally represented by strings of 1s or 0s. Each one or zero is referred to as bit. Often, but not always, these bit strings are interpreted as numbers in a binary number system Thus 1010012 = 4110. The information content of a digital signal is equal to the number of bit required to represent it. Thus a signal that may vary between 0 and 7 has an information content of 3 bits. Written as an equation this relationship is where n is the number of levels a signal may take. It is important to appreciate that information is a measure of the number of different outes a value may take. The information rate is a measure of the speed with which information is transferred. It is measured in bits/second or b/s. The conversion of analogue and digital signalsIn order to send analogue signals over a digital munication system, or process them on a digital puter, we need to convert analogue signals to digital ones. This process is performed by an analoguetodigital converter (ADC). The analogue signal is sampled and then Quantified, converted to discrete numeric values. The converse operation to the ADC is performed by a digitaltoanalogue converter (DAC).The ADC process is governed by an important law. The NyquistShannon Theorem states that an analogue signal of bandwidth B can be pletely recreated from its sampled form provided it is sampled at a rate equal to at least twice its bandwidth.That is S =2B. The rate at which an ADC generates bits depends on how many bits are used in the converter. For example, a speech signal has an approximate bandwidth of 4 kHz. If this is sampled by an 8bit ADC at the Nyquist sampling rate, the bit rate R to transform the signal without loss of information is R = 64000b/s BandwidthJust as fourlane freeway can carry more traffic then a twolane street, some munications systems can carry more data then others. The capacity of a munications system depends on the bandwidth of the channels it uses. Bandwidth is the transmission capacity of a munications channel. Typically, a channel with high bandwidth can carry more data then channel with low bandwidth. Foe example, the channels that make up the Internet backbone have a higher bandwidth then your home telephone line. Highbandwidth munications systems, such as cable TV, are sometimes referred to as broadband, whereas systems with l