Disclosed systems and methods transmit and receive data encoded as optical signals that include a progression of symbols, with each symbol represented as a combination of light frequencies. Light is used as the carrier medium to limit reception to devices that are within visible range of the transmitting device. No mapping of data to symbols is required for generation of the symbol progression by the transmitter and no mapping of symbols to data for recognition of the symbols is required by the receiver. Disclosed embodiments allow arbitrary selection among a plurality of mappings between symbols sent and symbols received. Embodiments are robust to: ambient lighting conditions, differences in optical and temporal response of the first and second devices, and differences in relative orientation between the first and second devices. Embodiments enable a variety of functions including device discovery, feature discovery, beacon identification, status reporting, error readout, key exchange, and authentication.