receiver_p2of2.m

数字音频信号的调制与解调的源码程序.可保证声音信号怒失真输出

%this is the second part of a receiver(total 2 parts)
%the main task is windowing,demodulation and verifying
%input:data_partition, whether we get it from receiver_p1 method 1 or 2
%We can check which one works or performs better under certain conditions

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%                        windowing，结果放在data_window里                       %
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%windowing is used to remove guard interval.However,because of the
%multipath effect, we cannot locate it in the traditional position,i.e.
%from the number delta+1 to the end. We have to shift the window backward
%for a certain numbers, say noff, the determaine of which will be another
%challange, we'll talk about that later
%note that I not only partition the data, but also rearrange them in a right order
noff=2;                                    % change noff to get better performance
data_window=[data_partition(:,delta+1:Ts-2),data_partition(:,delta-noff+1:delta)];

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%                    OFDM demodulation，结果放在OFDM_de里                       %
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%OFDM demodulation & ajusting
%因为发射端的信号在OFDM modulation之前经过了交插换位、加0处理，所以现在需要变回来
%得到DQPSK symbols
OFDM_f=[];
%OFDM_t的每行元素（对应每个data symbol）分别做FFT
for i_O_f=1:(n_of_s-1)
    OFDM_f(i_O_f,:)=fft(data_window(i_O_f,:));
end

%前后768个数交换位置，舍去中间的0
OFDM_de=[OFDM_f(:,1281:2048),OFDM_f(:,1:768)];

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%                   Differential demodulation,结果放在Diff_de里                 %              
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%还没找到合适的简化做法，只能先笨笨的用两次循环
Diff_de(1,:)=OFDM_de(1,:);
for i_O_f=1:(n_of_s-2)
    for i_k=1:k
        Diff_de(i_O_f+1,i_k)=OFDM_de(i_O_f+1,i_k)/OFDM_de(i_O_f,i_k);
    end
end

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%                     Freq deinterleaving,结果放在Freq_de里                     %              
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%采用了328目录下的de_interleaving简便算法，由于matrix_k_inv的求解需要较多时间，
%这里就直接拿过来用了。
Freq_de=Diff_de*matrix_k_inv;

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%                    QPSK demapping，结果放在data_rebuilt里                     %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%把deinterleave过的信号demapping，重建原始01序列data_rebuilt

%所有data的前1536个
data_rebuilt_1=-(real(Freq_de*(2^0.5))-1)/2;
%所有data的后1536个
data_rebuilt_2=-(imag(Freq_de*(2^0.5))-1)/2;
%将它们合并，得到完整的重建序列
data_rebuilt_3=[data_rebuilt_1,data_rebuilt_2];
%由于matlab对2^0.5是换算成小数计算的，造成恢复后的0点不是0，而是一些很小的数，
%所以再加一步取整,这一步未必是必要的，只是为了好看。。。也可以找别的更好的方法
data_rebuilt=round(data_rebuilt_3);

%对本例（自造n_data个数据symbol），验证extract的结果是不是跟origin一样
%方法是求origin的逆阵，再与extract的结果相乘，如果正确解调，结果应该
%是一个单位阵，阶数与数据symbol个数相同（本例中为n_of_s-1）
%注意，由于本例的矩阵并不是方阵，因此不能用求逆函数inv，只能求伪逆pinv
verify=data_rebuilt_3*pinv(mass_prj);
disp(verify);