Sorry I forgot to edit the title in the last post. On Thu, Jul 1, 2010 at 10:28 AM, Tuan Ta <[email protected]> wrote:
> Hello all, > > I am working in the same team with Shalabh. We have been trying to figure > out this problem for a week now and so far we found nothing concrete. We > have been looking in every corner of the archive. We found some people who > had similar problem with us (some dated back to 2008!) but no one had a > clear explanation. > > We found in some post that if the sampling rate of our signal is too small, > which leads to small bandwidth, our signal might get lost in the filtering > stage due to some frequency offset of the filter. Increasing the sampling > rate (e.g. 500k -> 1M) indeed improved the reception ratio at the receiver. > > We managed to successfully send a whole file (small) using gmsk, sampling > rate 1.5M, payload size 3 bytes. However, if we increased the payload size > (say 100 bytes), then we still got packet lost even at 1.5M. This leads to > another question: how does the size of the payload impact the reception at > the receiver? > > Since all packet lost occurred at the end of transmission (always last > packets that got lost), we suspected some kind of buffer overflow. But > frankly we don't know how to check that. We printed out the size of the > message buffer at the receiver USRP after every rx_callback but nothing > seemed to be out of the ordinary. > > This problem has been really bugging us. Since we are new to both the > hardware and software, we might miss some crucial details. We will be very > thankful if anyone can provide some pointers / suggestions / explanations > that help us clarify this issue. > > Thank you, > > Tuan > > > Message: 13 >> Date: Mon, 28 Jun 2010 19:25:01 -0400 >> From: Shalabh Jain <[email protected]> >> Subject: [Discuss-gnuradio] benchmark_tx/rx with RFX 2400 >> To: [email protected] >> Message-ID: >> <[email protected]> >> Content-Type: text/plain; charset="iso-8859-1" >> >> Hello, >> >> I am new to the USRP/gnu-radio world, trying to understand the basic >> working. I have been trying the following 2 experiments which I've not >> been >> able to successfully debug or find documentation for. Can somebody help me >> out to explain what is going wrong or point to some useful references. >> >> The hardware I am using is the RFX2400 daughterboard with USRP and a >> 2.4-2.48G antenna. I'm using two separate boards in receive and transmit >> configuration. >> >> 1. I tried the digital/benchmark_tx/rx.py provided with the examples >> (3.2.2 >> tarball). I tried to read from a simple ascii file containing a sequence >> of >> numbers repeated 1000 times. I've tried different options modulation >> schemes >> but the problems persist. Two main problems in this example >> a) It seems that using the default gmsk modulation, although 179 >> packets are sent, only 147 are received. Essentially, the last packet is >> always received in error and the end 15% of the file is always lost. >> b) The transmission seems to be very sensitive to the bit rate >> specified. i.e. there are several combination of big-rates at which the >> receiver receives nothing. >> >> 2. I tried so send a simple tone across by hooking a sine wave generator >> to >> the USRP using the grc. Even that seems the just end up in noise >> reception. >> I'm attaching a small snippet of the code generated. >> >> I appreciate any help. >> >> Thanks >> Shalabh >> >> >> -------------------------------tx------------------------------------------- >> self.gr_float_to_complex_0 = gr.float_to_complex(1) >> self.gr_sig_source_x_0 = gr.sig_source_f(500000, >> gr.GR_COS_WAVE, 100000, .5, 0) >> self.gr_sig_source_x_1 = gr.sig_source_f(500000, >> gr.GR_SIN_WAVE, 100000, .5, 0) >> self.usrp_simple_sink_x_0 = grc_usrp.simple_sink_c(which=0, >> side="A") >> self.usrp_simple_sink_x_0.set_interp_rate(256) >> self.usrp_simple_sink_x_0.set_frequency(2.44e9, >> verbose=True) >> self.usrp_simple_sink_x_0.set_gain(80) >> self.usrp_simple_sink_x_0.set_enable(True) >> >> self.connect((self.gr_float_to_complex_0, 0), >> (self.usrp_simple_sink_x_0, 0)) >> self.connect((self.gr_sig_source_x_0, 0), >> (self.gr_float_to_complex_0, 0)) >> self.connect((self.gr_sig_source_x_1, 0), >> (self.gr_float_to_complex_0, 1)) >> >> ------------------------------rx------------------------------------------- >> self.usrp_simple_source_x_0 = >> grc_usrp.simple_source_c(which=0, side="A", rx_ant="TX/RX") >> self.usrp_simple_source_x_0.set_decim_rate(256) >> self.usrp_simple_source_x_0.set_frequency(2.44e9, >> verbose=True) >> self.usrp_simple_source_x_0.set_gain(80) >> self.wxgui_fftsink2_2 = fftsink2.fft_sink_c( >> self.GetWin(), >> baseband_freq=0, >> y_per_div=10, >> y_divs=10, >> ref_level=50, >> sample_rate=500000, >> fft_size=1024, >> fft_rate=30, >> average=False, >> avg_alpha=None, >> title="FFT Plot", >> peak_hold=False, >> ) >> self.Add(self.wxgui_fftsink2_2.win) >> self.connect((self.usrp_simple_source_x_0, 0), >> (self.wxgui_fftsink2_2, 0)) >> >> >> ----------------------------------------------------------------------------- >> -------------- next part -------------- >> An HTML attachment was scrubbed... >> URL: >> http://lists.gnu.org/archive/html/discuss-gnuradio/attachments/20100628/e47fa55f/attachment.html >> >>
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