Dhrubojyoti,
In ur program u have set the Bitrate rate to 2MB/s. It exceeds the
computing power of ur PC that is why u are getting "". These 'O' means
overflow i.e. USRP is producing data at faster rate than the ability of PC
to process
Try changing bitrate to 100-500 KB/s
-Adeel
On Sun, Jan 8, 2012 at 4:01 PM, Dhrubojyoti Roy
wrote:
> 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 17.50 (from [0.00, 35.00])
>
> UHD Transmitter:
> Args:
> Freq:2.4GHz
> Gain:17.50 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.
> Differential:True
> ...(sending the
> data)
>
> We invoked the receiver as follows:
>
> *./benchmark_rx.py -f 2.4G -r 2M -v*
>
> linux; 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 49.50 (from [0.00, 99.00])
>
> UHD Receiver:
> UHD Args:
> Freq:2.4GHz
> Gain:49.50 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.
> 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
> Contact no.: +1-740-417-5890
>
>
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