In BPSK signal coherent demodulation, if the recovered coherent carrier has a static phase error of 10 degrees, how many DB does the BER performance of the system decrease? The degradation of BER performance of QPSK demodulation system using coherent carrier with 10 degrees static phase error is analyzed?
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2\$\begingroup\$ This looks like a conceptual question that would be assigned as part of a homework or exam. Can you show your attempt so far, including any assumptions made, mathematical steps taken, etc? \$\endgroup\$– nanofaradCommented Apr 12, 2021 at 3:51
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\$\begingroup\$ I don't know the relationship between static phase difference and BER, and how they can influence BER performence. \$\endgroup\$– apple MusicCommented Apr 12, 2021 at 4:21
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\$\begingroup\$ May there have any formula I'm not sure \$\endgroup\$– apple MusicCommented Apr 12, 2021 at 4:23
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\$\begingroup\$ It's my homework. \$\endgroup\$– apple MusicCommented Apr 12, 2021 at 4:31
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\$\begingroup\$ In that case, please look back at your textbook and other references to find how the BER of a BPSK/QPSK system was estimated using mathematical techniques. Then, add the phase error and perform the derivation again, comparing the formula you derived to the formula derived without phase error. \$\endgroup\$– nanofaradCommented Apr 12, 2021 at 14:01
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1 Answer
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The actual phase of the carrier during modulation depends on the start and end of changes in phase shift rather than absolute.
The method of demodulation must be determined before coherent phase error effects on BER may or may not be affected.
e.g. it depends on the mixer used for detected phase shift. If the modulation exceeds the phase detector’s 90 deg or 180 deg detection then the result is a reduction of Vpp phase to voltage conversion, i.e. signal level thus SNR ratio, otherwise if it does not exceed by closing the loop with PLL to null the carrier phase error to the middle of the detector range then no degradation of signal would occur. There are many types of phase detectors from analog multipliers to digital XOR and D FF phase/frequency types which inject more jitter but wider +/-180 phase detection and other types. The filter Q and group delay distortion also can introduce ISI in the detector so Raised Cosine filters with zero ISI would have to be assumed.
