Hi All,
I´m new to GNUradio and have run into the basic problem of the receiver USRP device not being able to decode the senderś transmission. For our experiments, we used GNUradio (MAJOR_VERSION=3, API_COMPAT=5, MINOR_VERSION=1) and USRP N210 with XCVR2450 daughterboards, and the benchmark_tx/rx programs for both narrowband and ofdm. We used the following transmitter arguments and got the result below:
./benchmark_tx.py -f 2.4G -r 2M -M 10 -v
linux; GNU C++ version 4.5.2; Boost_104200; UHD_003.004.000-f2388c0
>>> gr_fir_ccf: using SSE
Modulator:
bits per symbol: 4
RRC roll-off factor: 0.35
-- Opening a USRP2/N-Series device...
-- Current recv frame size: 1472 bytes
-- Current send frame size: 1472 bytes
No gain specified.
Setting gain to 17.500000 (from [0.000000, 35.000000])
UHD Transmitter:
Args:
Freq: 2.4GHz
Gain: 17.500000 dB
Sample Rate: 1Msps
Antenna: None
Subdev Sec: None
Modulator:
bits per symbol: 4
RRC roll-off factor: 0.35
Tx amplitude 0.25
modulation: psk_mod
bitrate: 2Mb/s
samples/symbol: 2.0000
Differential: True
...........................................................(sending the data)
We invoked the receiver as follows:
./benchmark_rx.py -f 2.4G -r 2M -vlinux; GNU C++ version 4.5.2; Boost_104200; UHD_003.004.000-f2388c0
>>> gr_fir_ccf: using SSE
Demodulator:
bits per symbol: 4
RRC roll-off factor: 0.35
FLL bandwidth: 6.28e-02
Timing bandwidth: 6.28e-02
Phase bandwidth: 6.28e-02
-- Opening a USRP2/N-Series device...
-- Current recv frame size: 1472 bytes
-- Current send frame size: 1472 bytes
No gain specified.
Setting gain to 49.500000 (from [0.000000, 99.000000])
UHD Receiver:
UHD Args:
Freq: 2.4GHz
Gain: 49.500000 dB
Sample Rate: 1Msps
Antenna: None
Spec: None
Demodulator:
bits per symbol: 4
RRC roll-off factor: 0.35
FLL bandwidth: 6.28e-02
Timing bandwidth: 6.28e-02
Phase bandwidth: 6.28e-02
Receive Path:
modulation: psk_demod
bitrate: 2Mb/s
samples/symbol: 2.0000
Differential: True
At this point, even with the transmitter running, the receiver program pauses for about a minute before bursting into a string of ´O´s. We found that our transmission was being detected by the receiving USRP, using the uhd_fft.py program. However, an interesting observation was that our signal was detected at center frequency 2.401GHz (screenshot attached). We doubt if this is due to oscillator differences, since switching the transmitter and receiver devices also resulted in detection at the same 2.401GHz center frequency.
We tried variations to the above programs by making the
benchmark_rx.py listen in th 2.401GHz frequency, other modulation schemes such as qam, different transmission gains and also the OFDM benchmarks with similar variations, but there was no output on the receiver. Could it be possible that the receiver can detect but cannot decode the signal? Your valuable advice in this regard would be sincerely appreciated.
Thanks and Regards,
Dhrubojyoti.
--
Dhrubojyoti Roy
1655, North 4th Street, Apt-D
Columbus, OH-43201