discuss-gnuradio
[Top][All Lists]
Advanced

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

[Discuss-gnuradio] Very confused on benchmark_rx.py


From: Songsong Gee
Subject: [Discuss-gnuradio] Very confused on benchmark_rx.py
Date: Wed, 23 Nov 2011 14:12:39 +0900

I have difficulties benchmark_xx.py

I use USRP1 with SBX and GNU Radio 3.5.0rc0 on Ubuntu 10.10 on VMWare.

Usually I do test with following commands.

$ ./benchmakr_tx.py -f 450e6 --tx-gain=30 -r 100e3 -S 10 -m psk (or gmsk) --tx-amplitude=0.02 (for a signal not being clipped)
$ ./benchmakr_rx.py -f 450e6 --tx-gain=50 -r 100e3 -S 10 -m psk (or gmsk)

Of course, I modified receive_path.py to have an appropriate carrier sensing threshold value:
        # Carrier Sensing Blocks
        alpha = 0.001
        thresh = 30   # in dB, will have to adjust
        self.probe = gr.probe_avg_mag_sqrd_c(thresh,alpha)
I changed thresh = 30 with thresh = -60 (it varies from 0 to -80 as I want)

So, everything is fine, but when I run programs, a PC on a rx side doesn't print
        "ok = %5s  pktno = %4d  n_rcvd = %4d  n_right = %4d" % (ok, pktno, n_rcvd, n_right)
which is in rx_callback()

When I modified following codes in receive_path.py:
        # receiver
        self.packet_receiver = \
            digital.demod_pkts(self.demodulator,
                               access_code=None,
                               callback=self._rx_callback,
                               threshold=-1)                        # by default, threshold=-1 results into threshold=12
I changed threshold=-1 with threshold=x (x is some arbitrary negative integer except -1)

Then, rx_callback is properly invoked. However, CRC check fails and it prints
ok = False pktno = xxx n_rcvd = xxx n_right = xxx
and also throws an error like
        (pktno,) = struct.unpack('!H', payload[0:2])
error: unpack requires a string argument of length 2

From all of these modification and results, I conclude that
a signal is not clipped and its spectrum looks good,
sensing a carrier is fine,
but it fails to correlate a signal with an access code which causes rx_callback keep silent

I'm confused because this basic and fundamental example doesn't work well...

please give me some advices
and I appreciate to all of you in advance


--
Seokseong Jeon, PhD Candidate
Communication & Networks Lab
IT Convergence Engineering (ITCE), POSTECH, Korea
+82 10 8338 1229, gee.songsong at gmail . com


reply via email to

[Prev in Thread] Current Thread [Next in Thread]