modulator.m

Matlab 模拟 CDMA 直接扩频。m序列生成矩阵为p(x) = 1 + x^5 + x^7 + x^8 + x^9 + x^13 + x^15。能画出每阶段的时域、频域图。

%% Made by Zheng Xiao (052815 05b04)
%% Group Member: Ji Yue, Sun Xin, Zheng Xiao

%clear
% Generate Signal
%M = 16; %-the number of Sample per Period in input signal
N = 32; %-the number of Sample per Period in BPSK Modulated signal
M = 64; %-the number of Sample per Period in input signal
P1 = [0 5 7 8 9 13 15];
P2 = [0];
%tk = 0:1/M:(1024/M);
%input = sin(2*pi*tk) + cos(pi*tk);
%ratio = max(input);
%input = input/ratio;
% A-law PCM encode

% Lengthen PCM code
%%pcmCode = [1];
original=[1 1 0 1 0]; % User Code
stem(original);
title('User Code');
pause

nOriginal = length(original);
pcmCode=expand_bit(original);%must be 64xN length
key1 = genM(M,P1);

%autocorrelation(genBipolar(key1)); % 画图: generated m-sequence (3000点)
m = genBipolar(genM(3000,P1));
mx = -length(m)+1:length(m)-1;
stem(mx,xcorr(m,m));
title('Auto-Correlation');
xlabel('Lags');ylabel('Auto-Correlation')
pause

pcmCode=xor(pcmCode,periodExpand(key1,nOriginal));
pcmCode = genBipolar(pcmCode); % 转换为双极性码

npcmCode = length(pcmCode); %-number of total symbol
pcmCode = [pcmCode;zeros((N-1),npcmCode)];
pcmCode = reshape(pcmCode,1,N*npcmCode);
pcmCode = conv(pcmCode,ones(1,N));
pcmCode = pcmCode(1:N*npcmCode);

% BPSK Modulation
tk = 0:1/N:(1-1/N);
carrier = sin(4*pi*tk);
carrier = padarray(carrier,npcmCode-1,'circular','post');
carrier = reshapeSeq(carrier);
signal = carrier .* pcmCode; %<= THIS IS THE MODULATED SIGNAL
plot(signal);
xlabel('Time');ylabel('Voltage');
title('BPSK Modulated Signal');
axis([600 900 min(signal) max(signal)]);
pause

%%%%% Here comes through the channel %%%%%
%=================[Media]================%
signal = addNoise(signal,sqrt(5)/5);
plot(signal)
xlabel('Time');ylabel('Voltage');
title('BPSK Modulated Signal (added Noise)');
axis([600 900 min(signal) max(signal)]);
pause

% BPSK Demodulation
signalIn = signal .*carrier; %<= INPUT SIGNAL OF DEMODULATOR
 %plot(signalIn)
judger = reshapeColumn(signalIn,N);
judger = sum(judger,2);
judger(find(judger>=0)) = 0; % 转化为单极性
judger(find(judger<0)) = 1;
judger = judger';

nFinal = length(judger)/M;
final = xor(judger, periodExpand(key1,nFinal));
finalFinal = finalJudge(final,M); % the final output
stem(finalFinal);
title('Decoded Codes');

% A-law PCM decode
%output = pcm_decode(judger).*ratio;
%axis([0,102,-ratio,+ratio])
%input = input*ratio;
%err = output - input;
%plot(1:length(output),output,1:length(input),input, 1:length(err),err)