Re: [Discuss-gnuradio] OFDM_TX_RX

[Marcus Müller]

After reading the original paper, you've meant "2D- or 3D-DCT" :)
On Sat, 2019-05-25 at 21:20 +0100, farid mihoub wrote:
> Hi,
> Discrete cosine transform
> 
> 
> 25.05.2019, 21:02, "Marcus Müller" <address@hidden>:
> > hi, what's 2DCT_or_3DCT?
> > 
> > Best regards,
> > Marcus
> > 
> > On Sat, 2019-05-25 at 19:38 +0100, farid mihoub wrote:
> > >  My application is to broadcast a video using softcast approach. 
> > >  Video-->2DCT_or_3DCT-->Floating coefficients-->complex_mapping
> > >  -->ofdm_phy
> > >  My video quality (PSNR) will depend linearly to my SNR so no
> > > need to
> > >  have an adaptive modulation.
> > > 
> > > 
> > >  25.05.2019, 18:27, "Marcus Müller" <address@hidden>:
> > >  > 1- So, you have an SNR of best-case 16 dB; that's not high for
> > > an
> > >  > OFDM
> > >  > system.
> > >  > 
> > >  > 2- No, there's no power normalization. Hint: you can look all
> > > this
> > >  > up
> > >  > by actually looking inside these blocks! This would make a lot
> > > of
> > >  > sense, since it sounds you don't actually want to use tzhe
> > > OFDM
> > >  > blocks
> > >  > at all. The whole advantage of the OFDM blocks compared to
> > > just
> > >  > doing
> > >  > an IFFT of your transmit vector is that you get a header and
> > >  > modulation
> > >  > scheme.
> > >  > 
> > >  > 3- Not quite sure what "information is linearly related to
> > > complex
> > >  > symbols" means? Can you elaborate?
> > >  > 3b- A case where you *don't* do FEC is either a non-
> > > communications
> > >  > system (i.e. you don't actually want to do OFDM for the reason
> > > of
> > >  > transmitting information) or the extremely-bad-SNR case (where
> > > FEC
> > >  > makes your BER better). For both cases, the existing OFDM
> > > blocks
> > >  > are
> > >  > more of an obstacle than a solution.
> > >  > 
> > >  > What are you building? What is your overall application.
> > > Please
> > >  > paint
> > >  > the bigger picture – it's a bit frustrating to try to help
> > > you, but
> > >  > then only get told that "this is not how I want to do it".
> > >  > 
> > >  > Best regards,
> > >  > Marcus
> > >  > 
> > >  > On Sat, 2019-05-25 at 18:39 +0200, Marcus Müller wrote:
> > >  > > Dear Farid,
> > >  > > 
> > >  > > please always respond on the mailing list.
> > >  > > Thank you,
> > >  > > Marcus Müller
> > >  > > 
> > >  > > On Sat, 2019-05-25 at 17:36 +0100, farid mihoub wrote:
> > >  > > > 1- For the noise : in the TX side the output is in the
> > > order
> > >  > > of 2A,
> > >  > > > the noise 0.05A.
> > >  > > > 2-Second even without noise, the const does not affect the
> > >  > > > transmission, is there any sort of power normalization?
> > >  > > > 3-For the FEC and the modulation I want to try my custom
> > >  > > mapping
> > >  > > > where information is linearly related to complex symbols,
> > > and
> > >  > > my
> > >  > > > application doesn't require error correction. 
> > >  > > > 
> > >  > > > Thank you.
> > >  > > > 
> > >  > > > 
> > >  > > > 25.05.2019, 17:06, "Marcus Müller" <address@hidden>
> > > :
> > >  > > > > Hello Farid,
> > >  > > > > On Sat, 2019-05-25 at 15:59 +0100, farid mihoub wrote:
> > >  > > > > > Hello,
> > >  > > > > > 
> > >  > > > > > In the OFDM_tx, rx examples in gr-digital :
> > >  > > > > > 1- Why just a low level of noise affect the
> > > transmission
> > >  > > and
> > >  > > > > > cause it
> > >  > > > > > to stop.
> > >  > > > > 
> > >  > > > > "low" is relative. It seems it's high enough to cause
> > > packet
> > >  > > > > losses,
> > >  > > > > iff it's actually the noise.
> > >  > > > > 
> > >  > > > > > 2- in the the Tx output and the Rx input no matter the
> > >  > > value
> > >  > > > > > of
> > >  > > > > > the
> > >  > > > > > multiply constant we apply
> > >  > > > > > that would not affect our transmission.
> > >  > > > > 
> > >  > > > > Then it's probably not only the noise!
> > >  > > > > 
> > >  > > > > > 3- Is there any way to separate channel estimation and
> > >  > > > > > tracking
> > >  > > > > > from
> > >  > > > > > data transmission, sometime I get the error "invalid
> > >  > > packet
> > >  > > > > > detected!" form the packet parser, also I need my data
> > > to
> > >  > > > > > bypass
> > >  > > > > > FEC
> > >  > > > > > and QAM.
> > >  > > > > 
> > >  > > > > Um, prior to QAM demodulation there is no data, and
> > > prior to
> > >  > > FEC
> > >  > > > > decoding there is no information bits, so I'm not sure
> > > what
> > >  > > you
> > >  > > > > want?
> > >  > > > > 
> > >  > > > > > My purpose is to stream raw complex data to the I/Q
> > >  > > > > > components
> > >  > > > > > directly.
> > >  > > > > 
> > >  > > > > Then it seems you don't want an OFDM transceiver but
> > > maybe
> > >  > > just
> > >  > > > > simply
> > >  > > > > a single IFFT? Not quite sure what you have in mind.
> > >  > > > > 
> > >  > > > > Best regards,
> > >  > > > > Marcus
> > >  > > > > 
> > >  > > 
> > >  > > _______________________________________________
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> > >  > > address@hidden
> > >  > > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
> > > 
> > > 
> > > 
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