At each booth there is, at an elevated position, an infra-red transmitter. The infra-red serves as a carrier for multiple audio messages. The audio messages are in various languages, and each language has a supplementary message of greater detail. The attendee carries an infra-red receiver, from which...http://www.google.de/patents/US5896215?utm_source=gb-gplus-sharePatent US5896215 - Multi-channel system with multiple information sources
