Is the comm.RaisedCosineTransmitFilter stateful?

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Michael Schwager 2017-5-17

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https://ww2.mathworks.cn/matlabcentral/answers/340582-is-the-comm-raisedcosinetransmitfilter-stateful

评论： Mason Huynh 2021-8-6

When I reuse an instance of comm.RaisedCosineTransmitFilter multiple times with the same vector, I get several different results until it stabilizes.

If I use a new instance each time, the result is the same. So it looks like the filter object is stateful, which I suppose makes sense, but I guess I expected the impulse definition to be essentially just a declaration of coefficients, not necessarily the state variable.

The first few times you run the below lines with the 4-long impulse vector, you get a different plot, and on ones with a 3-long impulse vector, the first time you run it, the plot is 8 samples shorter than the previous one, as I would expect, but subsequently running it several more times, the plot changes shape.

K>> rctFilt=comm.RaisedCosineTransmitFilter()
rctFilt = 
comm.RaisedCosineTransmitFilter with properties:
                     Shape: 'Square root'
             RolloffFactor: 0.2000
       FilterSpanInSymbols: 10
    OutputSamplesPerSymbol: 8
                      Gain: 1
K>> clf;plot(real(step(rctFilt, [1 0 0 0]')));xlim([0 32])
K>> clf;plot(real(step(rctFilt, [1 0 0 0]')));xlim([0 32])
K>> clf;plot(real(step(rctFilt, [1 0 0 0]')));xlim([0 32])
K>> clf;plot(real(step(rctFilt, [1 0 0 0]')));xlim([0 32])
K>> clf;plot(real(step(rctFilt, [1 0 0 ]')));xlim([0 32])
K>> clf;plot(real(step(rctFilt, [1 0 0 ]')));xlim([0 32])
K>> clf;plot(real(step(rctFilt, [1 0 0 ]')));xlim([0 32])

I'm just trying to figure out how the transmit filter differs from the receive filter.

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Mason Huynh 2021-8-6

I see exactly the same issue, which seems unreasonable as Raised Cosine Transmit Filter is a filter, and the output of each instance should not depend on previous instances.

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