Osmocom ADS-B generator/transmitter
(C) 2014-2015 by Harald Welte <laforge@gnumonks.org>
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adsb_gen - ADS-B / Mode-S transmitter

WARNING: ONLY USE THIS TOOL WITH DIRECT COAXIAL CABLE CONNECTION BETWEEN
TRANSMITTER AND RECEIVER OR INSIDE A SHIELDED CHAMBER. ADS-B OPERATES ON
LICENSED SPECTRUM AND THE AUTHOR IS NOT RESPONSIBLE FOR IMPROPER USE OF
THIS TOOL.

This is a small toolset for generating Mode-S / ADS-B test data,
intended for testing ADS-B receivers.  This includes production testing
but also comparison of various receivers against each other in terms of
sensitivity.

This is very early PoC code and can probably do with lots of
improvements, particularly related to the modulation depth, transmit
power, etc.

There are two ways of using the project:

1) Old style (with gnuradio before it had PDU abstraction)

The idea is as follows:

* provide a text file with ADS-B sentences in regular encoding like
  '*8D48415F600796758E', one sentence on every line.

* call adsb_gen with the synax '[-p pause_usec] <infname> <outfname>'
  where infname is the name of the ASCII input file and outfname is the
  binary.

* the above will generate the output file whihc contains the coded ADS-B
  data at one unsigned byte per bit at 2MS/s sample rate.

* you can use the file_to_usrp2.grc gnuradio companion block to actually
  send this file in an endless loop.

* the '-p' parameter can be used to configure the gap between subsequent
  ADS-B sentences (specified in microseconds).  The default is 1s.


2) New style (with gnuradio 3.7)

* Build the gr-adsbtx module like usual using cmake/make

* Run the adsb_gen.grc flow graph in gnuradio-companiion

* Connect to localhost port 52002 and send ADS-B sentences
  to it