US Patent 9710978 Access control system using optical communication protocol

System for controlling access comprises a reader unit (108) which is disposed at a portal (102) to a controlled access area (118) and a wearable access device (WAD) (114) which is worn by a user (116). The reader and the WAD implement a bidirectional optical communication protocol (BOCP) to communicate digital data. The WAD receives an interrogation signal from the reader for initiating an access control interaction. At least one of the reader and the WAD uses a predetermined optical beam width (142, 308) and a boresight direction (140, 306) of an optical beam associated with the wireless optical communication link to facilitate a selective determination as to whether the WAD will respond to the interrogation signal with a reply signal to continue with the access control interaction.