[Discuss-gnuradio] Benchmark_rx is giving weird output for high bit rate

[Nazmul Islam]

Hello,

This is Nazmul, a PhD student of Rutgers University. I am 
using a modified form of 'benchmark_Tx.py' and 'benchmark_Rx.py' for my 
research. I am transmitting a random binary sequence from an USRP2 testbed and calculating the
 bit error rate at the receiver (BER), another USRP2 testbed. Basically, I am generating a long
 binary sequence, grouping them into different packets and then 
transmitting the packets using 'benchmark_Tx' program. I receive the 
packets using 'benchmark_Rx.py' and then find the BER.

The program works well when bit rate is lower than 3 Mbps or 3.5 Mpbs. However, when the bit rate exceeds 3.5 Mbps, the benchmark_Rx produces a bunch of S characters. It produces a weird output like following!!


SSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSS

I don't know why this weird output occurs. Does it happen because I am exceeding the "capacity" of the path? Or is there an in built low pass filter at the receiver that only passes signals whose bandwidth is lower than 3 MHz? (let's say that I am using Differential BPSK here).

Your feedback on this will be highly appreciated.

Thanks,

Nazmul



-- 
Muhammad Nazmul Islam

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