An audience rating system for digital television and radio, using identification codes in control streams of time-multiplexed digital transmissions. When a television set or radio, that is being monitored pursuant to the system, is turned on and tuned into a channel, and each time that the channel is...http://www.google.es/patents/US6735775?utm_source=gb-gplus-sharePatente US6735775 - Audience rating system for digital television and radio
Audience rating system for digital television and radio
