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⛄ 内容介绍
交频分复用(OFDM)是一种多载波宽带数字调制技术,它具有频带利用率高和抗多径干扰能力强等优点,因而适合于高速率的无线通信系统.分析了OFDM技术的实现原理,用MATLAB软件对OFDM的传输性能进行了仿真模拟并对结论进行了分析.
⛄ 完整代码
%==========================================================================
% The mfile investigates the effects of high power amplifier on the ofdam
% signals. The effects on spectrum ang Modulation Error Rate (MER) is of
% more concern.
%
% Written By : Hamid Ramezani
% Date : 17-Jun-2007
% Code version : 1
% Matlab Version : 7.4.0.287 (R2007a)
%==========================================================================
% Initialization
clear all;
close all;
clc;
%==========================================================================
% Setting Parameters
%==========================================================================
% OFDM System Parameters
N = 256; % length of OFDM IFFT (16,32,64,...,2^n)
M = 64; % number of QAM constellation points (4,16,64,256)
numOfZeros = N/4+1; % numOfZeros must be an odd number and lower
% than N. The zero padding operation is
% necessarry in practical implementations.
GI = 1/4; % Guard Interval (1/4,1/8,1/16,...,4/N)
BW = 20; % OFDM signal Band width in MHz
numOfSym = 100; % number of OFDM Symbols
% Amplifire Parameters
satLevel = 5; % in dB , higher than the tx out mean of voltage
%==========================================================================
% Main Program
%==========================================================================
txData = randint(N-numOfZeros,numOfSym,M); % data generation
% QAM modulation
txDataMod = qammod(txData,M);
% zeros padding
txDataZpad = [txDataMod((N-numOfZeros+1)/2:end,:);...
zeros(numOfZeros,numOfSym);...
txDataMod(1:(N-numOfZeros+1)/2+1,:)];
% Note : in practice zero padding operation must be followed by
% a standard. Usually the last part of data frame shifts to the first
% part of zero padded frame.
% IFFT
txDataZpadIfft = sqrt(N)*ifft(txDataZpad,N);
% Guard Interval Insertion
txDataZpadIfftGI = [txDataZpadIfft((1-GI)*N+1:end,:);txDataZpadIfft];
% Amplifier Model
txDataZpadIfftGIAbs = abs(txDataZpadIfftGI); % tx data amplitude
% tx data amplitude standard deviation and mean
txDataZpadIfftGIAbsStd = mean(std(txDataZpadIfftGIAbs));
txDataZpadIfftGIAbsMean = mean(mean(txDataZpadIfftGIAbs));
% tx data phase in radian
txDataZpadIfftGIAng = angle(txDataZpadIfftGI);
% It is imagined that the amplifier has no effect on the phase of the
% signal. The solid state amplifier effects on signal phase is about 5
% degrees. The amplifier AM/AM response is followed by x/sqrt(1+(x/k)^2)
txDataZpadIfftGIAbsHPA = txDataZpadIfftGIAbs ./...
sqrt(1+(txDataZpadIfftGIAbs/(txDataZpadIfftGIAbsMean*10^(satLevel/10))).^2);
% no change in the phase
txDataZpadIfftGIAngHPA = txDataZpadIfftGIAng;
% mean of amplitude after amplification
txDataZpadIfftGIAbsHPAmean = mean(mean(txDataZpadIfftGIAbsHPA));
% standard deviation after amplification
txDataZpadIfftGIAbsHPAStd = mean(std(txDataZpadIfftGIAbsHPA));
% polar to cartesian conversion
txDataZpadIfftGIHPA = txDataZpadIfftGIAbsHPA.* ...
exp(sqrt(-1) * txDataZpadIfftGIAngHPA);
% receiver part
% Guard Interval removal
rxDataZpadIfftHPA = txDataZpadIfftGIHPA(GI*N+1 : N+GI*N,:);
% FFT operation
rxDataZpadHPA = 1/sqrt(N)*fft(rxDataZpadIfftHPA,N);
% zero removal and rearrangement
rxDataModHPA = [rxDataZpadHPA((N-(N-numOfZeros-1)/2+1):N,:);...
rxDataZpadHPA(1:(N-numOfZeros+1)/2,:)];
% demodulation
rxDataHPA = qamdemod(rxDataModHPA/mean(std(rxDataModHPA))*mean(std(txDataMod)),M);
%==========================================================================
% statistical computation
%==========================================================================
% Mean Error Rate computation
MER = 10*log10(mean(var(rxDataModHPA./mean(std(rxDataModHPA))...
- txDataMod./mean(std(txDataMod)))));
% Bit Error Rate computation
[num BER] = symerr(rxDataHPA,txData);
%==========================================================================
% graphical observation
%==========================================================================
f1 = figure(1);
set(f1,'color',[1 1 1]);
subplot(2,2,1);
spectrumFftSize = 2*N;
% spectrum of signal befor High Power Amplifier
txSpec = 20*log10(mean(abs(fft(txDataZpadIfftGI(:,:)./ ...
mean(std(txDataZpadIfftGI)),spectrumFftSize)),2));
% spectrum of signal after High Power Amplifier
HpaSpec = 20*log10(mean(abs(fft(txDataZpadIfftGIHPA(:,:)./ ...
mean(std(txDataZpadIfftGIHPA)),spectrumFftSize)),2));
% corresponding frequency
Freq = linspace(-BW/2,BW/2,length(txSpec));
plot(Freq,[txSpec(length(txSpec)/2:length(txSpec));...
txSpec(1:(length(txSpec)/2-1))]);
hold on
grid on
plot(Freq,[HpaSpec(length(txSpec)/2:length(txSpec));...
HpaSpec(1:(length(txSpec)/2-1))],'r');
grid on;
xlabel('representing frequency');
ylabel('spectrum signals (first symbol)');
title('Spectrum Effects')
legend('Befor Amplifier','After Amplifier')
subplot(2,2,2);
plot(real(reshape(rxDataModHPA,1,numOfSym*(N-numOfZeros)))/mean(std(rxDataModHPA)),...
imag(reshape(rxDataModHPA,1,numOfSym*(N-numOfZeros)))/mean(std(rxDataModHPA)),'.r')
hold on
plot(real(reshape(txDataMod,1,numOfSym*(N-numOfZeros)))/mean(std(txDataMod)),...
imag(reshape(txDataMod,1,numOfSym*(N-numOfZeros)))/mean(std(txDataMod)),'.b')
xlabel('I channel');
ylabel('Q channel');
title('signal Constelleations');
legend('After Amplifier','Before Amplifier');
subplot(2,2,3)
% normalize amplitude
txAmp = linspace(0,5,100);
amAmp = txAmp./(1+(txAmp/satLevel).^2);
plot(txAmp,txAmp,'b');
hold on
plot(txAmp,amAmp,'r');
plot(1,1,'om');
xlabel('Input Amplitude');
ylabel('Output Amplitude');
title('AM/AM response of power amplifier');
legend('Linear Response','Amplifier Response','Mean of OFDM Amplitude');
subplotHandel = subplot(2,2,4);
text(0,1 ,['Mean Error Rate : ',num2str(MER),' dB']);
text(0,.8,['Bit Error Rate : ',num2str(BER)]);
text(0,.6,['Modulation : ',num2str(M),' QAM']);
text(0,.4,['IFFT Size : ',num2str(N),' points']);
text(0,.2,['Guard Interval Size : ',num2str(N),' points']);
text(0,.0,['Saturation Level : ',num2str(satLevel),' dB relative to AM Avg']);
% setting the axes invisibale
set(subplotHandel,'Xcolor',[1 1 1]);
set(subplotHandel,'Ycolor',[1 1 1]);
⛄ 运行结果
⛄ 参考文献
[1]孙志雄. 基于MATLAB的OFDM系统仿真分析[J]. 信息技术, 2007, 31(12):4.
