modem.oqpskmod -> modem.oqpskdemod不同的结果

Question

我正在尝试模拟IEEE 802.15.4/ZigBEE PHY，...

   chip_values = [
   1,1,0,1,1,0,0,1,1,1,0,0,0,0,1,1,0,1,0,1,0,0,1,0,0,0,1,0,1,1,1,0;
   1,1,1,0,1,1,0,1,1,0,0,1,1,1,0,0,0,0,1,1,0,1,0,1,0,0,1,0,0,0,1,0;
   0,0,1,0,1,1,1,0,1,1,0,1,1,0,0,1,1,1,0,0,0,0,1,1,0,1,0,1,0,0,1,0;
   0,0,1,0,0,0,1,0,1,1,1,0,1,1,0,1,1,0,0,1,1,1,0,0,0,0,1,1,0,1,0,1;
   0,1,0,1,0,0,1,0,0,0,1,0,1,1,1,0,1,1,0,1,1,0,0,1,1,1,0,0,0,0,1,1;
   0,0,1,1,0,1,0,1,0,0,1,0,0,0,1,0,1,1,1,0,1,1,0,1,1,0,0,1,1,1,0,0;
   1,1,0,0,0,0,1,1,0,1,0,1,0,0,1,0,0,0,1,0,1,1,1,0,1,1,0,1,1,0,0,1;
   1,0,0,1,1,1,0,0,0,0,1,1,0,1,0,1,0,0,1,0,0,0,1,0,1,1,1,0,1,1,0,1;
   1,0,0,0,1,1,0,0,1,0,0,1,0,1,1,0,0,0,0,0,0,1,1,1,0,1,1,1,1,0,1,1;
   1,0,1,1,1,0,0,0,1,1,0,0,1,0,0,1,0,1,1,0,0,0,0,0,0,1,1,1,0,1,1,1;
   0,1,1,1,1,0,1,1,1,0,0,0,1,1,0,0,1,0,0,1,0,1,1,0,0,0,0,0,0,1,1,1;
   0,1,1,1,0,1,1,1,1,0,1,1,1,0,0,0,1,1,0,0,1,0,0,1,0,1,1,0,0,0,0,0;
   0,0,0,0,0,1,1,1,0,1,1,1,1,0,1,1,1,0,0,0,1,1,0,0,1,0,0,1,0,1,1,0;
   0,1,1,0,0,0,0,0,0,1,1,1,0,1,1,1,1,0,1,1,1,0,0,0,1,1,0,0,1,0,0,1;
   1,0,0,1,0,1,1,0,0,0,0,0,0,1,1,1,0,1,1,1,1,0,1,1,1,0,0,0,1,1,0,0;
   1,1,0,0,1,0,0,1,0,1,1,0,0,0,0,0,0,1,1,1,0,1,1,1,1,0,1,1,1,0,0,0];

   tx = [];
   values = randsrc(1,1,[0:15]);
   for k=1:length(values)
    sym = values(k);
    tx = [tx chip_values((sym+1),1:end)];
   end;

   tx = tx.';
   h = modem.oqpskmod;
   y = modulate(h, tx);
   g = modem.oqpskdemod(h);
   z = demodulate(g, y);
   length(z)
   for k=1:length(tx)
    if(tx(k)~=z(k))
     fprintf('%d %d\n',tx(k),z(k)); 
    end;
   end;

我的问题是，在这个简单的例子中，为什么我的tx和z不包含相同的值，即使我还没有引入任何噪声？谢谢!

tx的取值如下：

第1至13列

 0     1     1     0     0     0     0     0     0     1     1     1     0

第14至26列

 1     1     1     1     0     1     1     1     0     0     0     1     1

第27至32列

 0     0     1     0     0     1

Z的值如下：

第1至13列

 3     0     1     1     0     0     0     0     0     0     1     1     1

第14至26列

 0     1     1     1     1     0     1     1     1     0     0     0     1

第27至32列

 1     0     0     1     0     0


  h =

         Type: 'OQPSK Modulator'
            M: 4
  PhaseOffset: 0
Constellation: [1x4 double]
  SymbolOrder: 'Binary'
SymbolMapping: [0 1 2 3]
    InputType: 'Integer'

  g =

         Type: 'OQPSK Demodulator'
            M: 4
  PhaseOffset: 0
Constellation: [1x4 double]
  SymbolOrder: 'Binary'
SymbolMapping: [0 1 2 3]
   OutputType: 'Integer'
 DecisionType: 'Hard decision'

Answer 1

对我来说很难说，因为我没有安装通信工具箱，但我建议尝试使用文档中的示例中给出的更简单的输入。使用

tx = randint(10,1,8) 

例如。然后看看输出，而不仅仅是比较。差异是在机器精度上还是接近机器精度？你不用告诉我们打印出来的是什么(它们是否匹配？)试着看看tx和z之间的差异，是不是接近eps (我是2.2204e-016)？

数据传入和传出之间是否存在转换？告诉我们数据是怎么回事。

更新

我很高兴你发布了实际的输入和输出。它看起来像是z向右移动了一位(由于某种原因，开头有一个3)，这意味着你失去了最后一位。看看Matlab documentation，有一张纸条上写着

OQPSK解调器具有1个符号延迟。

我想这就解释了这个问题。基本上，只需在调制器的输入末尾填充一个额外的0，从解调器的输出中去掉第一个元素，就可以开始工作了。