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⛄ 内容介绍
交频分复用 (Orthogonal Frequency Division Multiplexing OFDM) 是第四代 (the4th Generation,4G) 移动通信的核心技术,它的最大优点是对抗频率选择性衰落,同时又提高了频谱利用率。它不仅仅可以增加系统容量,更重要的是它能更好地满足多媒体通信要求,将包括语音、数据、影像等大量信息的多媒体业务通过宽频信道高品质地传送出去。 但是OFDM技术对频率偏移和相位噪声很敏感,所以同步是OFDM系统中的关键问题。缺乏必要的同步机制,各子频道的正交性就会受到破坏,从而引入子载波间干扰ICI(Intemal Channel Interference)。
⛄ 完整代码
%---------------------------------------------------------------------------------------------------
% In this example we show how OFDM system perform over AWGN channel. The
% simulation results will be checked with ones we obtain through
% theoritical analysis.
%
%---------------------------------------------------------------------------------------------------
% Initiliazation
clear % clear all workspace variables
clc % clear command window
close all % close all open figures
mFileName = mfilename; % Get mfile name
mFileNameFull = mfilename('fullpath'); % Get mfile full name
mFileDirMain = mFileNameFull(1:end-length(mFileName)); % Extract the dir of the mfile directory
if ~isempty(mFileDirMain)
cd(mFileDirMain) % change matlab current folder to mfile directory
end
clear mFileName mFileNameFull mFileDirMain % clear variables
rng(0) % set the random seed to 0
if exist('OFDM_Class','class') == 8 % Check if OFDM_Class exits
OFDM_Class.checkForUpdatedVersion(); % Check if the class is updated
else
fprintf('The OFDM_Class does not exist or its path is not added. You can download the class from this %s \n',...
'<a href = "http://www.mathworks.com/matlabcentral/fileexchange/54070">Link</a>')
return
end
%---------------------------------------------------------------------------------------------------
% Main Part
%---------------------------------------------------------------------------------------------------
% Parameters
% First curve
Para1.NB = 5000; % Number of ofdm symbols per run
Para1.I = 1; % Number of iterations in each loop
Para1.M = 4; % Modulation order (4 QPSK) it can be changed by user
Para1.N = 64; % Number of sybcarriers
Para1.NFFT = 64; % Upsampling rate is 1, and FFT based interpolation is used
Para1.ifDoRaylieghChannel = 0; % No Rayliegh channel
Para1.ifDoAWGNChannel = 1; % Only AWGN Channel
% Second curve
Para2 = Para1; % all parameters are the same as what defined in Para1 except the modulation order
Para2.M = 16; % Modulation order (16 QAM) it can be changed by user
% Building class
Obj1 = OFDM_Class(Para1);
Obj2 = OFDM_Class(Para2);
% Loop Parameters
Loop.EbN0dB = 0:10;
Loop.SNRdBVec1 = 10*log10(log2(Obj1.M))+Loop.EbN0dB;
Loop.SNRdBVec2 = 10*log10(log2(Obj2.M))+Loop.EbN0dB;
Loop.EbN0dBL = length(Loop.EbN0dB);
Loop.Results = zeros(Loop.EbN0dBL,Obj1.I,8);
Loop.Cnt = 0;
% Main Loop
fprintf('-------------------------------------\n')
for LoopCnt1 = 1 : Loop.EbN0dBL
% Update parameters
Obj1.channSNRdB = Loop.SNRdBVec1(LoopCnt1);
Obj2.channSNRdB = Loop.SNRdBVec2(LoopCnt1);
for LoopCnt2 = 1 : Obj1.I
% Transmitter
Obj1.ofdmTransmitter();
Obj2.ofdmTransmitter();
% Channel
Obj1.ofdmChannel();
Obj2.ofdmChannel();
% Receiver
Obj1.ofdmReceiver();
Obj2.ofdmReceiver();
% BER calculation
Obj1.ofdmBER();
Obj2.ofdmBER();
% Store the results for the first curve
Loop.Results(LoopCnt1,LoopCnt2,1) = Obj1.BER;
Loop.Results(LoopCnt1,LoopCnt2,2) = Obj1.DER;
Loop.Results(LoopCnt1,LoopCnt2,3) = Obj1.BERTheoryAWGN;
Loop.Results(LoopCnt1,LoopCnt2,4) = Obj1.EbN0dB;
% Store the results for the second curve
Loop.Results(LoopCnt1,LoopCnt2,5) = Obj2.BER;
Loop.Results(LoopCnt1,LoopCnt2,6) = Obj2.DER;
Loop.Results(LoopCnt1,LoopCnt2,7) = Obj2.BERTheoryAWGN;
Loop.Results(LoopCnt1,LoopCnt2,8) = Obj2.EbN0dB;
% Display
Loop.Cnt = Loop.Cnt + 1;
fprintf('%10.1f percent of the simulation is done.\n',Loop.Cnt*100/(Loop.EbN0dBL * Obj1.I))
end
end
fprintf('-------------------------------------\n')
% Plots
figure(1)
clf
semilogy(mean(Loop.Results(:,:,4),2), mean(Loop.Results(:,:,1),2),'bo:') % Simulation BER (first curve)
hold on
semilogy(mean(Loop.Results(:,:,4),2), mean(Loop.Results(:,:,3),2),'b-') % Theory BER (first curve)
semilogy(mean(Loop.Results(:,:,8),2), mean(Loop.Results(:,:,5),2),'rs:') % Simulation BER (second curve)
semilogy(mean(Loop.Results(:,:,8),2), mean(Loop.Results(:,:,7),2),'r-') % Theory BER (second curve)
grid on
xlabel('EbN0 [dB]')
ylabel('BER')
legend([Obj1.ModulationStr,'-Simulation'],[Obj1.ModulationStr,'-Theory'],...
[Obj2.ModulationStr,'-Simulation'],[Obj2.ModulationStr,'-Theory'])
title('OFDM system performance over AWGN channel')
⛄ 运行结果
⛄ 参考文献
[1]任文超, 姜军. AWGN信道中一种改进OFDM系统信道估计算法[J]. 2013.
