On Thu, Jun 14, 2012 at 10:58 PM, jiajue ou <azalea.a...@yahoo.com.cn> wrote: > Hi all, > > > > I’m playing with qam modulation and demodulation blocks using GRC. > > To begin with, I built a flow graph in one computer as follows: > > File source---->packet encoder---->qam mod----->qam demod----> packet > decoder----->file sink > > It worked well. The file sink can get what is in the file source. > > > > Then, I separated the flow graph in two computers connected to a USRP N210 > each to test real environment performance: > > Computer1: File source---->packet encoder---->qam mod----->usrp sink > > Computer2:usrp source----> qam demod----> packet decoder----->file sink > > However, the file sink cannot get anything.(both with/without differential > encoding ) > > > > To find out why, I pinted out the transmitted symbols in qam mod block in > gnuradio/gnuradio-core/src/gengen/chunks_to_symbol_bc.cc in a txt file, and > received symbols in qam demod block in > gnuradio/gr-digital/lib/digital_constellation_recever_cb.cc in another txt > file. Next, I demodulate those symbols based on closet Euclidean distance > criterion by MATLAB, however,bit error rate turned to be around 0.5 (some > shift is made to find the minimum ber ) which implies that received symbols > and transmitted symbols are independent. AM I RIGHT ABOUT WHERE TO PRINTING > OUT THE SYMBOLS? > > > > One thing to notice, when I changed qam blocks to OFDM blocks, the file sink > can get what is transmitted properly even in the case of two computers. > > > > Therefore, I’m wondering if there is any problem with the qam blocks, like > synchronization or channel equalization etc. that result in transmission > failure. How can I solve it? MY PURPOSE IS TO GET correct symbols to demap > to bits by myself. > > > > Sorry for sending such a long mail. Thank you very much for your help. > > > > Best, > > Jia > > > _______________________________________________ > Discuss-gnuradio mailing list > Discuss-gnuradio@gnu.org > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio >
The synchronization can be slow, so if you're sending for only a short time, you might not ever be synchronizing. How does it work if you put a channel block with a frequency shift in the one computer flow graph? _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
