Re: Missings packets on OFDM system simulation

[Marcus Müller]

Definitely not dBW, unless you have a massive amplifier attached, AND somehow calibrated 
your system, AND apply that calibration. From where would the "decibel relative to Watts" 
know what a Watt is?



On 14.07.23 17:56, JORGE GONZALEZ ORELLANA via GNU Radio, the Free & Open-Source Toolkit 
for Software Radio wrote:

Hi Johannes,

I'm not sure what you mean with "Did you check the actual sample level on the "OFDM 
Transmitter" output port?" but in the output of the OFDM transmitter block I got about 15 
[dBW], this measurement was done like this: OFDM Transmitter -> complex to mag^2 -> moving 
average -> 10log(input) -> file sink


For the SNR, I calculate it with the attach flowgraph and test different levels of ''Noise 
Voltage", I can share the values if need it.


i understand that adding noise it results in losing packets, but I don't think it should 
be that aggressive, i really think there is something that I'm doing wrong or not seeing


thanks for your time and comments

kindly
Jorge

El vie, 14 jul 2023 a las 4:12, Johannes Demel (>) escribió:


Hi Jorge,

a couple of observations first:
- the "throttle" block needs to be part of the actual flowgraph to have
any effect. You might want to remove your null source -> throttle ->
null sink chain.
- for the sake of a Minimum Working Example (MWE) I suggest to remove
the file sink and virtual sinks as well.
- Did you check the actual sample level on the "OFDM Transmitter" output
port? I suspect these values do not have a mean energy of 1 but way
less. In your case probably 1/sqrt(64). You'd need to adopt the "Noise
Voltage" parameter in your "Channel Model" block accordingly.
- How did you compute your SNR value?
- As long as there's noise, you'd eventually lose packets.

Cheers
Johannes

On 13.07.23 20:08, JORGE GONZALEZ ORELLANA via GNU Radio, the Free &
Open-Source Toolkit for Software Radio wrote:
 > As you can see, it's the basic implementation of OFDM.
 > My goal it's to measure the BER, but as I mentioned earlier, below
 > certain level or SNR (20dB)
 >
 > El jue, 13 jul 2023 a las 8:05, Marcus Müller (mailto:mmuel...@gnuradio.org>
 > >>) escribió:
 >
 >     Hi Jorge,
 >
 >     yes, please share your flowgraph. It's moot even beginning talking
 >     about it without
 >     knowing it.
 >
 >     Best regards,
 >     Marcus
 >
 >     On 12.07.23 20:53, JORGE GONZALEZ ORELLANA via GNU Radio, the Free &
 >     Open-Source Toolkit
 >     for Software Radio wrote:
 >      > Hello everyone, I have some question related with a OFDM
 >     transmission simulation, in
 >      > particular, about losing packets.
 >      >
 >      > I am using the OFDM Transmitter and Receiver blocks to do the
 >     transmission (if you need
 >      > more details, I can upload an image of the flowgraph).
 >      >
 >      > The problem that I get is when put some noise (to get some level
 >     of SNR), when I have
 >      > about 20dB (or more) of SNR I don't lose any packet, but if I put
 >     less than 20dB of SNR,
 >      > almost all packets gets lost, (just 1 or 2 packets are received),
 >     all of this happen over
 >      > simulation.
 >      >
 >      > Any suggestions on why this might happen?
 >

Re: Missings packets on OFDM system simulation

[Johannes Demel]

Hi Jorge,

a couple of observations first:
- the "throttle" block needs to be part of the actual flowgraph to have 
any effect. You might want to remove your null source -> throttle -> 
null sink chain.
- for the sake of a Minimum Working Example (MWE) I suggest to remove 
the file sink and virtual sinks as well.
- Did you check the actual sample level on the "OFDM Transmitter" output 
port? I suspect these values do not have a mean energy of 1 but way 
less. In your case probably 1/sqrt(64). You'd need to adopt the "Noise 
Voltage" parameter in your "Channel Model" block accordingly.

- How did you compute your SNR value?
- As long as there's noise, you'd eventually lose packets.

Cheers
Johannes

On 13.07.23 20:08, JORGE GONZALEZ ORELLANA via GNU Radio, the Free & 
Open-Source Toolkit for Software Radio wrote:

As you can see, it's the basic implementation of OFDM.
My goal it's to measure the BER, but as I mentioned earlier, below 
certain level or SNR (20dB)


El jue, 13 jul 2023 a las 8:05, Marcus Müller (>) escribió:


Hi Jorge,

yes, please share your flowgraph. It's moot even beginning talking
about it without
knowing it.

Best regards,
Marcus

On 12.07.23 20:53, JORGE GONZALEZ ORELLANA via GNU Radio, the Free &
Open-Source Toolkit
for Software Radio wrote:
 > Hello everyone, I have some question related with a OFDM
transmission simulation, in
 > particular, about losing packets.
 >
 > I am using the OFDM Transmitter and Receiver blocks to do the
transmission (if you need
 > more details, I can upload an image of the flowgraph).
 >
 > The problem that I get is when put some noise (to get some level
of SNR), when I have
 > about 20dB (or more) of SNR I don't lose any packet, but if I put
less than 20dB of SNR,
 > almost all packets gets lost, (just 1 or 2 packets are received),
all of this happen over
 > simulation.
 >
 > Any suggestions on why this might happen?



smime.p7s
Description: S/MIME Cryptographic Signature

Re: Missings packets on OFDM system simulation

[Marcus Müller]

Hi Jorge,

yes, please share your flowgraph. It's moot even beginning talking about it without 
knowing it.


Best regards,
Marcus

On 12.07.23 20:53, JORGE GONZALEZ ORELLANA via GNU Radio, the Free & Open-Source Toolkit 
for Software Radio wrote:
Hello everyone, I have some question related with a OFDM transmission simulation, in 
particular, about losing packets.


I am using the OFDM Transmitter and Receiver blocks to do the transmission (if you need 
more details, I can upload an image of the flowgraph).


The problem that I get is when put some noise (to get some level of SNR), when I have 
about 20dB (or more) of SNR I don't lose any packet, but if I put less than 20dB of SNR, 
almost all packets gets lost, (just 1 or 2 packets are received), all of this happen over 
simulation.


Any suggestions on why this might happen?