A method of communicating a data chirp signal from a transmitter to a receiver, the data chirp signal comprising a sequence of symbols, each symbol encoding a first symbol value and a second symbol value such that the data chirp signal comprises a first symbol value sequence and a second symbol value sequence, the first and second symbol values being encoded via different properties of the symbol, the first symbol value sequence being selected from values in a primary predetermined sequence and a secondary predetermined sequence, the method comprising: selecting consecutive values of the first symbol value sequence from values in consecutive sequence positions of the primary predetermined sequence and the secondary predetermined sequence; encoding first data in the chirp signal via the selected first symbol value sequence; encoding second data in the chirp signal via the second symbol value sequence; and transmitting the data chirp signal to the receiver.