A transmitter configured to communicate a data chirp signal to a receiver, the chirp signal comprising at least one symbol, each symbol comprising one or more identical chirps, each symbol having a different gradient to another symbol in the chirp signal, each chirp encoding a symbol value, the transmitter comprising: an address encoding module configured to encode an address associated with the communication via the sequence of gradients of the symbols in the chirp signal; a data encoding module configured to encode data in the chirp signal via the symbol value of each chirp; and a transmitting module configured to transmit the data chirp signal to the receiver.