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I am a beginner again to signal processing, I did my degree over ten years ago, and I am relearning all my signal processing stuff.

I am a software developer by trade but now I am looking at some LTE PHY signal processing.

I am trying to understand how QPSK signals get recovered in LTE. As I understand things, the I/Q signal is passed through a low pass filter, which results in a sort of NRZ complex waveform.

However if I try to get a constellation diagram of this data it is a mess. So how do I recover this LPF baseband to see the constellation diagram?

All I get by Google is 'NRZ' or 'Zero-forcing' or 'DC offset'. I am awaiting my LTE matlab toolbox, but I should be able to recover the I/Q right? Do I need to do some sort of convolution?

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  • $\begingroup$ um, there's no NRZ in LTE, and you're missing the whole OFDM aspect – I think whatever you've been reading hasn't been right. $\endgroup$ – Marcus Müller Aug 27 '19 at 15:42
  • $\begingroup$ Thanks Marcus, I've been reading a lot of ETSI specs, very confusing. So what you are saying is my "base band" I/Q signal actually has lots of carriers in it? So to get a constellation diagram I need to apply an FFT to extract each of the carriers, and then check the constellation of each carrier's data I/Q? I do vaguely recall something about this. $\endgroup$ – hazel Aug 28 '19 at 11:18
  • $\begingroup$ yep, it's OFDM; you might really want to refresh your memory of that. $\endgroup$ – Marcus Müller Aug 28 '19 at 12:24

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