0
$\begingroup$

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?

$\endgroup$
2
$\begingroup$

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).

$\endgroup$
7
  • $\begingroup$ 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 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 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 at 12:47
  • $\begingroup$ If you are guaranteed a transition on every symbol it simplifies doing timing recovery. $\endgroup$ Jun 17 at 12:49
  • $\begingroup$ Now I understand.^^ Thank you for the explanation. $\endgroup$
    – agile
    Jun 17 at 13:17

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.