diff options
| author | Tom Rondeau <trondeau@vt.edu> | 2011-10-19 09:58:03 -0700 |
|---|---|---|
| committer | Tom Rondeau <trondeau@vt.edu> | 2011-10-19 09:58:03 -0700 |
| commit | 7e985e7f553a863df37cf39bfd2bd958d82ea46c (patch) | |
| tree | 5bdc21a7c1ab3290b6bd283f699befd77f23bc0f /gr-digital/examples/README | |
| parent | 792e9780cd48177a13416e5926b77f30526ae3ec (diff) | |
digital: fixed digital narrowband examples to use args instead of address and better default.
Diffstat (limited to 'gr-digital/examples/README')
| -rw-r--r-- | gr-digital/examples/README | 153 |
1 files changed, 0 insertions, 153 deletions
diff --git a/gr-digital/examples/README b/gr-digital/examples/README deleted file mode 100644 index 1c50ad69b8..0000000000 --- a/gr-digital/examples/README +++ /dev/null @@ -1,153 +0,0 @@ -Quick overview of what's here: - -* benchmark_tx.py: generates packets of the size you -specify and sends them across the air using the USRP. Known to work -well using the USRP with the RFX transceiver daughterboards. -You can specify the bitrate to use with the -r <bitrate> command line -parameter. The default is 500k. Some machines will do 1M or more. -You can select the modulation to use with the -m <modulation> command -line argument. The legal values for <modulation> are gmsk, dbpsk and dqpsk. - -* benchmark_rx.py: the receiver half of benchmark_tx.py. -Command line arguments are pretty much the same as rx. Works well -with a USRP and RFX transceiver daughterboards. Will also work -with TVRX daugherboard, but you'll need to fiddle with the gain. See -below. Prints a summary of each packet received and keeps a running -total of packets received, and how many of them were error free. -There are two levels of error reporting going on. If the access code -(PN code) and header of a packet were properly detected, then you'll -get an output line. If the CRC32 of the payload was correct you get -"ok = True", else "ok = False". The "pktno" is extracted from the -received packet. If there are skipped numbers, you're missing some -packets. Be sure you've got a suitable antenna connected to the TX/RX -port on each board. For the RFX-400, "70 cm" / 420 MHz antennas for ham -handi-talkies work great. These are available at ham radio supplies, -etc. The boards need to be at least 3m apart. You can also try -experimenting with the rx gain (-g <gain> command line option). - -Generally speaking, I start the rx first on one machine, and then fire -up the tx on the other machine. The tx also supports a discontinous -transmission mode where it sends bursts of 5 packets and then waits 1 -second. This is useful for ensuring that all the receiver control -loops lock up fast enough. - -* tunnel.py: This program provides a framework for building your own -MACs. It creates a "TAP" interface in the kernel, typically gr0, -and sends and receives ethernet frames through it. See -/usr/src/linux/Documentation/networking/tuntap.txt and/or Google for -"universal tun tap". The Linux 2.6 kernel includes the tun module, you -don't have to build it. You may have to "modprobe tun" if it's not -loaded by default. If /dev/net/tun doesn't exist, try "modprobe tun". - -To run this program you'll need to be root or running with the -appropriate capability to open the tun interface. You'll need to fire -up two copies on different machines. Once each is running you'll need -to ifconfig the gr0 interface to set the IP address. - -This will allow two machines to talk, but anything beyond the two -machines depends on your networking setup. Left as an exercise... - -On machine A: - - $ su - # ./tunnel.py --freq 423.0M --bitrate 500k - # # in another window on A, also as root... - # ifconfig gr0 192.168.200.1 - - -On machine B: - - $ su - # ./tunnel.py --freq 423.0M --bitrate 500k - # # in another window on B, also as root... - # ifconfig gr0 192.168.200.2 - -Now, on machine A you shold be able to ping machine B: - - $ ping 192.168.200.2 - -and you should see some output for each packet in the -tunnel.py window if you used the -v option. - -Likewise, on machine B: - - $ ping 192.168.200.1 - -This now uses a carrier sense MAC, so you should be able to ssh -between the machines, web browse, etc. - -* run_length.py: This program takes a single argument '-f FILE' and -outputs the number of runs of similar bits within the file. It is -useful as a diagnostic tool when experimenting with line coding or -whitening algorithms. - - - -********************************************************************** -********************************************************************** - - -BERT testing example scripts - -benchmark_tx.py - -This sets up a BPSK transmitter that is modulated with a pseudorandom -sequence of bits. The PN code is generated by sending an all 1s -sequence through a 7-bit scrambler. The transmitter performs the BPSK -modulation, then passes the complex baseband waveform through a -root-raised-cosine filter and onto the USRP. - -The --sps parameter controls how many baseband samples per symbol -are created and passed through the RRC filter, prior to going to the -USRP over the USB for interpolation to the final DAC rate. - -The baseband bit rate is controlled by -r or --rate. This value, when -multiplied by the --sps parameter, must result in valid interpolation -rate for the USRP. For example, if the baseband rate is 250k bits/sec, -and the samples per symbol is 4, then the final rate is 1M samples/sec, -which results in an interpolation rate of 128. The valid interpolation -rates for the USRP are multiples of 4 between 16 and 512. - -Finally, the RRC excess bandwidth may be specified by --excess-bw. -(See ./benchmark_tx.py -h for additional parameters.) - - -benchmark_rx.py - -This sets up a BPSK receiver to demodulate the received waveform. It -accepts a similar set of parameters as the transmitter, except that one -specifies the USRP decimation rate desired. The resulting sample stream -rate must be an integral number of baseband symbols. For example, the -parameters corresponding to the above transmitter would be to use a -decimation rate of 8 (32 sps), 16 (16 sps), 32 (8 sps), 64, (4 sps), or -128 (2 sps). The lower the USRP decimation, the more CPU is required to -demodulate the signal, so not all valid decimation rates will work. - -The baseband signal from the USRP is first passed through an AGC to -establish an average power of 1.0. It is then passed through a matched -filter (another RRC), a Costas phase-locked loop, and a Mueller and -Muller bit timing recovery loop. The resulting constellation has an SNR -estimation probe attached, and is then sliced into a bit stream. - -The recovered bits are then passed through a 7-bit descrambler. If -there are no channel errors, the all 1s sequence is recovered. In the -event of a channel error, there will be a 0 in the bit stream for each -feedback tap in the descrambler. In this case, the CCSDS descrambler is -using 3 feedback taps. - -Finally, the signal is passed into a bit density measurement probe. The -channel BER is measured by dividing the 0s density by three. This -measurement is inaccurate at high BER rates (>10%) as the error 0s -begin to overlap. - -The benchmark script will, once per second, output the Costas loop -frequency offset, the recovered timing error, the estimated SNR, and the -average BER. - -NOTE: The particular SNR estimator used is inaccurate below about 7dB, -and will report erroneously high values even for random noise. - -There are a variety of Costas and M&M loop parameters one can adjust. -See ./benchmark_rx.py -h for the full set. - - |