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Signal Processing

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  • $\begingroup$ Thanks Dan, but as i have written they are two separate blocks, one is Bpsk demodulator and one is level detector. $\endgroup$ Commented May 11, 2020 at 14:26
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    $\begingroup$ @Riva11 If there are 4 amplitude levels in the signal, this is not a BPSK modulated signal. That said, a BPSK demodulator that multiplies the recieved signal with the carrier and low pass filters will still put out 4 levels, and to demodulate you would set the thresholds as I have indicated. Am I missing something else? $\endgroup$ Commented May 11, 2020 at 15:00
  • $\begingroup$ What OP @Riva11 describes is not 4-PAM in the usual sense of the word. Standard 4-PAM would use equally-spaced levels $-3, -1, +1, +3$ instead of the $-2, -1, +1, +2$ used in the OP's system. Well, at least the dibits are assigned to the levels in Gray code order. Nonetheless, the first and second bits have different probabilities of error and so the BER calculation is messy too. $\endgroup$ Commented May 11, 2020 at 15:37
  • $\begingroup$ @DilipSarwate Ah yes, good point! $\endgroup$ Commented May 11, 2020 at 16:01
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    $\begingroup$ It is still called PAM not BPSK. PAM need not have equally spaced levels, but under AWGN would have the best BER if done as such. Here is an example of PAM with unequal levels to make up for non-linearity in the modulator. If the modulation is done by changing the amplitude of each pulse only, this is called PAM. $\endgroup$ Commented May 12, 2020 at 11:21