Realtime receiving live tetra signal;

Furkan Elibol felibol at yahoo.com
Tue Nov 26 14:15:43 UTC 2013


Hi Folks,

I have a sample tetra signal without encryption. I generate a test signal from the tetra sample with a vector signal generator.(@394MHz carrier and 96KHz sampling rate)
I try to receive and listen this test signal realtime with USRP N200 and osmocom tetra. I combine all the osmocom tetra parts in one script (seen below) but speech is not continuous and aplay gives underrun warnings. The cpu usage is approximately %30 and there is no memory or disk write/read speed problem. I wonder what is the problem and how can i listen realtime tetra speech.

I also test demodulator offline and then try the rest of the script realtime and there is no problem, i can listen continuous speech without any gap. So i suspect from the demodulator performance..

I am using Ubuntu 12.04 64bit, Gnuradio 3.6.5.1, UHD 003.005, SSD disk, 8GB Ram, Intel i7-3520M CPU.

Thanks..

------------------------------------------------------------------
#!/bin/bash
sudo sysctl -w net.core.wmem_max=1048576
sudo sysctl -w net.core.rmem_max=50000000

rm /tmp/out.float /tmp/out.bits /tmp/out.codec /tmp/out.pcm /tmp/traffic.out

mkfifo /tmp/out.float
mkfifo /tmp/out.bits
mkfifo /tmp/out.codec
mkfifo /tmp/out.pcm
mkfifo /tmp/traffic.out

~/Desktop/osmo-tetra/src/demod/python/uhd-tetra_demod.py -f 394E6 -o /tmp/out.float &
float_to_bits /tmp/out.float /tmp/out.bits & 
tetra-rx /tmp/out.bits &

cdecoder /tmp/traffic.out /tmp/out.codec &
sdecoder /tmp/out.codec /tmp/out.pcm &
aplay -fS16_LE /tmp/out.pcm

rm /tmp/out.float
rm /tmp/out.bits
rm /tmp/out.codec
rm /tmp/out.pcm
------------------------------------------------------------------
Furkan Elibol
PhD Candidate
Ozyegin University
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