[Discuss-gnuradio] Issues with benchmark_tx and benchmark_rx codes

[Nazmul Islam]

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

-- 
Muhammad Nazmul Islam

Graduate Student
Electrical & Computer Engineering
Wireless Information & Networking Laboratory
Rutgers, USA.