Is this normal behavior of benchmark_rx.py

Hi,
I have two USRPs (N210) connected to each other through a channel
emulator (via RF cable) which is emulating a lossless channel.
When I run the benchmark_rx.py I see some
spurious bytes being received by the receiver even when the sender
application (benchmark_tx.py) has not been started. I have enabled
VERBOSE in the file “digital_ofdm_frame_sink.cc”. Below is a sample
output from the receiver
(note the sender has not been started at all). I see that
intermittently
the cc layer prints out the following block which means it got some
bytes (symbols). How can receiver get these bytes when there is no
sender?
What is more bothersome is that when I change the occupied-tones
to 120 (i.e., I run it with “python benchmark_rx.py --args “addr=usrp4”
-f 795.5M --occ 120 -W 4M”),
(in this case “bytes from demapper = 14” printed instead of 29)
then the following block is printed continuously. I am wondering where
is the
receiver getting bytes/symbols when there is no transmitter? I am
running
gnuradio 3.6.2.

==================
@ enter_have_sync
Header Search bitcnt=0, header=0x00000000 bytes from demapper = 29
got header: 0xb06fe351
@ enter_search

$ python benchmark_rx.py --args “addr=usrp4” -f 795.5M --occ 240 -W 4M
linux; GNU C++ version 4.4.6 20120305 (Red Hat 4.4.6-4); Boost_104100;
UHD_003.004.003-221-g9d6f9492

– Opening a USRP2/N-Series device…
– Current recv frame size: 1472 bytes
– Current send frame size: 1472 bytes

UHD Warning:
Unable to set the thread priority. Performance may be negatively
affected.
Please see the general application notes in the manual for
instructions.
EnvironmentError: OSError: error in pthread_setschedparam

No gain specified.
Setting gain to 19.000000 (from [0.000000, 38.000000])
Using Volk machine: avx_64_mmx

gr_fir_ccf: using SSE
gr_fir_fff: using SSE
@ enter_search
Warning: failed to enable realtime scheduling
@ enter_have_sync
Header Search bitcnt=0, header=0x00000000 bytes from demapper = 29
got header: 0x50b5f4e3
@ enter_search
@ enter_have_sync
Header Search bitcnt=0, header=0x00000000 bytes from demapper = 29
got header: 0x10ffc9c1
@ enter_search
TIMEOUT
@ enter_have_sync
Header Search bitcnt=0, header=0x00000000 bytes from demapper = 29
got header: 0xb06fe351
@ enter_search
TIMEOUT

thanks and regards

–Anirudh Sahoo
Advanced Network Technology Div.
National Institute of Standards and Technology (NIST)
100 Bureau Drive,
Gaithersburg, MD - 20878
Room - B230, bldg.- 222
Phone- 301-975-4439

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