900字范文 > 【数字信号调制】基于matlab GUI PCM编码+QAM调制【含Matlab源码 1095期】

【数字信号调制】基于matlab GUI PCM编码+QAM调制【含Matlab源码 1095期】

时间：2021-02-18 03:41:27

一、PCM编码+QAM调制简介

1 PCM

数字信号是对连续变化的模拟信号进行抽样、量化和编码产生的，称为PCM（Pulse Code Modulation），即脉冲编码调制。

脉冲编码调制就是把一个时间连续，取值连续的模拟信号变换成时间离散，取值离散的数字信号后在信道中传输。脉冲编码调制就是对模拟信号先抽样，再对样值幅度量化，编码的过程。

抽样，就是对模拟信号进行周期性扫描，把时间上连续的信号变成时间上离散的信号。该模拟信号经过抽样后还应当包含原信号中所有信息，也就是说能无失真的恢复原模拟信号。它的抽样速率的下限是由抽样定理确定的。抽样速率采用8Kbit/s。

量化，就是把经过抽样得到的瞬时值将其幅度离散，即用一组规定的电平，把瞬时抽样值用最接近的电平值来表示。

一个模拟信号经过抽样量化后，得到已量化的脉冲幅度调制信号，它仅为有限个数值。编码，就是用一组二进制码组来表示每一个有固定电平的量化值。然而，实际上量化是在编码过程中同时完成的，故编码过程也称为模/数变换，可记作A/D。

话音信号先经防混叠低通滤波器，进行脉冲抽样，变成8KHz重复频率的抽样信号（即离散的脉冲调幅PAM信号），然后将幅度连续的PCM信号用“四舍五入”办法量化为有限个幅度取值的信号，再经编码后转换成二进制码。对于电话，CCITT规定抽样率为8KHz，每抽样值编8位码，即共有2^8=256个量化值，因而每话路PCM编码后的标准数码率是64kb/s。为解决均匀量化时小信号量化误差大，音质差的问题，在实际中采用不均匀选取量化间隔的非线性量化方法，即量化特性在小信号时分层密，量化间隔小，而在大信号时分层疏，量化间隔大。均匀量化的小信号的信噪比小。

非均匀量化: 由于一些信源信号, 如语音信号, 小幅度信号发生的概率大于大幅度信号的概率, 采用非均匀量化(即小幅度信号的量化步长小于大幅度信号的的量化步长) 效果更好好 (表现在语音信号上, 可以使信号具有足够的信噪比)。非均匀量化特性通常是把信号通过一个非线性的设备, 小信号幅度进行放大, 大信号幅度进行压缩, 再通过均匀量化实现。

2 常规双边带调幅AM

t 域：已调信号的波形，调制/解调方法

f 域：已调信号的频谱，带宽B

AM信号的包络正比于消息信号的规律，因此可以采用简单的**包络检波方法（非相干解调）**解调；

频谱由载波、上边带USB、下边带LSB组成。带宽BAM=2fH；

幅度调制又称为线性调制；

应用：中短波调幅广播。

缺点：功率利用率低，最多达到50%

二、源代码

function varargout = test(varargin)% TEST M-file for test.fig%TEST, by itself, creates a new TEST or raises the existing%singleton*.%%H = TEST returns the handle to a new TEST or the handle to%the existing singleton*.%%TEST('CALLBACK',hObject,eventData,handles,...) calls the local%function named CALLBACK in TEST.M with the given input arguments.%%TEST('Property','Value',...) creates a new TEST or raises the%existing singleton*. Starting from the left, property value pairs are%applied to the GUI before test_OpeningFunction gets called. An%unrecognized property name or invalid value makes property application%stop. All inputs are passed to test_OpeningFcn via varargin.%%*See GUI Options on GUIDE's Tools menu. Choose "GUI allows only one%instance to run (singleton)".%% See also: GUIDE, GUIDATA, GUIHANDLES% Edit the above text to modify the response to About test% Last Modified by GUIDE v2.5 04-Jul- 19:27:45% Begin initialization code - DO NOT EDITgui_Singleton = 1;gui_State = struct('gui_Name', mfilename, ...'gui_Singleton', gui_Singleton, ...'gui_OpeningFcn', @test_OpeningFcn, ...'gui_OutputFcn', @test_OutputFcn, ...'gui_LayoutFcn', [] , ...'gui_Callback', []);if nargin && ischar(varargin{1})gui_State.gui_Callback = str2func(varargin{1});endif nargout[varargout{1:nargout}] = gui_mainfcn(gui_State, varargin{:});elsegui_mainfcn(gui_State, varargin{:});end% End initialization code - DO NOT EDIT% --- Executes just before test is made visible.function test_OpeningFcn(hObject, eventdata, handles, varargin)% This function has no output args, see OutputFcn.% hObject handle to figure% eventdata reserved - to be defined in a future version of MATLAB% handles structure with handles and user data (see GUIDATA)% varargin command line arguments to test (see VARARGIN)% Choose default command line output for testhandles.output = hObject;% Update handles structureguidata(hObject, handles);% UIWAIT makes test wait for user response (see UIRESUME)% uiwait(handles.figure1);% --- Outputs from this function are returned to the command line.function varargout = test_OutputFcn(hObject, eventdata, handles) % varargout cell array for returning output args (see VARARGOUT);% hObject handle to figure% eventdata reserved - to be defined in a future version of MATLAB% handles structure with handles and user data (see GUIDATA)% Get default command line output from handles structurevarargout{1} = handles.output;% --- Executes on button press in LOAD.function LOAD_Callback(hObject, eventdata, handles)% hObject handle to LOAD (see GCBO)% eventdata reserved - to be defined in a future version of MATLAB% handles structure with handles and user data (see GUIDATA)global x fs t[x,fs] = audioread('test.wav');t = (1:length(x))/fs;t8 = length(x)*8;t8 = (1:t8)/fs;Bs = 0.5*fs;save('data.mat','x','fs','t','t8');N = length(x); X=fft(x,N);%进行fft变换mag=abs(X);%求幅值f=(0:length(X)-1)'*fs/length(X);%进行对应的频率转换subplot(2,1,1,'position',[0.3 0.57 0.6 0.3]);plot(t,x) %时域图xlabel('时间');ylabel('幅值');axis([min(t) max(t) min(x) max(x)]);subplot(2,1,2,'position',[0.3 0.2 0.6 0.3]);plot(f,mag);%做频谱图xlabel('频率');ylabel('幅值');axis([0 max(f) 0 1.1*max(abs(X)) ]);set(handles.LOAD,'enable','off');set(handles.PCM,'enable','on');%set(handles.Play_origin,'enable','on');set(handles.text1,'String','测试音频文件波形如图所示');% --- Executes on button press in PCM.function PCM_Callback(hObject, eventdata, handles)% hObject handle to PCM (see GCBO)% eventdata reserved - to be defined in a future version of MATLAB% handles structure with handles and user data (see GUIDATA)load data.mat;x1 = x./max(abs(x));sxx = floor( x1 * 4096 );y = pcm_encode(sxx);save('data.mat','y','-append');subplot(1,1,1,'position',[0.3 0.2 0.6 0.65]);plot(t8,y);xlabel('时间');ylabel('幅值');axis([0 0.1 -1 2]);set(handles.dePCM,'enable','on');set(handles.QAM,'enable','on');set(handles.text1,'String','经过PCM编码后，形成二进制码流');% --- Executes on button press in QAM.function QAM_Callback(hObject, eventdata, handles)% hObject handle to QAM (see GCBO)% eventdata reserved - to be defined in a future version of MATLAB% handles structure with handles and user data (see GUIDATA)prompt={'信道SNR:'};name='Input';numlines=1;defaultanswer={'20'};answer=inputdlg(prompt,name,numlines,defaultanswer);if ~isempty(answer) ,result = str2num(answer{1,1});load data.mat;Qt = my_qammod(y);Qr = awgn(Qt,result);yy= my_qamdemod(Qr);save('data.mat','yy','-append');subplot(1,1,1,'position',[0.3 0.2 0.6 0.65]);plot(t8,yy);xlabel('时间');ylabel('幅值');axis([0 0.1 -1 2]);set(pare2,'enable','on');set(handles.text1,'String','PCM信号通过QAM调制，送到AWGN信道，再经过解调还原为PCM信号');end% --- Executes on button press in dePCM.function dePCM_Callback(hObject, eventdata, handles)% hObject handle to dePCM (see GCBO)% eventdata reserved - to be defined in a future version of MATLAB% handles structure with handles and user data (see GUIDATA)load data.mat;xx = pcm_decode(y,max(abs(x)));save('data.mat','xx','-append');N = length(xx); XX=fft(xx,N);%进行fft变换mag=abs(XX);%求幅值f=(0:length(XX)-1)'*fs/length(XX);%进行对应的频率转换function qt = my_qammod(b)[nrow,ncol]=size(b);col=ncol/4;b_2=reshape(b,4,col);b_2=b_2';b_str2=int2str(b_2);b_10=bin2dec(b_str2);b_10=b_10'; % --- Executes on button press in Play_arrive.%function Play_arrive_Callback(hObject, eventdata, handles)% hObject handle to Play_arrive (see GCBO)% eventdata reserved - to be defined in a future version of MATLAB% handles structure with handles and user data (see GUIDATA)%load data.mat;%wavplay(xx);% --- Executes on button press in BYE.function BYE_Callback(hObject, eventdata, handles)% hObject handle to BYE (see GCBO)% eventdata reserved - to be defined in a future version of MATLAB% handles structure with handles and user data (see GUIDATA)close% --------------------------------------------------------------------function About_Callback(hObject, eventdata, handles)% hObject handle to About (see GCBO)% eventdata reserved - to be defined in a future version of MATLAB% handles structure with handles and user data (see GUIDATA)msgbox({' 本程序完成对简单音频信号的取样，' 'PCM编码，QAM调制，通过AWGN信道， ' 'QAM解调，PCM解码的一系列方针操作。' '作者：吕非彼' '电信工程学院 05114班 ' '学号:050430 序号:12'},'About','Help') % --- Executes during object creation, after setting all properties.%function Play_origin_CreateFcn(hObject, eventdata, handles)% hObject handle to Play_origin (see GCBO)% eventdata reserved - to be defined in a future version of MATLAB% handles empty - handles not created until after all CreateFcns called% --- Executes during object deletion, before destroying properties.%function Play_origin_DeleteFcn(hObject, eventdata, handles)% hObject handle to Play_origin (see GCBO)% eventdata reserved - to be defined in a future version of MATLAB% handles structure with handles and user data (see GUIDATA)% --- If Enable == 'on', executes on mouse press in 5 pixel border.% --- Otherwise, executes on mouse press in 5 pixel border or over Play_origin.%function Play_origin_ButtonDownFcn(hObject, eventdata, handles)% hObject handle to Play_origin (see GCBO)% eventdata reserved - to be defined in a future version of MATLAB% handles structure with handles and user data (see GUIDATA)