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

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');

Answer 1

[Walter Roberson]

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.

[RAGHAVENDRA]

Thank you, but how can i retain the same state. Can you please help me with the step()

[Walter Roberson]

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]

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.

Answer 2

[thirumalraj karthikeyan]

i have use this code...its very use full but i have problem in ...Nt = 4; Nr = 4;...any ideas to moreover this problem

[Yue Shang]

Can you be specific for your problem with Nt = Nr = 4?