From the peak to average power ratio point of view OQPSK is better than pi/4-DQPSK. What is the advantage of pi/4-DQPSK compare to OQPSK? Why Bluetooth 2 use pi/4-DQPSK instead of OQPSK?


1 Answer 1


One particular advantage of pi/4 QPSK and pi/4 DQPSK is that there is always a transition between symbols, making demodulation simpler. Differential - PSK (such as DQPSK) can be demodulated without a local oscillator (by comparing previous symbols to the current ones), making for extremely low cost receivers at a modest expense in performance (sensitivity).

  • $\begingroup$ Thank you for your answer. I don't understand your comment "that there is always a transition between symbols, making demodulation simpler" Could you explain this part easily? $\endgroup$
    – agile
    Jun 17, 2021 at 12:14
  • $\begingroup$ @agile Observe the state transitions for pi/4 QPSK and compare that to OQPSK. Every other symbol in pi/4 QPSK moves to another 4 point constellation that is completely rotated by 45 degrees, thus forcing a transition. With OQPSK in contrast it is possible that you stay on the same location in the constellation over multiple symbols. $\endgroup$ Jun 17, 2021 at 12:16
  • $\begingroup$ I already know what you said. But I don't understand why that thing simplifies the demodulation. $\endgroup$
    – agile
    Jun 17, 2021 at 12:47
  • $\begingroup$ If you are guaranteed a transition on every symbol it simplifies doing timing recovery. $\endgroup$ Jun 17, 2021 at 12:49
  • $\begingroup$ Now I understand.^^ Thank you for the explanation. $\endgroup$
    – agile
    Jun 17, 2021 at 13:17

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