從零開始學可見光通信，從開始到絕望…………………………

幾點說明。

1. 一般在仿真的時候，大家都喜歡直接做等效基帶仿真(類似于星座點的仿真)。

但實際要傳，還是要傳頻帶的波形信號。

2. 為了模擬真實的環境，先把基帶信號經過一個自定義的信道，然后再做脈沖成型，上變頻，加一點噪聲AWGN進去。

3. 為了模擬同步，應該用專用的同步算法。但是這里的重點不在同步。所以用了很簡單粗暴的辦法。假裝直接同步上了。

4. 為了造出不同步的結果，可以這樣寫 x_未同步 = [x(300:end); x; x]; 相當于循環發送，循環接收。

這是仿真。

Main

%%

%?單載波QPSK?接收端

%?2017年5月17日18:02:56

clear;

close?all;

clc

rand_seed?=?0;

rand('seed',rand_seed);

randn('seed',rand_seed);

%%

%?Set?up?parameters?and?signals.

M?=?4;?%?Alphabet?size?for?modulation

baud_rate?=?100;?%?Baud?rate

f_carrier1?=?75;?%?Carrier?frequency

Nsym?=?10000;?%?Number?of?symbols

msg?=?randi([0?M-1],Nsym,1);?%?Random?message

hMod?=?comm.RectangularQAMModulator(M);

modmsg?=?step(hMod,msg);?%?Modulate?using?QAM.?%?映射后的基帶信號

trainlen?=?1000;?%?Length?of?training?sequence

rolloff?=?.3;?%?滾降因子

span?=?20?;?%?截斷長度

sps?=?10;??%?Samples?per?symbol

rrcFilter=rcosdesign(rolloff,span,sps,'sqrt');?%根升余弦滾降濾波器，‘sqrt’均方根升余弦；‘normal’升余弦

fs?=?baud_rate*sps;?%?時間采樣率,時間采樣間隔為?1/fs?秒

Tsymbol=1/baud_rate;

%?2.?脈沖成型

%?txSig?=?upfirdn(modmsg,?rrcFilter,?sps);??%?發送端的基帶復波形信號

%?chan?=?[1;?.001];

chan?=?[.986;?.845;?.237;?.123+.31i];?%?Channel?coefficients

%?chan?=?[1?0.45?0.3+0.2i];?%?Channel?coefficients

filtmsg?=?filter(chan,1,modmsg);?%?Introduce?channel?distortion.(已經經過信道的畸變的基帶復信號，星座點)

txSig?=?upfirdn(filtmsg,?rrcFilter,?sps);??%?發送端的基帶復波形信號

txSig?=?awgn(txSig,20,'measured');?%?Add?AWGN

t?=?(0:1/fs:((length(txSig)-1)/fs)).';

T?=?t(end)+1/fs;

df?=?1/T;

freq?=?-fs/2:df:fs/2-df;

cos1?=?cos(2*pi*f_carrier1?*?t);

sin1?=?sin(2*pi*f_carrier1?*?t);

x_upconv?=?real(txSig).*?cos1?+?imag(txSig)?.*?sin1;

%%?===?接收端

x_training_wave?=?x_upconv;

x_training_msg?=?msg;

rxSig?=?[x_upconv(300:end)?;?x_upconv];

%?1.?同步

x_resampled?=?resample(rxSig,1,1);

x_sync?=?sync_two_signals(?x_resampled,x_training_wave,0);

figure(2);

plot(freq,20*log10(abs(fftshift(fft(x_sync))/max(abs(fftshift(fft(x_sync)))))));

ylim([-100,10])

xlim([0,freq(end)])

grid?on;

xlabel('頻率(Hz)');

title('接收信號');

%?2.?下變頻?+?匹配濾波

xi_dnconv?=?x_sync?.*?cos1;

xq_dnconv?=?x_sync?.*?sin1;

x_filtered?=?xi_dnconv?+?1j?*?xq_dnconv;

rxFilt?=?upfirdn(x_filtered,?rrcFilter,?1,?sps);

rxFilt?=?rxFilt(span+1:end-span);?%?這是接收端匹配濾波后的信號

%?3.?均衡

%?eq1?=?lineareq(6,?lms(0.01));?%?LMS

eq1?=?lineareq(30,?rls(0.99,0.01));?%?Create?an?equalizer?object.?%?40?taps，RLS算法，步長0.99，自相關矩陣逆矩陣的初值InvCorrInit對角線上的元素

eq1.SigConst?=?step(hMod,(0:M-1)')';?%?Set?signal?constellation.?%?標準星座圖

[symbolest,~]?=?equalize(eq1,rxFilt,x_training_msg(1:trainlen));?%?Equalize.?%?均衡器obj，需要均衡的信號，訓練序列

symbolest?=?symbolest?./?mean(abs(symbolest))?.*?mean(abs(eq1.SigConst));

%?Plot?signals.

h?=?scatterplot(rxFilt,1,trainlen,'bx');?hold?on;

scatterplot(symbolest,1,trainlen,'r.',h);

scatterplot(eq1.SigConst,1,0,'k*',h);

legend('Filtered?signal','Equalized?signal',...

'Ideal?signal?constellation');

hold?off;

%?Compute?error?rates?with?equalization.

hDemod?=?comm.RectangularQAMDemodulator(M);

demodmsg?=?step(hDemod,symbolest);?%?Demodulate?detected?signal?from?equalizer.

%?Create?ErrorRate?Calculator?System?object

serVec?=?step(comm.ErrorRate,msg(trainlen+1:end),demodmsg(trainlen+1:end));

srate?=?serVec(1)

snum?=?serVec(2)

%?Convert?integers?to?bits

hIntToBit?=?comm.IntegerToBit(log2(M));

Tx_bit?=?step(hIntToBit,?msg(trainlen+1:end));

Rx_bit?=?step(hIntToBit,?demodmsg(trainlen+1:end));

%?Calculate?BER

berVec?=?step(comm.ErrorRate,Rx_bit,Tx_bit);

brate?=?berVec(1)

bnum?=?berVec(2)

%%

% 單載波QPSK 接收端

% 2017年5月17日18:02:56

clear;

close all;

clc

rand_seed = 0;

rand('seed',rand_seed);

randn('seed',rand_seed);

%%

% Set up parameters and signals.

M = 4; % Alphabet size for modulation

baud_rate = 100; % Baud rate

f_carrier1 = 75; % Carrier frequency

Nsym = 10000; % Number of symbols

msg = randi([0 M-1],Nsym,1); % Random message

hMod = comm.RectangularQAMModulator(M);

modmsg = step(hMod,msg); % Modulate using QAM. % 映射后的基帶信號

trainlen = 1000; % Length of training sequence

rolloff = .3; % 滾降因子

span = 20 ; % 截斷長度

sps = 10; % Samples per symbol

rrcFilter=rcosdesign(rolloff,span,sps,'sqrt'); %根升余弦滾降濾波器，‘sqrt’均方根升余弦；‘normal’升余弦

fs = baud_rate*sps; % 時間采樣率,時間采樣間隔為 1/fs 秒

Tsymbol=1/baud_rate;

% 2. 脈沖成型

% txSig = upfirdn(modmsg, rrcFilter, sps); % 發送端的基帶復波形信號

% chan = [1; .001];

chan = [.986; .845; .237; .123+.31i]; % Channel coefficients

% chan = [1 0.45 0.3+0.2i]; % Channel coefficients

filtmsg = filter(chan,1,modmsg); % Introduce channel distortion.(已經經過信道的畸變的基帶復信號，星座點)

txSig = upfirdn(filtmsg, rrcFilter, sps); % 發送端的基帶復波形信號

txSig = awgn(txSig,20,'measured'); % Add AWGN

t = (0:1/fs:((length(txSig)-1)/fs)).';

T = t(end)+1/fs;

df = 1/T;

freq = -fs/2:df:fs/2-df;

cos1 = cos(2*pi*f_carrier1 * t);

sin1 = sin(2*pi*f_carrier1 * t);

x_upconv = real(txSig).* cos1 + imag(txSig) .* sin1;

%% === 接收端

x_training_wave = x_upconv;

x_training_msg = msg;

rxSig = [x_upconv(300:end) ; x_upconv];

% 1. 同步

x_resampled = resample(rxSig,1,1);

x_sync = sync_two_signals( x_resampled,x_training_wave,0);

figure(2);

plot(freq,20*log10(abs(fftshift(fft(x_sync))/max(abs(fftshift(fft(x_sync)))))));

ylim([-100,10])

xlim([0,freq(end)])

grid on;

xlabel('頻率(Hz)');

title('接收信號');

% 2. 下變頻 + 匹配濾波

xi_dnconv = x_sync .* cos1;

xq_dnconv = x_sync .* sin1;

x_filtered = xi_dnconv + 1j * xq_dnconv;

rxFilt = upfirdn(x_filtered, rrcFilter, 1, sps);

rxFilt = rxFilt(span+1:end-span); % 這是接收端匹配濾波后的信號

% 3. 均衡

% eq1 = lineareq(6, lms(0.01)); % LMS

eq1 = lineareq(30, rls(0.99,0.01)); % Create an equalizer object. % 40 taps，RLS算法，步長0.99，自相關矩陣逆矩陣的初值InvCorrInit對角線上的元素

eq1.SigConst = step(hMod,(0:M-1)')'; % Set signal constellation. % 標準星座圖

[symbolest,~] = equalize(eq1,rxFilt,x_training_msg(1:trainlen)); % Equalize. % 均衡器obj，需要均衡的信號，訓練序列

symbolest = symbolest ./ mean(abs(symbolest)) .* mean(abs(eq1.SigConst));

% Plot signals.

h = scatterplot(rxFilt,1,trainlen,'bx'); hold on;

scatterplot(symbolest,1,trainlen,'r.',h);

scatterplot(eq1.SigConst,1,0,'k*',h);

legend('Filtered signal','Equalized signal',...

'Ideal signal constellation');

hold off;

% Compute error rates with equalization.

hDemod = comm.RectangularQAMDemodulator(M);

demodmsg = step(hDemod,symbolest); % Demodulate detected signal from equalizer.

% Create ErrorRate Calculator System object

serVec = step(comm.ErrorRate,msg(trainlen+1:end),demodmsg(trainlen+1:end));

srate = serVec(1)

snum = serVec(2)

% Convert integers to bits

hIntToBit = comm.IntegerToBit(log2(M));

Tx_bit = step(hIntToBit, msg(trainlen+1:end));

Rx_bit = step(hIntToBit, demodmsg(trainlen+1:end));

% Calculate BER

berVec = step(comm.ErrorRate,Rx_bit,Tx_bit);

brate = berVec(1)

bnum = berVec(2)

同步的代碼

function?x_sync?=?sync_two_signals(?x_resampled,x_training_wave,idx?)

%?sync_two_signals(?x_resampled,x_training_wave,idx?)

%?x_resampled：收到的信號

%?x_training_wave：用發送的信號

%?idx：要找同步上的第幾段。idx?=?1,2,3,...

[hicorrI,lagsiI]=xcorr(x_resampled,x_training_wave);

[~,offsetindex]=max((hicorrI));

%?offsetindex

for?n?=?2?:?idx

%?figure;plot(lagsiI,abs(hicorrI));

hicorrI(offsetindex)?=?-inf;

[~,offsetindex]=max(hicorrI);

end

%?offsetindex

h=1;

x_sync=x_resampled(lagsiI(offsetindex)+h:lagsiI(offsetindex)+length(x_training_wave)+h-1);

end

function x_sync = sync_two_signals( x_resampled,x_training_wave,idx )

% sync_two_signals( x_resampled,x_training_wave,idx )

% x_resampled：收到的信號

% x_training_wave：用發送的信號

% idx：要找同步上的第幾段。idx = 1,2,3,...

[hicorrI,lagsiI]=xcorr(x_resampled,x_training_wave);

[~,offsetindex]=max((hicorrI));

% offsetindex

for n = 2 : idx

% figure;plot(lagsiI,abs(hicorrI));

hicorrI(offsetindex) = -inf;

[~,offsetindex]=max(hicorrI);

end

% offsetindex

h=1;

x_sync=x_resampled(lagsiI(offsetindex)+h:lagsiI(offsetindex)+length(x_training_wave)+h-1);

end

誤符號率

srate =? 0.0041

錯誤符號數

snum =? 37

誤比特率

brate =? 0.0021 錯誤比特數 bnum =? 38

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