[Discuss-gnuradio] Can not receive all bytes with BPSK loopback scenario

[王伟华]

Hi everyone,
I want to realize a BPSK modulation by using GRC to 
transmit some bytes of information. Simulation result under a pure 
software environment performs good. However, when I move to hardware 
step with two USRPs connected with cable and 6dB attenuator(a simplex 
scenario), less than half of the transmitted bytes can be received. I 
think may be a synchronization problem occurs. Then I decide to do a 
loopback setting (flow graph is attached and please check it) with one 
USRP N210. This time, again, I cannot receive all the the transmitted 
strings. Detailed information are shown below:
Ubuntu 10.04, GNU Radio software version 3.5.2.1, 2 samples/symbol, 
sample rate 195.312K, both Gray coding and Differential encoding are 
turned on, excess bandwidth 0.35, realtime scheduling, transmitted 
strings 468Bytes, UHD gain 0dB, payload length 1(nothing received when 
payload length equals 0) and central frequency at 1GHz.
Rx bytes: 82; 78; 79; 68; 51; (All 5 times shows very bad results, so I adjust some parameters)
I
 turn off the Gray coding, keep the Differential encoding on; increase 
samples/symbol to 5(5 samples/symbol gives the best receiving result); 
Rx bytes: 418; 421; 417; 405; 415; Still I cannot receive all 
transmitted bytes.I think synchronization is provided by packet encoder 
already. What could be the possible reasons? I also try the 'run to 
completion' option but nothing received. Why random results appear? I am
 sure the cable and Ethernet cable have no problem. 
Thanks a lot!
Kind Regards!
Wei

BPSK-Loopback.grc.png
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