US Patent 9252834 Low power long range transmitter

A transmitter device arranged to encode a set of digital input data into a succession of modulated chirps, whereby said digital input data are encoded according to a Gray code into codewords (320, 321, 322) having a plurality of bits, and having an interleaver that distributes the bits (C00, . . . Cnn) of each codeword into a series of digital modulation values (S0, . . . S7), at different bit positions, and to synthesize a series of modulated chirps whose cyclical shifts are determined by the modulation values. A special frame structure is defined in order to ensure high robustness, and variable bit-rate flexibility.