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## Re: [Discuss-gnuradio] OFDM demodulation problem / example video

**From**: |
Robert McGwier |

**Subject**: |
Re: [Discuss-gnuradio] OFDM demodulation problem / example video |

**Date**: |
Mon, 03 Apr 2006 10:48:32 -0400 |

**User-agent**: |
Thunderbird 1.5 (Windows/20051201) |

Jens:
This pi/4-DQPSK. That means

`New-symbol * (complex conjugate (Old-symbol)) is pi/4 modulo pi/2.
``Are you taking this into account on both the transmitter and the
``receiver and it in all of the bins before your inverse fft provides the
``time domain signal to transmit would be my best best.
`

`I will look at it more carefully today if I have time but this question
``would be the first one I would ask the code to tell me.
`
Bob
Jens Elsner wrote:

Here is my little problem in animated frames.
What you are seeing is already DQPSK. Displayed is the signal
constellation for one OFDM frame, 75 symbols. The code was posted earlier.

`The problem: The (differential!) signal constellation has a constant phase
``offset for each OFDM symbol. Why? What to do about it?
`
Jens

`
`

--
AMSAT VP Engineering. Member: ARRL, AMSAT-DL, TAPR, Packrats,
NJQRP/AMQRP, QRP ARCI, QCWA, FRC. ARRL SDR Wrk Grp Chairman
Laziness is the number one inspiration for ingenuity. Guilty as charged!

**[Discuss-gnuradio] OFDM demodulation problem / example video**, *Jens Elsner*, `2006/04/03`
**Re: [Discuss-gnuradio] OFDM demodulation problem / example video**,
*Robert McGwier* **<=**

**Re: [Discuss-gnuradio] OFDM demodulation problem / example video**, *Achilleas Anastasopoulos*, `2006/04/04`
**Re: [Discuss-gnuradio] OFDM demodulation problem / example video**, *Jens Elsner*, `2006/04/04`
**Re: [Discuss-gnuradio] OFDM demodulation problem / example video**, *Robert McGwier*, `2006/04/04`
**Re: [Discuss-gnuradio] OFDM demodulation problem / example video**, *Prateek Dayal*, `2006/04/05`
**Re: [Discuss-gnuradio] OFDM demodulation problem / example video**, *Robert McGwier*, `2006/04/05`
**Re: [Discuss-gnuradio] OFDM demodulation problem / example video**, *Jens Elsner*, `2006/04/05`
**Re: [Discuss-gnuradio] OFDM demodulation problem / example video**, *Robert McGwier*, `2006/04/05`
**Re: [Discuss-gnuradio] OFDM demodulation problem / example video**, *Jens Elsner*, `2006/04/06`