Re: [Discuss-gnuradio] OFDM_TX_RX

[Marcus Müller]

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
> > >  > > 
> > > 
> > >  _______________________________________________
> > >  Discuss-gnuradio mailing list
> > >  address@hidden
> > >  https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
> 
> 
> 
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