For the radio component - I suggest that you build a "block" of useful data and send that several times using very good Hamming (error correction) instead of er

For the radio component - I suggest that you build a "block" of useful data and send that several times using very good Hamming (error correction) instead of error detection. If using wifi then consider UDP. You'll get better range out of something proprietary, I've had success in the 915 Mhz band. A spread-spectrum approach is better if possible. Ideal would be if the car assumes it cannot receive anything and attempts to send each block several times before beginning to transmit the next block. Another approach could be to send a window of blocks each time. Receiving outside the car is likely to be much easier - a large antenna can be used away from all interference. An option could be a human operator holding a directional antenna, visually tracking the car. You might also store the blocks within the car for later 100% accurate download.