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Differential coding for ICI cancelation

Started by asmaatala 6 years ago3 replieslatest reply 6 years ago86 views

Differential QPSK (DQPSK)  is used with OFDM to transmit data over wireless fading channel. Is differential coding enough to solve the proplem of subcarriers phase shift  (ICI)?

Iam asking this question since this technique assumes that the phase shift between two consecutive symbols on the same subcarrier is constant.

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Reply by SlartibartfastMay 15, 2017

The differential modulation allows the data to be recovered without requiring phase coherence in the receiver.  It does not mitigate interference of any kind, including ICI.

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Reply by asmaatalaMay 15, 2017

"Even though a frequency offset introduces a time-varying phase error, as long as this error changes slowly relative to the symbol rate, the differential phase from one symbol to the next will remain accurate enough for reliable data transfer." , these words from this link  https://www.allaboutcircuits.com/technical-articles/differential-quadrature-phase-shift-keying-dqpsk-modulation/ , as i understand from this, differential coding can work well even if there is frequency or phase offset. 

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Reply by SlartibartfastMay 15, 2017

Yes, you don't have to maintain phase coherence, i.e., phase-lock.   Differential coding allows there to be a small amount of phase rotation between symbols, due to frequency offset or drift or whatever reason.   There is a performance penalty for using differential coding, but sometimes it is worth it for simplification of the system.   It doesn't really do anything to mitigate interference, though.