Hello All,
I am trying to measure packet error rates for different modulation schemes using benchmark_tx and benchmark_rx codes. I run my codes on XCVR2450 USRP2 dughterboard and I am using the UHD_003_002_001 image (That image was downloaded on June, 2011 from the website, I believe). Now, I am getting strange results in terms of packet error rate. The benchmark_rx codes don't receive anything for d8psk modulation. It receives packets for dqpsk and qbpsk, but the work-ability depends on the inputs in a weird way. I am listing down some of the results that I have observed for different commands:
Scenario 1:
./benchmark_tx.py -f 2.4G -r 1M -e eth2 --tx-ampl 0.8 --tx-gain 20 -m dbpsk
./benchmark_tx.py -f 2.4G -r 1M -e eth2 -m dbpsk --costas-alpha 0.05 --gain-mu 0.01
Results: All packets receiverd.
Scenario 2:
./benchmark_tx.py -f 2.4G -r 1M -e eth2 --tx-ampl 0.8 --tx-gain 25 -m dbpsk
./benchmark_tx.py -f 2.4G -r 1M -e eth2 -m dbpsk --costas-alpha 0.05 --gain-mu 0.01
Results: All packets are received as false.( The only difference between scenario 1 and scenario 2 is the in the increase of --tx-gain (from 20 to 25).)
Scenario 3:
./benchmark_tx.py -f 2.4G -r 1M -e eth2 --tx-ampl 0.8 --tx-gain 25 -m dqpsk
./benchmark_tx.py -f 2.4G -r 1M -e eth2 -m dqpsk --costas-alpha 0.05 --gain-mu 0.01
Result: All packets are received as OK. (The difference between scenario 2 and scenario 3 lies in the change of modulation (from dbpsk to dqpsk).)
Scenario 4:
./benchmark_tx.py -f 2.4G -r 1M -e eth2 --tx-ampl 0.8 --tx-gain 25 -m d8psk
./benchmark_tx.py -f 2.4G -r 1M -e eth2 -m d8psk --costas-alpha 0.05 --gain-mu 0.01
Result: No packet gets received. The receiver sits idle waiting for the packets.
I observed my transmitted signal in the spectrum analyzer and I did not see any carrier offset, i.e., the received signal was centered at 2.4 GHz. I think that the error is coming from either over-saturation of transmission signal or the costas-loop at the receiver. At present, I am simply walking in the dark and trying random input values to make the schemes work. Is there any suitable range for these options? (--tx-ampl, --tx-gain, --costas-alpha, --gain-mu, --rx-gain, etc.)? Please let me know if any of you have found a suitable range for these options. Your suggestions will be valuable.
Thanks for reading the long email.
Nazmul
You could try upgrading to version 3.5 of GNU Radio. There are a lot of changes in the digital modulation blocks that might help. There's still some work to be done with them, but the recovery loops used are more stable to the parameter settings than previously. It should help.
My guess from your post above is that, yes, you are having some issues with overloading the transmitters.