基于matlab的am信號(hào)的調(diào)制與解調(diào)(存儲(chǔ)版)
【正文】 n is the most basic, is also frequently used. To participate in the identification of such artificial methods, the ruling includes subjective factors, will vary from person to person, can identify the type of modulation is very limited. Automatic modulation recognition technology can be overe not only to participate in recognition of artificial difficulties, and the center frequency and bandwidth of the estimation error, adjacent channel crosstalk, noise and interference factors such as the decline of effect is relatively robust. Using AM modulation and demodulation circuit which can achieve a lot of features, creating a lot of useful and affordable electronic products, in order to facilitate our lives. Used in our daily lives is the use of AM radio modulation, but also in the field of military and civilian research topics are very important. The main content of this paper is to understand the mathematical model of the AM signal and the modulation and the demodulation method. Demodulation different methods in different circumstances of the demodulation signal to noise ratio the results of methods that better, to make the parison. Requirement is more than double the sound and the AM signal modulation and demodulation. AM modulation first study of its function and in real life use. AM demodulation followed by research, as well as some related knowledge, as well as through its use of munications more indepth understanding of it. AM signal from the tone of the mathematical model and the modulation and demodulation methods, the twotone AM signal to draw a mathematical model and the block diagram of modulation and demodulation and modulation and demodulation waveforms. MATLAB programming language to use to achieve the twotone AM signal modulation and demodulation, given the different circumstances of the demodulation signal to noise ratio pared the results.Keyword: AM signal, Modulation, Demodulation, Noise ratio signal, MATLABII第一章 緒論 背景以及意義現(xiàn)在的社會(huì)越來越發(fā)達(dá)，科學(xué)技術(shù)不斷的在更新，在信號(hào)和模擬通信的中心問題是要把載有消息的信號(hào)經(jīng)系統(tǒng)加工處理后，送入信道進(jìn)行傳送，從而實(shí)現(xiàn)消息的相互傳遞。信息的加工、處理和相互傳遞是現(xiàn)代通信的基礎(chǔ)，是通信所要解決的實(shí)質(zhì)問題。用所要傳播的語言或音樂信號(hào)去改變高頻振蕩的幅度，使高頻振蕩的幅度隨語言或音樂信號(hào)的變化而變化，這個(gè)控制過程就稱為調(diào)制。為什么要用語言或音樂信號(hào)去控制高頻振蕩呢？原來要使信號(hào)的能量以電場(chǎng)和磁場(chǎng)的形式向空中發(fā)射出去傳向遠(yuǎn)方，需要較高的振蕩頻率方能使電場(chǎng)和磁場(chǎng)迅速變化；同時(shí)信號(hào)的波長(zhǎng)要與天線的長(zhǎng)度相匹配。其幅度變化曲線與要傳遞的低頻信號(hào)是相似的。頻率解調(diào)要比幅度解調(diào)復(fù)雜，用普通檢波電路是無法解調(diào)出調(diào)制信號(hào)的，必須采用頻率檢波方式，如各類鑒頻器電路。(2) 脈沖噪聲脈沖噪聲表現(xiàn)為時(shí)域波形中突然出現(xiàn)的窄脈沖，在時(shí)間上表現(xiàn)為無規(guī)則的突發(fā)的短促噪聲。起伏噪聲可近似地看作高斯噪聲，且在相當(dāng)寬的頻率范圍內(nèi)具有平坦功率譜密度，可近似表述為高斯白噪聲。因此本文認(rèn)為信道中的噪聲都是平穩(wěn)加性高斯白噪聲?？芍猍7] () 設(shè)m(t)的頻譜為M(w），由傅氏變換的理論可得已調(diào)信號(hào) ()AM的波形和相應(yīng)的頻譜圖如下 AM信號(hào)的時(shí)域波形及其頻譜可以看出，第一：AM的頻譜與基帶信號(hào)的頻譜呈線性關(guān)系，只是將基帶信號(hào)的頻譜搬移，并沒有產(chǎn)生新的頻譜成分，因此AM調(diào)制屬于線性調(diào)制；第二：AM信號(hào)波形的包絡(luò)與基帶信號(hào)成正比，所以AM信號(hào)的解調(diào)即可以采用相干解調(diào)，也可以采用非相干解調(diào)（包絡(luò)檢波）。 AM信號(hào)的非相干解調(diào)所謂非相干解調(diào)是在接收端解調(diào)信號(hào)時(shí)不需要本地載波，而是利用已調(diào)信號(hào)中的包絡(luò)信號(hào)來恢復(fù)原基帶信號(hào)[7]。為了對(duì)不同調(diào)制方式下各種解調(diào)器性能進(jìn)行度量，通常采用信噪比增益G（又稱調(diào)制制度增益）來表示解調(diào)器的抗噪聲性能，即[9] （）有加性噪聲時(shí)解調(diào)器的數(shù)學(xué)模型如圖圖 AM信號(hào)的解調(diào)原理圖圖中為已調(diào)信號(hào)，n(t)為加性高斯白噪聲。由此可得AM信號(hào)在解調(diào)器的輸入信噪比為
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