Thank you so match for your detailed and accurate answers. I received a second answer from Phil Frost in which he explained my result. So now i am doing same thing with QPSK and 8PSK.
Cheers, 2017-07-04 14:25 GMT+02:00 Phil Frost <ind...@bitglue.com>: > On Tue, Jul 4, 2017 at 6:30 AM Rafik ZITOUNI <rzito...@gmail.com> wrote: > >> Could you give me an explanation how it was possible to obtain a good snr >> and ber with a wrong constellation with good SNR and BER? >> > > for BPSK the value of the bit is determined only by examining the sign of > the real part. There will be errors only when the cluster of points > approaches the imaginary axis, where the sign of the real point changes. If > the frequency offset it small (it rotates slowly) and the SNR high, then > for most rotations there will be negligible errors. > > In practice you will probably have great difficulty tuning the receiver > accurately enough for this to work. Furthermore, doppler shift in the > channel may make the frequency change over time. Thus, the need for the > Costas loop or some other frequency synchronization. > > Alternately, you can compare the phase of the current signal to the > previous symbol: https://en.wikipedia.org/wiki/ > Phase-shift_keying#Demodulation > -- <http://www.ece.fr/>Rafik
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