Dear Nathan, I know QAM is the fastest modulation because it can carry more bits per symbol. This is a reason why I use QAM modulation.
As bits per symbol level is higher, bit error rates will be increased. I expected it returns feasible error rate. However, error rates were too high. So I wondered "is this normal case or what is it I'm missing". Recently I could reduce bit error rates of benchmark example (ofdm one). In my case, the problem was sub-bandwidth. In OFDM, total bandwidth is divided by # sub-carrier. I changed related parameters(occupied_tones, fft_size) to small. Now, I'm researching how transmit rate be maximized and how error rate be minimized (I think it can be solved by maximizing sample rate) Thank you for your advice. 2016-03-16 1:30 GMT+09:00 West, Nathan <n...@ostatemail.okstate.edu>: > There's been some subtle miscues in this thread. Let's start over from the > fundamentals. > > First, think about what the flowgraph is. You must understand the transmit > and receive chains to do meaningful work with GNU Radio flowgraphs. > > This is a rather old example of sending packetized data that doesn't use > error correction. There is a function that checks the CRC of packets. If a > single bit is wrong the packet fails. (As a side note building > packetized/bursty modems in the way these flowgraphs work is NOT > recommended). > > Given this information, for the same SNR and channel what would you expect > to happen to bit error rates (and therefor packet error rates) as you > change modulations from GMSK, BPSK, etc to QAM? > > Finally, as I mentioned these flowgraphs are sort of deprecated. Maybe you > can tell us what you're really going for and someone can suggest a better > tool. > > Cheers, > Nathan > > On Sun, Mar 13, 2016 at 4:22 AM, SangHyuk Kim <tkdgur7...@gmail.com> > wrote: > >> Hi all. >> >> I'm using benchmark_tx(rx).py example >> >> I experimented variety modulation schemes and GMSK, BPSK, QPSK modulation >> worked well >> >> However, when I used QAM modulation, most of received packet were >> corrupted (FALSE) >> >> ENV) >> both TX and RX uses USRP N210 with ANT500 and CBX 40MHz >> distance between TX and RX is shorter than 3m >> >> TX) >> ./benchmark_tx.py -f 1.5G -m qam -S 8 --tx-gain=30 >> >> RX) >> ./benchmark_rx.py -f 1.5G -m qam -S 8 >> >> RESULTS ON RX) >> ok = FALSE pktno = 1 n_rcvd = 1 n_right = 0 >> ok = FALSE pktno = 2 n_rcvd = 2 n_right = 0 >> ok = FALSE pktno = 3 n_rcvd = 3 n_right = 0 >> ... >> ok = TRUE pktno = N n_rcvd = N n_right = 1 >> ... >> >> Is this normal case of qam modulation ? >> How can I get more TRUE packet using QAM modulation ? >> >> Thanks. >> >> _______________________________________________ >> Discuss-gnuradio mailing list >> Discuss-gnuradio@gnu.org >> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio >> >> >
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