On Tue, Jan 4, 2011 at 6:49 AM, You Lizhao <youlizhao2...@gmail.com> wrote: > Hi all, > > Recently I want to implement a OFDM based multi-rate system, and I am using > benchmark_ofdm_tx/benchmark_ofdm_rx programs in ofdm directory. I know I can > use unlock/lock mechnism to disconenct/connect the exising blocks to change > modulation block, and it indeed works. However, I also notice that the > difference between all modulation, i.e. BPSK, QPSK, QAM16, QAM64, is > rotated_const paramter in gr.ofdm_mapper_bcv block. So I write a new block > howto.ofdm_mapper_bcv which can change rotated_const (d_constellation in > gr_ofdm_mapper_bcv.h/.cc) with a defined function call. But it does not > work. When I change BPSK to QPSK by altering rotated_const, I can receive > nothing but TIMEOUT in QPSK demodulator. If I still use BPSK demodulator, it > works in compromised performance with some packets failed to pass CRC check. > Why does it happen, since I already change rotated_const? Is there any > misunderstanding on this ofdm benchmark program? > > Furthermore, I also find that if I use QAM16, it seems that the packet > reception simuation is very bad, about 50% PRR or even lower. When > using QAM64, PRR~0%, almost all packets failed CRC check. I think if I use > channel coding, the situation will be better. I am wondering how to add > channel coding block to existing architecture. Is there any possible > examples? > > Any comments are welcomed! Thank you very much! > > Regards, > -Lizhao > _______________________________________________ > Discuss-gnuradio mailing list > Discuss-gnuradio@gnu.org > http://lists.gnu.org/mailman/listinfo/discuss-gnuradio > >
I don't know whether this is relevant or not but just in case: The QAM constellations produced by blks2impl/qam.py aren't set up for differential modulation which was causing me some problems with the benchmark_qt_loopback2.py program. In my github repo (github.com/benreynwar/gnuradio) i've got a modified qam.py which fixes this. Cheers, Ben _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
