Hi GP 2014 On 13.07.2014 21:49, GP 2014 wrote: > Hi, > I hope if someone can help me, i have some questions related to the Ofdm > transmitter block: > - I take the input of the transmitter from a sip phone, i can find from > wireshark that the length of the packet of Sip protocol which contains a > registration request is of 485 bytes and the packet which represents an > invitation (SIP/SDP) to the other sip phone is of 724 bytes, i want to send > both kinds of packets using the OFDM transmitter block.
> I used a udp sink, You mean a UDP source, to get the network packets into GNU Radio? > a stream to tagged stream block Well, you drop all the UDP header information and get a stream of bytes out of the UDP source, so this does not sound like it would work. > ofdm transmitter block with fft len =128, > rate= 125 Kbps, and a usrp for which i used a UHD sink block. The only way > that made the transmitter to send all the data coming from the sip phone > correctly is the case where, i put the packet length in the stream to > tagged stream block =1, however i put the packet length in the transmitter > parameter =850 or 724, or whatever length.It seems, that it doesn't depend > on the packet length parameter which i enter to the transmitter block, if i > put the same parameters in the receiver block at the other end (the same > fft len ,the same occupied and pilots carriers). can someone explain me the > concept behind that? The UDP source takes the *content* of UDP packets and treats that as samples. What you want is a network PDU to tagged stream block. > > - Also, i use a tag debug block before and after the transmitter block, i > find that the first one before the transmitter displays 442 successive > bytes each of 1 byte length as the packet length in the stream to tagged > stream block =1, and then the tag debug after the transmitter block > displays 255168 bytes of data packets each of 576 byte, which means that > the transmitter buffer the packets till reach 442 packets and then output > them each of size 576 byte.why this happens ? why 442 bytes espicially ? > Note: in this case i put the packet length=850. can someone explain me what > happens here ? Sorry, I don't really understand your question. Could you rephrase for us? > -My last question is :in my design for the OFDM system i want to send the > packet on 4 OFDM symbols: here i put the fft_len =128 and specified the > occupied and pilots carriers as: > occupied = (range(-61, -42) + range(-41, -14) + range(-13, -7) + range(-6, > 0) + range(1, 7) + range(7, 14)+range(15,42)+range(43,61),) > pilot carriers= ((-42,-14,14,42 ,),) > does this satisfy to distribute the packet on 4 OFDM symbols ? This is a bad idea, generally. Your system is designed to carry network packets, so it should be able to deal with a variable packet length. This means that you will need to add a header to your data on the first OFDM symbol, saying how long this transmission is going to be. Have you had a look at the payload-header-demux architecture? > Thanks for your help. > > > > _______________________________________________ > Discuss-gnuradio mailing list > [email protected] > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
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