Challenge

Edit June 24th 2021: the winners are Daniel Estevez and Christoph Mayer, the only two complete solutions we received 1-month after posting the challenge and by the time the conference started. Alban Meffre additionnally provided a partial solution. Daniel's solutions along the files used to generate the challenge have been posted on github for you to analyze and forked to include the original data file. Thank you all for participating !

Two B205mini provided by our sponsor NI will be distributed to the best answers to the following challenge, with the winners to be announced by the end of the oral presentations June 24th. We already have one amazing answer to the challenge, but more prizes will be distributed to contestants with the right answer(s).

The signal to be decoded was synthesized, transmitted by a B210 and recorded with a radiofrequency grade oscilloscope, generating a binay floating point sequence.

Seven European citizens have been discussing in an HF amateur band: a (512 MB) recording of their exchange is stored at https://filesender.renater.fr/?s=download&token=5d71b1a3-1d71-48f2-8a74-29a3b14d34eb, sampled at 10 MS/s after offseting the input signal by a mixer with a 25 MHz local oscillator. Six of these seven speakers enjoy receiving and decoding GPS signals, although Gold codes are too complex and simpler coding schemes are best suited for their exchanges at 1.2281 Mb/s. Can you identify what messages have been exchanged and from which countries the messages were transmitted ?

Six intermediate steps have been identified to help reach the objective:

1. what is the message from the speaker who does not enjoy GPS reception? what is the common communication protocol followed by this bitstream?

2. what is the coarse frequency offset complying with the legal HF ham radio band, notwithstanding possible channelization considerations? what is the fine frequency offset between transmitter and receiver local oscillator?

3. what is the coding scheme of the six GPS receiver enthusiasts, considering their datarate is known?

4. what are the bit sequences transmitted by these six speakers?

5. how are these bits packed as sentences?

6. what coutries do the speakers come from?

Feel free to contact the challenge designer (jmfriedt@femto-st.fr) to share ideas and improve the challenge statement. Intermediate answers can be sent to this email as well, although I would prefer a complete technical report rather than too many intermediate statements that I might loose track of.

Good luck.