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how to set samplerate in QAM Modulator?

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Giovanni on 31 Aug 2015
since some time I am struggling with a little inconvenient. I am trying to generate a M-QAM signal. In past I always did it by generating a stream of binary data with a certain length by using the "randi" function, I was configuring a modem.qammod object by using the parameter M (order of the modulation) in advance, and using it to generate my transmitted symbols. After this I was adding my pulse shaping raised cosine filter, filtering the number of samples I gave as input parameter after the apposite upsampling. Unfortunately the quality of the signal´s constellation I was obtaining was not optimal, after the raised cosin filter I get a constellation which is not really clean. My problem is also, defining the bandwidth of my signal. This normally depends on the symbolrate and on the pulse shaping filter. I have tried to use the function implementing the Rectangular QAM Modulator (comm.RectangularQAMMModulator()), but still my problem is related to the way I define the reltationship between the samplerate and the band occupied by my signal. In general with those functions I get the constellation I am looking for, but how can I then get the relationship with the samplerate and draw the PSD of my baseband signal with pwelch for instance???


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