Re: Detected an invalid packet at item

[Johannes Demel]

Hi Hamed,

you mentioned that increasing the TX and RX gain reduced the number of 
invalid packets. Still, as long as you transmit over an imperfect 
channel, there will be reception errors.

The reports you receive stem from the logging system. They are tagged 
":info:" because this might be an interesting information in some cases. 
However, this is not a software system error. This is a reception error 
and should be treated as such.
You already mentioned a few channel effects that influence your reception:
- multipath
- interference
I'd like to stress that:
- noise
- hardware imperfections
- any unfortunate condition in your receiver chain
may also affect your reception.

The questions that arise are:
- What do you want to fix here?
- Did you observe anything that you didn't expect?

Cheers
Johannes

On 14.05.23 05:33, Hamed Al-Zubi wrote:
> Ed,
>
> I tried the NLOS scenario to avoid distortion, but still the same error 
> occurs.
>
> Thanks!
> HZ
> On Saturday, May 13, 2023 at 11:07:22 AM CDT, Ed Criscuolo 
> <ed@chessie.com> wrote:
>
>
> 2 meters seems like an incredibly short distance unless you have an 
> attenuator in series with the Tx antenna. You may be overdriving the 
> receiver and causing distortion errors.
>
> @(^.^)@ Ed
> Sent from my iPhone
>
> > On May 12, 2023, at 8:10 PM, Hamed Al-Zubi <hamed.zubi1980@yahoo.com> 
> > wrote:
> >
> > 
> > Hello,
> >
> > I am utilizing two USRPs, specifically the X300 models, along with 
> > GNURadio for the purpose of transmitting and receiving OFDM signals. I 
> > have implemented the OFDM flowgraphs available on Github for this 
> > purpose. The transmission and reception setup involves LOS 
> > (Line-of-Sight) configuration, where the transmit and receive antennas 
> > are positioned with a separation distance of 2 meters. To minimize the 
> > impact of multipath interference, the antennas are surrounded by 
> > absorption boards. Although the transmission and reception process 
> > itself is functioning without issues, I have encountered a problem 
> > when displaying the channel state information. In particular, there 
> > are instances where invalid packets are detected, as evidenced by the 
> > following occurrences.
> >
> > *packet_headerparser_b :info: Detected an invalid packet at item 167472*
> > *header_payload_demux :info: Parser returned #f*
> >
> > I have searched the possible causes of the error I'm encountering, and 
> > there are a few factors that have been suggested:
> >
> > 1- Interference--> I used different frequencies and ensured they are 
> > not in use.
> > 2- Multipath --> absorption boards were used to minimize the impact of 
> > multipath.
> > 3- Some people suggested to change  the FFT length and CRC length as a 
> > potential solution, however, modifying these papermeters did not 
> > resolve the issue.
> >
> > When I used a channel model instead of USRPs, the error did not occur.
> > I am still uncertain about the exact cause of the error I am experiencing.
> >
> >
> > Thanks,
> > HZ

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