SNR of BPSK vs. OOK
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From: Jerry Avins on 15 Feb 2010 20:24 rbb wrote: >> I don't understand how increasing signal by 2x with noise >> remaining the same ***decreases*** SNR by 3 dB. >> > > Sorry. Increases the SNR by 3dB. Coherent addition doubles the signal *voltage*, increasing S by 6 dB. Doubling the bandwidth doubles the noise *power*, increasing N by 3 dB. This gives a net gain in S/N of 3 dB as it should, considering that the bandwidth (and the sideband power) has doubled. You wanted a free lunch? Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
From: Vladimir Vassilevsky on 16 Feb 2010 11:01
Jerry Avins wrote: > rbb wrote: > >>> I don't understand how increasing signal by 2x with noise >>> remaining the same ***decreases*** SNR by 3 dB. >>> >> >> Sorry. Increases the SNR by 3dB. > > > Coherent addition doubles the signal *voltage*, increasing S by 6 dB. > Doubling the bandwidth doubles the noise *power*, increasing N by 3 dB. > This gives a net gain in S/N of 3 dB as it should, considering that the > bandwidth (and the sideband power) has doubled. You wanted a free lunch? It is not very simple to make good receiver for OOK because you have to establish 0/1 decision threshold. The receiver performance depends on that threshold dramatically, especially if incoherent detector is used. In any realistic scenario, the amplitude of the signal is variable, and the threshold has to track the variation. Fortunately, they use OOK mostly for the applications where +/- 6dB of performance doesn't matter. Vladimir Vassilevsky DSP and Mixed Signal Design Consultant http://www.abvolt.com |