Jenny, we have a limit in place for packet sizes, which depends on your system. If you type sysctl -a, it'll say something like
kernel.shmmax = 18446744073692774399 100 OFDM symbols seems pretty long, though. If your packet length is 96, as in the example, that means a total packet length of 100 (including CRC). With 48 useful carriers, you get 6 bytes per OFDM symbol, which results in 17 OFDM symbols, plus 2 more for the header. You'll need to give us some more info for us to help you. Cheers, Martin On 03/19/2016 11:44 AM, Jingyi Sun wrote: > Hi, > > I'm using the examples rx_ofdm.grc and tx_ofdm.grc together to transmit > and receive packets over the air. Both work over a simulated channel, > but when I actually transmit and receive over the air, I get the error: > > *"Detected a packet larger than max frame size (100 symbols)"* > > I saw the previous thread on this called "OFDM transmitter receiver" > which goes as follows, but I don't really know what to make of this... > > I tried to run /sysctl kernel.shmmax /in terminal, but I got the message > "No such file or directory". I'm also not sure what kernel.shmmax is. > > These are my parameters: > > fft length= 64 > > cyclic prefix = 16 > packet length = 96 > no. of occupied carriers = 53 > no. of pilot carriers = 4 > > > I'm very new to gnuradio, and any insights into this would be appreciated!! > > > Thanks, > Jenny > > ------------------------------------------ > > *From*: Martin Braun > *Subject*: Re: [Discuss-gnuradio] OFDM transmitter receiver > *Date*: Tue, 26 Aug 2014 11:10:53 +0200 > *User-agent*: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 > Thunderbird/24.6.0 > > ------------------------------------------------------------------------ > > Try and not kill the context in a mailing list thread; these are also > archived and are used by others for referral. > > Max frame size depends on max_output_buffer(). 80 symbols at a 64-sized > FFT would be ~40kB... that doesn't seem unreasonable. Not sure if > there's a problem here. I suggest you have a look at the buffer sizes to > track down this problem. > > M > > On 08/25/2014 03:31 PM, Martin Braun wrote: >>/What's your kernel.shmmax value? (run sysctl kernel.shmmax)/ >>// >>/M/ >>// >>/On 08/25/2014 12:47 PM, sreena p h wrote:/ >>/> Hi/ >>/> I used the ofdm transmitter receiver blocks to create a simple system as/ >>/> shown in the attachment. I used the system parameters as those used in/ >>/> the example transmitter and receiver grcs. Now I get error that/ >>/> 'Detected a packet larger than max frame size (80 symbols)'. I would/ >>/> like to know how the max frame size is set and should I add more/ >>/> information to the grc. / >>/>/ >>/> My transmitter- receiver parameters/ >>/>/ >>/> fft length= 64/ >>/> cyclic prefix = 16/ >>/> packet length = 96/ >>/> no. of occupied carriers = 48/ >>/> no. of pilot carriers = 4/ >>/>/ >>/>/ >>/>/ >>/> ___________________________________/ > > > > _______________________________________________ > Discuss-gnuradio mailing list > Discuss-gnuradio@gnu.org > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio