missed off the filename: ofdm_receiver.py :)
On 17 June 2010 10:27, Mike Jameson <[email protected]> wrote: > Hi Rahman, > > Try broadening the bandwidth of the receiver to allow for the frequency > offset between your USRP2s: > > In /usr/lib/python2.6/dist-packages/gnuradio/blks2impl > > on line 67 look for "tb = bw*0.08" > > change this to a higher value such as "tb = bw*1.5" > > This works for me using usrps. > > Mike > > On 16 June 2010 23:13, Rahman Doost <[email protected]> wrote: > >> Guys, >> >> I'm working on the same thing, I'm trying to receive something with OFDM >> example, USRP2 and XCVR boards. But it doesn't work. The transmitter is >> sending and the rx signal is crystal clear with spectrum analyzer but no >> packet is caught. >> Could anyone of you send me the command you're using at both transmitter >> and receiver with benchmarks? I really appreciate it. >> >> Thanks >> Rahman >> >> On Tue, Jun 15, 2010 at 5:53 AM, Mike Jameson <[email protected]> wrote: >> >>> Hi Chris, >>> >>> The default settings do drop alot of packets as you are seeing. >>> >>> These are some of the things I've adjusted which happen to have brought >>> my packet reception rate up to 99% using 1 USRP with a Basic RX and >>> TX joined with a 10db attenuator: >>> >>> - For benchmark_tx.py and benchmark_rx.py add '-m qpsk' to the command >>> line for qpsk instead of bpsk. >>> - For benchmark_tx.py add '-s 4' to the command line to reduce the packet >>> size sent. >>> - For benchmark_tx.py add '-d 1' to the command line to reduce the rate >>> and change the benchmark_tx.py script to sleep for 0.01 seconds instead of >>> 1. >>> - For benchmark_tx.py add '--tx-amplitude=3000' to the command line to >>> boost the default output power. >>> - In transmit_path.py pad_for_usrp=true and msgq_limit=1 >>> >>> Cheers, >>> >>> Mike >>> >>> On 15 June 2010 10:20, Chris_Spain <[email protected]> wrote: >>> >>>> >>>> Thank you Fisheep, you confirmed what I was thinking but, I don't Know >>>> why, >>>> the packets are been received with no errors, I lost packets but the >>>> packets >>>> that I receive are good. >>>> >>>> I don't Know how GNU Radio implementation maps 1024 bytes over 200 >>>> carriers >>>> with a bpsk modulation, and then the transmission it's OK. >>>> >>>> Cheers >>>> >>>> >>>> Fisheep wrote: >>>> > >>>> > Hi, >>>> > >>>> > I'm not sure why you can't receive all the packet correctly, but I can >>>> > briefly tell you how ofdm implement in GNU Radio. >>>> > >>>> > First, fft_length=512 means it will take 512 subcarriers to do >>>> ifft/fft, >>>> > and occupied_tones=200 means it only take 200 subcarriers to put your >>>> > modulation symbol. Besides, the 200 subcarriers are set at the center >>>> of >>>> > 512 subcarriers. Then you will see there are the remaining >>>> 312(512-200) >>>> > subcarriers which is zero outside the occupied_tones. >>>> > >>>> > likes this: >>>> > >>>> > xxxxxOOOOOOxxOOOOOOxxxxx >>>> > --------------+----------------> f >>>> > >>>> > O => occupied_tones >>>> > x => remaining subcarriers >>>> > the two x at the center is to avoid DC offset. >>>> > After ifft, the CP is added. >>>> > >>>> > OFDM is sensitive to the bitrate(interpolate/decimate), so set the >>>> bitrate >>>> > carefully. >>>> > >>>> > Hope this will help you little. >>>> > >>>> > Fisheep. >>>> > >>>> > >>>> > >>>> > >>>> > Chris_Spain wrote: >>>> >> >>>> >> Hello everybody, >>>> >> >>>> >> >>>> >> I' am trying to test and understand the OFDM Modulation implemented >>>> in >>>> >> GNU Radio. I'm using the deafult values, fft_lenth=512, >>>> occupied_tones >>>> >> =200, cp_length= 128 and bpsk modulation, besides, I'm using a RFX900 >>>> >> Daughterboards on USPR and I'm connecting the TX and RX with a >>>> coaxial >>>> >> cable. >>>> >> >>>> >> I try to send a package of 1024 bytes but I'm not receiving all >>>> packets, >>>> >> always lost the first packet and then is a little bit random, >>>> sometimes I >>>> >> receive and I demodulated the 2º,3º,4º package and lost 5º, or lost >>>> 3º >>>> >> and recive ok 2 ºand 4º... >>>> >> I don't know what are happening, because I don't know how the OFDM >>>> >> implementation map the 1024 bytes onto 200 carriers of data. >>>> >> >>>> >> If I'm understanding the OFDM theory, with a bpsk modulation each >>>> carrier >>>> >> are modulated for two bits and my OFDM symbol length are 512+128 >>>> >> (fft_length+cp_length).So, ¿with 2 bits per data carrier (200), each >>>> >> symbol transport 400 bits, 50 bytes? >>>> >> >>>> >> That can´t be true because I receive some packages with no errors. >>>> >> Somebody can explain me, How works OFDM Modulation implemented in GNU >>>> >> Radio? >>>> >> >>>> >> >>>> > >>>> > >>>> >>>> -- >>>> View this message in context: >>>> http://old.nabble.com/OFMD-TX-and-RX-tp28871027p28888978.html >>>> Sent from the GnuRadio mailing list archive at Nabble.com. >>>> >>>> >>>> _______________________________________________ >>>> Discuss-gnuradio mailing list >>>> [email protected] >>>> http://lists.gnu.org/mailman/listinfo/discuss-gnuradio >>>> >>> >>> >>> _______________________________________________ >>> Discuss-gnuradio mailing list >>> [email protected] >>> http://lists.gnu.org/mailman/listinfo/discuss-gnuradio >>> >>> >> >> _______________________________________________ >> Discuss-gnuradio mailing list >> [email protected] >> http://lists.gnu.org/mailman/listinfo/discuss-gnuradio >> >> >
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