Re: [Discuss-gnuradio] OFDM TX/RX

[Martin Braun]

On 03/16/2018 09:33 AM, address@hidden wrote:
> Hello all,
> 
> I want to make a flow graph for transmitting and receiving OFDM
> modulated data. To be precise, I want to do a LTE-M "like"
> transmission/reception, so I am trying to transmit data with a BW of
> 1.08 MHz OFDM.
> To do so, I use the following configuration : samp_rate = 1.92 MHz, fft
> length = 128, number of sub carriers = 72 , cp = 32
> 
> I modified the tx_ofdm.grc example file
> (/gnuradio/gr-digital/examples/ofdm/tx_ofdm.grc)
> To summary, I change the occupied carriers : range(-36, -21) +
> range(-20, -7) + range(-6, 0) + range(1, 7) + range(8, 21) + range(22,
> 37),) ; pilot carriers and symbols unchanged ; double the sync words to
> be equal to fft length.
> 
> The problem is at the output of the "Tag debug" I have just those
> messages :
> INFO: Parser returned #f
> INFO: Detected an invalid packet at item 1496
> ......
> INFO: Parser returned #f
> INFO: Detected an invalid packet at item 681901
> 
> And the spectrum isn't "stable" at 1.08 MHz BW.

Are you going across the air? The most common cause for this is too much
gain, and resulting distortions caused by large PAPR. If you've
increased the number of carriers, PAPR also goes up (a bit).

-- M
>  
> 
> What am I doing wrong ? How the sync words are determine ? Should I add
> pilot/symbol carriers ?
> 
> 
> Best Regards and thanks by advance,
> 
> Guillaume Tochou
> 
> 
> 
> 
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