I am executing the following code to realize 2X2 MIMO using comm.MIMOchannel system object. In the last line the variables chan_out and chan_out1 are having different outputs even though the instructions are same. Please help me rectifying the error

Question

RAGHAVENDRA 2016-11-2

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/310223-i-am-executing-the-following-code-to-realize-2x2-mimo-using-comm-mimochannel-system-object-in-the-l

评论： Yue Shang 2018-2-20

Nt=2;Nr=2;
inpt=randi([0 1],Nt,3);
hchan = comm.MIMOChannel(...
    'SpatialCorrelation',false, ...
    'NumTransmitAntennas',Nt, ...
    'NumReceiveAntennas',Nr);
chan_out=step(hchan,inpt');
chan_out1=step(hchan,inpt');

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Answer 1

Walter Roberson 2016-11-2

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https://ww2.mathworks.cn/matlabcentral/answers/310223-i-am-executing-the-following-code-to-realize-2x2-mimo-using-comm-mimochannel-system-object-in-the-l#answer_241646

You are applying step() to the same system both times. After you step() the first time, its state changes so the next step() produces different output.

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Walter Roberson 2016-11-2

在 MATLAB Online 中打开

Nt = 2; Nr = 2;
inpt = randi([0 1],Nt,3);
hchan = comm.MIMOChannel(...
    'SpatialCorrelation',false, ...
    'NumTransmitAntennas',Nt, ...
    'NumReceiveAntennas',Nr);
chan_out = step(hchan, inpt');
reset(hchan)
chan_out1 = step(hchan, inpt');

It is unlike that you want to do this. step is defined as:

"Call step to filter the input signal through a MIMO multipath fading channel according to the properties of comm.MIMOChannel. The behavior of step is specific to each object in the toolbox."

The channel is intended to update after each step; the result of applying step() one sample (per channel) at a time should be the same as if you passed in an array of samples.

MIMOChannels use random number generation. To be sure you get the same result each time, you also need to deal with the random number seed. Please read https://www.mathworks.com/help/comm/ref/comm.mimochannel.reset.html

RAGHAVENDRA 2016-11-2

Thank you very much for the help. I have understood now. Followed the procedure in the link and have done the required changes as mentioned. I am getting the desired output.

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