HorusHighSpeed

Modulator and glue code for the 100kbps SSDV experiment.

The transmit side is designed to run on a Raspberry Pi, and the UART (/dev/ttyAMA0) is used to modulate a RFM22B in direct-asynchronous mode. I expect other transmitters could probably be used (i.e. NTX2's or similar) at lower bandwidths.

Dependencies

• Python (2.7, though 3 might work with some small mods)
• SSDV (https://github.com/fsphil/ssdv)
• crcmod (pip install crcmod)
• numpy (for debug output tests)
• PyQt4 (for SSDV GUI)

Main Programs

• rx_ssdv.py - Reads in received packets (256 byte SSDV frames) via stdin, and decodes them to JPEGs. Also informs other processes (via UDP broadcast) of new data.
• rx_gui.py - Displays last received image, as commanded by rx_ssdv.py via UDP.
• tx_picam.py - TODO.

Testing Scripts

• Run python compress_test_images.py from within ./test_images/ to produce the set of test ssdv-compressed files.

TX Testing

• tx_test_images.py transmits a stream of test images out of the RPi UART. Check the top of the file for settings.
• This script can also be used to produce a one-char-per-bit output, which is what would be seen by the modulator.

RX Testing

• rx_tester.py produces a stream of packets on stdout, as would be received from the fsk_demod modem (from codec2 - still under development).
• Run python rx_tester.py | python rx_ssdv.py to feed these test packets into the command-line ssdv rx script.
• add --partialupdate N to the above command to have rx_gui.py update every N received packets.

Sending/Receiving Images

TX Site

• Run either python tx_picam.py (might need sudo) or python tx_test_images.py on the transmitter Raspberry Pi.

RX Side

To be able to run a full receive chain, from SDR through to images, you'll need:

• GnuRadio + libraries for whatever SDR you plan on using.

• fsk_demod and drs232 from codec2-dev. You can get these using

• svn checkout http://svn.code.sf.net/p/freetel/code/codec2-dev/

• cd codec2-dev && mkdir build-linux && cd build-linux && cmake ../

• Build drs232 using gcc src/drs232.c -o src/drs232 -Wall

• Then copy src/fsk_demod and src/drs232 to this directory.

• A few example gnuradio-companion flow-graphs are in the grc directory, for different SDRs. These receive samples from the SDR, demodulate a 500KHz section of spectrum as USB, resamples them to fsbaud*8 (which fsk_demod requires), then presents these samples via a TCP sink, which is acting as a TCP server. You will probably need to modify these to set the appropriate receive frequency.

• To receive the FSK data and display the images 'live', run:

• In another terminal: python rx_gui.py, which will listen via UDP for new images to display.

• Start the appropriate GNURadio Companion Flowgraph. This will block until a client connects to the TCP Sinks TCP socket.

• Start the FSK modem with:

• nc localhost 9898 | ./fsk_demod 2X 8 921600 115200 - - | ./drs232 - - | python rx_ssdv.py --partialupdate 8